CHOICE OF ANESTHETIC TECHNIQUE

Dr abdollahi 04/19/23

1

Anesthesiologists care for the surgical patient in the preoperative, intraoperative, and postoperative period . Important patient care decisions reflect the preoperative evaluation, creating the anesthesia plan, preparing the operating room, and managing the intraoperative anesthetic.

04/19/23

3

The anesthesiologist is ultimately responsible for:

(1) Determining the medical status of the patient,

(2) Developing a plan of anesthesia care,

(3) Reviewing with the patient or a responsible adult the proposed care plan.

After review of the patient's medical history and laboratory and other test results from the patient's medical record, confirmation by a focused physical examination, and review of the patient's fasting status, the anesthesiologist chooses the anesthetic technique.

ANESTHETIC TECHNIQUE

04/19/23

4

The anesthesiologist selects as the anesthetic technique:

(1) General anesthetic

(2) Regional anesthetic

(3) Peripheral nerve block

(4) Monitored anesthetic care (MAC).

The choice of anesthetic technique (or combination of techniques) is determined by surgical and patient considerations; frequently, more than one anesthetic technique is appropriate.

Considerations That Influence the Choiceof Anesthetic Technique

04/19/23

5

04/19/23

6

Intraoperative and postoperative monitoring considerations may influence the choice of anesthetic technique. For example, if rapid

neurologic evaluation is needed, a general anesthetic with

short-acting drugs or a regional anesthetic may be selected.

04/19/23

7

Conversely, if intraoperative transesophageal echocardiography is required, a general endotracheal anesthetic will probably be preferred. There are few circumstances in which a specific anesthetic technique has been demonstrated to be safer or more efficacious than another technique,but anesthesiologists may perform better with techniques with which they are more experienced.

04/19/23

8

Unpleasant side effects associated with anesthesia may influence the choice of anesthetic technique. Because the relative safety of different anesthetic techniques is often viewed as similar, patient satisfaction may become the principal determinant of the anesthetic technique selected.

04/19/23

9

Assuming equivalent safety, both the anesthesiologist and patient are likely to place the greatest importance on avoidance of pain, followed by vomiting, nausea, and to a lesser extent, urinary retention, myalgia, and pruritus. For some patients, avoiding an awake technique is the predominant concern, perhaps because of anxiety. For these patients, even in the absence of pain, the sights, sounds, and smells of the operating or procedure room are an experience to be avoided.

04/19/23

10

An ideal anesthetic technique would incorporate optimal

patient safety and satisfaction, provide excellent operating

conditions for the surgeon, allow rapid recovery, and

avoid postoperative side effects. In addition, it would be

low in cost, allow early transfer or discharge from the

postanesthesia care unit , optimize postoperative

pain control , and permit optimal operating room efficiency, including turnover times.

Physical Status Classification of the American Society of Anesthesiologists

04/19/23

11

General Anesthetic

04/19/23

12

General anesthesia may be initiated by the administration

of intravenous drugs or inhalation of a volatile anesthetic

with or without nitrous oxide.

INTRAVENOUS INDUCTION OF ANESTHESIA

04/19/23

13

Induction of general anesthesia (loss of consciousness) in adult patients is most often accomplished by the intravenous administration of drugs (propofol, thiopental, or etomidate) that produce rapid onset of unconsciousness. After loss of consciousness, the anesthesiologist may place a laryngeal mask airway (LMA) and or administer a neuromuscular blocking drug intravenously to produce skeletal muscle relaxation for facilitation of direct laryngoscopy.

04/19/23

14

The intravenous injection of a drug to produce unconsciousness followed immediately by a neuromuscular blocking drug that produces a rapid onset of skeletal muscle paralysis (succinylcholine, rocuronium, mivacurium) is referred to as "rapid-sequence" induction of anesthesia. Frequently, the patient is breathing oxygen (3 to 5 Umin) via a facemask (preoxygenation) before rapid-sequence induction of anesthesia.

04/19/23

15

Preoxygenation is intended to replace nitrogen (denitrogenation) in the patient's functional residual capacity (about 2500 mL of

21% oxygen) with oxygen. This practice should increase

the margin of safety during periods of upper airway obstruction or apnea (drug induced during direct laryngoscopy for tracheal intubation) that may accompany induction of anesthesia.

04/19/23

16

In healthy awake patients, the increase in arterial hemoglobin oxygen saturation achieved with eight vital capacity breaths of 100% oxygen over a period of 60 seconds is similar to that achieved by breathing 100% oxygen for 3 minutes at normal tidal volumes. Four vital capacity breaths over a 30-second

period also increases arterial oxygenation, but the time

until hemoglobin desaturation is shorter than in patients

breathing oxygen for 3 minutes or taking eight deep breaths.

Rapid-Sequence Induction of Anesthesia

04/19/23

17

A typical rapid-sequence induction of anesthesia includes

preoxygenation followed by the administration of a nonparalyzing (defasciculating) dose of a nondepolarizing

neuromuscular blocking drug (pancuronium, 1 to 2 mg IV or its equivalent) and succinylcholine (1 to 2 mg/kg IV).

Cricoid pressure may be applied by an assistant just before

the onset of drug-induced unconsciousness and loss of

protective upper airway reflexes.

04/19/23

18

Rocuronium, though not as rapid in onset as succinylcholine, is used as an alternative when a depolarizing muscle relaxant is contraindicated.

It is common practice to administer an opioid (fentanyl, 1 to 2 µg/kg IV or its equivalent) 1 to 3 minutes before administration of the induction drug.

04/19/23

19

The opioid is intended to blunt the subsequent presser and heart rate responses to direct laryngoscopy and tracheal intubation and also to initiate preemptive analgesia. Remifentanil and alfentanil undergo more rapid blood-brain equilibration than fentanyl does and thus may be more reliable in blunting the sympathetic nervous system responses evoked

by direct laryngoscopy and tracheal intubation.

04/19/23

20

with the onset of unconsciousness, the patient's head is positioned to optimize patency of the upper airway, and positive-pressure inflation of the patient's lungs with oxygen is instituted. Direct laryngoscopy for tracheal intubation is initiated only after the onset of skeletal muscle paralysis (often verified by a peripheral nerve stimulator), which is typically 45 to 90 seconds after the administration of succinylcholine.

04/19/23

21

Facilitation of tracheal intubation by skeletal muscle paralysis with pancuronium, vecuronium, atracurium, cisatracurium, or mivacurium is possible if it is acceptable to wait 3 to 5 minutes for their peak pharmacologic effect.

04/19/23

22

Monitoring of arterial hemoglobin oxygen saturation with a pulse oximeter provides early warning should arterial oxygen desaturation occur during the period of apnea required for tracheal intubation. It is mandatory that proper placement of the tube in the trachea be confirmed after direct laryngoscopy .

Evidence of a Patent Upper Airway after Induction of Anesthesia

04/19/23

23

04/19/23

24

After tracheal intubation, it may be prudent to insert a gastric tube through the mouth to decompress the stomach and remove

any easily accessible fluid. This orogastric tube should be

removed at the conclusion of anesthesia. Then gastric

suction is needed postoperatively, nornlally the tube should

be inserted through the nares rather than the mouth.

INHALATION INDUCTION OF ANESTHESIA

04/19/23

25

An alternative to rapid-sequence induction of anesthesia is the inhalation of sevoflurane (non pungent) with or without nitrous oxide.s Prior intravenous administration of a "sleep dose" of an induction drug may be used if an intravenous catheter is in place.

04/19/23

26

Desflurane produces a rapid onset of effect but is not selected for inhalation induction because of its airway irritant effects. Inhalation or "mask induction" of anesthesia is most often selected for pediatric patients when prior insertion of a venous catheter is not practical.

04/19/23

27

Sevoflurane may also be useful when difficult airway management is anticipated because of the absence of salivation and preservation of spontaneous breathing. The traditional

"awake look" in a patient with a suspected difficult airway,

which included titration of intravenous drugs until the patient tolerated direct laryngoscopy, has been modified to include spontaneous ventilation of high concentrations of sevoflurane until laryngoscopic evaluation is possible.

Characteristics of Inhalation Induction withSevoflurane

04/19/23

28

Loss of consciousness typically occurs within about 1 minute

when breathing 8% sevoflurane. LMA placement can usually be achieved within 2 minutes after administering 7% sevoflurane by facemask. The addition of nitrous oxide to the inspired gas mixture does not add significantly to the induction sequence. Prior administration of benzodiazepines may facilitate inhalation induction, whereas opioids may complicate this technique by increasing the likelihood of apnea.

04/19/23

29

A technique for induction of anesthesia with sevoflurane includes priming the circuit (emptying the reservoir bag and opening the adjustable pressure-limiting ["pop-off"] valve), dialing the vaporizer setting to 8% while using a fresh gas flow of 8 l/min, and maintaining this flow for 60 seconds before applying the facemask to the patient.

At this point a single breath from end-expiratory volume to maximum inspiration followed by deep breathing typically produces loss of consciousness in 1 minute.

04/19/23

30

After inhalation induction of anesthesia, a depolarizing or nondepolarizing neuromuscular blocking drug is administered intravenously to provide the skeletal muscle relaxation needed to facilitate direct laryngoscopy for tracheal intubation. If the anesthesiologist decides to not place a tube in the trachea, anesthesia is maintained by inhalation through a face mask or LMA.

MAINTENANCE OF ANESTHESIA

04/19/23

31

The objectives during maintenance of general anesthesia are amnesia, analgesia, skeletal muscle relaxation, and control of the sympathetic nervous system responses evoked by noxious stimulation. These objectives are achieved most often by the use of a combination of drugs that may include inhaled or injected drugs (or both), with or without neuromuscular blocking drugs. Each drug selected should be administered on the basis of a specific goal that is relevant to that drug's known pharmacologic effects at therapeutic doses.

04/19/23

32

For example, it is not logical to administer high concentrations of volatile anesthetics to produce skeletal muscle relaxation when neuromuscular blocking drugs are specific for achieving this goal.

Likewise, it is not acceptable to obscure skeletal muscle

movement by administering excessive amounts of neuromuscular blocking drugs because of insufficient doses of

anesthetics.

04/19/23

33

Indeed, a volatile drug is seldom administered as the sole anesthetic but is more often administered in combination with nitrous oxide. Substitution of nitrous oxide for a portion of the dose of the volatile anesthetic allows a decrease in the delivered concentration of the volatile drug, resulting in less cardiac depression despite the same total dose of anesthetic drugs.

04/19/23

34

Volatile anesthetics may provide inadequate analgesic effects, may be associated with postoperative hepatic dysfunction, and introduce the possibility of carbon monoxide production should they be exposed to desiccated carbon dioxide absorbents that

contain strong bases.

04/19/23

35

In certain instances it is acceptable to administer neuromuscular blocking drugs to ensure lack of patient movement and permit a decrease in the delivered concentration of volatile anesthetics. This use of neuromuscular blocking drugs, however, must not be interpreted as an endorsement for the administration of an inadequate dose of anesthetic that is obscured by skeletal muscle paralysis.

In this regard, intraoperative awareness is a recognized risk of minimal concentrations of anesthetic drugs ("light anesthesia"), especially when patient movements are obscured by drug-induced skeletal muscle paralysis.

04/19/23

36

Opioids that generally do not depress the cardiovascular system are combined most often with nitrous oxide . In patients with normal left ventricular function, however, the lack of opioid-induced cardiovascular depression and the absence of attenuation of sympathetic nervous system reflexes may be manifested as systemic hypertension. when this occurs, the addition of low concentrations of a volatile anesthetic to the

delivered gases is often effective in returning the increased

systemic blood pressure to an acceptable level.

04/19/23

37

Neuromuscular blocking drugs are often necessary, even in the absence of the need for skeletal muscle relaxation, because adequate doses of opioids administered in the presence of nitrous oxide are unlikely to prevent patient movement in response to painful stimulation. Another disadvantage of injected drugs versus inhaled anesthetics is an inability to accurately titrate and maintain a therapeutic concentration of the injected drug. This disadvantage can be offset to some extent by continuous intravenous infusion of the injected anesthetic at a rate previously determined in other patients to be associated with therapeutic concentrations in blood.

04/19/23

38

Brain function monitoring (bispectral index, entropy, auditory evoked potentials) may be helpful in titrating the dose of inhaled or injected anesthetic drugs to produce the desired degree of central nervous system depression .

Regional Anesthetic

04/19/23

39

A neuraxial regional anesthetic (spinal, epidural, caudal) is selected when maintenance of consciousness during surgery is desirable. Spinal anesthesia and epidural anesthesia each have advantages and disadvantages that may make one or the other technique better suited to a specific patient or surgical procedure.

04/19/23

40

Spinal anesthesia:

(I) takes less time to perform,

(2) produces a more rapid onset of better-quality sensory and motor anesthesia,

(3) is associated with less pain during surgery.

04/19/23

41

The principal advantages of epidural anesthesia are:

(I) a lower risk for post-dural puncture headache,

(2) less systemic hypotension if epinephrine is not added to the local anesthetic solution,

(3) the ability to prolong or extend the anesthesia through an indwelling epidural catheter,

(4) the option of using the epidural catheter to provide postoperative analgesia.

Skeletal muscle relaxation and contraction of the gastrointestinal tract are also produced by a regional anesthetic.

04/19/23

42

Patients may have preconceived and erroneous conceptions about regional anesthesia that will require the anesthesiologist to reassure them regarding the safety of this technique. The only absolute contraindication to spinal or epidural anesthesia is patient refusal. Certain preexisting conditions increase the relative risk of these techniques, and the anesthesiologist must balance the perceived benefits of this technique before proceeding.

Conditions That May Increase the RiskAssociated with Spinal or Epidural

Anesthesia

04/19/23

43

04/19/23

44

Disadvantages of this anesthetic technique include the occasional failure to produce sensory levels of anesthesia that are adequate for the surgical stimulus and the decrease in systemic blood pressure that may accompany the peripheral sympathetic nervous system blockade produced by the regional anesthetic, particularly in the presence of hypovolemia.

04/19/23

45

A regional anesthetic technique is most often selected for surgery that involves the lower part of the abdomen or the lower extremities in which the level of sensory anesthesia required is associated with minimal sympathetic nervous system blockade. This should not,

however, imply that a general anesthetic is an unacceptable

technique for similar types of surgery.

Bier block

04/19/23

46

For procedures lasting between 20 and 90 minutes, intravenous regional anesthesia (IVRA, or Bier block) may be used. IVRA provides reliable anesthesia for both the upper and lower extremities, although the latter may be more problematic because of the size of the lower extremities in adults. After the application of a tourniquet and exsanguination of the extremity, lidocaine (0.5%) is commonly administered into a catheter previously placed in the involved extremity.

04/19/23

47

Double tourniquets (distal cuff inflated over the area where local anesthetic has infiltrated with time) help ameliorate tourniquet pain. Intravenous analgesics such as ketorolac may be useful for treatment of patient discomfort during IVRA. IVRA is more cost- effective than general anesthesia or brachial plexus block

for outpatient hand surgery.

Peripheral Nerve Block

04/19/23

48

A peripheral nerve block is most appropriate as a technique

of anesthesia for superficial operations on the extremities . Advantages of peripheral nerve blocks include maintenance of consciousness and the continued presence of protective upper airway reflexes.

The isolated anesthetic effect produced by a peripheral

nerve block is particularly attractive in patients with

chronic pulmonary disease, severe cardiac impairment,

or inadequate renal function.

04/19/23

49

For example, insertion of a vascular shunt in the upper extremity for hemodialysis in a patient who may have associated pulmonary and cardiac disease is often accomplished with anesthesia provided by a peripheral nerve block of the brachial plexus. Likewise, avoidance of the need for neuromuscular blocking drugs in this type of patient circumvents the possible prolonged effect produced by these drugs in the absence of renal function.

04/19/23

50

A disadvantage of peripheral nerve block as an anesthetic

technique is the unpredictable attainment of adequate sensory and motor anesthesia for performance of the surgery. The success rate of a peripheral nerve block is often related to the frequency with which the anesthesiologist uses this anesthetic technique.

Patients must be cooperative for a peripheral nerve block to be effective. For example, acutely intoxicated and agitated patients are not ideal candidates for a peripheral nerve block

Monitored Anesthesia Care

04/19/23

51

MAC is defined by the ASA as a procedure in which an anesthesiologist is requested or required to provide anesthetic services; the anesthesiologist is responsible for preoperative evaluation, care during the procedure, and management after the procedure. This responsibility includes

(1) diagnosis and treatment of clinical problems during the procedure;

(2) support of vital functions;

(3) administration of sedatives, analgesics, hypnotics, anesthetic

drugs, or other medications as necessary for patient safety;

(4) psychological support and physical comfort;

(5) provision of other services as needed to complete the

procedure safely.

04/19/23

52

The care of a patient undergoing MAC is held to the same standard as any other anesthetic technique, given that the level of sedation may progress rapidly, go beyond consciousness, and lead to an "unplanned“ general anesthetic (specifically defined by the ASA as any instance in which the patient loses consciousness as defined by the ability to respond purposefully).when this occurs, extra care may be needed in monitoring to prevent airway mishaps such as upper airway obstruction and arterial hypoxemia, as reflected by the pulse oximeter reading.

04/19/23

53

while caring for a patient under MAC, it is important to consider the total dose of local anesthetic administered by the surgeon and the risk for local anesthetic toxicity, with an eye to potentially toxic doses . In addition to monitoring the patient, the anesthesiologist makes the decision to administer supplemental oxygen (may not be necessary if pulse oximeter readings are

acceptable while breathing room air), typically by nasal cannula. In addition to oxygen, the anesthesiologist may administer drugs intravenously to provide anxiolysis (midazolam), sedation (propofol), and analgesia (remifentanil, ketorolac, ketamine).

04/19/23

54

MAC may facilitate avoidance of side effects (sympatholysis, respiratory depression, delayed emergence) and can be particularly cost-effective in comparison to general or regional anesthetics in the ambulatory care setting.

PREPARATION FOR ANESTHESIA

04/19/23

55

Preparation for anesthesia after the preoperative medication

has been administered and the patient is transported to the operating room is similar regardless of the anesthetic

technique that has been selected . On arrival in the operating room, the patient is identified and the planned surgery reconfirmed.

Routine Preparation before Induction ofAnesthesia Independent of the Anesthetic

TechniqueSelecte

04/19/23

56

Anesthesia machine •Attach an anesthetic breathing system with a properly sized facemask•Occlude the patient end of the anesthetic breathing system and fill with oxygen from the anesthesia machine ("flush valve") (applying manual pressure to the distended reservoir bag checks for leaks in the anesthetic breathing system and confirms the ability to provide positive-pressure ventilation of the patient's lungs with oxygen)•Check the anesthetic breathing system valves•Calibrate the oxygen analyzer with air and oxygen and set alarm limits•Check the carbon dioxide absorbent for color change•Check the liquid level of vaporizers•Confirm proper function of the mechanical ventilator

04/19/23

57

• Confirm the availability and function of wall suction• Check the final position of all flowmeter, vaporizer, and

monitor (visual and audible alarm) settings

Monitors• Blood pressure• Pulse oximetry• Electrocardiography• Capnography

04/19/23

58

Drugs•Local anesthetic (lidocaine)•Induction drug (propofol, thiopental, etomidate)•Opioid (fentanyl, sufentanil, alfentanil, remifentanil)•Benzodiazepine (midazolam, diazepam)•Anticholinergic (atropine, glycopyrrolate)•Sympathomimetic (ephedrine, phenylephrine)•Succinylcholine•Nondepolarizing neuromuscular blocking drug (mivacurium, rocuronium, atracurium, vecuronium, cisatracurium, pancuronium)•Anticholinesterase (neostigmine, edrophonium)

04/19/23

59

• Opioid antagonist• Benzodiazepine antagonist• Catecholamine to treat an allergic reaction (epinephrine)

Equipment• Intravenous solution and connecting tubing• Catheter for vascular cannulation• Suction catheter• Oral and/or nasal airway• Laryngeal mask airway• Tracheal tube• Nasogastric tube• Temperature probe

04/19/23

60

The patient's medical record, including the nurse's notes, is consulted by the anesthesiologist to learn of any unexpected changes in the patient's medical condition, vital signs, or body temperature and to determine that the preoperative medication

and, if indicated, prophylactic antibiotics have been

administered. Likewise, any laboratory data that have become available since the anesthesiologist's previous visit should be reviewed.

04/19/23

61

Initial preparation for anesthesia, regardless of the technique of anesthesia selected, usually begins with insertion of a catheter in a peripheral vein and application of a blood pressure cuff. This initial preparation may be accomplished in a holding area or in the operating room. The use of separate rooms (induction rooms) distinct from the operating room for induction of anesthesia is not recommended by some because of the questionable safety of routinely moving anesthetized patients

with the necessary attached equipment from one area to

another.

04/19/23

62

An exception to this recommendation may be the performance of peripheral nerve blocks or institution of epidural anesthesia in a holding area so that the block is in place when the operating room becomes available.

Likewise, an epidural catheter for postoperative pain management may be placed in the holding area before transport of the patient to the operating room and induction of general anesthesia.

04/19/23

63

Monitors such as the pulse oximeter, electrocardiogram, and peripheral nerve stimulator are also applied while the patient is still awake.

Immediately before induction of anesthesia, baseline vital

signs (systemic blood pressure, heart rate, cardiac rhythm, arterial hemoglobin oxygen saturation, breathing rate)

and the corresponding time are recorded.

PHARMACOECONOMICS

04/19/23

64

The desire for cost containment often leads to recommendations that low-cost drugs (antiemetics, intravenous

induction drugs, volatile anesthetics, neuromuscular blocking drugs) be used in preference to newer, but more expensive drugs with desirable pharmacologic profiles. The ultimate goal must be to obtain the best results (low toxicity, rapid awakening, absence of nausea and vomiting) at the most practical cost. A useful method to decrease the cost of volatile anesthetics is the use of low fresh gas flow (2 L/min) during maintenance of anesthesia.