Electroencephalograph variables, drug concentrations and sedation scores in children emerging from propofol infusion anaesthesia

Background: Inadequate sedation or oversedation are common problems in Paediatric Intensive Care because of wide variations in drug response and the lack of objective tests for sedative depth. We undertook a pilot study to try to identify correlates of propofol drug concentration, electroencephalographic (EEG) variables and observed behaviour during a stepwise reduction in propofol infusion after paediatric cardiac surgery. Methods: This was a prospective pilot study with 10 children (5 months to 8 years) emerging from propofol anaesthesia following cardiac surgery with cardiopulmonary bypass (CPB). Patients under-went a stepped wake-up from propofol anaesthesia during which the propofol infusion rate was decreased from 4 mg·kg-1 ·h-1 in 1 mg·kg-1·h-1 steps at 30 min intervals. EEG variables, propofol blood concentrations and clinical sedation scores (COMFORT scale) were recorded during the stepped wakeup. Analgesia was maintained with a standardized continuous infusion of fentanyl. Results: Mean (SD) whole blood propofol concentrations at arousal varied considerably [973 ng·ml-1 (SD 523 ng·ml -1)]. The summed ratio (SR) of high frequency to low frequency bands correlated with both propofol infusion rate (R2 value = 0.47) and propofol blood concentrations (R2 value = 0.64). The mean SR in deeply sedated patients was significantly different from that in the 5 min prior to wakening (6.84 vs 1.55, P = 0.00002). There was no relationship between COMFORT scores and SR. Conclusions: In this group of patients receiving opioid analgesia and relatively high doses of propofol, sedation scores were unhelpful in predicting arousal. The SR correlated with propofol blood concentrations and clinical arousal and may have potential as a predictive tool for arousal in children.