Muscle Relaxants

Muscle relaxants are used to facilitate intubation in the induction phase and provide effective surgical exposure during the maintenance stage of the procedure (Table 4.2).

Succinylcholine is used mostly for tracheal intubation at induction due to its quick onset of action and rapid spontaneous recovery. Succinylcholine has many well known side effects:

1. Increased intracranial pressure

2. Increased intragastric pressure (predisposing to aspiration)

3. Sinus bradycardia and asystole from repetitive doses

4. Increase in serum potassium (avoided in patients with burns and spinal cord injury >24 hours out)

Nondepolarizing muscle agents often cause hypotension and bradycardia and are used in conjunction with other agents to support cardiac function. Reversal of muscle relaxants can be produced by either through the use of pyridostigmine, edrophonium or a combination of neostygmine and atropine.

Table 4.2. Characteristics of muscle relaxants

Muscle Relaxant

Dose (mg/kg)

Duration

Comments

Depolarizing

Succinylcholine

1

5 min

Hyperkalemia

Nondepolarizing

Mivacurium

0.2

10 min

Useful for intubation with quick onset and short duration

Atracurium

0.5

1 hour

Hoffman elimination without hepatic elimination

Vecuronium

0.1

1 hour

Rapid onset with little cardiac effects

Pancuronium

0.1

>1 hour

Analgesia, although partially created through use of inhalational agents and ketamine, is primarily the domain of the opioids (Table 4.3).

Meperidine is the most effective agent in stopping postoperative shivering. Me-peridine is metabolized to normeperidine that has significant CNS toxicity with prolonged administration or in patients with renal insufficiency.

Sufentanyl has a similar potency to fentanyl with shorter recovery times and greater cardiac and respiratory depressant effects. Alfentanil is only one fifth to one third as potent as fentanyl but has faster times to awakening, orientation and ambulation. The central nervous system effects and respiratory depression caused by opioids can be reversed using naloxone which also acts to partially reverse the effects of benzodiazepines and barbiturates.

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