Background: This study was designed to investigate the impact of patient age on propofol consumption and recovery time using a propofol–remifentanil anaesthetic standardized with Narcotrend™ EEG monitoring. The Narcotrend is a monitor for measuring the depth of anaesthesia based upon a six-letter classification from A (awake) to F (increasing burst suppression) including 14 substages.
Methods: In 200 patients scheduled for minor orthopaedic surgery Narcotrend EEG electrodes were positioned on the patient's forehead as recommended by the manufacturer. Anaesthesia was induced with remifentanil 0.4 μg kg−1 min−1 and 2 mg kg−1 propofol. Immediately after intubation remifentanil was reduced to a constant rate of 0.2 μg kg−1 min−1 whereas a propofol infusion was now started at 3 mg kg−1 h−1 and then adjusted accordingly to achieve a target Narcotrend stages of D0–2 indicating general anaesthesia. At the end of surgery the propofol and remifentanil infusions were stopped without tapering, the time to unstimulated opening of eyes was determined, and the propofol consumption (given as mg kg−1 h−1) was calculated from the total amount of infused propofol but without the induction bolus, from the actual body weight and the duration of propofol infusion. Furthermore, a linear regression analysis was applied for propofol consumption vs. age.
Results: The ages of the patients studied ranged from 16 to 83 yr old and patients were classified as ASA I–III. Propofol consumption significantly decreased with the patients' age: 30 yr of age or below the propofol consumption was calculated as 5.9 ± 1.7 mg kg−1 h−1, for 31–50 yr as 5.4 ± 1.8 mg kg−1 h−1, for 51–70 yr as 4.5 ± 1.7 mg kg−1 h−1 and above 70 yr as 3.5 ± 1.4 mg kg−1 h−1. Linear regression analysis revealed propofol (mg kg−1 h−1) = 9.136 − (0.0597 × age (yr)); R = 0.53. Concomitantly, the recovery time to opening of eyes increased with the patients' age: ≤30 yr, 7.4 ± 3.7 min; 31–50 yr, 9.5 ± 4.0 min; 51–70 yr, 9.8 ± 4.1 min; and ≥71 yr, 14.9 ± 12.1 min.
Conclusions: We conclude that with Narcotrend guidance, mean propofol consumption and recovery times are age dependent. However, as a result of large inter-individual variability, age per se does not allow a prediction of individual propofol need or recovery time.