Hemostasis in cardiac arrest patients treated with mild hypothermia initiated by cold fluids

Application of mild hypothermia (32-33 degrees C) has been shown to improve neurological outcome in patients with cardiac arrest. However, hypothermia affects hemostasis, and even mild hypothermia is associated with bleeding and increased transfusion requirements in surgery patients. On the other hand, crystalloid hemodilution has been shown to induce a hypercoagulable state. The study aim was to elucidate in which way the induction of mild therapeutic hypothermia by a bolus infusion of cold crystalloids affects the coagulation system of patients with cardiac arrest.

This was a prospective pilot study in 18 patients with cardiac arrest and return of spontaneous circulation (ROSC). Mild hypothermia was initiated by a bolus infusion of cold 0.9% saline fluid (4 degrees C; 30ml/kg/30min) and maintained for 24h. At 0h (before hypothermia), 1, 6 and 24h we assessed coagulation parameters (PT, APPT), platelet count and performed thrombelastography (ROTEM) after in vitro addition of heparinase.

A total amount of 2528 (+/-528)ml of 0.9% saline fluid was given. Hematocrit (p<0.01) and platelet count (-27%; p<0.05) declined, whereas APTT increased (2.7-fold; p<0.01) during the observation period. All ROTEM parameters besides clotting time (CT) after 1h (-20%; p<0.05) did not significantly change.

Mild hypothermia only slightly prolonged clotting time as measured by rotation thrombelastography. Therefore, therapeutic hypothermia initiated by cold crystalloid fluids has only minor overall effects on coagulation in patients with cardiac arrest.