Hypothermic Coagulopathy Characteristics
Hypothermic coagulopathy is characterized by prolonged prothrombin time (PT) and prolonged partial thromboplastin time (PTT) when measured at the patient's actual hypothermic temperature, though standard laboratory testing at 37°C will show normal or near-normal values—making answer (a) the correct response in clinical practice, despite the underlying pathophysiology causing both PT and PTT prolongation. 1, 2, 3
Laboratory Testing Paradox
The critical issue with hypothermic coagulopathy is the disparity between clinical coagulopathy and laboratory results 2:
- Standard coagulation tests (PT and PTT) performed at 37°C will appear normal or near-normal, even when the patient has severe clinical coagulopathy 4, 1, 2
- When PT and PTT are measured at hypothermic temperatures (≤35°C), both become significantly prolonged 4, 3
- At 34°C, PT increases from 11.8 seconds to 12.9 seconds, and PTT increases from 36.0 seconds to 39.4 seconds 3
- At 28°C, PT increases to 16.6 seconds and PTT increases to 57.2 seconds 3
Mechanism: Enzyme Dysfunction, Not Factor Depletion
Hypothermic coagulopathy does NOT involve depletion of clotting factors (eliminating answers d and e) 1, 2:
- Hypothermia impairs the enzymatic activity of normally present coagulation factors, not their quantity 4, 1
- Each 1°C drop in temperature causes approximately 10% reduction in coagulation factor function 4, 1
- Platelet function becomes impaired between 33-37°C 4, 1
- Below 33°C, thrombin activity, glycoprotein Ib-IX complex, and platelet aggregation are inhibited 4, 1
Clinical Implications
The appropriate treatment is rewarming, not administration of clotting factors or fresh frozen plasma 1, 2:
- Hypothermia-induced coagulopathy is completely reversible with rewarming to 37°C 4, 1
- Administering clotting factors is ineffective because the factors are already present but non-functional due to temperature 2
- Rewarming strategies include removing wet clothing, forced air warming, warmed IV fluids, and in severe cases, extracorporeal rewarming 4, 1
Common Pitfall
Do not rely on standard PT/PTT results performed at 37°C to rule out coagulopathy in hypothermic patients 4, 1, 2, 3:
- These tests will underestimate or completely miss the coagulopathy 4, 5
- Clinical bleeding may be severe despite "normal" laboratory values 2, 6
- Thromboelastography (TEG) and bleeding time are better predictors of actual coagulopathic bleeding than PT in hypothermic patients 6
Synergistic Effects
Hypothermia combined with acidosis creates a synergistic impairment of coagulation that is worse than either condition alone 4, 1: