Question 18

Last updated 20/01/2022 - 01:14
 Topic: Thermoregulation
Pass rate
7%
Other SAQs in this paper:
Other SAQs in this topic:

Outline the consequences of mild hypothermia in a patient following major surgery.

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College Answer

This is another very important, and not an infrequently seen, aspect of almost daily intensive care
practice which was poorly understood by candidates. For a good answer candidates were
expected to outline pharmacological (eg alteration in drug behaviour), physiological (eg shivering,
vasoconstriction, impaired coagulation, etc) consequences. Additional points such as poor wound
healing, discomfort also attracted a small number of marks. Candidates would have benefited by
illustrating their answers with examples, eg prolonged recovery from anaesthesia and duration of
neuromuscular blokade.
Syllabus: L2e
References: Hemmings, Foundation of Anaesthesia: Basic and Clinical Science pg 815

Discussion

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

References

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.

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