Introduction

The history of induced hypothermia began in the 1950s with elective moderate hypothermia of the brain, introduced under anesthesia, for the protection–preservation during brain ischemia needed for surgery on heart or brain. In the early 1960s, Peter Safar recommended the use of therapeutic resuscitative hypothermia for humans after cardiac arrest in his cardiopulmonary–cerebral resuscitation algorithm. At this time, it was thought that moderate hypothermia (28–32 °C) was required for brain protection. Resuscitative hypothermia research was then given up for 25 years, as experimental and clinical trials had been complicated by the injurious systemic effects of total body cooling, such as shivering, vasospasm, increased plasma viscosity, increased hematocrit, hypocoagulation, arrhythmias, and ventricular fibrillation, when temperatures dropped below 30 °C, and lowered resistance to infection during prolonged moderate hypothermia. Moderate hypothermia was too difficult to induce and to maintain.

Peter Safar deserves most of the credit that mild therapeutic hypothermia was re-discovered in the mid 1980s. When he considered the reasons for various outcomes with the same durations of cardiac arrest in his dog experiments, he observed that relatively small differences in brain temperature in the range of mild hypothermia (33–36 °C) at the start of the experiments had a major influence on neurologic outcome. He and his research group then confirmed these observations in systematic studies of mild hypothermia before, during, and after cardiac arrest in dogs.