Failure to Regain Consciousness
Evaluation of a patient who does not regain consciousness after
general anesthesia requires careful assessment
of the patient. Preoperative factors such as drug or alcohol intoxication should
be sought. The most common reason for persistent somnolence is the residual effects
of anesthetics, sedatives, and preoperative medications.[115]
Initial management should include pharmacologic reversal agents
aimed at the most likely sedative drug. Naloxone in small doses will increase the
ventilatory rate if narcotic sedation is the problem. Physostigmine (1.25 mg intravenously)
can reverse the effects of some sedatives and inhaled anesthetics.[116]
The sedative and amnestic effects of the benzodiazepines can be reversed by the
use of flumazenil (up to 1.0 mg intravenously).[117]
[118]
Because profound neuromuscular blockade can make a patient appear
unconscious, such blockade should also be considered. This etiology is unlikely,
however, in the absence of significant respiratory compromise, as well as unconsciousness.
Once pharmacologic etiologies are ruled out, metabolic and structural causes must
be sought.
Profound hypothermia (temperature <33°C) can produce unconsciousness,
as can profound abnormalities in serum glucose such as hyperglycemia or hypoglycemia.
Blood glucose, electrolytes, and blood gases should be evaluated in all such cases.
If one has reason to suspect hypoglycemia, 50% dextrose should
be administered immediately and blood glucose determination not awaited. If the
diagnosis remains unclear, a structural neurologic abnormality should be sought.
Raised intracranial pressure may occur after head trauma or neurosurgery. Thromboembolic
cerebrovascular accidents can occur in the postoperative period but are uncommon.
[119]
[120]
Intraoperative
cerebral hypoxia from hypoxemia or poor cerebral perfusion can produce a diffuse
encephalopathy. Emergency computed axial tomographic scanning can be used to evaluate
the presence of raised intracranial pressure or an acute intracranial hemorrhage
as the cause of the delayed emergence. Rarely, overdose with lidocaine can be manifested
as unconsciousness.[121]
Old age per se does not
account for delayed emergence from general anesthesia (see Chapter
62
).[122]
