Classes
  • Tepid 34 - 35C
  • Mild 30 - 34C
  • Mod 25 - 30C
  • Deep 20 - 25C
  • Profound <20C


Anatomic & physiological changes
Cutaneous vasoconstriction -- ↓ convection & radiation
Piloerection
  • ↓ convective healoss by limiting air movement near skin
  • Insulates body from external cold as effectively as application of equal tickness of polyurethane foam

Metabolism
  • Rate ↓ 6% for each 1C of body temp
  • Linear ↓ w/ NMB b/c no shivering
  • <32 33C = body incapable of countering heat loss b/c impairment of heat production & retention systems
  • 22 24C = poikilothermia (assumes temp of surroundings)

CV
  • Initial stimulation = ↑HR ↑BP ↑ CO
  • <33C = initial stimulation ↓ as heart function is impaired
  • <31C = atrial & ventricular irritability
  • <30C = profound bradycardia w/ VF likely
  • 28C = VF threshold (cardioversion possible when warmed to 32C)
  • 21 24C = max risk of VF
  • 19 20C = Asystole
  • EKG changes


  • May persist for days after rewarming
  • Initial ↑ PR interval
  • Broadening QRS
  • ↑ QT interval
  • J wave @ QRS ST junction especially in lateral precordials
  • ST segment ↑ or ↓
  • T wave diphasic & then inverted
  • Phase 4 action potential ↓ slope w/ ↑ rate
Respiratory

  • 35C = ↑ RR
  • Linear ↓ RR until 30C
  • <30C = RR irregular, ↓ to 1 2 gasps/min, ↑ bronchial secretions
  • 28C = Apnea
  • ↓ETCO2
  • ↓ O2 release from cells = left shift of oxyhemo curve
  • 24C = Pulmonary edema likely
  • ↑ anatomic & physiologic dead space w/ bronchodilation of hypothermia
  • ↓1C = ph ↑ 0.0147


Neuro
  • 33 34C necessary for spinal cord protection
  • ↓ IOP from ↓ formation of aqueous humor & vasoconstriction
  • Initial stimulation of SNS in effort to restore normothermia
  • Depressed CNS & PNS
  • Q10 of 2 -- ↓ metabolic rate & O2 comsumption by 50% for each ↓ 10C
  • CNS

  • <35C = ↓ freq & amp  progressive slowing of activity (EEG)
  • 33C = cerebration ↓ from clouded conciousness
  • 30C = loss of conciousness
  • <20C = No EEG activity
  • Subcortical & spinal activity depressed = loss of purity of reflexes --> hyperreflexia --> areflexia @ 27 degrees celsius
  • CBF & CMRO2 ↓ 7% for each 1C ↓ unless shivering then ↑ O2 consumption & CBF requirements 100%
  • ↓CSF pressure & BF = ↓ brain volume