Electrocerebral silence versus rectal temperature to start the circulatory arrest in cardiovascular surgery During deep hypothermic total circulatory arrest that is used for treatment of various cardiac and aortic diseases, patients cooled down until the brain activities is lost. between November 1993 and April 1997, 71 patients have been treated surgically for ascending and/or arcus aortic diseases, retrospectively studied to investigate if there is a safe rectal temperature to provide the electrocerebral silence to start the circulatory arrest. Thirty-five of these patients were acute type l dissection, 2 were acute rype II, 9 were chronic type I, 5 vvere chronic type II, 16 vvere ascending and arcus aortic aneurysm and 4 vvere arch aneurysm. Ali patients were operated under deep hypothermic total circulatory arrest and retrograde cerebral perfusion was used as an adjunct to hypothermia. Monitorization of electroencepha- logram {EEG) was used during the operation in ali. Total circulatory arrest was begun when the patients are EEG flat and have fixed dilated pupils. Rectal temperatures were measured at this point. The mean circulatory arrest and cardiopulmonary bypass time were 33.42±14.02 (2-74) and 194.64+54.68 (115-409) respectively. The mean rectal temperature was 16.39±1.74 (10-21)°C when the patients are electrocerebrally silence, in statistical analysis, the level of standard deviation and variance of the data have been found high, coefficient of variation was over 10 % and confidence interval was under 95%. These results show us that only rectal temperature monitorization is not a safe method for to start circulatory arrest period.