What is true about hypothermic (low body temperature) coagulopathy?

Hypothermic Coagulopathy: Mechanisms and Clinical Implications

Hypothermic coagulopathy is primarily associated with impaired coagulation enzyme and platelet function rather than clotting factor depletion, and cannot be corrected with fresh-frozen plasma transfusion alone. 1, 2

Pathophysiology of Hypothermic Coagulopathy

Hypothermia affects coagulation through several mechanisms:

• Enzymatic dysfunction: Each 1°C drop in temperature causes approximately 10% decrease in coagulation enzyme function 1
• Platelet dysfunction: Hypothermia impairs platelet function between 33-37°C 1
• Clotting factor activity: Temperatures below 33°C inhibit thrombin, glycoprotein Ib-IX complex, platelet aggregation, and thromboxane B2 production 1
• Fibrinolysis: Hypothermia increases fibrinolytic activity 1

Laboratory Findings in Hypothermic Coagulopathy

A critical aspect of hypothermic coagulopathy is the discrepancy between clinical bleeding and laboratory tests:

• PT and PTT prolongation: When measured at the patient's actual hypothermic temperature, both PT and PTT are significantly prolonged 2, 3
• Laboratory artifact: Standard coagulation tests are routinely performed at 37°C, which masks the coagulopathy present at the patient's actual body temperature 1, 2
• Temperature effect on test results: PTT levels increase from 36.0 seconds at 37°C to 39.4,46.1, and 57.2 seconds at 34°C, 31°C, and 28°C respectively 1, 3

Why Fresh Frozen Plasma Doesn't Correct Hypothermic Coagulopathy

FFP transfusion alone cannot correct hypothermic coagulopathy because:

• The coagulopathy is primarily due to temperature-dependent enzyme dysfunction rather than factor depletion 2, 4
• At temperatures below 33°C, coagulation factor activity is reduced to less than 50% of normal despite normal factor levels 4
• The appropriate treatment is rewarming rather than factor replacement 2, 5

Clinical Implications and Management

The management of hypothermic coagulopathy should focus on:

1. Rewarming: Primary intervention should be restoration of normothermia 1, 2

   • Remove wet clothing
   • Cover patient to prevent heat loss
   • Increase ambient temperature
   • Use forced air warming
   • Administer warm fluids
   • Consider extracorporeal warming in extreme cases

2. Target temperature: Aim for normothermia with core temperatures between 36-37°C 1

3. Addressing other factors: Correct acidosis, hypocalcemia, and anemia which can exacerbate coagulopathy 1

Common Pitfalls in Management

• Relying on standard coagulation tests: Tests performed at 37°C will underestimate the severity of coagulopathy in hypothermic patients 2, 3
• Focusing solely on factor replacement: Administering FFP without rewarming will not effectively correct the coagulopathy 2, 5
• Overlooking synergistic effects: Hypothermia has synergistic effects with acidosis on coagulation impairment 1
• Misinterpreting laboratory results: Normal PT/PTT at 37°C may give false reassurance when the patient is hypothermic 1, 2

Based on the evidence presented, option C (hypothermic coagulopathy is associated with prolonged prothrombin time and partial thromboplastin time) is true, but only when measured at the patient's actual hypothermic temperature, not at the standard 37°C laboratory temperature.