Patient hypothermia is a continuous concern during surgery under a general anaesthetic. It is caused by:
- the anaesthetic:
- unconscious patient, therefore, lack of behavioural measures to maintain warmth
- cutaneous vasodilatation with increased heat loss due to indirect hypothalamic depression of agent and direct peripheral action
- lack of shivering due to central depression
- cold anaesthetic gases respired
- cold fluids given intravenously
- surgery:
- patient usually has relatively large proportion of body surface area exposed
- immobile, no possibility of skeletal muscle activation
- low ambient theatre temperature encourages radiation and conduction losses
- theatre air systems e.g. laminar flow, increase heat loss by convection
- cold surgical instruments applied to skin
- haemorrhage of relatively warm blood at core temperature
Prevention is the aim. Most measures are simple e.g. insulating all but surgical field, warming blood.