Index of consciousness and bispectral index values are interchangeable during normotension and hypotension but not during non pulsatile flow state during cardiac surgical procedures: a prospective study

Abstract

Awareness under anesthesia is an avoidable complication during general anesthesia. Anesthetic depth monitors assist anesthesiologists in providing appropriate levels of anesthesia. Index of consciousness monitoring is a recently introduced monitor in the array of anesthesia depth monitors. The objective of this study was to assess the interchangeability of bispectral index, which is already in clinical use and the recently introduced index of consciousness techniques. The other objective was to assess this interchangeability during normotension, hypotension and during pulseless state in patients undergoing coronary artery bypass graft surgery. This study is a prospective observational study, conducted in a tertiary referral hospital. Fifteen cardiac surgical patients undergoing off pump and conventional coronary artery bypass under cardiopulmonary bypass participated in the study. Bispectral index and index of consciousness monitoring were carried out simultaneously during various stages of consciousness, and assessed for interchangeability. Bland Altman plotting and 'mountain plot' were used to assess the interchangeability. Eleven in the cohort underwent off pump and the rest (n = 4) conventional coronary artery bypass surgery under cardiopulmonary bypass. A set of 887 data were obtained during the study period. The data were classified as those obtained during normotension, hypotension and pulseless state during cardiopulmonary bypass. 732 sets of data were obtained during normotension, 84 during hypotension and 71 during cardiopulmonary bypass. Overall interchangeability was good, suggested by low bias (0.96), high precision (0.54), r value of 0.7 and P value of <0.0001. It was found that the data obtained during normotension was also interchangeable, suggested by low bias (0.8), high precision (0.54) and r value of 0.7. The data obtained during hypotension was not as highly interchangeable as during normotension-bias 0.4, precision 1.66 and r value of 0.7. The analysis of value during cardiopulmonary bypass suggested non interchangeability (bias 3.87, precision 3.05, r value 0.3 and P value = 0.0067. The bispectral index and index of consciousness values may be interchangeable. The interchangeability is better appreciated during normotension and hypotension but not during non pulsatile state of cardiopulmonary bypass.