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The problem of masseter rigidity

Created: 16/11/2004

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.
Saddler JM
Br J Anaesth 1991; 67: 515-16

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