Increased masseter tone occurs in 0.3% of those under halothane anaesthesia given succinylcholine, but only 50% of those referred have positive muscle biopsy.
There are at least three degrees
- Poor relaxation - "common" response
- Mild increase in tone - can intubate and ventilate
- Jaws of steel - can't intubate
- Check nerve stimulator to see if relaxant dose is adequate
- Check muscle tone in extremities
- Clinical picture does not prospectively predict susceptibility
Management of spasm is controversial. Termination of anaesthesia, treatment with dantrolene, proceeding with caution or referral for muscle biopsy have all been recommended.
[i] Jaw stiffness - an ill understood condition.
Br J Anaesth 1991; 67: 515-16