Neuromuscular Blocking Drugs (also
see Chapter 13
)
Succinylcholine remains the neuromuscular blocker with fastest
onset—less than 1 minute—and shortest duration of action—5 to 10
minutes. These properties make it popular for rapid-sequence induction. Although
the use of succinylcholine may allow for return of spontaneous respiration before
the development of significant hypoxia in a "can't intubate-can't ventilate" situation,
this is unlikely to be the case in an emergency intubation in a trauma patient.
The anesthesiologist should not rely on return of spontaneous breathing in time to
salvage a difficult airway management problem but, instead, should proceed with efforts
to obtain a definitive airway, including cricothyroidotomy if other possibilities
have been exhausted.
Administration of succinylcholine is associated with several adverse
consequences. Serum potassium increases of 0.5 to 1.0 mEq/L are expected, but in
certain patients potassium may increase by more than 5 mEq/L.[29]
The hyperkalemic response is typically seen in burn victims and patients with muscle
pathology caused by direct trauma, denervation (as with SCI), or immobilization.
Hyperkalemia is not seen in the first 24 hours after these injuries, and succinylcholine
may be safely used for acute airway management.
Succinylcholine causes an increase in intraocular pressure and
should be used cautiously in patients with ocular trauma.[30]
Succinylcholine may also increase ICP,[31]
so its
use in brain trauma patients is controversial. In both these cases, however, hypoxia
and hypercapnia may be as damaging as the transient increase in pressure caused by
the drug. The provider must weigh the risks and benefits of succinylcholine administration
in each individual situation based on the severity of the CNS injury, the anticipated
speed with which intubation can be accomplished, and the likelihood of hypoxia.
Alternatives to succinylcholine include rocuronium (1 mg/kg) and
vecuronium (0.1 to 0.2 mg/kg). These drugs have no significant cardiovascular toxicity,
so large doses can be used to achieve rapid (1 to 2 minutes) systemic relaxation.
Unfortunately, at this dose, the duration of action of either rocuronium or vecuronium
will be 1 to 2 hours, which may be of significance if inadequate sedation leads to
patient awareness of paralysis or if it prevents ongoing neurologic assessment.
There will always be specific situations where maintaining spontaneous
ventilation during intubation is the preferred and indeed the safest manner in which
to proceed. If patients are able to maintain their airway temporarily but have clear
indications for an artificial airway (e.g., penetrating trauma to the trachea), slow
induction with ketamine or inhaled sevoflurane through cricoid pressure will enable
placement of an endotracheal tube without compromising patient safety. Fiberoptic
intubation can also be performed under such circumstances, as in the patient shown
in Figure 63-5
.
