CHOICE OF ANESTHETIC TECHNIQUE

1. CHOICE OF ANESTHETIC TECHNIQUE Dr abdollahi

2. 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.

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.

4. ANESTHETIC TECHNIQUE • 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.

5. Considerations That Influence the Choiceof Anesthetic Technique

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.

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.

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.

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.

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.

11. Physical Status Classification of the American Society of Anesthesiologists

12. General Anesthetic • General anesthesia may be initiated by the administration • of intravenous drugs or inhalation of a volatile anesthetic • with or without nitrous oxide.

13. INTRAVENOUS INDUCTION OF ANESTHESIA • 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.

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.

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.

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.

17. Rapid-Sequence Induction of Anesthesia • 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.

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.

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.

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.

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.

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 .

23. Evidence of a Patent Upper Airway after Induction of Anesthesia

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.

25. INHALATION INDUCTION OF ANESTHESIA • 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.

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.

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.

28. Characteristics of Inhalation Induction withSevoflurane • 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.

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.

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.

31. MAINTENANCE OF ANESTHESIA • 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.

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.

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.

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.

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.

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.

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.

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 .

39. Regional Anesthetic • 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.

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.

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.

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.

43. Conditions That May Increase the RiskAssociated with Spinal or Epidural Anesthesia

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.

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.

46. Bier block • 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.

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.

48. Peripheral Nerve Block • 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.

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.

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