Perioperative hypothermia and coagulopathy

Why examiners ask this

Hypothermia is the quiet complication that turns a bleeding patient into an exsanguinating one. Examiners use it to see whether you prevent rather than react, whether you understand that a normal lab coagulation panel can hide a cold patient's coagulopathy, and whether you connect temperature, acidosis and dilution into one problem. It stresses application of knowledge and judgment.

The 60-second answer

Decision points and the "why"

• Prewarming — it reduces the core-to-periphery gradient so redistribution costs less heat; it is the single most effective preventive step and it costs 30 minutes in holding.
• Core site — esophageal, nasopharyngeal, bladder or pulmonary artery temperature;¹ skin and axillary readings lag and underestimate. I use distal esophageal in a general anesthetic.
• Why cold bleeds — clotting factor activity falls about 10% per degree, platelet function fails, and fibrinolysis increases.³ Even mild hypothermia of less than 1 °C raises blood loss by about 16% and transfusion risk by about 22%,⁴ and in massively transfused trauma patients a temperature below 34 °C independently predicts death.³
• The lab lies — PT and aPTT are run at 37 °C, so a cold patient's coagulopathy looks normal on paper. I ask for TEG or ROTEM and tell the lab the patient's temperature, or I treat clinically.
• The lethal triad — hypothermia, acidosis and coagulopathy feed each other. In trauma I aim for damage control: short surgery, rewarm in the ICU, return later. I say this to the surgeon early.
• Calcium — citrate in transfused blood binds ionized calcium, and a cold liver clears citrate slowly. I keep ionized calcium in the normal range, 1.1–1.3 mmol/L,³ because calcium is factor IV and low calcium also depresses contractility.
• Rewarming targets — at least 36 °C before emergence and before ward transfer,² because postoperative hypothermia increases myocardial events, wound infection, and prolongs neuromuscular block and drug action.

The complication they will inject

During a pelvic fracture fixation after 8 units of red cells the field is oozing everywhere, the temperature is 33.8 °C, pH 7.21, ionized calcium 0.85, and the lab INR is 1.4. I tell the surgeon we are in the lethal triad and ask for packing and a damage-control plan. I give calcium chloride 1 g, continue plasma and platelets at a 1:1:1 ratio, give cryoprecipitate or fibrinogen concentrate if fibrinogen is 150 mg/dL or less,³ and check TEG. I give tranexamic acid if within 3 hours of injury and not yet given, because later doses increased bleeding deaths in CRASH-2.⁵ I raise the room temperature, add a second warming blanket and an underbody pad, run every fluid through a warmer, warm the irrigation, and consider a bladder or esophageal warming device. I recheck temperature, gas and coagulation every 30 minutes and plan transfer to the ICU intubated.

Pitfalls that cost points

• Reacting to hypothermia instead of describing prevention first.
• Trusting a normal PT in a cold, bleeding patient.
• Forgetting calcium during massive transfusion.
• Treating each part of the triad in isolation rather than as one problem with damage control as the strategic answer.
• Extubating a cold patient: shivering raises oxygen consumption up to several-fold and residual block is prolonged.

Rapid-why

Q: Why is the first-hour drop larger than later losses? A: It is redistribution, not loss: vasodilation lets core heat flow to the cooler periphery.

Q: When is deliberate hypothermia acceptable? A: Targeted temperature management after cardiac arrest and some cardiac or neurosurgical cases; otherwise normothermia is the standard.

Q: Why does shivering matter after surgery? A: It increases oxygen consumption and CO2 production; in a patient with coronary disease it provokes ischemia. Meperidine 12.5–25 mg IV stops it.

Q: Which patients cool fastest? A: Neonates, the elderly, burn patients, and those with large exposed body cavities or major regional plus general anesthesia, because both central and peripheral thermoregulation are impaired.

Numbers to know

Links

• Temperature monitoring and intraoperative hypothermia, Massive hemorrhage and transfusion, Trauma: initial management and damage control, dic, Arterial blood gas and acid-base interpretation
• ASA Practice Guidelines for Perioperative Blood Management; ACS TQIP Massive Transfusion in Trauma Guidelines