Chapter 27: Skeletal Muscle Relaxants

Chapter 27: Skeletal Muscle Relaxants

Characteristics of phase I depolarizing neuromuscular blockade due to succinylcholine include

(A) Easy reversibility with nicotinic receptor antagonists

(B) Marked muscarinic blockade

(C) Muscle fasciculations only in the later stages of block

(D) Reversibility by acetylcholinesterase (AChE) inhibitors

(E) Sustained tension during a period of tetanic stimulation

Phase I depolarizing blockade caused by succinylcholine is not associated with antagonism at muscarinic receptors, nor is it reversible with cholinesterase inhibitors. Muscle fasciculations occur at the start of the action of succinylcholine. The answer is E.

A patient underwent a surgical procedure of 2 h. Anesthesia was provided by isoflurane, supplemented by intravenous midazolam and a nondepolarizing muscle relaxant. At the end of the procedure, a low dose of atropine was administered followed by pyridostigmine.

The main reason for administering atropine was to

(A) Block cardiac muscarinic receptors

(B) Enhance the action of pyridostigmine

(C) Prevent spasm of gastrointestinal smooth muscle

(D) Provide postoperative analgesia

(E) Reverse the effects of the muscle relaxant

Acetylcholinesterase inhibitors used for reversing the effects of nondepolarizing muscle relaxants cause increases in ACh at all sites where it acts as a neurotransmitter. To offset the resulting side effects, including bradycardia, a muscarinic blocking agent is used concomitantly. Although atropine is effective, glycopyrrolate is usually preferred because it lacks CNS effects. The answer is A.

A patient underwent a surgical procedure of 2 h. Anesthesia was provided by isoflurane, supplemented by intravenous midazolam and a nondepolarizing muscle relaxant. At the end of the procedure, a low dose of atropine was administered followed by pyridostigmine.

A muscarinic receptor antagonist would probably not be needed when a cholinesterase inhibitor was given for reversal of the skeletal muscle relaxant actions of a nondepolarizing drug if the NM blocking agent used was

(A) Cisatracurium

(B) Mivacurium

(C) Pancuronium

(D) Tubocurarine

(E) Vecuronium

One of the distinctive characteristics of pancuronium is that it can block muscarinic receptors, especially those in the heart. It has sometimes caused tachycardia and hypertension and may cause dysrhythmias in predisposed individuals. The answer is C.