[Plasma concentrations of lidocaine in bronchial fibroscopy]

Certain accidents related to local anaesthesia during bronchial fibroscopy may be due to overdosage of local anesthetic drugs. In view of the various techniques employed, the various doses used and the different serum levels obtained, we decided to study the passage of lidocaine into the systemic circulation during bronchial fibroscopy in order to confirm that the doses required for good anaesthesia are not toxic. We studied the kinetics of lidocaine on 10 occasions in 9 patients. All patients had normal renal, hepatic and cardiac function. The anaesthetic was administered in standardized doses (by pharyngo-laryngeal spray of a 5% solution followed by injection via a laryngeal syringe and finally by the operating lumen of the fibroscope with a 1% solution). The total dose of anaesthetic was administered at the beginning of the examination in order to avoid contamination of the aspirated secretions after connection of the traps. The mean dose administered was 9.2 +/- 0.5 mg/kg (range of 380 to 800 mg). The maximal serum levels never attained toxic levels (9 mcg/ml). The highest levels (7 mcg/ml and 5.7 mcg/ml) were observed in a patient with a bronchial epithelioma, normal biochemistry and normal liver ultrasonography, who died two months later with hepatic metastases. The mean maximal serum levels for this group of patients was 2.8 +/- 0.6 mcg/ml between the 5th and 45th minute, which is equivalent to anti-arrhythmic doses (therapeutic level of 1.2 to 5 mcg/ml). The levels obtained are not negligible, but they achieve very good quality anaesthesia with a good margin of safety, apart from the one case with hepatic metastases.