MCQ MAHE 2000 Anesthesia Answer 1

The Correct Answer is A

Succinylcholine is the only depolarizing muscle relaxant used clinically. Its duration of action with the typical induction dose of 1 mg/kg is very short (five minutes) because of rapid hydrolysis by plasma cholinesterases. Patients with abnormal production of plasma cholinesterase due to genetic abnormalities cannot hydrolyze succinylcholine resulting in prolonged paralysis.

A “phase II block” resulting from repeated dosing can result in repolarization of the end plate that is only made more dense by administration of typical reversal agents. This desensitization is poorly understood, but may result in delay in recovery of muscle tone.

There are several characteristics unique to succinylcholine that may cause undesired effects.

• The sustained depolarization by the administration of succinylcholine typically produces transient fasiculations. Fasciculation of damaged or weakened myocytes may cause myocyte rupture and intracellular extravasation of potassium in patients at risk (burn patients, trauma patients, and patients with neuromuscular disease).
  
• Postoperative myalgias of the muscles of the neck, back, and abdomen are occasionally seen with its use. It is speculated that unsynchronized contractions of skeletal muscle fibers may lead to this side effect. Prior administration of low-dose nondepolarizing muscle relaxant (tubocurarine) can attenutate fasciculation, although it requires an increase of the Succinylcholine dose by 50-75%.
  
• Sinus bradycardia, junctional rhythms, and even sinus arrest may follow its administration. These responses likely reflect the action of succinylcholine at cardiac postganglionic muscarinic receptors where this drug mimics the normal response of acetylcholine. These effects are more likely to occur with doses given close together. Atropine, the muscarinic receptor blocker, can attenuate these effects if given prior to its administration.
  
• Increases in intraocular pressure, intragastric pressure, and trismus have been associated with the use of succinylcholine. Patients who develop severe trismus with the use of this drug should be considered susceptible to the triggering effect of succinylcholine on malignant hyperthermia.

Category: MAHE 2000 MCQs