Chapter 14 Hazards of Anesthesia Machines and Breathing Systems Although enormous strides have been made in improv ing the sa fety of anesthesia

apparatus, problems continue to be reported . Studies show that human error is

more frequent than equipment failure (1,2,3,4,5 ,6,7,8,9,10,11).

This chapter wi l l examine hazards of anesthesia mach ines and breathing sys tems

f rom the perspec tive of thei r ef fect on the pat ient. Many examples are g iven, bu t

these should not be considered a comple te l is ting of a ll possible dangers. Many

hazards involve older apparatus that may have been modif ied and is no longer sold

or serv iced by the manufacturer. A discuss ion of anes thesia machine obsolescence

is found in Chapter 5.

Hypoxia

Hypoxic Inspired Gas Mixture Incorrect Gas Supplied

Piping System The wrong gas may be supp lied to the central oxygen supply

(12,13,14,15,16,17,18,19). Crossovers between oxygen and other gases may occur

in the piping system (20,21,22,23). During or fo llowing construc tion or repair, a

pipel ine may be f i l led wi th air o r ni trogen rather than oxygen (24,25).

A gas mixer, anesthesia machine, or venti lator may allow a crossover and

contaminate one p ipeline gas with the contents of the other

(26,27,28,29,30,31,32,33,34). I f the oxygen pressure is lower than the other gas,

that gas may enter the oxygen pipeline.

Ins ide the operat ing room, incorrect outlets may be instal led

(35,36,37,38,39,40,41,42). A te rminal unit may accept an incorrect connector

(43,44,45,46,47,48). An incorrect connec tor may be placed on a hose

(49,50,51,52,53,54,55) o r the pipeline inlet of the anesthesia mach ine (40). I t may

be possible to attach an oxygen tubing or hose to the out le t from an air f lowmeter

(56,57,58,59).

I f i t is suspec ted that the pipe line oxygen system is del ivering less than 100%

oxygen, it is importan t to open an oxygen cylinder AND to disconnec t the oxygen

pipel ine hose. If the pipe line hose is no t disconnected, gas f rom the piping system

will s ti l l be delivered. If the cause of a low oxygen concentration is not obv ious and

the si tua tion is not corrected by disconnec ting the oxygen pipeline hose and

opening an oxygen cylinder, the pat ient should be venti la ted wi th room air by using

a manua l resuscitat ion bag (Chapter 10).

Cylinders I t is possible for a cyl inder labeled oxygen to contain another gas

(60,61,62,63,64,65). A cyl inder may be painted a color other than that normal ly

used for a part icular gas. Care shou ld be taken when using cy linders in o ther

countries, because four different colors (green, wh ite, b lue , and black) are used

around the world for oxygen (66). In a cylinder containing a mix ture of two gases,

incomplete mix ing may result in a hypoxic mix ture being del ivered (67,68). Such a

cylinder may require 45 minutes of rotating before mix ing is complete.

Despite almost universal use of the Pin Index Safe ty System, reports of incorrect

cylinders be ing connected to yokes continue to appear

(69,70,71,72,73,74,75,76,77,78,79,80,81,82). An incorrect yoke block may be

inserted (83 ,84). A pin may become unsc rewed from the yoke (85).

Crossovers in the Anesthesia Machine Crossovers between oxygen and other gases can occur ins ide the anesthesia

machine and are espec ially likely if the machine piping has been al tered (49,86).

Hypoxic Mixture Set

Flow Control Valve Malfunction A f low control valve malfunc tion may resul t in more or less gas being del ivered. If

the oxygen flow control valve is damaged and the f low is decreased, hypoxia can

resul t (87,88,89). If the f low control valve for another gas malfunct ions in such a

way that excessive gas is del ivered, hypoxia could a lso resu lt .

Incorrect Flowmeter Setting Some older anes thesia machines do not have a minimum oxygen ratio device that

prevents the user from dia ling a hypoxic fresh gas mixture. On these machines, a

hypoxic mix ture can be caused by partly or fully clos ing the oxygen f low control

valve, whi le a llowing the nitrous oxide f low to cont inue (90,91,92,93). Absence of a

minimum oxygen rat io device is one of the cri teria fo r machine obsolescence

(Chapter 5). Unfortunately, many anesthes ia machines in serv ice s ti l l lack th is

device (94). There may be prob lems wi th the minimum oxygen rat io device

(95,96,97,98,99,100,101,102,103,104,105), or the machine may have add it ional

gases that are not incorpora ted into the minimum oxygen ratio device.

Oxygen f low can be inadvertent ly lowered (or the f low o f another gas increased) if

the f low control knob is inadverten tly ro tated by an i tem on the surface below (106)

or by a hose or wire al lowed to drape around it . With some f lowmeters , in and out

movement of the f low contro l valve can change the f low s ignif icant ly (107).

Someone helping to move the machine could grab a f low control valve knob and

change the f low (F ig. 14.1). Most new machines have a guard over o r around the

f low control valves to prevent this problem.

The abil i ty to deliver 100% ni trous oxide was found in an anesthesia machine where

the tub ing to the common gas outlet became k inked (108,109). In this case,

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the ni trous ox ide regulator was set at a h igher pressure than the oxygen regulator,

which caused ni trous oxide to preferent ial ly pass through the tubing.

View Figure

Figure 14.1 A dangerous practice. The flow control knob may look like a good thing to grab to someone moving an anesthesia machine. Flows may be altered in the process.

Incorrect Flowmeter Reading On some older machines , the f lowmeter indicator can disappear f rom view at the

top of the tube when the flow of gas exceeds the maximum scale cal ib ration. Such

a flowmeter is very similar in appearance to one wi th the ind icator resting at the

bottom. I f the f lowmeter carries a gas o ther than oxygen, a hypox ic mixture may

resul t .

I f an ai r flowmeter is present on a machine, dialing ai r instead of oxygen can resul t

in a hypox ic mixture (110). To prevent this , most modern anes thesia machines do

not allow administra tion of ai r and nitrous oxide wi thout addi tional oxygen flow.

Inaccurate Flowmeter Causes of f lowmeter inaccuracy include di rt , grease, or o il on the indicator o r tube;

a stuck or damaged indicator; misalignment of the tube; stat ic e lec tricity; improper

ca libration ; the s top at the top of the tube fa ll ing down onto the indicator (Fig.

14.2); and transposi tion of indica tor, scale, or tube (111,112,113,114,115,116,117).

Oxygen Lost to Atmosphere I f there is a leak a t the top of the oxygen f lowmeter tube, oxygen wil l be

preferential ly los t, even if the oxygen flowmeter is downs tream of the other

f lowmeters (118,119,120,121,122,123). The posi t ion of the indica tor may not be

af fected. Of ten, the defect cannot be seen unti l the tube is d isassembled.

Other leaks in the anes thesia machine can resu lt in hypoxia, the magni tude of

which wi l l depend on the s ize of the leak and its locat ion

(121,122,124,125,126,127,128,129). I t is important to use a yoke p lug in any yoke

not containing a

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cylinder so that gas wi l l not leak out of the yoke if the f low control valve to that

yoke is open.

Figure 14.2 The stop at the top of the flowmeter tube has broken off and fallen onto the indicator. The flowmeter will read less than the actual flow.

View Figure

Air Entrainment I f the pressure in the breathing system falls below atmospheric , ai r may be drawn

into the system through a leak or disconnect ion . Subatmospheric p ressure may be

caused by the pat ient 's insp iratory effort ; suct ion appl ied to an enteric tube

inadvertent ly placed in the tracheobronchial tree or to the work ing channel of a

f iberscope in the ai rway; a problem wi th a closed scavenging system interface; a

venti lato r wi th a hang ing bellows ; a piston venti lator; or a sides tream gas analyzer

wi th a low f resh gas f low (130,131,132,133,134,135,136,137). Ai r can enter the

breathing sys tem if the venti lator be llows is improperly connected or has a hole

(138,139,140,141,142,143,144) or the f resh gas f low is directed to the wrong ci rcui t

(145).

In many cases, ai r en trainment is manifested by a decrease in anesthet ic agent as

wel l as oxygen concentrat ions (135,146).

Hypoventilation

Causes Insufficient Gas in the Breathing System

Low Inflow Pipeline Problems Loss of pipel ine oxygen pressure was d iscussed in Chapter 2. Causes inc lude

damage during cons truct ion, debris in the l ine following instal lation, unannounced

system shutdown, pressure regulator malfunction , central supply sys tem

malfunct ion, a disrupted l ine between the central supply and the piping sys tem,

compressor fai lure resul t ing f rom an elec trical s torm, f i res, and a c losed isolat ion

valve (51,147,148,149,150,151,152,153,154,155,156,157,158,159). A station outlet

may become blocked or not accept a quick connector (159,160).

A hose may develop a leak, become b locked, or develop a kink tha t obs tructs gas

f low (152,161,162,163,164,165,166,167). The anesthesia machine may rol l over a

hose, occluding gas f low (164). The check valve at the pipeline inlet o f the

anesthesia mach ine may malfunc tion (168), or the f i l ter may become c logged,

reduc ing gas f low (169).

I f piped oxygen pressure is lost, an oxygen cylinder shou ld be opened and the

pipel ine hose disconnected from the wa ll to prevent f low from the cylinder into the

pipel ine. To minimize oxygen use, a gas-powered venti lato r should be turned OFF

(this is not necessary if an elec trically powered p is ton vent i lator is being used),

manual or spontaneous vent ilation ins ti tu ted , and the fresh gas f low lowered as

much as possible.

I f open ing an oxygen cylinder does not repressurize the anesthesia machine, then

there is a problem in the machine's high or intermedia te pressure system or the

cylinder is empty or not properly connected (164). A resusci tation bag should be

used to venti late the pat ient unti l another machine can be obtained.

View Figure

Figure 14.3 Failure to remove the dust protection cap from a cylinder before installing it on a machine caused a portion of the cap to be pushed into the cylinder valve port, and this blocked the exit of gas from the cylinder.

Cylinder Problems

A cylinder may be empty a t delivery or af ter use. The cyl inder valve may be

inoperab le, or the valve out let may be blocked (170,171,172,173).

Before a cyl inder can be used, it must be correct ly ins tal led on the machine. Of ten,

the most inexperienced person in the operat ing room is told, wi thout suff icient

instructions, to replace an empty cylinder. He or she may fai l to c rack the valve;

instal l the cylinder wi thout a washer, wi th a damaged washer, or wi th two washers;

fail to remove the dus t pro tection cap (Fig. 14 .3); or fail to check tha t the cyl inder

is full . Another error is to penetrate the safe ty relief valve on the cyl inder valve with

the retaining screw on the yoke (174). I t is sometimes possible to spot an

incorrect ly placed cyl inder s imply by look ing at it . An improperly instal led cyl inder

may hang at an angle instead of paral lel to the machine and perpendicu lar to the

f loor (F ig. 14.4).

The fact tha t a ful l cylinder is p resent on an anes thesia machine does not mean

that there wil l be oxygen avai lable when needed. F irst, there mus t be a means of

opening the cylinder. A good pract ice is to chain a handle to each mach ine so tha t

i t wi l l a lways be there when needed.

A cylinder may be empty, and there may not be another one avai lable to replace i t.

This should be determined during the preuse checkout (Chapter 33). The amount of

oxygen that needs to be in the cyl inder depends on the c linical s i tuation. If there is

a s ingle yoke for oxygen on the machine and the cylinder is to be the

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primary source of oxygen for the anes thetic, the cylinder needs to be fu ll and the

number of addi tiona l cy linders immediate ly avai lab le needs to be determined (175).

I f the p ipeline is to be the primary oxygen supply, the oxygen cylinder is the backup

for th is source. In this case, i t is l ikely that a quarter- to half -full cyl inder is

adequate. The anesthesia provider mus t be watchful of the cylinder pressure gauge

when checking or us ing the cyl inder as the primary oxygen source to de termine how

much oxygen remains in the cyl inder.

View Figure

Figure 14.4 A sure sign that a cylinder is not correctly fitted in its yoke is that it hangs at an angle to the machine rather than perpendicular to the floor.

Anesthesia machines have a number of ways that warn the anesthesia provider tha t

the oxygen cyl inder has become exhausted. Many anesthesia providers do not

recognize when this occurs and furthermore do not know how to react to the

problem (176). This has been a ttributed in part to the fac t that anesthesia

technic ians usua lly maintain the cylinders on the machine and that many

anesthesia providers do not have experience wi th changing cy linders. This s lows

their react ion during an emergency si tuat ion .

Machine Problems

Obstruction Obstruct ion to gas f low in the anesthesia machine may be caused by problems in

the oxygen flush valve, f low control valve, yoke, or vaporizer connec tions

(117,177,178,179,180,181,182,183,184).

Leaks I f the check valve in the pipel ine inlet of the anesthesia machine fa ils , gas may flow

into the room (if the p ipeline hose is disconnected) or into the p iping system (if the

hose is connec ted) (185,186,187). Gas can be lost through a broken f lowmeter tube

or an open f low control valve with an opening to atmosphere upstream of the

f lowmeter (121).

Leaks can occur in the machine piping (188,189); at a loose or defect ive vaporizer

connec tion

(190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206); a

loose, defect ive, o r absent vaporizer f i l le r cap or d rain screw (207,208,209) (F ig.

14.5); or a defec t in the vaporizer itse lf (210). Vaporizer leaks do not manifest

themselves unt i l the vaporizer is turned ON. These can be

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discovered if the vaporizer is turned ON during the checkout process (Chapter 33).

Some machines are designed so tha t when a vaporizer is removed, a manifold cap

must be placed where the vaporizer was s i tua ted. Fai lure to do so wil l resu lt in a

major leak. The pressure rel ief device on the mach ine may vent f resh gas if

downstream resistance causes the pressure to rise (211,212).

View Figure

Figure 14.5 When the block on the filling block is not in place, there will be a leak when the vaporizer is turned on.

Gas Supply Switched OFF The main ON-OFF switch on the machine may be accidental ly turned to the OFF

posit ion (213,214,215,216,217). Some mach ines have a two-posi t ion switch to turn

i t ON. One posit ion places the machine in standby, which enables only the

electrical portion of the machine, wh ile the other act ivates both the elec trical and

pneumatic port ions of the mach ine. If i t is not not iced tha t the switch is in the

standby posit ion, f resh gas wi l l not be de livered. Newer machines have a s imple

swi tch that enables al l functions.

Problems with the Fresh Gas Supply The f resh gas hose can be detached, occluded, develop a leak, o r be attached to

the wrong posi t ion

(131,150,172,218,219,220,221,222,223,224,225,226,227,228,229,230,231). The

inner tube of the Ba in or Lack system, which carries the f resh gas f low, can become

obstructed (232,233,234).

Whi le mos t anesthesia machines have one fresh gas outlet that supplies gas to the

breathing (usual ly c irc le) system, some have a second out let that can be used wi th

other types of breathing sys tems. A hazard of this design is that gas may f low

through the auxi l iary outlet when i t is not intended to be in use (235). Having an

inte rlock to c lose this secondary out le t is one solution to this problem (236).

Excessive Outflow Breathing System Leaks Most breathing system leaks are too small to be of c linical signif icance, but some

are large enough that the pat ient cannot be adequately vent i lated, especially if low

f resh gas flows are used. Leaks also cause pol lution of operat ing room air (Chapter

13).

A common location fo r leaks in the c i rc le system is the absorber. I f the can is ters do

not f i t together p roperly, a large leak can resul t (237,238,239,240,241,242,243). A

canis ter may become disengaged f rom the absorber (150,244,245,246). Leaks have

been reported in humid if iers , respiratory volume meters , breathing tubes, e lbow

adapters , bags, temperature probe s i tes, connectors for respiratory gas analyzers

or p ressure moni tors, bag/vent i la tor selector valves, f i l ters , heat and moisture

exchangers (HMEs), oxygen analyzer adaptors, adjustable pressure limi ting (APL)

valves, the reservoir bag mount, and Y-pieces

(150,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,

265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,2

84,285,286,287,288,289,290,291,292,293,294,295,296) (Fig. 14.6). The cap for the

gas sampl ing l ine to a s ides tream gas analyzer a ttachment may become lost

(297,298). A heated humid if ie r may mel t a hole in a breathing tube

(299,300,301,302).

The APL valve may fail to c lose (303,304,305,306,307,308). This leak may not be

easily found, because the exhausted gas wi l l flow into the scavenging system. The

t ransfer tubing may need to be removed from the APL valve to de tec t the problem

(308,309). Mos t present bag/venti lator selec tor valves cause the APL valve to be

excluded f rom the system when swi tched to the automatic mode or when the

venti lato r is turned ON. With older machines where the APL valve is not excluded,

the user may forget to close i t when switching to automatic vent ilation .

View Figure

Figure 14.6 Parts of the breathing system may have holes in them when they are received from the manufacturer.

A leak may occur in a vent ilator (310,311) or in i ts a ttachment to the breathing

system (312,313,314). If the pilot l ine becomes d isconnected or k inked during

expirat ion, the spi l l valve ruptures or becomes stuck in the open posit ion, or the

exhaus t valve mal funct ions, gas can be lost (315,316,317,318,319). A large leak

wi l l occur if the bag/venti lator switch is placed in the venti lator pos it ion with no

connec tion to the venti lato r (320).

A defect ive nonrebreathing valve or misassembly of a manual resusci tator can

resul t in part or al l of the gas volume leaving the bag during inspirat ion and

escaping to a tmosphere (321,322,323).

Most leaks can be detected by the preuse check. Many reported leaks involve

equipment that was added after the checkout was performed (287,324). I t is

importan t that al l equipment that is to be used during a case be in place before the

preuse checkout is performed. Checking is discussed in more detail in Chapter 33.

Leaks may occur during an anesthetic (252). Such a leak may be evident by a low

expired volume or an inc rease in end-tidal carbon dioxide. With a s tanding bellows

venti lato r, the bel lows may not return to i ts fully expanded posi tion (325), and there

may be a change in the vent i lator sound. An airway pressure moni tor

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may alarm wi th a leak but cannot be rel ied on, especial ly if the leak is no t large or

the alarm limi t is set low (258,326).

When a leak is suspected, a systematic search of the anes thesia machine and

breathing sys tem should be made, following the route of gas travel . It may be

easier to de tec t a leak if gloves are not worn (279). A leak can sometimes be

located by plac ing alcohol on the hands and moving the hands over components

whi le gas f low is occurring . The leaking gas evapora tes the alcohol and cools the

sk in.

Disconnections A disconnect ion is an unin tended separation of components (327). Disconnect ions

in b reath ing c ircui ts a re among the most common type of p reventable anes thetic

mishap involv ing equipment (1,2,11,238,328,329). Most b reathing system

connec tors are s lip fi t tings that rely on fr ic tion to hold them together. They wil l

come apart if suffic ient tens ion is app lied. If the connec tion is under a drape, th is

wi l l make it dif f icult to spot the disconnect ion (329,330).

Disconnec tions can occur anywhere in the breath ing system. The most common s ite

is between the breath ing system and tracheal tube connector or HME (1 ,331,332).

Disconnec tions are of ten associated wi th a third party interfering with the breathing

system and with surgery on the head and neck (238).

Disconnec tions can be made less f requent by making secure connec tions .

Connectors with lugs or other features that make them easy to grip may be easier

to t ighten. Push and twis t (wrung) connections are much stronger than those made

wi th a stra igh t push (333). Metal -to-metal or p las tic-to -plast ic joints are s tronger

than metal-to-plastic join ts (334).

Ant idisconnect devices for b reathing system components have been desc ribed

(327,335,336). Locking connectors use a mechan ical means to ensure that the

connec tors do not separate under any force tha t is common during use. Many

believe that they should not be used at the connec tion between the tracheal tube

connec tor and the breath ing system, reasoning tha t it is safer for such a union to

come apart under tension than for the tracheal tube to be pu lled out of the pat ient

(337). I t may be necessary to make a disconnection rap idly at this point for

suction ing or to re lieve a high pressure in the breathing system. Latch ing

connec tors are s imi lar but a re designed to “break away” wi th a certain

disconnection force (327). Adhes ive tape is sometimes used to prevent

disconnections. Unfortunate ly, tape can prevent the disconnect ion from being seen,

inhibi t reconnect ion, and cause an obstruc tion (327).

The anesthesia works tat ion standard (338) requires tha t the worksta tion be

provided wi th an a la rm tha t is activated in the event of a complete disconnect ion in

the breathing system. Alarms considered to comply wi th this requirement inc lude a

low airway pressure a larm, a low exhaled carbon d ioxide ala rm, and a low volume

alarm. These devices are discussed in Chapters 22 and 23. With spontaneous

breathing, no movement of the reservoir bag wi l l be seen if a disconnec tion occurs

(339).

Negative Pressure Applied to the Breathing System I f the a ir inlet valve of a closed scavenging inte rface or the opening to atmosphere

of an open interface becomes blocked or the inte rface is omitted, a subatmospheric

pressure may be transmitted across an open APL valve to the breathing system

(339,340,341,342,343,344).

I f suc tion is appl ied to the work ing channel of a f iberscope passed into the a irway

or to an enteric tube that has entered the trachea rather than the esophagus ,

respira tory gases wi l l be removed rap id ly f rom the lungs and breathing sys tem

(132,345,346,347).

Improper APL Valve Adjustment When manual ly control led or assis ted vent ilat ion is used, gas is vented from the

system during inspiration (unless a c losed system technique is used). Part of the

gas displaced f rom the bag goes to the pat ien t, and the rest is discharged from the

breathing sys tem. The person squeezing the bag may f ind it dif f icult to est imate

how much gas is entering the pat ien t and how much is escaping to a tmosphere.

Hypoventi lation can occur if too much gas escapes through the valve.

Blocked Inspiratory and/or Expiratory Pathway A partial o r complete block in the breathing sys tem can result in hypoventilation . In

most cases, the problem can be detected before the case has begun by having the

anesthesia provider o r the patien t breathe through the system (348). Lack of

obstruct ion to breathing, a satisfactory capnogram, and reservoir bag movement

should be seen. It is importan t that al l equipment that is planned to be used for the

case is in place in the system when the preuse checking is performed, as added

equipment may cause an obstruc tion (349,350,351,352).

Causes of b reathing system obstruction include manufacturing defec ts ; foreign

bodies (e.g., caps, plast ic wraps, tape); misconnect ions; blood; secret ions; or o ther

problems

(260,267,297,349,350,351,352,353,354,355,356,357,358,359,360,361,362,363,364,

365,366,367,368,369,370,371,372,373,374,375,376,377,378,379,380,381,382,383,3

84,385,386,387,388,389,390,391,392,393,394,395,396,397,398,399,400,401,402,40

3,404,405,406,407,408,409,410). Obs truction can resul t if the seals on a

disposable absorbent package are not removed, from occ lusions in the holes in the

top and bottom panels, o r from compacted absorbent (150,411,412,413,414,415)

(Fig . 14.7).

A posit ive end-exp iratory pressure (PEEP) valve may stick in the closed posit ion

(351,383,410). Connecting a flow-direction-sensi tive component such as a PEEP

valve or humidifier in reverse wil l resul t in l i tt le o r no f low (416,417,418). I f the

bag/vent i lator se lector valve is lef t in the wrong posi tion when automatic venti la tion

is ini t iated , complete obstruction to gas f low wi l l resul t. An HME or f i l ter can

become obs tructed (332,419,420,421,422,423).

Breathing tubes can become obstructed f rom kinking or twist ing (424) (Fig. 14.8),

as can the reservoir bag neck

P.411

(425,426) (Fig. 14.9). A heated humid if ie r may cause the tubing to melt and become

obstructed (427) (Fig. 14 .10).

View Figure

Figure 14.7 Prepacked absorbent container. Failure to remove the label from the top and/or bottom will result in obstruction to flow through the absorber.

Ventilator Problems Hypoventi lation secondary to vent i la tor p rob lems is discussed in Chapter 12.

Causes inc lude cycling fai lu re, leaks of d riving or breathing sys tem gas,

inappropriate settings , and the venti la tor being turned OFF. If an anesthesia

machine is turned OFF and then turned ON aga in , the vent i lator may defau lt to

se tt ings that are d if ferent from those origina lly set (428).

View Figure

Figure 14.8 Kinking of a breathing tube.

Detection Vigilance aids used to detec t hypoventila tion inc lude ai rway pressure, resp iratory

volume, and carbon d ioxide moni tors. These are discussed in Chapters 22 and 23.

An oxygen analyzer may detect some disconnections (238,429,430) but shou ld not

be relied on, because i t is effective in on ly a l imi ted set of c i rcumstances . The low

temperature alarm on a heated humidif ier may s ignal loss of gas f low in the

breathing sys tem (238). Because any s ingle monitoring modal ity may fail to detec t

a problem, i t is advisab le to use more than one (428,431,432,433).

As stated previous ly, obstruct ions in the breathing system are best de tected by

breathing th rough the system before i t is used but af ter a ll components tha t wi l l be

used are in place. The checkout procedure is discussed in Chapter 33 .

Response to Hypoventilation

When hypoventilat ion occurs during mechanical vent ilat ion, the f i rs t s tep should be

to switch to manual vent i lat ion (434,435,436,437). The anesthesia provider can

then determine whether or not breathing sys tem resistance and compl iance is

normal and if there is adequate gas in the breathing system. I f manual venti lat ion

can be used to vent ilate the patien t sat is factori ly , the problem probably l ies wi th

the vent i la tor o r venti la tor c ircu it . If the problem cannot be d iagnosed or corrected

quick ly, manual venti lation can be cont inued or a backup anesthesia machine

brought in.

I f manua l venti la tion shows obs truct ion to venti la tion, the next s tep is to attach a

resusci tation bag to the ai rway device (mask, tracheal tube, or supraglo tt ic device).

I f i t remains dif ficul t to venti late the pat ien t, the problem is probably wi th the ai rway

device or wi th the pat ient. Compl ications related to supraglo tt ic a irways and

tracheal tubes are discussed in Chapters 17 and 19.

I f manua l venti la tion shows that there is gas f low into the breathing system, but i t is

not adequate to venti late the patient properly, the fresh gas flow should be

increased. I f increasing the fresh f low does not a llow adequate venti la tion, a

resusci tation bag should be used.

I f adequate vent i lation can be achieved by using a resusci tation bag, the tubing to

the bag should be connected to the anesthesia machine outlet , if poss ib le. Inspired

gas monitoring should be continued, if possible. This wi l l determine if the

resusci tation bag is being supp lied f rom the anes thesia machine or room air. I f the

resusci tation bag cannot be connected to the machine outlet or there is no f low

f rom the anesthesia machine, a source of oxygen should be connected to the

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resusci tation bag and anesthes ia maintained by using intravenous agents .

View Figure

Figure 14.9 Twisting has caused this bag to become obstructed. Many bags have a guard in the neck to prevent this.

Af ter adequate vent ilation and anesthesia level have been established, the cause of

the problem can be invest igated. A second knowledgeable person should be sought

and serious considerat ion given to bringing in a second anesthesia machine, if this

has not al ready been done. Even if the problem can be found, i t may not be

possible to correct i t quick ly.

View Figure

Figure 14.10 Contact with a heated humidifier can cause a breathing tube to melt and become obstructed.

Hypercapnia

Hypoventilation Hypercapnia can be the resul t of hypoventilat ion, wh ich was discussed previously.

Inspired carbon dioxide wi l l be zero if hypoventilat ion is the sole cause of

hypercarbia. Other causes of hypercapnia mentioned below are associated wi th an

increased inspired carbon dioxide concentra tion.

Inadvertent Carbon Dioxide Administration A few anesthesia machines are equipped wi th a carbon dioxide cyl inder and

f lowmeter (438). This f lowmeter may be accidentally turned ON but no t not iced,

especial ly when the ind ica tor is at the top of the tube (439). An apparent ly OFF

f lowmeter may leak carbon dioxide into the breathing sys tem (440).

In one reported case, a ni trous oxide hose was connected to the carbon dioxide

stat ion outlet (441). A cylinder may be mis takenly f i l led with carbon dioxide (65).

Rebreathing without Carbon Dioxide Removal Absorbent Failure or Bypassed Absorbent I t is important to watch for the appearance of carbon dioxide in the insp ired gas .

The smaller canisters on some new machines have a shorter l ife span than the

larger ones on older machines. Hypercarbia can occur if channel ing allows gases to

bypass the absorbent (150,442).

Bypassed Absorber An absorber bypass allows some or all of the exhaled gases to bypass the

absorbent. Unintent ional activation

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of this bypass can lead to hypercarbia. The absorber may be defec tive so that gas

f low is not di rected th rough the absorbent (443). Most new anesthesia breathing

systems tha t have small absorbers al low the canister(s) to be changed wi thout the

breathing sys tem integri ty being in terrupted. I t is possible that the anes thesia

provider may not no tice that a canister is loose or missing. Some anesthes ia

providers in tentiona lly remove the canister to allow carbon d ioxide to increase in

the breathing system at the end of a case. This may not be noticed by the nex t

anesthesia provider.

View Figure

Figure 14.11 Damaged unidirectional valve leaflet.

Unidirectional Valve Problems Correct movement o f gases in a ci rc le system depends on properly func tioning

unidi rect ional valves. If they do not c lose properly, rebreathing wil l occur. The disc

may become displaced, wet, s t icky, or damaged so that i t wi l l not seat properly

(150,444,445,446,447,448,449,450,451,452,453,454,455,456,457,458,459) (Fig.

14.11). The disc may not be replaced after removal for clean ing or serv icing. The

cage holding the disc may become dis lodged (460,461).

Unidi rectional valve prob lems can be discovered preoperat ively during the

breathing sys tem checkout (Chapter 33). Problems wi th the unidi rect ional valves

may be indicated by a respirometer indicat ing reversed flow (Chapter 23), a rise in

the inspired carbon dioxide above zero (Chapter 22) o r a capnogram wi th a slan ting

downstroke (Fig. 22.32). Pressure-volume loops (Chapter 23) may also indicate this

problem.

View Figure

Figure 14.12 Possible problems with the inner tube of the Bain system that can result in hypercarbia. The fresh gas supply tube can become detached (A), the inner tube can become kinked or develop a leak (B), and the inner tube may not extend to the patient port (C).

Problems with Nonrebreathing Valves Improperly assembled or s ticky nonrebreathing valves can resul t in part ial or total

rebreathing. Th is is discussed more ful ly in Chapter 9.

Inadequate Fresh Gas Flow to a Mapleson System In systems wi thout carbon d ioxide absorption, a low fresh gas f low can resul t in

dangerous rebreathing (Chapter 8). Reported causes include the fresh gas f low

being set too low; a leak or obs truction in the machine, common gas outlet , f resh

gas supply l ine , or a vaporizer; o r an empty cyl inder (263,462,463,464,465).

Problems with Coaxial Systems In Mapleson systems in which the fresh gases are delivered to the dista l end of the

system by an inner tube, rebreathing wi l l occur if the inner tube is avulsed,

damaged, k inked, or omitted; has a leak at the mach ine end; or does not extend to

the pat ient port (233,466,467,468,469,470,471,472,473,474,475,476) (F ig. 14.12).

I f the inner tube of a coaxial c i rc le system is displaced or develops a leak, an

increase in inspired carbon dioxide wi l l be seen, as previous ly exhaled gas wi l l be

reinhaled wi thout carbon d ioxide having been removed (477).

Excessive Dead Space An increase in dead space wi l l increase rebreathing. Th is increase is especial ly

importan t in small patien ts (478). An HME is placed between the pat ient port and

the breathing system. These come in a varie ty of s izes, and if a large one is used

on a patient wi th a small t idal volume, dangerous rebreathing may occur (479).

Often, a connector is added between the pat ien t port of the breathing sys tem and

the pat ient to move the breathing system away from the surgical field

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(Fig . 14.13). These increase dead space and must be used wi th caut ion.

View Figure

Figure 14.13 Increased dead space between the breathing system and the patient can result in serious hypercarbia in pediatric patients and spontaneously breathing adults.

I f a disconnect ion occurs in a c losed space, such as under a plas tic drape over the

face during spontaneous breathing , exhaled gas containing carbon dioxide can

accumulate in that space and the inspired carbon diox ide level wi l l r ise (339).

Hypercarb ia is best detected using capnometry. Inspired carbon dioxide wi l l be zero

i f a c i rc le sys tem wi th properly function ing absorbent and un idirect ional valves is

used and hypoventilation is the sole cause of the hypercarbia. I f the hypercarbia is

not caused by added carbon diox ide and is the resul t of hypoventilat ion, increasing

the minute volume wi l l reduce the carbon diox ide in the breathing system. If the

carbon d ioxide absorbent or a un idi rectional valve is no t work ing properly ,

increasing the fresh gas flow wil l lower the carbon dioxide levels in the c i rc le

system. Hypercarbia when using a Mapleson system is usually the resul t of low

f resh gas flow, so inc reasing the f resh gas f low wi l l lower the inspired carbon

dioxide level. Chapters 8 and 9 discuss the Mapleson systems and c irc le sys tems.

Chapter 22 offers a ful ler discussion of carbon dioxide moni toring.

Hyperventilation A hole or tear in the vent i lator bel lows can cause inadverten t hypervent ilat ion

(138,139,480). This can be detected by an increased oxygen concentrat ion , if

oxygen is the driv ing gas (or a dec reased concentration if ai r is used); increased

venti lation as indica ted by a spirometer; or decreased end-t idal carbon dioxide.

These moni to rs are discussed in Chapters 22 and 23.

Excessive Airway Pressure In addi tion to interfering with venti la tion, a h igh pressure can cause barotrauma

and adverse effects on the cardiovascular sys tem. Neurologic changes and

otorrhagia have been reported (481,482). A hyperinf la ted lung may interfere with

surgery (483).

Modifying Factors The rate and extent of the pressure rise are important and wil l be affected by a

number of factors, includ ing the reservoir bag; the volume and compliance of the

system; the f resh gas f low; and use of a cuffed or uncuffed trachea l tube, face

mask, or supraglottic airway device.

The pressure in the breath ing system is normal ly l imited to 50 cm H2O by the

reservoir bag. Non-latex bags may allow s l igh tly higher pressures (484). When an

automatic vent i lator is in use, the bel lows buf fe rs increases in pressure. I f the bag

or bellows is excluded from the system, this buffering capaci ty is removed and

dangerously high pressures may be reached rapidly if there is coincidental

obstruct ion to the outflow of gases f rom, or high inflow in to, the system. Bag

exclusion is mos t commonly caused by an obstructed exp iratory l imb upstream of

the bag. The bag may become obs tructed at i ts neck (485) (Fig. 14 .9).

Unfortunately, an anesthesia provider who f inds a reservoir bag that is not f i l led

may incorrect ly assume that there is a leak in the system and operate the oxygen

f lush in an attempt to compensate (486). The high gas f low f rom the oxygen flush

can raise the pressure in the breathing system to dangerous levels very rapidly

when the bag is exc luded.

Protective Devices The anesthesia works tat ion standard requires that there be a dev ice to l imi t the

pressure in the breathing system to 125 cm H2O (338). These devices may

malfunct ion (487). In addi tion, there mus t be a means to continuously display the

pressure in the breathing system and a pressure moni tor tha t activates a high

prio ri ty alarm when the pressure in the breath ing system exceeds the operator-

adjustable l imi t for high pressure .

Some of the newer venti lato rs have pressure-controlled venti lat ion in which peak

ai rway pressure is lower than when volume control venti lat ion is used. Some of

these vent i lators automatica lly swi tch f rom the inspira tory to the expiratory phase

when the peak pressure th reshold is exceeded (488).

Another factor that can reduce the a irway pressure rise is an uncuffed tracheal tube

or a trachea l tube in which the cuff is not inf lated to a h igh pressure. Adjus ting cuff

pressure to 34 cm H2O or less wi l l a llow it to ac t as a safety valve fo r excessive

pressure in the a irway. The use

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of a mask or supraglo tt ic ai rway dev ice wi l l also provide a means of pressure re lief .

Automatic disconnect ion of breathing sys tem components cannot be rel ied on to

provide pressure relief , because the pressures required for disconnection are fa r in

excess of those that cause lung inju ry (334).

Causes of Excessive Airway Pressure High Inflow I f the oxygen f lush valve s ticks in the ON posi tion, 35 to 75 L/minute of oxygen wil l

be de livered. Oxygen f lush valves on newer machines are designed to c lose

automatical ly but can fai l (489,490,491). It is possible for personnel to accidental ly

ac tua te some oxygen f lush valves. Other equipment may cause the f lush valve to

st ick in the ON posi tion (492,493,494,495). I f the oxygen f lush valve is act ivated

during inspira tion when a mechanical vent i lator is being used, a large volume of

gas wi l l be added to the inspired tidal volume, resul ting in a greatly increased

pressure wi th certain breathing system configurations (496,497). A vent i lator

control valve can malfunction, resul ting in a constant f low of d riv ing gas (498).

Low Outflow

Obstruction in the Expiratory Limb As noted previously, excluding the bag from the breathing sys tem resul ts in loss of

buffering capaci ty. Thus, breathing system obstruc tion in the expiratory l imb is

part icula rly hazardous if i t occurs ups tream of the reservoir bag. The expiratory

pathway can be obstructed by fore ign bodies (inc luding ampules, coins, plas tic

wraps, discs, tape, and caps) (361,499,500,501,502), water (503), or equ ipment

defec ts or misassembly

(383,410,497,504,505,506,507,508,509,510,511,512,513,514,515,516,517,518). A

PEEP valve may s tick or be placed backward (383,410,519,520,521,522,523).

The expiratory limb of a T-piece sys tem can become obstruc ted by the user's

f inger, k ink ing, external compression, misassembly, or adhesive tape

(524,525,526).

I f a pediatric breathing system with an adapter that has the f resh gas in le t

protrud ing near the end is used wi th a “low dead space” tracheal tube connector,

the fresh gas supp ly tube may c lose ly approximate or even press against the end o f

the connector, causing partial or complete obstruct ion of the exhalat ion pathway

(527,528,529). The same problem has been reported wi th a bronchoscope (530).

Obstruction at the Ventilator I f the venti lator sp il l valve becomes stuck, the pressure in the breathing system wi l l

r ise (317,531,532,533,534). The exi t of d riving gas f rom the bel lows housing may

be blocked (535).

Obstruction at the Adjustable Pressure-Limiting Valve APL valve omission, malfunct ion, or blockage may occur

(485,486,536,537,538,539,540,541). The user may fail to open the valve when

swi tching from automatic to spontaneous vent i lat ion if the APL valve is not

automatical ly excluded f rom the breathing sys tem during mechanical vent i lat ion and

automatical ly inc luded during manual or spontaneous venti la tion. With some APL

valves, subambient pressure from an act ive scavenging system wil l cause the valve

to c lose, p reventing excess gas f rom leaving the breath ing system

(542,543,544,545).

Obstruction in the Scavenging System The scavenging system is essent ially an extension of the breathing system. If

malfunct ions in the scavenging system occur, the pressure in the breathing system

may be affected. Obstruction in the transfer tubing between the APL valve in the

breathing sys tem or between the spi l l valve in the venti la to r and the interface can

prevent gas f rom leav ing the breathing sys tem (544,545,546,547,548,549,550,551).

The transfer tubing may be connected to an incorrec t s i te (552,553,554).

I f the pressure relief valve in a c losed ac tive scavenging interface (Chapter 13)

fails to open, sustained posi tive pressure in the breathing system can result . In one

reported case, a valve in tended for negative pressure rel ief ra ther than one fo r

posit ive pressure re lief was accidenta lly installed (555).

Problems with Nonrebreathing Valves in Resuscitators A sudden high inf low of gas or a quick squeeze or bump on the self-re fi l l ing bag of

a resusc itator may generate suff ic ient pressure to lock the nonrebreathing valve in

the inspiratory posi t ion (556). Continuing inf low wi l l cause a rise in pressure.

Incorrect nonrebreath ing valve assembly or malfunct ion may resu lt in obs truct ion to

exhalation (557,558,559,560).

Misconnected Oxygen Tubing Misconnection of oxygen tubing di rect ly to an indwel l ing tracheal or tracheos tomy

tube or supraglott ic airway device without provis ion fo r vent ing has occurred, of ten

wi th disastrous results (561,562,563,564,565,566,567,568,569) (Fig. 14 .14).

Another cause of increased pressure is connection to a T-piece wi th a c losed

expiratory l imb (570).

Unintentional Positive End-expiratory Pressure An external PEEP valve may remain in the c ircui t and not be removed, or an

integra l PEEP valve may be lef t in the ON posi t ion a t the end of a case and not

noticed by the nex t user (523,571) (Fig. 14 .15). With older b reathing systems, the

ai rway pressure gauge is loca ted on the absorber side of the unidi rect ional valves,

and PEEP cannot be observed on the gauge (483,523,572). Newer breathing

systems measure the pressure on the patien t s ide of the unidi rectional valve.

Inadvertent PEEP may be caused by water that is condensed in the tubing

connec ting the venti lator to the

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breathing sys tem (573) o r an inadequate opening in the bag of a Mapleson F

system (574).

View Figure

Figure 14.14 A: The oxygen tubing is attached to the mask. B: The adapter has become detached from the mask and is attached to the tracheal tube connector. There is no way for the gas to escape.

Detection When an automatic venti la tor is used, i t is essential tha t the chest wal l motion ,

deflections on the breath ing system pressure gauge, t idal and minute volumes

registered on a resp irometer, and breath sounds be carefully moni tored. Observ ing

the ai rway pressure waveform, if available, can detect some problems . Pressure-

volume loops (Chapter 23) are also useful . The vent ilator may change sound wi th

stacked breaths. A continu ing or high airway pressure alarm may a le rt the operator

to this hazard . The capnograph (Chapter 22) may show an ascending l imb wi th a

prolonged rise time and no plateau.

Obs truct ions to the breathing system can be detected by performing a thorough

anesthesia mach ine

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and breathing system check , including hav ing someone breathe through the sys tem

prio r to use (383). The procedure for preuse checking is discussed in Chapter 33.

View Figure

Figure 14.15 A: PEEP valve with 0 PEEP. B: Same valve with PEEP. Note the similarity in appearance.

Response I f there is a pressure bui ldup in the sys tem, a disconnect ion shou ld be made

IMMEDIATELY at the tracheal tube connec tor (575). T ime spent look ing for the

cause of the problem may resul t in ever-increasing pressure.

Venti la tion should be cont inued by us ing a resusci ta tion bag unti l the problem is

diagnosed and correc ted.

Inhalation of Foreign Substances A foreign body in the breath ing system can of fe r more risk than obstruction . In

some cases , it could migrate in to the pat ient 's respiratory trac t (576,577).

Absorbent Dust Inhaling absorbent dust can cause bronchospasm, laryngospasm, cough, decreased

compliance, and burns to the pat ient's face (578,579). Th is can be avoided by using

a fi l ter at the pat ient port, releasing breathing system pressure at the APL valve

when checking for leaks, tapp ing each canis ter to remove dus t before it is put into

the absorber, and not overf i l l ing can isters (581,582).

Medical Gases Contaminants Reported contaminants in medical gases inc lude water, o il , hydrocarbons , higher

ox ides of ni trogen, and metal l ic f ragments

(35,53,170,582,583,584,585,586,587,588,589,590,591). Bac teria may be found,

especial ly in compressed ai r (592,593,594,595).

Parts of Breathing System Components Part of a breathing system component may break and become detached. Reported

cases have involved parts of the sampl ing si te fo r an asp irat ing resp iratory gas

moni tor, an APL valve, an oxygen sensor, and HMEs

(297,388,596,597,598,599,600,601,602,603). Some manufac turers pla te the inside

surfaces of components wi th materials that may f lake off (604,605).

Other Foreign Bodies A number of other foreign bodies have been found in breathing sys tems

(377,378,379,381,396,400,499,500,501,502,577,606,607,608,609). Of ten, these

enter during c leaning.

Carbon Monoxide Dry absorbents contain ing sodium or potassium hydroxide can resul t in carbon

monoxide formation when

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exposed to volat ile anesthet ic agents. Th is is discussed in detail in Chapter 9.

Anesthetic Agent Overdose An anesthet ic agent overdose can result in severe cardiovascular depression.

Chapter 6 offers a more complete discussion of overdose caused by vaporizer

malfunct ion.

Tipped Vaporizer I f a vaporizer charged wi th l iquid is tipped or agi tated, a very high concentra tion

may be de livered when the vaporizer is turned ON (610). Some newer vaporizers

have a “travel” setting that isolates the vaporizing chamber f rom the res t of the

vaporizer when the vaporizer is removed f rom the anesthesia mach ine.

Vaporizer or Nitrous Oxide Inadvertently Turned ON Previous vaporizer se tt ings by a colleague or serv ice technician can resu lt in the

vaporizer control dial being lef t in the ON pos it ion (611,612,613). Someone he lping

to move the machine may grasp a control dial , inadvertent ly turning it ON.

Inadvertent administrat ion of ni trous ox ide may occur if gas from the main

f lowmeters is used to supply supplementary oxygen (614).

Incorrect Agent in the Vaporizer

I f an agent is incorrect ly placed in a vaporizer designed for an agent wi th a lower

vapor pressure and/or a higher minimum alveolar concentrat ion (MAC) value, a

hazardous ly high concentrat ion may be delivered (615,616,617,618). An example is

plac ing isof lurane or halothane in a vaporizer designed for enf lurane.

Improper Vaporizer Installation I f a vaporizer not designed to be exposed to high gas flows is p laced in the f resh

gas supply tube between the anesthesia machine and the breathing system, there

wi l l be a h igher-than-usual f low of gas through the vaporizer when the oxygen f lush

is act ivated (619). Some vaporizers del iver a considerably higher-than-expected

vapor ou tput if connected so that gas f low is reversed, al though some wil l del iver a

normal concentrat ion (620,621).

Overfilled Vaporizer Most vaporizers are now designed so tha t they cannot be overf i lled. Many agent-

specif ic fi l ling devices prevent overf il l ing by connect ing the ai r intake in the bottle

to the ins ide of the vaporizing chamber. This safety feature can often be overridden

by s light ly unscrewing the bottle adapter and tu rning the concentra tion dial ON

during fi l ling (622,623,624). A drain has been added to some fi l ling devices to help

prevent overf i l l ing.

Vaporizer Interlock System Failure I f the vaporizer interlock system fa ils, i t is poss ib le to turn on more than one

vaporizer at a t ime (625,626).

An agent moni tor (Chapter 22) wil l measure the concentration of volati le agent in

the breathing system. When an overdose of anes thetic agent is suspected, the

patient should be disconnec ted f rom the breathing system and venti lated by using a

resusci tation bag and gas from a source other than the anes thesia machine out let.

Inadequate Anesthetic Agent Delivery Inadequate anes thetic agent delivery can cause serious morbidi ty and result in

patient awareness during the surgical p rocedure (627,628,629,630).

Decreased Nitrous Oxide Flow Pipel ine nitrous oxide may be lost as a resul t of leaks, a frozen regula tor, improper

maintenance, deplet ion of the system supp ly, and del iberate tampering with the

equipment (51,631,632,633). Cylinder supplies also can fail . An obstruc tion or leak

in the anesthes ia mach ine may cause decreased nitrous oxide f low (634). Another

potential problem is inadvertently us ing ai r instead of nitrous oxide (635).

Unexpectedly High Oxygen Concentration I f a connection between the n itrous oxide and oxygen sources occurs in the

pipel ine sys tem, a mixer, or the anesthesia machine, and the oxygen pressure is

higher than tha t of ni trous oxide, oxygen wil l f low into the ni trous oxide l ine

(636,637).

Accidental ac tivation of the oxygen f lush may occur (490,493,638,639,640,641).

Repeatedly using the oxygen f lush to keep the reservoir bag f i l led can lead to

patient awareness (491,642,643). Damage to the oxygen f lush valve can cause it to

leak oxygen into the f resh gas (644).

On some electronic machines, a machine problem wil l cause i t to switch into a “safe

mode” where only oxygen is delivered (645).

Air Entrainment As discussed earl ier in this chapter, a ir entrainment can cause dilu tion of inha led

anesthet ic agents.

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Faulty Vaporizer Vaporizer leaks and prob lems wi th the mounting or interlock device are relatively

common

(630,646,647,648,649,650,651,652,653,654,655,656,657,658,659,660,661,662,663,

664). Such a leak of ten does not occur unt i l the vaporizer is turned ON. Therefore,

i t is essential that the preuse checking procedure for leaks be performed with the

vaporizers turned ON (Chapter 33).

Whi le the overf il led vaporizer has usually been associated with a h igher-than-

expected vapor ou tput, there is one reported case where it was associated with no

vapor ou tput (665).

Empty Vaporizer Another cause of underdosage is a vaporizer that runs empty (627). Cases have

been reported in wh ich a l iquid level was v is ible in the vaporizer s ight g lass

al though the vaporizer was empty (666). In one report, a fragment of rubber

obstructed the channel f rom the lower end of the l iquid level indica tor, showing a

l iquid level despi te the vaporizer being empty (667). Some electronic vaporizers wi l l

ac tivate an alarm when the l iquid level reaches a certain point.

Incorrect Agent in Vaporizer I f a vaporizer that is designed for use wi th a high ly vola ti le agent is fi l led wi th an

agent of low volati l i ty , the pat ient wi l l fail to receive the concentrat ion expec ted

(615,616). An example is plac ing enflurane in a vaporizer that is des igned fo r

isof lu rane.

Incorrect Vaporizer Setting An incorrect vaporizer sett ing can be a cause of anesthet ic underdosage. I t is

importan t to check se tt ings frequently during a case because they can be al tered

wi thout the operator's knowledge. It is not uncommon to forget to turn ON a

vaporizer af ter f i ll ing it during use. I f an anesthesia mach ine is tu rned OFF and

then tu rned ON again, the vaporizer sett ing may defaul t to zero (428).

Anesthetic Agent Breakdown The reac tion between some desiccated absorbents and sevoflurane (Chapter 9) can

be so rapid and ex tensive tha t it is dif f icul t to main tain a sat is factory inspired

concentration . If there is a large discrepancy between the vaporizer setting and the

agent level in the breathing sys tem, anesthetic breakdown shou ld be considered.

Inadvertent Exposure to Volatile Agents I t is possible that halothane-related hepati tis or mal ignant hyperthermia may be

triggered by small amounts of agent p resent in a machine and breathing system

even if the vaporizers are tu rned OFF (661,668,669,670,671,672,673,674). When a

patient wi th a history or suspicion of one of these ent i ties must be anesthetized,

the anes thesia machine should be prepared for use by removing all vaporizers i f

possible (673). Other necessary act ions inc lude changing the absorbent, replacing

the fresh gas supp ly hose, us ing new tub ings and bag, and f lushing wi th a high f low

of oxygen for a prolonged time (675,676,677,678,679,680).

Should an episode of malignant hyperthermia occur during adminis trat ion of

anesthesia and the department has a machine f rom which vaporizers have been

removed and tha t has been thoroughly flushed of vola ti le agents, i t should be

subst ituted fo r the machine in use. A fresh breathing system should be used. If the

department does not have such a mach ine, the fol lowing measures should be taken

to reduce the inhaled concentration of volati le anesthet ic (675,677):

• Change the breathing system hoses and bag.

• Change the fresh gas supply hose.

• Change the absorbent.

• Use very high oxygen f lows.

• Insert a charcoal f il ter on the inspiratory port of the absorber.

• Avoid using a contaminated vent i lator.

• Remove vaporizers from the machine if possible.

Inadvertent anes thetic agent exposure can occur i f the anesthesia machine is used

to deliver oxygen to a pa tient undergoing loca l or MAC anesthesia if the f resh gas

delivery port or the pat ient port of the breathing system is used to del iver oxygen to

a nasal cannula. If a vaporizer is inadvertently tu rned ON, the patient may become

deeply sedated or anes thetized wi th the agent (681,682). These problems can be

avoided by using the aux il ia ry f lowmeter on the anesthes ia machine, an oxygen

f lowmeter attached to the pipel ine system, or a cylinder as the oxygen source.

Physical Damage Older anesthes ia machines of ten have equ ipment added to the top of the machine.

This may resul t in the machine becoming top heavy. If the equipment contacts a

ce il ing column or other s tructure, equipment may be knocked onto the f loor or

personnel . Whi le newer anesthesia mach ines have a generally lower prof ile and

tend to include many of the moni to ring dev ices tha t are o ften placed on the top of

older machines , it is s ti l l poss ible to do physical damage to the machine.

Another hazard to anes thesia equipment is the presence of wires and tubings on

the f loor. These make i t more l ikely that the machine wi l l tip during movement,

spewing equipment to the floor. Many machines come

P.420

wi th op tiona l arms that hold breathing system hoses, tubings, and wires off the

f loor. A number of devices have been manufactured to move the impediments from

the machine wheels (683,684,685,686) (Fig. 14.16). The cas tors on a machine can

break , causing the anesthes ia machine to tip over (687).

View Figure

Figure 14.16 A: If the machine's wheels go over the hose, the machine will be tipped and the line blocked. B: This device allows easier movement of the machine by pushing hose out of the way. (Picture courtesy of CASTrGard.)

Electromagnetic Interference Over the past few decades, the number of wireless radio frequency (RF)

transmitters in medical fac il i ties has increased dramatica lly (688,689,690,691).

Wireless computer ne tworks , paging systems, handheld radios, cellula r telephones,

and o ther RF transmitters, wh ich are sources of electromagnetic energy, have

become prevalent in c linical envi ronments. In the future , it is l ikely that moni tors

and o ther devices wil l be connec ted to the data management system through a

wi reless connection. These produce electromagnetic radiat ion even when the

device is in standby mode, as they constantly send s ignals to the base station .

I t has long been recognized that equipment that emits radio waves can in terfere

wi th the operat ion of electronic medical equipment (electromagnetic in terfe rence or

EMI). The extent of the prob lem is unknown. Availab le c l inical data indicate that

serious malfunctions are rare (689). Equipment reported being affected inc ludes

moni tors , venti la to rs, and infusion pumps. The risk of interfe rence depends on

transmission power and f requency, dis tance to the transmitter, and immuni ty

(cons truction) of the medical dev ice.

The wide variety of RF transmitters and medica l dev ices used in and around heal th

care fac i li ties makes inte rac tions dif ficul t to predic t. A reas such as the operating

room and crit ical care areas , which have a h igh concentrat ion of electronic medical

devices, a re most l ikely to be affected by EMI. Diagnostic , moni toring, and

therapeutic equipment that is direct ly attached to pa tients is part icularly susceptible

to EMI.

To help prevent EMI, newer medical devices are manufac tured to enhance their

immuni ty to, or compatibil i ty wi th , external sources of electromagnetic energy.

Newer cel l phones and newer equipment offer better shielding to mitigate or

prevent electromechanical interference. Older med ical equipment is of more

concern because i t may not have been designed to be immune to the increasing ly

complex electromagnetic envi ronment that can be found in heal th care fac il i t ies.

For most RF transmitters , the f ield s trength dec reases wi th distance. I t follows that

in general , the greater the separat ion between a RF transmitter and a medical

device, the lower the RF exposure to the device, and the lower the potent ial for

EMI.

Careful considerat ion must be given to weighing the risks and benef i ts of wireless

equipment used in and around health care fac il i ties to determine whether i t can be

used safely and effec tively. Unless each medical device is tes ted for immuni ty to

each RF transmitter, i t is dif f icul t to identify which devices may be affec ted by a

part icula r transmitte r and what transmiss ion condi t ions are l ikely to cause

inte rference.

Since the time that cel lular telephones were introduced, health care organizat ions

have struggled to determine a prudent pol icy fo r their use in c linical settings . Some

faci li t ies have banned the use of cel lu lar telephones on their premises . Others

al low them to be used f ree ly, whereas others have banned the ir use in certain

areas or within a certain dis tance of medical equipment (688).

Al though appropriate medical device design and test ing for elec tromagnetic

compatibi l i ty (EMC) can

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reduce potential EMI risks in the c linica l env ironment, they cannot ensure that a

device wil l no t experience problems. Under certain c ircumstances, EMI can st i l l

occur, even i f the dev ice conforms to current EMC standards. Therefore , di rec t or

c lose contact between the medical device and wire less communica tion devices

should be avoided. Wireless phones in public areas do not appear to cause

problems (690). Periodical test ing of wireless transmitt ing dev ices and medica l

equipment wi l l be required to ensure a safe env ironment.

Accident Investigation

Any t ime a pat ient has an unexplained problem, equipment malfunct ion or misuse

should be suspected, and the apparatus should not used again unt il this has been

disproved (692,693,694,695,696).

When there has been a patient injury, the health care fac il i ty safety off icer (or r isk

manager) should be contacted at once to superv ise investigat ion of the incident. An

es tablished pro tocol should be designed and followed so tha t all important areas

are systematical ly covered. All indiv iduals involved in the inc ident should document

their observations soon af te r the event whi le detai ls a re sti l l f resh in their minds.

This should be a s imple statement of facts, wi thout judgments about causali ty or

responsibi li ty .

The fol lowing quest ions need to be asked:

• What was the date and time of the prob lem?

• In what area did the problem occur?

• What monitors were being used?

• What were the set a larm l imits?

• What was the f irs t ind ica tion that there was a problem?

• At what t ime did the problem occur?

• Who f i rs t no ted the problem?

• What changes attracted attention? Were any alarms act ivated?

• What s igns or symptoms did the pat ient exhibit?

• Had there been any recent mod if ications to the electrical system or gas

pipel ines in tha t area?

• Was anyth ing al tered shortly before the inc ident?

• Was this the f i rs t case perfo rmed in tha t area on tha t day?

• Were there any problems during previous cases performed in that area on

that day or on the previous day?

• Were there any unusual occurrences in o ther areas on that day or on the

previous day?

• Had any equipment been moved in to that area recently? Were there any

problems noted in the room where it was prev iously used?

• What preuse anesthesia equipment checks were made?

• Who last f il led the vaporizers on the anesthes ia machine?

• I f a vaporizer was recent ly attached to the machine, were precautions taken

to prevent l iquid from being spi l led into the outf low trac t?

• Af ter the ini tial indica tion that a problem had occurred, what was the

sequence of events?

An importan t s tep involves construction of a t ime l ine, on wh ich all events are l is ted

in chronological order (692). This wi l l help to sort out events and may lead to

identif icat ion of miss ing data. Trend data f rom moni tors or a data management

system can help.

Numerous photographs should be taken of the area from various angles , wi th al l

equipment s i tuated where it was at the time of the inc ident. Each p iece of

equipment should be photographed separa tely.

Af ter pic tu res have been taken, al l suppl ies and equipment assoc iated wi th the

case should be saved and sequestered in a secure loca tion and labe led “DO NOT

DISTURB.” Settings should not be changed. Re levant identifying information such

as the manufac turer and lot and/or serial numbers shou ld be recorded.

I f af ter a ll this has been done i t appears possible that the equipment may be

implica ted in causing the problem, a thorough inspect ion of the equipment by an

uninvolved third party in the presence of the primary anesthes ia personnel ,

insurance carrier, heal th care faci l i ty safety off icer, pat ient representa tive, and

equipment manufacturers should be conducted. The invest igation should consist of

an in-depth examination of the equipment s imilar to the checking procedures

described earlier in this chapter. Vaporizers should be calibrated and checked to

determine if vapor is del ivered in the OFF pos it ion. An analys is shou ld be made of

the vaporizers ' contents, i f necessary. Following the investigation, a report should

be made, detail ing all facts, analyses, and conc lus ions.

I f a problem wi th the equ ipment is found, an a ttempt should be made to reconstruct

the accident, if this can be done without danger to anyone, and the equipment

should again be locked up unti l any li tiga tion is settled. If the invest igat ion reveals

no problems, the equipment can be re turned to serv ice with the consent of all

part ies .

Problem Reporting In the Uni ted Sta tes, the Center fo r Device and Radiological Heal th (CDRH) of the

Food and Drug Admin istration (FDA) receives postmarket adverse event reports

submitted by manufacturers, user fac il i ties , hea lth care

P.422

professionals , and consumers involv ing death, serious injury, or i l lness and produc t

malfunct ions (698,699). The FDA analyzes the reports to determine the impact on

the publ ic heal th and makes recommendations to manufacturers, heal th care

professionals , and consumers . MedWatch is the FDA's name for i ts medical

products report ing program. I t is a broad program that encompasses both voluntary

and mandatory report ing for medical products.

User facil i ties are required to report to the FDA medical device problems tha t have

or may have caused or contribu ted to death, serious i l lness, o r serious in ju ry.

Serious i l lness or in ju ry is def ined as life -threatening or resul ting in permanent

impairment of a body funct ion or permanent damage to a body structure or tha t

necessitates immedia te medica l or surgica l inte rvention to prevent damages to the

body.

User facil i ties mus t report a prob lem no later than 10 days after becoming aware of

i t. Failure to report accurately and in a timely manner can lead to c iv il o r even

criminal penalt ies. Problems resul ting in patient deaths are to be sent to the FDA

and to the equipment manufacturer. Serious i l lness or injury events are reported to

the manufacturer or, i f the manufacturer is not known, to the FDA. The

manufac turer has the respons ibil i ty to invest iga te the incident and, if appropriate,

report the inc ident to the FDA. Adverse events, inc lud ing those in which a dev ice

failed to performed as intended but did not resul t in a death or serious injury may

also be reported voluntari ly through the FDA's MedWatch program.

Reports sha ll not be admitted into evidence or otherwise used in a c iv il act ion

unless the fac i l i ty or personnel making the report knew that the information was

false. There are a number of ways that the information could become available,

including the Freedom of Information Act. It is therefore possible tha t th is

info rmation could be available for a c iv i l suit (698).

The user faci l i ty shou ld se t up a pro tocol for handl ing adverse inc idents in order

that they wi l l be properly reported in a timely fashion. Medical personnel need to

know who (the heal th care fac il i ty safety off icer, risk management, b iomedical

department, or other des ignated personnel) should receive the report.

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Questions For the fol lowing quest ions, answer

• f A, B , and C are correct

• i f A and C are correct

• i f B and D are correct

• is D is correct

• i f A, B, C, and D are correct.

1. Hypercarbia due to an incompetent unidirectional valve can be distinguished from that due to exhausted absorbent by A. The shape of the carbon dioxide waveform

B. An increase in inspired carbon dioxide

C. Increas ing the f resh gas f low

D. Absence of heat in the absorber

View Answer2. Causes of air entrainment include A. Suction applied to an nasogas tric tube curled in the esophagus

B. Malfunct ion of the in terface of a c losed scavenging system

C. Use of a mainstream gas analyzer

D. A leak in the venti lato r bel lows

View Answer3. What course of action should be taken if a gas crossover in the pipeline system is suspected? A. Use the oxygen f lush on the machine to purge the crossed gas

B. Disconnect the pipel ine, and open an oxygen cylinder

C. Turn up the f lowmeter for the crossed gas, and tu rn off the oxygen flowmeter

D. Use a resusci ta tion bag to vent i late wi th room a ir

View Answer4. Color(s) which an oxygen cylinder may be painted include

A. Black

B. Whi te

C. Blue

D. Green

View Answer5. Safety mechanism(s) that prevent a hypoxic mixture being delivered because the flowmeters are incorrectly set include A. The oxygen failure safe ty valve

B. An oxygen analyzer

C. The oxygen pressure fa ilure a la rm

D. Proport ioning system

View Answer6. A lower-than-expected anesthetic level may be caused by

A. Sevoflu rane breakdown by desiccated absorbent

B. A leak in a venti lator bellows

C. Vaporizer leak

D. Air f rom a light source

View Answer7. Which measures should be taken in the event that the oxygen pipeline supply is lost? A. Use low f resh gas flows

B. Open an oxygen cyl inder

C. Disconnect the machine f rom the centra l supply

D. Turn the pis ton venti lator OFF

View Answer8. A leak in the breathing system should be suspected if

A. The end-tidal carbon dioxide begins to increase

B. There is a change in the venti la tor sound

C. A standing venti lator bellows fails to return to the top of i ts housing

D. The FiO2 decreases during controlled vent i la tion

View Answer9. Which situations would result in a negative pressure in the breathing system?

A. Nasogastric tube p laced in the trachea

B. Suction applied to a work ing channel of a f iberscope

C. Malfunction of valves in a closed scavenging interface

D. Loss of oxygen pressure to the machine.

View Answer10. An obstruction in the breathing system may cause A. An increase in the peak breathing system pressure

B. Ac tivat ion of the high pressure alarm

C. Hypoventi lat ion

D. Decreased movement of the vent ilator bellows

View Answer11. Which monitors are reliable detectors of a breathing system disconnection?

A. Carbon d ioxide

B. Airway pressure

C. Respirometer

D. Oxygen analyzer

View Answer12. Causes of carbon dioxide in the inspiratory gas include A. Absorbent being bypassed

B. Inadequate f resh gas flow to a c i rc le breathing system

C. An incompetent unidirect ional valve

D. Excess carbon dioxide produc tion

View Answer13. Excessive airway pressure may be caused by

A. Malfunct ion of the APL valve

B. Use o f the oxygen f lush during inspira tion wi th certain mechanical venti lators

C. Obs truction in the scavenging system

D. A unidi rect ional PEEP valve p laced in the expiratory l imb

View Answer14. Anesthetic agent overdosage may be caused by

A. Isof lurane in a halothane vaporizer

B. Reversed f low through a vaporizer

C. Enf lurane in an isof lurane vaporizer

D. Overf i l led vaporizer

View Answer