Impact of deep hypothermic circulatory arrest on the BIS index

Study objective: To investigate the influence of duration of deep hypothermic circulatory arrest (DHCA) on recovery of the bispectral index (BIS).

Design: Prospective cohort study.

Setting: Operating room of university teaching hospital.

Patients: 30 adult, ASA physical status III and IV patients scheduled for cardiac surgery with extracorporeal circulation (ECC) and DHCA.

Interventions: There were no study-specific interventions undertaken with the study patients.

Measurements: After induction of anesthesia, propofol and sufentanil were used for maintenance. Duration until BIS values reached indices of 10, 20, and 30 after DHCA was measured. DeltaBIS was defined as the difference between BIS before the start of ECC and after DHCA at the same nasopharyngeal body temperature. Data are means + or - SD (ranges).

Main results: Duration of DHCA was 24 + or - 15 min (8-71 min). The deepest nasopharyngeal temperature was 20.1 + or - 2.7 degrees C at the end of DHCA. BIS reduction was 1.8/ degrees C. At the end of DHCA, BIS was 2 + or - 6 and at the end of ECC, BIS was 33 + or - 11. Duration until BIS reached a value of 10 (BIS10) was 23 + or - 21 min (0-83 min); until BIS reached 20 (BIS20): 36 + or - 36 min (0-140 min); and until BIS reached 30 (BIS30): 43 + or - 29 min (1-130 min). Regression analysis between duration of DHCA and BIS10 was R = 0.76; BIS20: R = 0.67; and BIS30: R = 0.54.

Conclusion: Deep hypothermia influences BIS linearly. In addition, there appears to be a reasonable correlation between recovery of BIS values and duration of DHCA.