A 56-year-old man is hospitalized due to worsening fever, chills, and perirectal pain. Physical examination reveals a large perirectal abscess. Empiric antibiotics are begun, and surgical drainage is planned. The patient receives succinylcholine and propofol prior to the procedure. The intraoperative course is uneventful, but postoperative spontaneous recovery of respiration and voluntary muscle activity does not occur. Mechanical respiratory support is continued, and several hours later, the patient is successfully weaned from the ventilator. Which of the following is the most likely underlying cause of this patient's postoperative complications?

Question

A 56-year-old man is hospitalized due to worsening fever, chills, and perirectal pain.  Physical examination reveals a large perirectal abscess.  Empiric antibiotics are begun, and surgical drainage is planned.  The patient receives succinylcholine and propofol prior to the procedure.  The intraoperative course is uneventful, but postoperative spontaneous recovery of respiration and voluntary muscle activity does not occur.  Mechanical respiratory support is continued, and several hours later, the patient is successfully weaned from the ventilator.  Which of the following is the most likely underlying cause of this patient's postoperative complications?

Quizplus · Accepted Answer

Succinylcholine is a depolarizing neuromuscular blocking agent used to induce skeletal relaxation during intubation and surgery. It acts as a competitive agonist of nicotinic acetylcholine receptors of the motor endplate, where it induces persistent depolarization, leading to endplate desensitization and skeletal muscle paralysis. Succinylcholine is rapidly metabolized by plasma pseudocholinesterase; only around 10% of the administered dose reaches the neuromuscular junction, where it typically has a duration of action of <10 minutes. This patient, who developed prolonged muscle weakness (eg, failure of spontaneous respiration and voluntary muscle activity) after receiving succinylcholine, most likely has pseudocholinesterase deficiency, an autosomal recessive disorder caused by a genetic polymorphism in the BCHE gene. Patients are unable to metabolize succinylcholine, leading to a large amount of the drug reaching the neuromuscular junction and prolonged paralysis. Heterozygotes may experience double the normal duration of paralysis, and homozygotes can have persistent paralysis for several hours. Patients with pseudocholinesterase deficiency also experience prolonged effects of mivacurium (a nondepolarizing neuromuscular blocker) and cocaine. (Choices A and D) Succinylcholine is metabolized by plasma pseudocholinesterase, not the liver or kidneys. Because pseudocholinesterase is produced in the liver, patients with severe liver disease may have prolonged drug effects due to impaired synthetic function. However, paralysis would not be expected to last for hours. (Choice B) Propofol is highly lipid soluble and has a very short duration of action (seconds) because of rapid redistribution from the brain, where it activates the GABA-A receptor, to other tissues. Propofol is a hypnotic agent; it does not cause muscle paralysis. (Choice E) Patients with myasthenia gravis (ie, autoantibodies to the acetylcholine receptors of the neuromuscular junction) have fewer active acetylcholine receptors and are therefore highly resistant to succinylcholine. Paralysis can occur with high doses but is unpredictable. Use is usually avoided in this population. Educational objective: Succinylcholine is a depolarizing neuromuscular blocking agent used to induce skeletal muscle relaxation; it typically has a very short duration of action due to metabolism by plasma pseudocholinesterase. Pseudocholinesterase deficiency is an autosomal recessive disorder that results in the inability to metabolize succinylcholine, leading to prolonged neuromuscular paralysis after drug administration.

A 56-Year-Old Man Is Hospitalized Due to Worsening Fever, Chills