Burns
After a period of immobilization, burn injury causes upregulation
of both fetal (α2
βγδ) and mature (α2
βepsilonδ)
nAChRs.[740]
[741]
[742]
[743]
[744]
[745]
Upregulation of nAChRs is usually associated
with resistance to nondepolarizing neuromuscular blockers and increased sensitivity
to succinylcholine.[746]
Causes of upregulation
of nAChRs are listed in Table 13-16
.
A significant increase in the quantal content of evoked acetylcholine release is
noted by 72 hours after scald injury in rats.[747]
This increased acetylcholine release also contributes to the resistance to nondepolarizing
blockers in burn patients. In mice, thermal injury induces changes in diaphragm
acetylcholinesterase with respect to total content and specific molecular forms.
[748]
Anesthetic Implications
Resistance to the effects of nondepolarizing neuromuscular blocking
drugs is usually seen in patients with greater than 25% total-body surface area burns.
[244]
[746]
Recovery
of neuromuscular function to preburn levels may take several months[749]
or even years after the burn injury.[750]
The increase
in serum potassium that normally follows succinylcholine administration is markedly
exaggerated in burned victims.[119]
[751]
Potassium concentrations as high as 13 mEq/L and resulting in ventricular tachycardia,
TABLE 13-16 -- Conditions associated with upregulation and downregulation of acetylcholine
receptors
|
nAChR Upregulation |
nAChR Downregulation |
|
Spinal cord injury |
Myasthenia gravis |
|
Stroke |
Anticholinesterase poisoning |
|
Burns |
Organophosphate poisoning |
|
Prolonged immobility |
|
|
Prolonged exposure to neuromuscular blockers |
|
|
Multiple sclerosis |
|
|
Guillain-Barré syndrome |
|
|
nAChR, nicotinic acetylcholine receptor. |
|
From Naguib M, Flood P, McArdle JJ, et al: Advances
in neurobiology of the neuromuscular junction: Implications for the anesthesiologist.
Anesthesiology 96:202–231, 2002. |
fibrillation, and cardiac arrest have been reported.[751]
[752]
The magnitude of the hyperkalemic response
does not appear to closely correlate with the magnitude of the burn injury. Potentially
Iethal hyperkalemia was seen in a patient with only an 8% total-body surface area
burn.[753]
Succinylcholine has been safely administered
within 24 hours of a burn injury. After this initial 24 hours, however, sufficient
alteration in muscle response may have occurred, and the use of succinylcholine is
best avoided.
The time course of abnormal muscle membrane function corresponds
with that of the healing process. Once normal skin has regrown and any infection
has subsided, return of normal acetylcholine receptor populations appears to occur.
[754]
Normal responses to succinylcholine have
been
demonstrated in burn patients studied 3 years postinjury.[754]
The length of time during which a burn patient may be at risk for a hyperkalemic
response is not well defined. A conservative guideline would therefore be to avoid
the use of succinylcholine in patients 24 to 48 hours after a thermal injury and
for at least 1 to 2 years after the burned skin has healed.
