SummaryThe lack of a gold standard complicates the evaluation and comparison of anaesthetic depth monitors. This randomised study compares three different depth-of-anaesthesia monitors during cardiopulmonary bypass (CPB) at 34°C with fentanyl ⁄ propofol anaesthesia adjusted clinically and blinded to the monitors. Coronary artery bypass grafting patients (n = 21) were randomly assigned to all three possible paired combinations of three monitors: Bispectral Index (Aspect Medical), AAI TM auditory evoked potential (Danmeter), Entropy TM (Datex-Ohmeda). Indices were manually recorded every 5 min during CPB. Agreement between paired indices was classified as good, non-, or disagreement. Anaesthesia was classed as adequate, inadequate, or excessive according to recommended index values. Of the 255 paired indices recorded, 62% showed good agreement, 33% showed non-agreement, and 5% showed disagreement. Using good agreement between two monitors as a gold standard, a quarter of the measurements indicate inappropriate anaesthetic depth monitoring during CPB with clinically titrated anaesthetic depth.

Gastric tonometry was used to study the possible effect of dopexamine infusion on a low calculated intramucosal pH (pHi) as a sign of splanchnic ischemia. Measurements were made during surgery and for approximately 18 hours postoperatively on 19 non-selected adult patients undergoing valve replacement. Patients developing a postoperative pHi > 7.30 were randomized to receive dopexamine (2 micrograms.kg-1 min-1) or placebo in a double blind fashion. Eighteen patients were randomized, 10 to receive dopexamine and 8 to placebo. The calculated pHi remained unchanged for the first 2 hours in both groups. After 4 hours a significant (P < 0.05) decrease in pHi was noted in the dopexamine group which remained significantly below the placebo group during the monitoring period. The dopexamine treated patients had a significantly longer period of low pHi but the pH-gap i.e. the difference between arterial pH and pHi did not differ between the two groups. Patients with postoperative complications, defined as infections (2), myocardial infarction (1), single- (2) or multiple organ failure and death (1), did not have longer periods with pHi below 7.30. In these patients, however, a pH-gap > 0.12 occurred more often than in those without complications, indicating that an increased incidence of complications was related to a pH-gap > 0.12. It is our opinion that true mucosal ischemia is best detected by estimating the difference in carbon dioxide tension between arterial blood and mucosa. This can be expressed either directly as PCO2-gap (PtonCO2-PaCO2) or indirectly as pH-gap.

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