Bispectral Index in Total Circulatory Arrest: What Is the Safe Value?

Abstract

Bispectral index (BIS) is a measure of cerebral activity. It is near zero in comatose patients, and zero in brain-dead patients.1Benoit V. Xavier P. Philippe L.C. et al.Detection of brain death onset using the bispectral index in severely comatose patients.Intensive Care Med. 2002; 28: 419-425Crossref PubMed Scopus (87) Google Scholar Correlation between BIS and neurologic injury is uncertain.2Gill M. Green S.M. Krauss B. Can the bispectral index monitor quantify altered level of consciousness in emergency department patients?.Acad Emerg Med. 2003; 10: 175-179Crossref PubMed Google Scholar Patients undergoing total circulatory arrest (TCA) induced during aortic arch surgery are prone to neurologic injuries. A few studies mention BIS values during TCA3Reich D. Patel R. Krol M. et al.Slower BIS recovery following hypothermic circulatory arrest is associated with longer hypothermia time and postoperative ICU stay.Anesth Analg. 2004; 98: SCA125Google Scholar; none mention any safe value for BIS during TCA and aortic surgery. We recorded BIS during TCA in 10 consecutive patients undergoing aortic arch surgery and tried to find a safe value, if any, for BIS during TCA. Standard cardiac anesthetic techniques were used. A BIS monitor (Aspect Medical Systems) was attached at the standard location and continuously monitored during and after hypothermic circulatory arrest. Thiopental, 30 mg/kg, and methylprednisolone, 30 mg/kg, were added to the pump before TCA, and ice packs were placed on the patients' foreheads for cerebroprotection. Postoperatively, neurologic outcomes were clinically assessed. Mean cardiopulmonary bypass time was 150 ± 23 minutes, and aortic cross- clamp time was 87 ± 16 minutes. Mean TCA time was 29 ± 6 minutes. The BIS index gradually dropped with hypothermia. At 18°C, when TCA was started, it remained at 6 ± 4.2 minutes. On rewarming, it gradually increased to 40 to 60 in the operating room. No patients had any adverse neurologic outcomes. The BIS could represent an objective quantification of impairment of consciousness, because it is easily performed and interpreted. Previous studies have shown a decrease in BIS with hypothermia and mention a BIS of 0 with TCA.3Reich D. Patel R. Krol M. et al.Slower BIS recovery following hypothermic circulatory arrest is associated with longer hypothermia time and postoperative ICU stay.Anesth Analg. 2004; 98: SCA125Google Scholar The authors' experience found that a BIS of less than 10 was associated with good neurologic outcome. Bispectral Index Monitoring During Aortic Arch RepairJournal of Cardiothoracic and Vascular AnesthesiaVol. 21Issue 3PreviewI read with great interest the report by Dr Saxena and colleagues detailing their experience with bispectral index monitoring (BISM) in adult aortic arch repair with deep hypothermic circulatory arrest (DHCA).1 They found in a small series (N = 10) that a score of less than 10 with BISM was associated with good neurologic outcome. Full-Text PDF