Effect of different sedation on critical flicker frequency, a diagnostik tool for minimal encephalopathy

Introduction: Critical flicker frequency measurements are a valid tool for assessing early stages of cerebral dysfunction in patients with acute and chronic liver diseases. However, it may also serve as a tool for assessing the fitness of these patients after specific diagnostic or therapeutic interventions. Driving after sedation for endoscopic procedures is a matter of debate, in particular since recent results from a large study (Horiuchi et al. Am J Gastroenterol 2009) have suggested that driving home after propofol sedation might be safe. We used CFF analysis to asses the time-dependent effect of different sedation methods on brain function in the endoscopy unit of a tertiary referral centre.

Methods: In total, 83 patients were included in the study. All patients received a CFF analysis before, 30, 60, 90 and 120 min after the endoscopy. CFF results were correlated to sedation methods. Differences in the CFF between groups and within groups were tested by non-parametric Mann-Whitney U or paired t-tests comparisons as appropriate

Results: Overall, 33.7% of patients received no sedation, 26.5% were sedated with propofol (P) alone, and 38.6% of patients received a combination of propofol with midazolam (P/M). While in the control group no changes in CFF results were detected, patients with sedation experienced a clear drop in CFF results at 30 min. This drop was more pronounced in patients P/M-sedation as compared to P-mono sedation (30 min CFF: 37.6 Hz vs. 42.2 Hz). In addition the effect of sedation was detectable for > 120 min in P/M sedated patients, while CFF results in patients with P-mono sedation recovered to baseline values after 60 min.

Discussion/Conclusion: Our study clearly shows that the use of CFF assessment may be beyond testing for hepatic encephalopathy. We here show that the combination of propofol with midazolam leads to long lasting effects on CFF, which may affect driving capability, whereas sedation with propofol wares off within one hour. CFF analysis may be an easy to use tool to asses driving ability in this setting.