29 September 2020
Surgery on ice
Published online 19 June 2012
Purposefully dropping a surgical patient's core temperature to below 20°C and draining the blood from their body has been used since 1975 to protect neural activity during heart surgery. All the while the patient's heart has stopped beating and lungs breathing: the patient is technically dead.
At normal body temperature, brain damage occurs about 4 minutes after the heart stops. Cooling the brain, however, reduces its oxygen requirements and prolongs the time before the brain is damaged — for every 1°C drop in temperature there is a 6-7% decrease in brain metabolism. Most patients can survive unscathed for 30 minutes, at 40 minutes most patients suffer brain injury; at 60 minutes, the vast majority suffer irreversible brain damage.
A team of heart surgeons led by Antonio Calafiore of the Prince Sultan Cardiac Centre in Riyadh has extended the time during which a person can undergo this deep hypothermic circulatory arrest (DHCA). By reperfusing the brain with cold blood at 20°C at low pressure for 10 minutes before warming, they not only reduced the incidence of neurological events, but extended the protective period to 40 minutes
Calafiore and his colleagues evaluated the outcomes of 456 patients who underwent aortic surgery using DHCA between January 1998 and April 2009. They found that 22 of these patients had experienced temporary neurological dysfunction following their operations, and 36 patients suffered a stroke.
Analysis of the patients' medical records confirmed that DHCA longer that 30 minutes was associated with a higher risk of temporary brain dysfunction and stroke. The cold reperfusion provides additional protection against brain damage by washing out free radicals and other potentially harmful substances before brain activity resumes, claim the study's authors.
- Di Mauro, M. et al. Cold reperfusion before rewarming reduces neurological events after deep hypothermic circulatory arrest. Eur. J. Cardiothor Surg. (2012). doi:10.1093/ejcts/ezs281