heatloss & thermoregulation

• Humans require a nearly constant internal body temperature for maintaining normal physiological functions
• The body temperature increases during exercise and fever and varies with temperature extremes of the surroundings
• Thermoregulatory system


  The homeostatic mechanisms for regulating body temperature
• Body temperature is controlled by balancing heat production against heat loss
• Anaesthetic-induced impairment of thermoregulatory control, combined with the operating room environment, imposes thermal stress on most patients
• Core


  Core temperature is uniform and high compared to the rest of the body, varies between 35.7C to 37.8C
• Periphery


  Normally thermoregulatory vasoconstriction maintain a temperature gradient between core and periphery about 4-2C
• Standard operating room temperature

  • For adults 21°C
  • For full term newborns 27°C
  • For premature newborns 29°C
• Heat loss mechanisms


  • Radiation
  • Convection
  • Conduction
  • Evaporation
• Hypothermia


  Core temperature 35°C or below

  
• Deleterious effects of hypothermia

  • Cardiac arrhythmias and ischaemia
  • Increased peripheral vascular resistance
  • Left shift of the hemoglobin-oxygen saturation curve
  • Reversible coagulopathy (platelet dysfunction)
  • Postoperative protein catabolism and stress response
  • Altered mental status
  • Impaired renal function
  • Decreased drug metabolism
  • Poor wound healing
  • Increased incidence of infection
• Equipment and methods to keep patient warm

  • Forced air warmers
  • Conductive warmers
  • Infusion warmers
  • Warming of irrigation fluids
  • Insulation
  • Radiative warmers
  • Airway heating and humidification
  • Esophageal warmers, endovascular warming catheters
  • Augmentation of heat production by aminoacids and fructose