Therapeutic hypothermia

Pioneer works on therapeutic hypothermia (TH) half a century ago already showed promising results but clinical application was limited by a lack of understanding of the underlying pathophysiology, lack of reliable method for temperature control and lack of intensive care facilities to deal with possible complications. More recently, 2 studies in 2002 supported the application of moderate TH (32.0-34.0℃) in post-cardiac arrest patients. Although the studies included only patients suffering from out-of-hospital VF, many ICUs world-wide are applying the therapy to all post-cardiac arrest patients irrespective of site or presenting rhythm. While primary coagulopathy and cardiogenic shock are usually stated as relative contraindications, evidences are accumulating to support the application of TH in patients with cardiogenic shock. TH can be divided into 4 phases: Induction, maintenance, de-cooling and normothermia. Induction is usually achieved by infusion of cold isotonic fluid. The precautions included avoidance of over-cooling, hypokalaemia, hyperglycaemia, and shivering. TH can be maintained by many different methods, varying in their level of invasiveness, cost and effectiveness. Issues including changes in pharmacokinetics and haemodynamics, and susceptibility to infection need to the addressed. The optimal duration of maintenance is unknown but the usual practice is 12-24 hours. De-cooling and rewarming is especially challenging because complications can be serious if temperature rise by more than 1℃ every 3-5 hours. Life-theatening hyperkalaemia can occur especially if patient suffers from renal insufficiency. Fever is a frequent complication either due to infection or post-cardiac arrest syndrome but patient must be kept normothermic for 72 hours.