Maintaining Muscle Relaxation
Once the trachea is intubated you must decide whether or not it is necessary to maintain muscle paralysis.
Maintenance of paralysis is indicated for:
- Surgery where muscle relaxation is essential
- Mechanical ventilation in ICU when lung compliance is low
Remember that muscle relaxation and tolerance of mechanical ventilation does not necessarily require the use of a NMB. Deep anaesthesia or the use of high-dose opioids also allows an anaesthetized patient to be ventilated.
For elective surgery, where a standard induction was used with a non-depolarizing agent, repeated doses of the same relaxant can be used to maintain paralysis. The exact dose and frequency of administration should be guided by the response to a nerve stimulator.
For surgery where an Rapid Sequence Induction (RSI) was used, it is important to check that the effects of succinylcholine have worn off before using a non-depolarizing agent.
Question: Why is this?
Answer: To exclude succinylcholine apnoea.
Occasionally, patients have genetically abnormal plasma cholinesterase (the enzyme that metabolizes succinylcholine) so that its effects are significantly prolonged. In this situation paralysis could be still be present at the end of surgery.
If a non-depolarizing relaxant had been given without using the nerve stimulator to confirm recovery from succinylcholine, it would be unclear which muscle relaxant was responsible for the continued paralysis.
It is important to check with a PNS that the effects of the succinylcholine have worn off prior to administration of a non-depolarizing agent.