The Relation between Tourniquet Hypertension and Bispectral Index in Patients Undergoing a Total Knee Arthroplasty

Lee, Jeong Rak; Kwon, Sam Hee; Gwak, Mi Jeung; Leem, Chung Gill

Abstract

BACKGROUND: Tourniquet hypertension (TH) may develop from an autonomic reflex consequent to the sensitization of the central nervous system (CNS) due to ischemia of the affected limb and noxious surgical stimulation. TH could be preventable when anesthetic depth is sufficient enough to block plastic changes of the CNS during an operation. This study was aimed to evaluate the efficacy of the bispectral index (BIS) to predict development of TH by assessing correlations between BIS changes and hemodynamic changes during the skin incision.
METHODS
Sixty patients who had undergone a total knee arthroplasty with a pneumatic tourniquet during isoflurane anesthesia were selected, and the samples were randomly divided into two groups: BIS 30 (30 - 39) and BIS 40 (40 - 49). Several variables such as BIS, mean arterial pressure (MAP), heart rate (HR) and end tidal concentraion of isoflurane were monitored during the operation. TH was defined as more than a 30% increase in MAP compared with the baseline values during the skin incision. The correlation between BIS changes and MAP and HR changes, and the incidence of TH between BIS groups were compared.
RESULTS
The MAP and HR were meaningfully increased in both the BIS 30 and the BIS 40 groups (P < 0.05), but no significant correlations were found between the BIS changes and the MAP and HR changes during the skin incision. The incidence of intraoperative hypertension was not different between the BIS groups. The BIS of the patients who had TH was not different from those who did not have TH.
CONCLUSIONS
BIS may not reflect the changes of the CNS and autonomic nervous system induced by noxious surgical stimulation during an operation, and BIS changes during a skin incision cannot be a predictor of TH.