Cold, shivering and ischaemic in recovery — inadvertent perioperative hypothermia

Immediate assessment and the physiological diagnosis

This is a time-critical recovery-room scenario. The patient is hypothermic (34.9 degrees C), shivering, hypoxaemic, hypertensive with ventricular ectopy, and showing ST depression in a man with known ischaemic heart disease. The unifying diagnosis is demand ischaemia driven by shivering and hypothermia — the single most important complication of inadvertent perioperative hypothermia, and the leading cause of excess mortality attributable to it.^[4]

The physiology is the key to management and to the examination answer. Shivering is involuntary asynchronous skeletal-muscle contraction; it markedly raises whole-body oxygen consumption and carbon dioxide production.^[3] In a man with fixed coronary stenoses, that surge in demand cannot be matched by supply, and the myocardium becomes ischaemic (ST depression, ectopy). Hypothermia itself raises sympathetic tone and noradrenaline, causing vasoconstriction and hypertension (further raising demand) and, below about 34.5 degrees C, predisposes to arrhythmia. The hypoxaemia has several contributors: the shivering doubles carbon dioxide production (so the patient is hypoventilating relative to need), he is difficult to rouse (likely a combination of residual volatile, opioid, and prolonged neuromuscular blockade — hypothermia roughly doubles vecuronium duration), and cold shifts the oxyhaemoglobin dissociation curve leftward (less oxygen unloading). Frank et al (JAMA 1997) showed perioperative normothermia reduces morbid cardiac events from 6.3 to 1.4 per cent and ventricular tachycardia from 7.9 to 2.4 per cent — this patient is exactly that high-risk group, and the mechanism is playing out in front of you.