RESUMO
BACKGROUND: Propofol sedation using target-controlled infusion (TCI) system can be used in MAC (Monitored Anesthesia Care).Remifentanil is an ultra-short-acting opioid that is advantageous in combination with propofol due to its rapid onset and offset times and analgesic effect.The present study sought to identify the EC50 of propofol for 'loss of response to command' when administered alone or with 2 or 3 ng/ml remifentanil using TCI. METHODS: Seventy patients were randomly allocated to one of three treatment groups:Group 1 = propofol only (n = 20), Group 2 = propofol plus 2 ng/ml remifentanil (n = 25) and Group 3 = propofol plus 3 ng/ml remifentanil (n = 25).The EC50 was determined by calculating the mean of the midpoint dose of all independent pairs of patients who manifested crossover from 'response to command' to 'loss of response to command'. RESULTS: The EC50 of propofol was found to be 3.41 +/- 0.25microgram/ml in Group 1, 2.04 +/- 0.22microgram/ml in Group 2, and 1.98 +/- 0.15microgram/ml in Group 3.Statistical analysis showed the EC50 for Group 1 was higher than those for Groups 2 and 3, and that the EC50 of latter groups were similar. CONCLUSIONS: Using the modified Dixon's up and down method, the present study estimated the EC50 of propofol for 'loss of response to command' when remifentanil was infused in analgesic doses using TCI.Those concentrations can safely and effectively generate sedation and analgesia without clinically significant side effects in MAC.