Monday, 14 March 2016

Perioperative thermoregulation and heat balance. The Lancet Jan 2016.

This is a well-written review article which revisits the topic of thermoregulation under anaesthesia.
Important points to note include:

  • General anaethetic agents – volatiles, nitrous oxide and propofol – all reduces vasoconstriction and shivering threshold in a concentration-dependent manner, but has minimal effect on sweating threshold
  • Sedatives such a midazolam even combined with typical opioid doses do not appreciably impair thermoregulatory control
  • Neuraxial anaesthesia impairs thermoregulatory control such that patients are as hypothermic as those given a GA for similar operations. Effects of neuraxial and general anaesthesia on thermoregulatory control are additive
  • Peripheral nerve blocks do no have substantive thermoregulatory effects beyond preventing local thermoregulatory responses
  • Consequences of hypothermia include
    • coagulopathy – 1°C of hypothermia significantly increases blood loss by about 20%
    • delays wound healing
    • increases risk of wound infection
    • prolongs drug action – vecuronium, atracurium, propofol
    • prolongs recovery stay and hospital stay
  • Measures to maintain normothermia
    • Prewarming – prewarmed patients stay 0.4°C warmer
    • Most surgical patients will be hypothermic from passive insulation alone, forced air warmer is recommended
    • Fluid warming should be used if being given to patients in large volume (>1L/h). Each litre of room temperature fluid and each unit of blood reduces mean body temperature by 0.25°C in a 70kg patient
  • Temperature monitoring is recommended for general anaesthesia case over 30 minutes and substantial neuraxial cases
    • Best sites to monitor core temperature include the pulmonary artery, distal oesophagus, nasopharynx with the probe inserted 10-20cm and tympanic membrane,

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