Question 2

Describe the consequences of mild hypothermia in the early post-operative setting.

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College Answer

A well organised answer would provide details on domains of physiology, pharmacology and 
“other”, such as patient centred effects. Few answers mentioned pharmacology. Providing a 
definition of “mild” was often overlooked but doing so assisted a focused answer. Many answers 
spread beyond “mild” hypothermia or address the “causes” rather than the consequence –
neither of which gained marks as they were not answering the question asked. 


The Physiological Consequences of
Mild Hypothermia (32-35° C)

Endocrine and metabolic consequences

  • Decreased metabolism and oxygen consumption

  • Decreased carbohydrate metabolism and hyperglycaemia

  • Decreased drug metabolism and clearance

  • Essentially unchanged electrolytes

Haematological consequences

  • Increased hematocrit and blood viscosity

  • Neutropenia and thrombocytopenia

  • Coagulopathy and platelet dysfunction

Respiratory consequences

  • Decreased respiratory rate and medullary sensitivity to CO2

Acid-base changes: alkalosis and hypocapnea

  • Rise of pH with falling body temperature

  • Fall of PCO2 with falling body temperature

  • Increased oxygen solubility and O2-haemoglobin affinity

Pharmacological consequences

  • Delayed absorption
  • Decreased drug metabolism, especially hepatic metabolism
  • Delayed hepatic and renal clearance
  • Poorer affinity of receptors (eg. for catecholamines)

Cardiovascular consequences

  • Decreased cardiac output and bradycardia

  • QT prolongation and the J wave

  • Arrhythmias - classically AF and VF

  • Resistance to defibrillation

  • Vasoconstriction

Renal consequences

  • "Cold diuresis" due to decreased vasopressin synthesis

Central nervous system effects

  • Confusion and decreased level of consciousness

  • Shivering

  • Increased seizure threshold

Immunological consequences

  • Decreased granulocyte and monocyte activity


Wong, K. C. "Physiology and pharmacology of hypothermia." Western Journal of Medicine 138.2 (1983): 227.

Polderman, Kees H. "Application of therapeutic hypothermia in the intensive care unit." Intensive care medicine 30.5 (2004): 757-769.

Polderman, Kees H. "Mechanisms of action, physiological effects, and complications of hypothermia." Critical care medicine 37.7 (2009): S186-S202.