Haemodynamic consequences of mild therapeutic hypothermia after cardiac arrest

Mild therapeutic hypothermia (MTH) is used after out-of-hospital cardiac arrest (OHCA) to minimize cerebral damage. Induced hypothermia may further interfere with cardiac function and influence haemodynamics after OHCA.

This was a prospective study of haemodynamic variables in 50 consecutive patients with OHCA treated with MTH. Patients were cooled to a core body temperature of 32.5 degrees C for 24 h. Induction and maintenance of cooling was accomplished via infusion of 2 l of cold isotonic saline (4 degrees C) and a cooling blanket. Rewarming was performed to 36 degrees C at a rate of 0.3 degrees C per hour. Haemodynamic data were analysed and compared in individual patients during different temperature phases.

Heart rate dropped from a mean of 85 to 60 beats per min (P=0.001) during hypothermia. Mean arterial pressure dropped from 79 to 72 mmHg, despite a rise in vasopressors and inotropes. Lactate levels were elevated throughout the induction (mean+/-SD) and maintenance phase (mean+/-SD); however, this did not correlate with a decrease in SVO2. Pulmonary artery pressures decreased during induction of hypothermia despite rapid infusion.

MTH after OHCA lowered the heart rate. Despite induction of hypothermia with cold fluids, filling pressures decreased. Lower mean arterial pressure and cardiac output were observed during MTH, without deleterious effect on ScVO2. Lactate levels were elevated during MTH; however, levels did not correlate with outcome. Although the need for vasopressors and inotropes increases, this hypothermia-induced metabolic beta-blocker-like effect seems to have no negative effect on oxygen consumption and only temporarily affects anaerobic metabolism. No association of haemodynamic changes during MTH with outcome was found.