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Tourniquet Pain — FRCA Final MCQ

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ModerateGeneral AnaesthesiaTourniquet PainFRCA Final

A 25-year-old man undergoes arthroscopic anterior cruciate ligament reconstruction under general anaesthesia with an effective femoral nerve block. A thigh tourniquet is inflated to 250 mmHg. After 90 minutes of inflation, he develops progressive hypertension and tachycardia. The end-tidal anaesthetic concentration has been increased to 1.2 age-adjusted MAC without improvement. End-tidal carbon dioxide and core temperature remain normal, and there is no muscle rigidity. What is the most likely cause?

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Correct answer: D — Tourniquet pain

The correct answer is D, tourniquet pain. Prolonged cuff compression and limb ischaemia activate nociceptive afferents, including unmyelinated C fibres, producing sympathetic activation that may manifest under general anaesthesia as progressive hypertension and tachycardia. It commonly becomes apparent after prolonged inflation and may persist despite increasing hypnotic depth. A conventional femoral nerve block does not reliably block all cutaneous and perivascular afferents supplying the thigh tourniquet region. Inadequate hypnosis is less likely at 1.2 age-adjusted MAC without improvement after deepening. Malignant hyperthermia would usually produce an unexplained rise in carbon dioxide, often followed by rigidity and hyperthermia. Hypercapnia is excluded by normal capnography. Local anaesthetic systemic toxicity usually occurs around the time of injection and causes neurological excitation, arrhythmias or cardiovascular collapse rather than delayed isolated hypertension.

Reference: Xu F et al. Combined femoral artery block and femoral nerve block reduces thigh tourniquet-induced hypertension. Journal of Clinical Anesthesia. 2023;85:111039. https://pubmed.ncbi.nlm.nih.gov/36549034/