High daily caffeine intake is associated with lower propofol requirements for anesthetic induction

BACKGROUND AND AIMS: There is significant interindividual variation in the dose of propofol required for anesthetic induction. Factors dictating this are poorly described, but understanding them would be useful for anesthetic drug dosing. It has been shown in rats and recently in humans that caffeine administration accelerates recovery from anesthesia, but no study has assessed the effect on anesthetic induction. MATERIAL AND METHODS: Forty American Society of Anesthesiologists (ASA)-I, 18–65-year-old patients, undergoing day case general anesthesia with propofol and fentanyl took part in this observational study. Total daily caffeine intake (mg) was estimated using the caffeine assessment tool and caffeine content values from the US Department of Agriculture National Nutrient Database. Pharmacokinetic–pharmacodynamic modeling was used to estimate the effect site concentration of propofol at loss of consciousness (Ce(p) LOC). RESULTS: Median (interquartile range [IQR]) daily caffeine intake was 106 (51–193) mg. Ce(p) LOC was lower in those with caffeine intake greater than or equal to the median of 106 mg (median (IQR) = 0.64 μg/ml (0.51–0.72) vs. 0.70 μg/ml (0.57–1.10), P = 0.04). The effect was robust when controlling for weight-adjusted fentanyl dose, age, smoking status, and alcohol intake (F (1,34) = 4.66, P = 0.04). CONCLUSION: High daily caffeine intake is associated with lower propofol requirements for day case anesthetic induction. We propose that high daily caffeine intake may cause lower arousal levels prior to surgery due to a relative caffeine deficit caused by being nil by mouth. As such, assessment of daily caffeine intake preoperatively may aid anesthetic drug dosing.