Auditory information processing during adequate propofol anesthesia monitored by electroencephalogram bispectral index.

UNLABELLED: Memory for intraoperative events may arise from inadequate anesthesia when the hypnotic state is not continuously monitored. Electroencephalogram bispectral index (BIS) enables monitoring of the hypnotic state and titration of anesthesia to an adequate level (BIS 40 to 60). At this level, preserved memory function has been observed in trauma patients. We investigated memory formation in elective surgical outpatients during target-controlled propofol anesthesia supplemented with alfentanil. While BIS remained between 40 and 60, patients listened to a tape with either familiar instances (exemplars) from two categories (Experimental [E] group, n = 41) or bird sounds (Control [C] group, n = 41). After recovery, memory was tested directly and indirectly. BIS during audio presentation was on average (+/- SD) 44 +/- 5 and 46 +/- 5 for Groups E and C, respectively. No patient consciously recalled the intraoperative period, nor were presented words recognized reliably (Group E, 0.9 +/- 0.8 hits; Group C, 0.8 +/- 0.8 hits) (P = 0.7). When asked to generate category exemplars, Group E named 2.10 +/- 1.0 hits versus 1.98 +/- 1.0 in Group C (P = 0.9). We found no explicit or implicit memory effect of familiar words presented during adequate propofol anesthesia at BIS levels between 40 and 60 in elective surgical patients. IMPLICATIONS: This study suggests that stable levels of adequate hypnosis may prevent information processing and memory formation during general anesthesia and supports the feasibility of electroencephalogram bispectral index as a monitor of adequate anesthesia.

Measurement of arterial pressure after cardiopulmonary bypass with long radial artery catheters.

Radial arterial pressure can significantly underestimate central aortic pressure in the postcardiopulmonary bypass (post-CPB) period. At the study institution, routine monitoring of perioperative arterial pressure in adult patients undergoing cardiac surgery is performed with a long radial artery catheter with the distal end positioned in the subclavian artery. In 68 patients presenting for elective cardiac surgery, both a conventional short radial artery catheter and a contralateral long radial artery catheter were placed. Analysis of radial and subclavian arterial pressures post-CPB in the first 47 patients showed average maximum differences of 7 mm Hg systolic and 4 mm Hg mean. In 15% of patients, the differences were clinically significant (greater than 20 mm Hg systolic and/or greater than 14 mm Hg mean). In 28 patients, central aortic pressure was measured post-CPB, and subclavian artery pressure was found to be an excellent estimator of central aortic pressure. There were no significant complications related to using long radial artery catheters in the 68 patients who were followed prospectively. Monitoring subclavian arterial pressure by percutaneous insertion of a long radial artery catheter provides a reliable estimation of central aortic pressure, even in patients with significant radial artery-to-central aortic pressure gradients post-CPB.