Comparison of the Effects of Dexmedetomidine on the Induction of Anaesthesia Using Marsh and Schnider Pharmacokinetic Models of Propofol Target-Controlled Infusion

Background: The study aimed to determine the effects of dexmedetomidine on the induction of anaesthesia using different models (Marsh and Schnider) of propofol targetcontrolled infusion (TCI). Methods: Sixty-four patients aged 18-60 years, American Society of Anaesthesiologists (ASA) class I-II who underwent elective surgery were randomised to a Marsh group (n = 32) or Schnider group (n = 32). All the patients received a 1 mu g/kg loading dose of dexmedetomidine, followed by TCI anaesthesia with remifentanil at 2 ng/mL. After the effect-site concentration (Ce) of remifentanil reached 2 ng/mL, propofol TCI induction was started. Anaesthesia induction commenced in the Marsh group at a target plasma concentration (Cpt) of 2 mu g/mL, whereas it started in the Schnider group at a target effect-site concentration (Cet) of 2 mu g/mL. If induction was delayed after 3 min, the target concentration (Ct) was gradually increased to 0.5 mu g/mL every 30 sec until successful induction. The Ct at successful induction, induction time, Ce at successful induction and haemodynamic parameters were recorded. Results: The Ct for successful induction in the Schnider group was significantly lower than in the Marsh group (3.48 [0.90] versus 4.02 [0.67] mu g/mL; P = 0.01). The induction time was also shorter in the Schnider group as compared with the Marsh group (134.96 [50.91] versus 161.59 [39.64]) sec; P = 0.02). There were no significant differences in haemodynamic parameters and Ce at successful induction. Conclusion: In the between-group comparison, dexmedetomidine reduced the Ct requirement for induction and shortened the induction time in the Schnider group. The inclusion of baseline groups without dexmedetomidine in a four-arm comparison of the two models would enhance the validity of the findings.