Valoración de la reducción de la dosis de propofol en relación al tiempo desde la administración de fentanilo durante la inducción anestésica

Abstract

Introduction and objective. Age is a determining factor in propofol needs. Older patients are more sensitive to it, due to the decrease of their central compartment, the concentration of plasma proteins and the cardiac output. The concomitant administration of fentanyl during anesthetic induction is not only aimed to reduce the catecholaminergic response to orotracheal intubation, but also to allow the reduction of propofol dose based on the pharmacological synergy between them. However, no studies have been found that assess the optimal time between the administration of both drugs to enhance this supraadditive relationship. The objective of this study is to determine if, by increasing the time elapsed between the administration of fentanyl and propofol and decreasing the dose of the latter, the hemodynamic response before and after orotracheal intubation is improved. Materials and methods. Patients scheduled for non-cardiac surgery who required general anesthesia with orotracheal intubation were included. Patients were randomized into six groups using a computerized randomizer. The sample was divided into two time groups (2 and 1 minute) and each was subdivided into three dose groups: 1 mg/kg, 1.5 mg/kg and 2 mg/kg. All patients received a dose of 2 μg/kg of fentanyl and, according to the group, after the predetermined time, the hypnotic was administered. The time it took for patients to reach BIS less than 60 and the hemodynamic parameters at the time of pre-induction, pre-intubation and postintubation were registered. Results. A sample of 192 patients was collected, 6 of which were excluded. The rest were divided into six time-dose groups. No significant differences were observed in the time it took patients to reach a BIS of less than 60. Blood pressure decreased after administration of propofol and increased after intubation in all groups. In patients younger than 55 years, there were no significant differences in the percentages of blood pressure reduction. In patients older than 55 years, the 2-min – 2 mg/kg group showed the greatest reduction in blood pressure at the time of pre-intubation (36% and 31% for SBP and MBP respectively). While the one that showed the least hemodynamic alterations between pre and postintubation was the group 1 minute - 1.5 mg/kg with 4% and 1%. Conclusion. Increasing the time between the administration of fentanyl and propofol at two minutes does not generate hemodynamic benefits in patients younger than 55 years. In the elder population, increasing the time between the opioid and the hypnotic produces greater variation of the blood pressure. If one wants to achieve greater hemodynamic stability with a decrease in the dose of propofol in this age group, it is advisable to wait one minute from the administration of fentanyl 2 μg/kg and reduce the dose to 1.5 mg/kg.