Fundamentalof Ventilation & Pacemaker

7/28/2019 Fundamentalof Ventilation & Pacemaker

1/22

Fundamentals of Ventilation

The Lungs

The lungs consist of two cone shaped spongy organs that contain alveoli and trap air forgas exchange. The lung is designed for gas exchange. Its prime function is to allowoxygen to move from the air into the venous blood and carbon dioxide to move out.Although the lung performs other functions, its primary responsibility is to exchangegas. Oxygen and carbon dioxide (CO2) move between air and blood by simple diffusionthat is from an area of high to low partial pressure. Ficks Law of diffusion states thatthe amount of gas that moves across a sheet of tissue is proportional to the area of thesheet but inversely proportional to its thickness.The airways consist of a series of branching tubes which become narrower, shorter, andmore numerous as they penetrate deeper into the lung. The trachea divides into rightand left main bronchi, which in turn divide into lobar, then segmental bronchi. The

process continues down to the terminal bronchioles, which are the smallest airwaysoutside the alveoli. All these bronchi make u p the conducting airways. Their function isto lead inspired a ir to the gas exchanging regions of the lungs. Since conducting

airways contain no alveoli, they do not participate in gas exchange. The terminalbronchioles divide into respiratory bronchioles, which have few alveoli. Finally, we comethe alveolar ducts that are completely lined with alveoli. This alleviated area of the lung

where gas exchange occurs is called the respiratory zone.

During inspiration, the volume of the thoracic cavity increases and air is drawn into thelung. The increase in volume is brought about partly by contraction of the diaphragmand partly by the actions of the intercostals muscles. These muscular actions increasethe size of the thoracic cavity and air flows in due to the reduced pressure inside the

chest (inhalation; governed by Boyles law which states that the pressure of a gas isinversely proportional to its volume). Inspired air flows down to the terminal

bronchioles by bulk flow. Beyond that point, the combined cross-sectional area of theairways is so enormous because of the large number of branches, that the forwardvelocity of the gas becomes very small. Diffusion of gas within the airways then takes

over as the dominant mechanism of ventilation in the respiratory zone. The rate ofdiffusion within the airways is so rapid, and the distances covered arson short, thatdifferences in concentration within the alveoli are virtually abolished within a second.

An increase in thoracic volume results in a decrease in intrapulmonary pressure causing

air to be pushed out of the lungs (exhalation). The lung is elastic and returns passivelyto its pre-aspiratory volume during resting breathing. It is remarkably easy to distend.

For example, a normal breath of about 500 ml requires distending pressure of 3 cmwater. By contrast, a balloon may need a pressure of up to 30 cm water f or the samechange in volume.

Blood in need of oxygenation enters both lungs via the pulmonary arteries (from the

hearts right ventricle). Oxygenated blood leaves the lungs through the pulmonary veinsto the hearts left atrium. Air inspired through the nose, is passed through the tracheaand bronchea, eventually entering the terminal bronchioles which supply the alveoli or


2/22

air sacs, each 0.2mm in diameter. An estimated 300 million alveoli are contained in thelungs, generating up to 50 square metres of internal surface area at a lung volume of

3000ml.(The area of an average tennis court).

This gives rise to a total lung capacity of:3.6 litres to 9.4 litres in an adult male.

2.5 litres to 6.9 litres in an adult female.

RespirationRespiration is the interchange of gases between an organism and the medium in whichit lives. Internal respiration is the exchange of gases between the blood stream andnearby cells.

The mechanics of respirationInspiration results from the contraction of the diaphragm and intercostal muscles. Therib cage swings upwards and outwards. The enlarged cavity housing the lungsundergoes a pressure reduction (-3 mm Hg) with respect to the pressure existingoutside the body. Since the lungs are passive (no muscle tissue), they expand due tothe positive external pressure.

e.g. if the environmental pressure is 760 mm Hg, the lung pressure is 757 mm Hg uponinspiration.Expiration results from the relaxation of the diaphragm and intercostal muscles. The ribcage moves inward and downwards. The elastic recoil of the lungs creates a higher than

atmospheric intrapulmonic pressure (plus 3 mm Hg) that forces air out of the lungs.

Parameters of respiration

Tidal VolumeThe volume of gas inspired or expired during each respiratory cycle. Typically 500 ml.Inspiratory reserve volumeThe maximum amount of gas that can be inspired from the end-aspiratory position.

Expiratory reserve volumeAmount of air that can be forced out of lungs after normal expiration Typically 1200 ml

Residual volumeThe volume of gas remaining in the lungs at the end of a maximum expiration. Typically1200 ml.


3/22

Totaling capacityThe amount of gas contained in the lung at the end of a maximum inspiration.

Vital capacity

The maximum volume of gas that can be expelled from the lungs following a maximuminspiration.

Tidal volume, plus insp.reserve volume, plus exp.eserve volume. Typically 4800 ml.

Inspiratory capacityThe maximum volume of gas that can be inspired from the resting expiratory position.Typ.3600 ml.

Inspiritory reserve volumeAdditional volume that can be inspired after a normal inspiration. Typically 3100 ml.

Functional residual capacityThe volume of gas remaining in the lungs at the resting end-expiratory position.

Typically 2400 ml.

Minute volumeThe total volume of air ventilated over a minute period. Should be qualified eitherinspiratory or expiratory.

Maximum voluntary ventilationThe maximum volume of air that can be ventilated per minute (also referred to aMaximum Breathing Capacity).

Total lung capacity

Amount of gas contained in lungs at end of maximum inspiration Typically 6000 ml.

Lung compliance(The pulmonary volume change per unit pressure change).Essentially, lung compliance is the ability of the alveoli and lung tissue to expand oninspiration. In clinical terms it is defined as the volume increase in the lungs per unitincrease in the lung pressure. While clearly not a complete description of the pressure-volume properties of the lung, it is nevertheless useful in practice as a measure of thecomparative stiffness of the lung. The stiffer the lung, the less the compliance.Compliance is reduced by diseases which cause an accumulation of fibrous tissue in the

lung or by oedema in the alveolar spaces. It is increased in pulmonary emphysema and

also with age, probably because of alterations in the elastic tissue in both cases. There are two types of compliance, staticand dynamic.

The static compliance of the lung is the change in volume for a given change intranspulmonary pressure with zero gas flow.


4/22

Dynamic compliance measurements are made by monitoring the tidal volume used,while intra thoracic pressure measurements are taken during the instance of zero air

flow that occur at the end inspiritory and expiratory levels with each breath.

Lung compliance varies with the size of the lungs; a child has a smaller compliance thanan adult does. Furthermore the volume-pressure curve is not linear, hence compliance

does not remain constant. Fortunately, over the tidal volume range in which dynamiccompliance measurements are usually performed, the relationship is approximatelylinear and a constant compliance is assumed. Compliance values are given as litres percm of water.

Airway resistanceAirway resistance relates to the ease with which air flows through tubular respiratorystructures. Higher resistance occurs in smaller tubes such as bronchioles and alveolithat have not emptied properly. It is a pneumatic analogy of hydraulic or electricalresistance(R=V/I) and, as such, is a ratio of pressure to flow. Thus for thedetermination of airway resistance, intra alveolar pressure and airflow measurementsare required. As was the case with compliance, airway resistance is not constant over

the respiratory cycle. As pressure in the thoracic cavity becomes more negative, theairways are widened and the resistance is lowered. Conversely, during expiration, when

the pressure in the thorax becomes positive, the airways are narrowed and resistance isincreased. The intra alveolar pressure is given in cm water and the flow in litres persecond; the airway resistance is expressed in cm water per litre per second.

Lung elasticityLung elasticity is the ability of the lung elastic tissues to recoil during expiration. Thelungs should return to rest state easily to ensure sufficient exhaust of gas. Intra-thoracic pressure is the positive and negative pressure occurring within the thoracic

cavity. These are critical to proper inspiration (negative internal pressure) andexpiration (positive internal pressure). Intra alveolar pressure is of importance inmaintaining proper respiration and gas exchange to and from the blood.Only a portion of the air entering the respiratory system actually reaches the alveoli.The volume of air that is not available for gas exchange with the blood resides in theconducting spaces, known as 'dead air' and fills dead spaces consisting of and 150 ml.

Patient lung ventilatorsPatients lung ventilators connect to the patients airway and are designed to replace oraugment the patients ventilation automatically. They are used with a mask,endotracheal tube, (within the trachea) or tracheostomy tube (through an artificialopening in the trachea via the throat).Most ventilators are positive pressure during inhalation to inflate the lungs with variousgases or mixture of gases (air, oxygen, carbon dioxide, helium). Expiration is usually


5/22

passive, although under certain conditions pressure may be applied during expiratoryphase as well, in order to improve arterial oxygen tension. Only in rare circumstances is

negative airway pressure utilised during expiration.

Most ventilators are operated in any of three modes Assistor mode.

Controller mode.

Assistor/controller mode.

These three modes differ only in the method by which inspiration is initiated.

Assistor mode: Inspiration is triggered by the patient. A pressure sensor responds tothe slight negative pressure that occurs each time a patient attempts to inhale and

triggers are equipment to begin inflating the lungs. Thus, the ventilator helps thepatient inspire when he wants to breathe. A sensitivity adjustment is provided to selectthe amount of patient effort required to trigger the ventilator. The assistor mode is

used for patients who are able to control the breathing but are unable to inhale asufficient amount of air without assistance, or for whom the breathing requires toomuch effort (i.e. asthmatics, pulmonary pneumonia, etc.)

Controller mode: Breathing is controlled by a timer set to provide the desiredrespiration rate. Controlled ventilation is required for patients who are unable tobreathe on their own. In this mode, the ventilator has complete control over thepatients respiration and does not respond to any respiratory effort on the part of thepatient.

Assistor/controller mode: The ventilator is normally triggered when the patientattempts to breathe (as in the assistor mode). However, if the patient fails to breathe

within a pre-determined time, a timer automatically triggers the ventilator to inflate thelungs. Thus the patient controls his own breathing as long as he can, but if he shouldfail to do so, the equipment is able to take-over for him. On the other hand, this modecan be used to wean the patient from the controlled ventilation. If the patient attemptsto breathe during controlled ventilation, the equipment will sense the attempt andoperate in the assist mode immediately, irrespective of which part of the control phaseit had reached.

Ventilators in clinical use can be classified into two main groups: Pressure cycled Volume cycled.

Pressure cycled, positive pressure, controller or assistor/controllertype.


6/22

This device is powered pneumatically from a source of gas and requires no electricalpower. The equipment in this category may contain an electrically powered compressor,

or can be used with a separate compressor to commence ventilation with ambient air.Timing for operation in the controller mode is accomplished by filling a chamber with agas and letting it bleed off through an adjustable needle valve. Pressure cycle

ventilators can be quite small, but at the same time they can incorporate all the

necessary equipment to control the flow of gas, mixed air and oxygen, sense thepatients efforts to inspire, terminate inspiration when the desired pressure is reached,

permit adjustment of the sensitivity of the triggering mechanism and the desiredpressure level, and even generate negative pressure to assist expiration of somedevices. In the assistor/controller type, a special type of valve senses the smallnegative pressure created by patients attempts to breathe.

Volume cycled ventilators use either a piston or bellows to dispense precisely

controlled volume for each breath. In the intensive care setting where patients havepulmonary abnormalities and require calculated volumes (derived from blood gasanalysis) and concentrations of gas, this type of ventilator is preferred. It is much

larger than the pneumatically operated ventilator and electrically operated to provide a

much greater degree of control over the ventilation than the pressure cycle types. Mostvolume-cycled equipments have adjustable pressure limits and alarms for safety. Also,

their provision for adjusting pressure limits, and both inspiritory and expiratory times,can be used in conjunction with the volume setting to ensure therapeutic pulmonary

function in the patient who needs it most. Volume cycle ventilators used in mostintensive care units are always supplied with a spirometer to permit accuratemonitoring of the patients ventilation.Other available features may include a humidifier, and optional capabilities for negativepressure and positive end expiratory pressure (P. E. E. P.)

Non- invasive ventilation (CPAP/BiPAP)Use of CPAP and BiPAPThere is evidence that CPAP (Continuous Positive Airway Pressure) and BiPAP (BilevelPositive Airway Pressure) are effective in preventing need for intubation and alsodecreasing mortality in patients with Acute Respiratory Failure in properly selectedpatients.Noninvasive treatment doesn't involve the use of surgery to provide breathingassistance; it relies on the use of masks and mouthpieces to deliver air.

BiPAP differs from CPAP in that the pressure during expiration may be adjustedseparately from the pressure delivered during inspiration. This ability to setindependent pressures during inhalation and exhalation result in lower average airwaypressures than those produced by nasal CPAP.

Bi-PAP stands for Bilevel Positive Airway Pressure. The use of Bi-PAP machines is oftencalled non-invasive face mask ventilation. This is because the trachea is not intubatedso there is less trauma to the airway and more importantly there is a lower incidence ofnosocomial infections.


7/22

CPAP delivers a continuous positive air pressure, most frequently at about 10 cm ofwater. This is delivered throughout the respiratory cycle and has been described as

being similar to breathing with your head stuck out of a moving car. Continuous meansthat the pressure delivered to the patient is the same for any given breath. C-PAP canactually increase the work of breathing and be lethal to some patients.

BiPAP (Bilevel) means that the pressure varies during each breath cycle. When the userinhales, the pressure is similar to C-PAP. When they exhale, the pressure drops, makingit much easier to breath. Inhale, pressure rises, exhale, pressure drops. BiPAP deliversCPAP but also senses when an inspiratory effort is being made and delivers a higherpressure during inspiration. When flow stops, the pressure returns to the CPAP level.This positive pressure wave during inspirations unloads the diaphragm decreasing thework of breathing. This form of ventilation has been used for years in patients withchronic respiratory failure due to neuromuscular problems or chest wall abnormalities.In patients with respiratory failure, a common technique is begin with the expiratorylevel at 5 and the inspiratory level at 15. The levels are adjusted based on patient

comfort tidal volume achieved and blood gases.

As the use of BiPAP machines has increased, their cost has gone down. There are alsomore types of masks available and this has has improved patient comfort andcompliance. The use of BiPAP machines is often called non-invasive face mask

ventilation. This is because the trachea is not intubated so there is less trauma to theairway and more importantly there is a lower incidence of nosocomial infections.

Bi-PAP is a registered trademark of Respironics, Inc. Other manufacturers make VPAP

and Bilevel machines that provide this same basic feature.

Sometimes you will see a "ST" behind Bi-PAP, VPAP, or Bilevel. The ST stands forSpontaneous Timed. This means that if the user does not breath on their own, the

machine will initiate a breath for them. This feature is very useful in treating centralsleep apnea and a host of pulmonary disorders.

For those patients who present to the emergency department with acute respiratoryfailure but with normal levels of consciousness, no major secretion problems and whoare hemodynamically stable, a trial of BiPAP or CPAP could be attempted prior toconsidering intubation and a mechanical ventilator.


8/22

ACQUIRED ATRIOVENTRICULAR AND FASCICULAR BLOCKS INADULTS

Atrioventricular (AV) block is classified as first-, second-, or third-degree.

First-degree AV block is defined as an abnormally prolonged PR interval.

Second-degree, Mobitz type I AV block (Wenckebach) is manifested byprogressive prolongation of the PR interval eventuating in a dropped QRScomplex. It usually is associated with a narrow QRS complex. Second-degree,

Mobitz type II AV block demonstrates a constant PR interval before adropped QRS and usually is associated with a wide QRS complex.

Advanced AV block refers to blockage of two or more consecutive Pwaves, whereas complete (third-degree) AV block is defined as absence of

all atrioventricular conduction.

First-degree and type I second-degree AV block usually are caused bydelayed conduction in the AV node irrespective of QRS duration. Type IIsecond-degree AV block usually is infra-nodal, especially when the QRS iswide. Third-degree AV block may occur at any anatomic level.

The decision to implant a pacemaker in a patient with abnormal AVconduction depends on the presence of symptoms related to bradycardiaor ventricular arrhythmias and their prognostic implications.

BASIC FACTS A pacemaker is a small device that's placed under the skin of your chest or

abdomen to help control irregular heartbeats. This device uses electricalpulses to prompt the heart to beat at a normal rate.

Pacemakers are used to treat heart rhythms that are too slow, fast, orirregular. These abnormal heart rhythms are called arrhythmias.

Pacemakers can relieve some symptoms related to arrhythmias, such asfatigue (tiredness) and fainting, and can help people who have arrhythmiasresume a more active lifestyle.

A pacemaker is similar to an implantable cardioverter defibrillator (ICD),but an ICD can use higher energy electrical pulses to treat certain


9/22

dangerous arrhythmias. (To treat fast heart rhythms, a pacemaker iscombined with an ICD in a single device.)

Your doctor may recommend a pacemaker if aging, heart disease, or otherfactors make your heart beat too slow, too fast, or irregularly.

Symptoms such as fainting, shortness of breath, and fatigue (tiredness)may be due to an irregular heartbeat that a pacemaker could correct. Yourdoctor will confirm whether you need a pacemaker based on yoursymptoms, any medicines you take, and test results.

A pacemaker consists of a battery, a computerized generator, and wires.The generator sends the electrical pulses that correct or set your heartrhythm, and the wires carry pulses to and from various chambers of yourheart and the generator.

A pacemaker is similar to an implantable cardioverter defibrillator (ICD), but anICD can use higher energy electrical pulses to treat certain dangerous arrhythmias. (Totreat fast heart rhythms, a pacemaker is combined with an ICD in a single device.)

Your doctor may recommend a pacemaker if aging, heart disease, or other factorsmake your heart beat too slow, too fast, or irregularly.

Symptoms such as fainting, shortness of breath, and fatigue (tiredness) may be due toan irregular heartbeat that a pacemaker could correct. Your doctor will confirm whether

you need a pacemaker based on your symptoms, any medicines you take, and testresults.

A pacemaker consists of a battery, a computerized generator, and wires. The generatorsends the electrical pulses that correct or set your heart rhythm, and the wires carrypulses to and from various chambers of your heart and the generator.

Pacemaker surgery is usually done in a hospital or special heart treatment laboratory.You will be given medicine to help you relax. The surgery takes just a few hours, butyou will stay in the hospital overnight so your doctor can monitor your heart rhythm andmake sure your pacemaker is working properly.

Problems from pacemaker surgery are rare. Most people can return to normal activitieswithin a few days.

Your doctor may ask you to avoid any vigorous exercise or heavy lifting for a shortperiod after your surgery. After you have fully recovered from surgery, discuss with yourdoctor how much and what kinds of physical activity are safe for you.


10/22

Once you have a pacemaker, you have to avoid close or prolonged contact withelectrical devices or devices that have strong magnetic fields. You also need to avoidcertain medical procedures that can disrupt your pacemaker.

Let all of your doctors, dentists, and medical technicians know that you have apacemaker.

Have your pacemaker checked regularly. Some pacemaker functions can be checkedremotely through a telephone call or a computer connection to the Internet. Your doctormay ask you to come to his or her office to check your pacemaker.

Pacemaker batteries have to be replaced every 5 to 15 years, depending on how activeyour pacemaker is. The wires of your pacemaker also may need to be replacedeventually. Your doctor can tell you whether you need to replace your pacemaker or itswires.Back to Top

WHO NEEDS A PACEMAKER?

Doctors recommend pacemakers to patients for a number of reasons. The mostcommon reason is when a patient's heart is beating too slow or there are long pausesbetween heartbeats.

A pacemaker may be helpful if:

Aging or heart disease damages your sinus node's ability to set the correct pace foryour heartbeat. Such damage can make your heart beat too slow, or it can cause longpauses between heartbeats. The damage also can cause your heart rhythm to alternate

between slow and fast. You need to take certain heart medicines (such as beta blockers), but these medicines

slow down your heartbeat too much. The electrical signals between your heart's upper and lower chambers are partially or

completely blocked or slowed down (this is called heart block). Aging, damage to theheart from a heart attack, or other heart conditions can prevent electrical signals fromreaching all the heart's chambers.

You often faint due to a slow heartbeat. For example, this may happen if the main arteryin your neck that supplies your brain with blood is sensitive to pressure. In you have thiscondition, just quickly turning your neck can cause your heart to beat slower thannormal. When that happens, not enough blood may flow to your brain, causing you to

faint. You have had a medical procedure to treat an arrhythmia called atrial fibrillation. A

pacemaker can help regulate your heartbeat after the procedure. You have heart muscle problems that cause electrical signals to travel through your

heart muscle too slow. (Your pacemaker will provide cardiac resynchronization therapyfor this problem.)
http://www.cardiosmart.org/heartdisease/ctt.aspx?id=898http://www.cardiosmart.org/heartdisease/ctt.aspx?id=898http://www.cardiosmart.org/heartdisease/ctt.aspx?id=898


11/22

To decide whether a pacemaker will benefit you, your doctor will consider anysymptoms you have of an irregular heartbeat, such as dizziness, unexplained fainting,or shortness of breath. He or she also will consider whether you have a history of heartdisease, what medicines you're currently taking, and the results of heart tests.

A pacemaker won't be recommended unless your heart tests show that you haveirregular heartbeats.

TESTS THAT HELP DETERMINE WHETHER YOU NEED A PACEMAKER

A number of tests are used to detect an arrhythmia. Your doctor may recommend someor all of these tests.

EKG (Electrocardiogram)

This simple and painless test detects and records the electrical activity of the heart. An

EKG shows how fast the heart is beating and the heart's rhythm (steady or irregular). Italso records the strength and timing of electrical signals as they pass through each partof the heart.

Holter Monitor

A Holter monitor, also called an ambulatory EKG, records the electrical signals of yourheart for a full 24- or 48-hour period. You wear small patches called electrodes on yourchest that are connected by wires to a small, portable recorder. The recorder can beclipped to a belt, kept in a pocket, or hung around your neck.

During the 24 or 48 hours, you do your usual daily activities and keep a notebook,noting any symptoms you have and the time they occur. You then return both therecorder and the notebook to your doctor to read the results. Your doctor can see howyour heart was beating at the time you had symptoms.

The purpose of a Holter monitor is to record heart signals during typical daily activitiesand while sleeping, and to find heart problems that may occur for only a few minutes outof the day.

Echocardiogram

This test uses sound waves to create a moving picture of your heart. Anechocardiogram shows the size and shape of your heart and how well your heart ispumping blood. The test can identify areas of heart muscle that aren't contractingnormally or getting enough blood flow.

Electrophysiology Study


12/22

For an electrophysiology study, your doctor threads a small, flexible wire from a bloodvessel in your arm or leg to your heart. The wire electrically stimulates your heart to seehow your heart's electrical system responds. The electrical stimulation helps to findwhere the heart 's electrical system is damaged.

Stress Test

Some heart problems are easier to diagnose when your heart is working harder andbeating faster than when it's at rest. During stress testing, you exercise to make yourheart work harder and beat faster while heart tests, such as an EKG or echocardiogram,are performed.

HOW DOES A PACEMAKER WORK?

A pacemaker consists of a battery, a computerized generator, and wires with electrodeson one end. The battery powers the generator, and a thin metal box surrounds both it

and the generator. The wires connect the generator to the heart.

The pacemaker's generator sends the electrical pulses that correct or set your heartrhythm. A computer chip figures out what types of electrical pulses to send to the heartand when those pulses are needed. To do this, the computer chip uses the informationit receives from the wires connected to the heart. It also may use information fromsensors in the wires that detect your movement, blood temperature, breathing, or otherfactors that indicate your level of physical activity. That way, it can make your heart beatfaster when you exercise.

The computer chip also records your heart's electrical activity and heart rhythms. Your

doctor will use these recordings to set your pacemaker so it works better at making sureyou have a normal heart rhythm. Your doctor can program the computer in thepacemaker without having to use needles or directly contacting the pacemaker.

The wires in your pacemakersend electrical pulses to and from your heart and thegenerator. Pacemakers have one to three wires that are each placed in differentchambers of the heart.

The wires in a single-chamber pacemaker usually carry pulses between the rightventricle (the lower right chamber of your heart) and the generator.

The wires in a dual-chamber pacemaker carry pulses between the right atrium and theright ventricle and the generator. The pulses help coordinate the timing of these twochambers' contractions.

The wires in a triple-chamber pacemaker are used for heart muscle weakness and carrypulses between an atrium and both ventricles and the generator. The pulses helpcoordinate the timing of the two ventricles with each other.


13/22

TYPES OF PACEMAKER PROGRAMMING

There are two main types of programming for pacemakersdemand pacing and rate-responsive pacing.

A demand pacemaker monitors your heart rhythm. It only electrically stimulates yourheart if its beating too slow or if it misses a beat.

A rate-responsive pacemaker will speed up or slow down your heart rate depending onhow active you are. To do this, the rate-responsive pacemaker monitors your sinusnode rate, breathing, blood temperature, or other factors to determine your activity level.Most people who need a pacemaker to continually set the pace of their heartbeat haverate-responsive pacemakers.

WHAT TO EXPECT DURING PACEMAKER SURGERY

Placement of a pacemaker requires minor surgery, which is usually done in a hospital orspecial heart treatment laboratory. You will be given medicine right before the surgerythat will help you relax and may make you fall nearly asleep. Your doctor will give you alocal anesthetic so you won't feel anything in the area where he or she puts thepacemaker.

First, your doctor will place a needle in a large vein, usually near the shoulder oppositeyour dominant hand. The doctor will then use the needle to thread the pacemaker wires

into a vein and to the correct location in your heart.

An x-ray "movie" of the wires as they pass through your vein and into your heart willhelp your doctor place the wires. Once the wires are in place, your doctor will make asmall cut into the skin of your chest or abdomen. He or she will then slip the pacemakergenerator/battery box through the cut, place it just under your skin, and connect it to thewires that lead to your heart.

Once the pacemaker is in place, your doctor will sew up the cut. The entire surgerytakes a few hours.

How Do I Prepare for the Biventricular Pacemaker Implant?

Ask your doctor what medications you are allowed to take before getting your biventricular

pacemaker. Your doctor may ask you to stop certain medications several days before your

procedure. If you havediabetes, ask your doctor how you should adjust your diabetic medications.
http://www.medicinenet.com/script/main/art.asp?articlekey=343http://www.medicinenet.com/script/main/art.asp?articlekey=343http://www.medicinenet.com/script/main/art.asp?articlekey=343http://www.medicinenet.com/script/main/art.asp?articlekey=343


14/22

Do not eat or drink anything after midnight the night before the procedure. If you must take

medications, drink only small sips of water to help you swallow your pills.

When you come to the hospital, wear comfortable clothes. You will change into a hospital gown for

the procedure. Leave all jewelry and valuables at home.

WHAT TO EXPECT AFTER PACEMAKER SURGERY

Expect to stay in the hospital overnight so your heartbeat can be monitored and yourdoctor can make sure your pacemaker is working properly. You probably will have toarrange for a ride to and from the hospital because your doctor may not want you todrive yourself.

For a few days to weeks after surgery, you may have pain, swelling, or tenderness inthe area where your pacemaker was placed. The pain is usually mild and often relieved

by over-the-counter medicines. Consult with your doctor before taking any painmedicines.

Your doctor also may ask you to avoid any vigorous activities and heavy lifting for abouta month. Most people return to normal activities within a few days of having pacemakersurgery.

Back to Top

WHAT ARE THE RISKS OF PACEMAKER SURGERY?

Your chance of having any problems from pacemaker surgery is less than 5 percent.

These problems may include:

Swelling, bleeding, bruising, or infection in the area where the pacemaker was placed Blood vessel or nerve damage A collapsed lung A bad reaction to the medicine used to make you sleep during the procedure Infections that can become difficult to treat

Risks of Pacemaker Surgery

Nerve damage at the incision site Damage to the tissues or blood vessels around the heart or the incision

site Pneumothorax(collapsed lung) Bruising at the site of placement (this is an expected effect of surgery)
http://www.cardiosmart.org/heartdisease/ctt.aspx?id=898http://www.cardiosmart.org/heartdisease/ctt.aspx?id=898http://adam.about.net/encyclopedia/Pneumothorax-series.htmhttp://adam.about.net/encyclopedia/Pneumothorax-series.htmhttp://adam.about.net/encyclopedia/Pneumothorax-series.htmhttp://www.cardiosmart.org/heartdisease/ctt.aspx?id=898


15/22

Faulty pacemaker that does not function as intended after the surgery(very rare)

Faulty lead wires that connect the pacemaker to the heart (very rare) Lead wires that become dislodged after surgery due to activity or poor

placement

HOW WILL A PACEMAKER AFFECT MY LIFESTYLE?

Once you have a pacemaker, you have to avoid close or prolonged contact withelectrical devices or devices that have strong magnetic fields. Devices for which closeand prolonged exposure can interfere with a pacemaker include:

Cell phones iPods Appliances, such as microwave ovens

High-tension wires Metal detectors Industrial welders Electrical generators

These devices can disrupt the electrical signaling of your pacemaker and stop it fromworking properly. You may not be able to tell whether your pacemaker has beenaffected. How likely a device is to disrupt your pacemaker depends on how long you'reexposed to it and how close it is to your pacemaker.

To be on the safe side, some experts recommend not putting your cell phone or iPod in

a shirt pocket over your pacemaker (if they are turned on). You may want to hold thecell phone up to the ear thats opposite the site where your pacemaker was implanted. Ifyou strap your iPod to your arm while listening to it, put it on the arm farthest from yourpacemaker.

You can still use household appliances, but avoid close and prolonged exposure, as itmay interfere with your pacemaker.

You can walk through security system metal detectors at your normal pace. You alsocan be checked with a metal detector wand as long as it isn't held for too long over yourpacemaker site. You should avoid sitting or standing close to a security system metal

detector.

Stay at least 2 feet away from industrial welders or electrical generators.

You also need to avoid some medical procedures that can disrupt your pacemaker.These procedures include:

Magnetic resonance imaging (also called MRI)


16/22

Shock-wave lithotripsy to get rid of kidney stones Electrocauterization to stop bleeding during surgery

Let all of your doctors, dentists, and medical technicians know that you have apacemaker. You also should notify airport screeners. Your doctor can give you a card

that states what kind of pacemaker you have. Carry this card in your wallet.

PHYSICAL ACTIVITY

In most cases, having a pacemaker won't limit you from doing sports and exercise,including strenuous activities. You may need to avoid full-contact sports, such asfootball. Such contact could damage your pacemaker or shake loose the wires in yourheart. Ask your doctor how much and what kinds of physical activity are safe for you.

FOLLOWUP

Your doctor will want to check your pacemaker regularly. Over time, a pacemaker canstop working properly because:

Its wires get dislodged or broken Its battery fails Your heart disease progresses Devices giving off strong electrical, magnetic, or radio waves have disrupted its

electrical signaling

To check your pacemaker, your doctor may ask you to come in for an office visit severaltimes a year. Some pacemaker functions can be checked remotely through a telephone

call or a computer connection to the Internet. Your doctor also may ask you to have anEKG (electrocardiogram) to monitor changes in the electrical activity of your heart.

BATTERY REPLACEMENT

Pacemaker batteries last between 5 and 15 years, depending on how active thepacemaker is. Your doctor will replace the generator along with the battery before thebattery begins to run down.

Replacement of the generator/battery is a less involved surgery than the originalsurgery to implant the pacemaker. The wires of your pacemaker also may need to bereplaced eventually. Your doctor can tell you whether you need to replace yourpacemaker or its wires.

WAVEFORMS


17/22

The principle of defibrillation is to deliver a current to depolarise a criticalamount of myocardium so that ventricular fibrillation (VF) is abolished. If theheart is viable, the natural pacemaker of the heart takes over after a

variable pause. Since the process of depolarisation of the critical amount ofmyocardial cells occurs in the 300 to 500 seconds after delivery of shock,successful defibrillation is defined as termination of ventricular fibrillation forat least 5 seconds following a shock. Recurrence of VF should not beconsidered as a failure of the shock. Shock success cannot be equated torestoration of a perfusing rhythm or survival.

Waveforms of defibrillation can be monophasic or biphasic. Olderdefibrillators deliver monophasic waveforms while the newer ones

deliver biphasic wave form.

Monophasic as the name implies, delivers current in only one direction. Inmonophasic damped sinusoidal waveform, the current returns to baselinegradually while in the monophasic truncated expontenial waveform, currentabruptly returns to baseline of zero. Though no waveform is consistentlyassociated with higher return of spontaneous circulation or survival,biphasic waveforms are found to be safe and effective in lower doses thanmonophasic waveforms.

Biphasic shocks of 200 Joules seem to have efficacy similar, if not betterthan 360 Joules of monophasic shocks. High efficacy of biphasic shockswould mean that final outcome will depend more on the interval betweencollapse and CPR or defibrillation.

Two types of waveforms for biphasic shock are 1) biphasic truncatedexponential waveform and 2) rectilinear biphasic waveform. Selected anddelivered energies differ for rectilinear biphasic waveform in the usualrange of thoracic impedance, usually the delivered energy is higher than

that selected. Hence lower energies are selected with this waveforminitially. Automatic external defibrillators have been programmed to deliverfixed or escalating energy levels on repeated shock, though evidence iffavour of either protocol is lacking (Circulation. 2005;112:IV-35 IV-46).


18/22

UNDERSTANDING DEFIBRILLATION WAVEFORMS

Before we start, lets define a few terms:

Energy: Energy in a defibrillator is expressed in joules. A joule is the unit of

work associated with one amp of current passed through one ohm ofresistance for one second.

When we express it in a formula, it is generally stated as follows:Joules (Energy) = Voltage X Current X TimeJoules have become a surrogate for current in modern defibrillatorlanguage.

Current: Current is what actually defibrillates the heart. It is also expressedas Voltage/Impedance (resistance).

Impedance: Resistance to Flow; there is resistance in the electrical circuititself as well as in the patient. The amount of impedance in a patient isdifficult to determine as it relates to body mass, temperature, diaphoresisquality of the contact with paddles or pads. Impedance is expressed inohms.

Monophasic Waveforms: A type of defibrillation waveform where a shockis delivered to the heart from one vector as shown below. It is showngraphically as current vs. time.

In this waveform, there is no ability to adjust for patient impedance, and it isgenerally recommended that all monophasic defibrillators deliver 360J ofenergy in adult patients to insure maximum current is delivered in the faceof an inability to detect patient impedance.

Biphasic Waveforms: A type of defibrillation waveform where a shock isdelivered to the heart via two vectors. Biphasic waveforms were initially


19/22

developed for use in implantable defibrillators and have since become thestandard in external defibrillators.

While all biphasic waveforms have been shown to allow termination of VFat lower current than monophasic defibrillators, there are two types of

waveforms used in external defibrillators. These are shown below.

Defibrillator manufacturers have approached biphasic defibrillationdifferently.

Both Physio Control and Philips use the biphasic truncated exponential

(BTE) waveform originally developed for internal defibrillators, though theyuse different energy settings with the waveform. Physio Control uses whatthey term a high energy biphasic waveform, which they term ADAPTIVBiphasic. Physio Control energy settings go up to 360 joules of energy andthey essentially distribute the voltage and current available over a widerrange of energy settings. Additionally they vary the voltage and extend theduration of the shock in higher impedance patients.

Therefore, with a Physio Control BTE Waveform, you might see thefollowing differences in the waveform when patient impedance differs:


20/22

Philips Medical also uses the biphasic truncated exponential waveform in

their SMART Biphasic device, but in this case, they distribute the voltageand current available over a more narrow range of energy with themaximum current delivered at 200J, roughly equivalent to that delivered bythe Physio Control device at 360J.

The Rectilinear Biphasic Waveform (RBW) is used by ZOLL Medical, and itdiffers from both of the BTE waveform devices. ZOLL fixes voltage at themaximum and varies resistance in order to deliver constant current acrossthe broad range of patients. Like Philips, 200 Joules is the maximumsetting on the defibrillator, however this maximum represents more voltage

on the capacitor than either Physio Control or Philips has available.Additionally, the duration of the ZOLL RBE waveform is fixed at 10 msecbased upon work by Gliner et al.1 which indicates that the defibrillationthreshold decreases with increasing time up to a point around 10-12 msec,after which is begins to increase. As there is concern in the literature aboutthe effects of current on myocardial stunning, ZOLL chooses not to gobeyond that threshold.2

The ZOLL RBW defibrillator actually divides impedance into twocomponents: equipment-based impedance and patient-based impedance.

Rather than adjusting the secondary variables, such as voltage and time,the ZOLL RBW adjusts the equipment-based impedance, and adds orsubtracts resistors in the equipment as required to control for an essentiallyconstant current during the course of the first phase.

For example, for a 200J energy setting, the ZOLL RBW charges thecapacitor to the maximum voltage regardless of patient impedance. In the


21/22

case of a patient with 50 ohms of impedance, the defibrillator controlleradds ohms of resistance to effectively dampen the amount of currentbeing delivered to the patient. For a patient with 150 ohms of impedance,no equipment-based resistors are added, and the full amount of current isdelivered to the patient. In laboratory bench tests, at 200J, ZOLL delivered27.8A peak current and 24.0A average current to a 50 ohm resistor, and14.8A peak current and 12.5A average current to a 150 ohm resistor. Atenergy settings less than 200J, the difference between peak and averagecurrent is even less, typically a maximum of 1A.

Note:

It is really not a good idea to try to compare manufacturers biphasic waveforms as each is appropriate forthe device in which it is found and none has been shown to be superior to others despite a number of

clinical trials.

1. Gliner et al. Circulation 1995;92:1634-45

Provide postoperative monitoring, analgesia, and care

Obtain a chest X-ray as ordered. A postoperative chest X-ray is

used to identify lead location and detect possible complications,


22/22

such as pneumothorax or pleural effusion.

Position for comfort. Minimize movement of the affected arm

and shoulder during the initial postoperative period.

Restricting movement minimizes discomfort on the operative

side and allows the leads to become anchored, reducing the risk

of dislodging.

Assist with gentle ROM exercises at least three times daily, beginning 24

hours after pacemaker implantation. ROM exercises

help restore normal shoulder movement and prevent contractures on theaffected side.

Monitor pacemaker function with cardiac monitoring or intermittent ECGs.Report pacemaker problems to the physician:

Failure to pace. This may indicate battery depletion, damage

or dislodgement of pacer wires, or inappropriate sensing.

Failure to capture (the pacemaker stimulus is not followed

by ventricular depolarization). The electrical output of the

pacemaker may not be adequate, or the lead may be dis
http://cardiophile.org/2010/09/biphasic-and-monophasic-waveforms-for-defibrillation/?share=linkedin&nb=1

Fundamentalof Ventilation & Pacemaker

Documents

Transcript of Fundamentalof Ventilation & Pacemaker