Thermoregulation

Input: Peripherally, cutaneous cold receptors (unmyelinated C fibres, thinly-myelinated A-delta) – DRG – to posterolateral tract (Lissauer) for 1 or 2 segments up to 2nd order neurons –> 2ON decussate and travel up spinothalamic tract to ventral posterior lateral thalamus.

Processor: hypothalamus; Locus coeruleus, nuclear raphe magnus pons, pre-optic anterior hypothalamus

Output: sympathetic, endocrine, behavioural, extra-pyramidal

 

Measurements

Ranges: Mean core 36.4 to 37.4, Mean core-periph gradient 2-4 for Ambient 20-22,

Measurements: Nasopharynx, Distal oesophagus, PA, Bladder, Rectum, Tympanic membrane

Thermistors, Infrared, Electrical

 

Response to hypothermia

earliest is vaso- but anaesthesia causes periph vasodilatation

vasoconstriction – alpha1 adrenergic receptors, arterioles

non-shivering thermogenesis – beta3 adrenergic receptors, brown fat, doubles thermogenesis in infants, not very much in adults

 

Neuro – amnesia, confusion, coma

Neuromuscular – shivering, ataxia, dysarthria, stiffening, rigor

CVS – tachy, vasocons, BP/CO increase, brady, SVR increase/CO decrease, J waves, QRS wide, ST/TWI, AV block, QT prolong, VF/asystole

Resp -tachy, left shift Hb, brady, bronchospasm, right shift

Metabolic – diuresis, reduced H/glucose reabsorption

GI – decrease drug metab, lactic acid, ileus, ulcer, hep dysfunction

Haem – viscosity/hct increase, coagulopathy/cascade/platelets

imm – infection, leuc deplete, neutrophil impaired,

 

Rewarming methods

Forced air rewarming – Bair Hugger

Fluid rewarming

Passive insulators

Radiant

Humidification

Mattress

CPB

 

Effects of Anaesthesia

GA

Redistribution due to vasodilatation from core to periphery; starting temp, core:periphery size ratio, obesity

Linear due to cold cleaning fluids, cool air flow, ambient temperature, radiation, conduction, convection, evaporation, respiratory, iv fluids

Plateau due to central thermoregulatory threshold triggering peripheral vasoconstriction. Impaired sympathetic (T2dM) means plateau not reached

RA – input reduced, output (motor, sympathetic) reduced