Moderate hypothermia has been demonstrated to improve neurologic outcome and mortality in patients who remain comatose despite return of spontaneous circulation (ROSC) after ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT)–induced cardiac arrest. This type of event leads to global cerebral ischemia with the potential for severe anoxic or hypoxic brain injury and progression to brain death. The patient populations studied in the original trials, which demonstrated this benefit, were those who had out-of-hospital events and as such there has been considerable debate as to whether this treatment would be useful for in-hospital cardiac arrests. In-hospital cardiac arrests are often secondary to long-developing deteriorations and are often the end result of a terminal illness. This is in contrast to out-of-hospital arrests, which are usually secondary to an acute coronary event. While the data are imperfect, there is some suggestion that inpatients with witnessed arrests from VF and VT may also benefit from this treatment.

The time between the witnessed arrest and ROSC is important. ROSC may not occur promptly and there is an outer limit that should obviate initiating hypothermia. The time limit adhered to for the out-of-hospital arrests was 60 minutes from time of collapse. Most in-hospital resuscitations do not continue this long and it is unclear what the outer limit for ROSC should be for initiating of cooling for in-hospital arrests.