The influence of duration of fluid abstinence on hypotension during propofol induction

Abstract

Background: Prolonged preoperative fasting might be expected to exacerbate hypotension during the induction of general anesthesia. We aimed to establish whether the duration of preoperative abstinence from fluids independently contributed to arterial blood pressure changes and dosage requirements during propofol induction.

Methods: We prospectively recruited 130 ASA I or II nonhypertensive patients, ages 18 to 65 years scheduled for surgery under general anesthesia. Standard physiological and electroencephalographic bispectral index (BIS) monitoring was applied to each patient. Intravenous propofol infusion was commenced at 40 mg · kg(-1) · h(-1) and reduced to 8 mg · kg(-1) · h(-1) when the BIS decreased to 50. Frequent cardiovascular data were collected for 15 minutes. The primary endpoint was maximal percentage decrease from baseline mean arterial blood pressure (max%ΔMAP). The secondary endpoint was the propofol dose at which BIS decreased to 50 (PDBIS50). Univariate linear regression and then multivariate linear regression was used to analyze the associations between potential predictors, including fasting time, and these 2 endpoints.

Results: Mean fluid abstinence time was 694 minutes (range: 115 to 1263 minutes). Unstandardized regression coefficients (95% confidence intervals [CIs]) for fluid abstinence (minutes) versus max%ΔMAP (%) and PDBIS50 (mg) were, respectively, 0.003% (-0.002% to + 0.009%) and 0.021 mg (-0.017 mg to + 0.059 mg). On adjusting for other, significant predictors in a multivariate model and applying type II sum of squares tests, the corresponding values were -0.0001% (-0.004% to + 0.004%, P = 0.94) and -0.006 mg (-0.039 mg to + 0.026 mg, P = 0.70). The effect of a 1-hour increase in fluid abstinence on max%ΔMAP was therefore -0.01% (-0.26% to + 0.24%) and on PDBIS50, -0.38 mg (-2.34 mg to + 1.58 mg).

Conclusion: When propofol is infused rapidly for induction of anesthesia in healthy adults younger than 65 years, the duration of preoperative fluid abstinence does not appear to affect MAP or propofol dose requirements.