How hypothermic surgery works

During cardiac surgery, the heart sometimes needs to be stopped to allow surgeons to perform delicate procedures, such as replacing valves. If left uncorrected, the subsequent lack of oxygen supply would lead to brain damage within minutes. Cardiopulmonary bypass can overcome most of these effects, although it is technically not possible in all patients.

Hypothermic cardiac surgery can now be used to overcome these limitations. The body is cooled from its normal 37 degrees Celsius (98.6 degrees Fahrenheit) to as low as 24 degrees Celsius (75.2 degrees Fahrenheit). Cold saline solutions are infused into the bloodstream via the major vessels and the heart is surrounded by ice. This stabilises cell membranes and reduces the metabolic rate. Once cool enough, the heart is stopped using a potassium-rich solution. In this reduced oxygen-dependent state, the body can temporarily survive without the heart beating.

When surgery is completed, the potassium solution is rinsed out and the body re-warmed before the heart is restarted. Hypothermic cooling isn’t without its risks, however; there is a chance that once a procedure is finished and the body re-warmed, the heart might not restart.