What is hypothermic coagulopathy and how is it managed?

Hypothermic Coagulopathy: Mechanisms and Management

Hypothermic coagulopathy is primarily caused by temperature-dependent impairment of clotting enzyme function and platelet activity, not by clotting factor depletion, and is best managed through rewarming rather than fresh frozen plasma transfusion. 1

Pathophysiology of Hypothermic Coagulopathy

• Hypothermia impairs platelet function between 33-37°C and inhibits the activity of clotting factors and fibrinogen synthesis below 33°C, without causing actual depletion of clotting factors 1
• Temperatures below 33°C inhibit thrombin, glycoprotein Ib-IX complex, platelet aggregation, and thromboxane B2 production 1
• A 1°C drop in temperature is associated with approximately 10% drop in coagulation factor function, though the factors themselves remain present 1
• Hypothermia causes progressive prolongation of coagulation tests - partial thromboplastin time (PTT) increases 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, 2
• Prothrombin time (PT) similarly increases from 11.8 seconds at 37°C to 12.9,14.2, and 16.6 seconds at 34°C, 31°C, and 28°C 2

Clinical Significance in Trauma

• Hypothermia is one of seven key mechanisms in trauma-induced coagulopathy (TIC), alongside shock, tissue trauma, inflammation, acidemia, hemodilution, and massive transfusion 1
• Hypothermia below 35°C is often associated with acidosis, hypotension, and coagulopathy, forming part of the "lethal triad" in trauma patients 1, 3
• Hypothermia significantly increases mortality in trauma patients (7% vs 43% mortality in normothermic vs hypothermic patients) 3
• Temperatures below 34°C are associated with greater than 80% independent risk of mortality after controlling for differences in shock, coagulopathy, injury severity, and transfusion requirements 1

Laboratory Assessment Challenges

• Standard coagulation tests (PT and PTT) are routinely performed at 37°C in clinical laboratories, which underestimates the actual coagulopathy present in hypothermic patients 1, 4
• The coagulation effects of hypothermia can only be detected when tests are performed at the patient's actual low temperature, not at the standard 37°C 1, 4
• This creates a disparity between clinically evident coagulopathy and near-normal laboratory results in hypothermic patients 4

Relationship with Massive Transfusion

• Massive transfusion can contribute to hypothermia through the administration of cold blood products and fluids 5
• Hypothermia is a complication of massive transfusion, not the other way around 5
• Cold fluid infusion significantly decreases core temperature - one study showed that infusing 3 liters of cold fluids into trauma patients was associated with cardiac arrest in 12 patients, compared to only 3 patients when fluids were warmed 1

Management Approach

• The primary treatment for hypothermic coagulopathy is rewarming to 37°C, not administration of clotting factors or fresh frozen plasma 1, 4
• Hypothermia-induced coagulopathy is reversible, with studies showing that complications resolve with rewarming back to 37°C 1
• Management strategies include:
  • Removing wet clothing immediately and covering with warm blankets 3
  • Increasing ambient temperature in the trauma bay to 36-37°C 3
  • Using forced air warming devices and warming blankets 1
  • Administering warmed intravenous fluids 1, 3
  • In extreme cases, considering extracorporeal rewarming devices 1

Synergistic Effects with Other Factors

• Acidosis combined with hypothermia has a synergistic effect on impairing coagulation, while acidosis alone causes minimal change in clot formation 1
• Patients with extreme coagulopathy, hypothermia, and acidosis have extremely poor outcomes - one 8-year study found no survivors in this group 1
• Hemodilution from crystalloid resuscitation can worsen trauma-induced coagulopathy by diluting clotting factors and inducing hypothermia 1

Clinical Pitfalls to Avoid

• Do not rely on standard coagulation tests (PT, PTT) performed at 37°C to assess coagulopathy in hypothermic patients, as they will underestimate the severity 1, 4
• Avoid administering fresh frozen plasma as primary treatment for hypothermic coagulopathy, as the issue is not factor depletion but temperature-dependent dysfunction of normally present factors 1, 4
• Do not use cold intravenous fluids in trauma patients at risk for hypothermia 1
• Avoid focusing solely on blood product replacement while neglecting temperature management in bleeding patients 1, 3
• Remember that hypothermia below 33°C produces a coagulopathy functionally equivalent to having less than 50% of normal clotting factor activity, despite normal factor levels 6