The lethal triad - Hypothermia, Acidosis and Coagulopathy

acidosis coagulopathy hypothermia massive transfusion Mar 02, 2026

The lethal triad

Major haemorrhage is rarely a single problem. It is a cascade. As perianaesthesia nurses, we often meet patients at the point where physiology is beginning to unravel. The lethal triad describes the dangerous interplay between hypothermia, acidosis and coagulopathy during severe bleeding. Once established, each element worsens the others.

Hypothermia reduces platelet function and slows enzymatic reactions within the coagulation cascade. Even mild drops in core temperature can impair clot formation. At the same time, ongoing blood loss and hypoperfusion lead to metabolic acidosis. Reduced tissue oxygen delivery drives anaerobic metabolism and lactate accumulation. Acidosis then further impairs myocardial performance and clotting factor activity.

Coagulopathy develops from dilution, consumption of clotting factors, hypothermia and acidosis. The blood loses its ability to clot effectively. More bleeding follows. The cycle deepens.

🩸 Hypothermia slows clotting enzyme activity and platelet function
🩸 Acidosis reduces cardiac output and impairs coagulation pathways
🩸 Coagulopathy increases bleeding and factor depletion
🩸 Each component amplifies the others if not corrected early

For perianaesthesia practice, early recognition is everything. Active warming, minimising exposure, warmed fluids and blood products, and close temperature monitoring are simple but powerful interventions. Monitor arterial blood gases, lactate and haemodynamic trends. Escalate concerns promptly and support massive transfusion or haemorrhage protocols when indicated.

The lethal triad is not inevitable. It develops when bleeding and physiological stress outpace correction. Interrupting the cycle, even in small ways, protects clot integrity and organ perfusion. Timely, coordinated care is what changes the trajectory.

References

Cosgriff, N., Moore, E.E., Sauaia, A., et al. (2010). Predicting life-threatening coagulopathy in the massively transfused trauma patient. Injury.
Maegele, M. (2015). The coagulopathy of trauma: mechanisms and management. Transfusion and Apheresis Science.
Australian College of PeriAnaesthesia Nurses. (Year not provided). The lethal triad in perianaesthesia practice. Journal of PeriAnaesthesia Nursing.

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