Anaesthetic Implications of Hypothermia (5-Mark Answer)

1. Cardiovascular Effects

• Increased peripheral vascular resistance and cardiac arrhythmias (bradycardia, atrial fibrillation, even ventricular fibrillation in severe cases)
• Myocardial ischemia risk rises due to shivering-induced increase in O2 consumption combined with reduced O2 delivery
• "Left shift" of the oxyhemoglobin dissociation curve, reducing O2 release to tissues

2. Coagulation and Bleeding

• Reversible platelet dysfunction and impaired clotting enzyme activity cause coagulopathy
• Increased intraoperative blood loss and higher transfusion requirement

3. Drug Metabolism and Recovery

• Hepatic and renal blood flow/enzyme activity fall, delaying metabolism of anaesthetic agents (volatile agents, muscle relaxants, opioids)
• Prolongs emergence from anaesthesia and recovery of neuromuscular block; delayed awakening
• Minimum alveolar concentration (MAC) of volatile anaesthetics is reduced

4. Postoperative/Metabolic Effects

• Postoperative shivering increases O2 consumption by up to 2-3 times, stressing cardiopulmonary reserve
• Increased protein catabolism and surgical stress response
• Impaired wound healing and increased risk of surgical site infection
• Impaired renal function and altered mental status/cognitive recovery
• Increased overall perioperative morbidity and mortality

5. Monitoring and Management Implications

• Continuous core temperature monitoring is mandatory intraoperatively
• Active warming (forced-air warmers, warmed IV fluids/blood products, warmed and humidified gases, increasing ambient OT temperature) should be used, especially at extremes of age and in long/abdominal procedures
• Extra vigilance needed in cardiac/vascular cases where arrhythmia risk is heightened, and in patients on anticoagulants due to coagulopathy risk