RESUMO
BACKGROUND: The study aimed to determine the effects of dexmedetomidine on the induction of anaesthesia using different models (Marsh and Schnider) of propofol target-controlled 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 µg/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 µg/mL, whereas it started in the Schnider group at a target effect-site concentration (Cet) of 2 µg/mL. If induction was delayed after 3 min, the target concentration (Ct) was gradually increased to 0.5 µg/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] µg/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.
