Anestesia tópica da orofaringe: concentraçöes plasmáticas de lidocaína, interaçåo com agentes indutores e proteçåo hemodinâmica à intubaçåo traqueal / Topical anesthesia of the oropharynx: lidocaine plasma concentrations, interaction with induction agents and hemodynamic protection to tracheal intubation

Background and Objectives - Laringotracheal instillation of local anesthetics and its consequences are largely documented in the literature; on the other hand, little information is available on the oropharyngeal instillation of these drugs. The purpose of this study was to evaluate the lidocaine plama concentrations following topical anesthesia of the oropharynx, their hemodynamic effects, the interaction between such effects and the cardiovascular action of the induction agents (propofol and etomidate) and he hemodynamic protection to tracheal intubation induced by the technique. Methods - Forty patients undergoing general anesthesia were allocated into 4 groups of 10, according to the agent which was instilled in the oropharynx and the drug used in the induction of anesthesia: Group 1, lidocaine and etomidate; Group 2, distilled water and etomidate; Group 3, lidocaine and propofol; Group 4, distilled water and propofol. A standard dose of 150 mg of lidocaine spray 10 per cent was given to the patients receiving local anesthetic. Hemodynamic data (SBP, DBP and HR) were evaluated in the following moments; T1, admission to the operating room; T2, immediately following topical instillation; T3, five minutes following topical instillation; T4, immediately following induction of anesthesia; T5, immediately following tracheal intubation; T6, two minutes folowing tracheal intubation. Patients receiving lidicaine had blood sample taken 5, 10 and 20 minutes following the conclusion of topical anesthesiafor the evaluation of plasma concentrations. Results - Plasma concentrations of lidocaine were similar in the studied groups and the highest concentration observed was 3.05 ug/ml at 10 minutes. The groups receiving lidocaine showed a significant increase in SBP and DBP in the initial moments, preceding the induction of anesthesia. Following induction, the reduction in DBP was significantly greater in the groups induced with propofol as compared to that observed in the groups induced with etomidate, regardless of the agent instilled in the oropharynx. Following intubation the increases in SBP, DBP and HR were significantly greater in the groups induced with etomidate as compared to those induced with propofol. Conclusions - topical anesthesia of the oropharynx does not provide hemodynamic protection to tracheal intubation. Lidocaine plasma concentrations associated with the technique are low and do not induce significant hemodynamic effects or major interaction with induction agents