Virtual Disaster Medicine

Training Center (VDMTC)

Module 12

The American Society of Anesthesiologists' Management

of the Difficult Airway Algorithm and Explanation-Analysis of the Algorithm

Problems with the ASA Algorithm and Likely Future Directions

DURATION OF ACTION OF MUSCLE RELAXANT

In patients presenting for elective surgery who end up in a CICV situation, the following is a common story.  Preoperatively, the anesthesiologist does not recognize a difficult airway or feels the difficult airway is questionable and induces general anesthesia with an intravenous drug and paralyzes the patient with succinylcholine.  Mask ventilation is initiated without difficulty, but endotracheal intubation with conventional laryngoscopy fails.

Appropriately, gas exchange is controlled by mask ventilation for a second time, and then, after some adjustment, endotracheal intubation with conventional larngoscopy is attempted and fails for a second time.  Mask ventilation controls gas exchange for a third time, but is now perceptibly more difficult than before.  After some adjustments, endotracheal intubation with conventional laryngoscopy is attempted for the third time and fails.  At this point, approximately 5-8 mins have passed since the administration of succinylcholine.  Although the anesthesiologist may want to exercise the awake option, the patient is not breathing spontaneously and mask ventilation is now attempted for a fourth time.  However, mask ventilation is extremely difficult or impossible because the chest wall is rigid due to the patient sustaining a forceful exhalation mode and the presence of laryngospasm and edema due to the prior 3 laryngoscopies and intubation attempts.  Now a race begins and the question arises whether the patient will resume adequate spontaneous ventilation (awaken) before experiencing severe hypoxemia, possibly resulting in organ or body damage.  The answer is not certain and depends on many pharmacologic and physiologic variables.  From this common story in patients who have ended up in a CICV situation, the advantages and disadvantages of muscle relaxants with different duration of action become obvious (Table 2).  With the induction of general anesthesia in an uncooperative patient with a recognized difficult airway, the anesthesiologist should consider the relative merits of the preservation of spontaneous ventilation versus the use of muscle relaxants.

Table 2. Advantages and disadvantages of muscle relaxants with different duration of action

The use of succinylcholine in a patient either with a recognized or questionable difficult airway may not be the best choice, particularly if it is thought that mask ventilation will be possible and a smooth transition to an alternative plan of action (e.g., fiberoptic bronchoscopy⁴⁸), is desirable.  The key elements in the choice of a nondepolarizing muscle relaxant is the decision that mask ventilation will be adequate (see optimal attempt at mask ventilation) rescue plans have been made.

Alternatively, endotracheal intubation can be successfully accomplished without the use of any muscle relaxant, and this option should be considered in certain situations.⁵⁵  Also, if a small dose of succinylcholine (0.5-0.75 mg/kg) is used, good intubating conditions can be achieved within 75 sec for a duration of 60 sec, thus allowing an early-awaken option.  Another consideration is that in a large majority of patients, prior administration of a small dose of a nondepolarizing neuromuscular blocker may slightly diminish the duration of action of succinylcholine,⁵³ and thus the time to spontaneous recovery of airway reflexes may be shortened.

Lastly, whether to administer a second dose of succinylcholine following a cannot-intubate situation in which the patient resumes spontaneous ventilation is debatable, depending on the situation.  If the chances of achieving successful endotracheal intubation are high (i.e., a fairly good laryngoscopic grade), yet it is difficult to accomplish intubation because of incomplete paralysis, the administration of a second dose of succinylcholine may be appropriate.  It may also be considered appropriate in situations in which mask ventiatlion is possible, the laryngoscopist is highly skilled, and a simple change in either the patient’s position or the type of laryngoscope is necessary.  A small dose of glycopyrrolate (0.2-0.4mg) should be administered in conjunction with the repeat dose of succinylcholine in order to prevent a bradycardic response.

go to page      previous    1  2  3  4  5    next