[Plasma concentration of lidocaine during bronchoscopy]

Lidocaine is commonly used for local anesthesia during fiberoptic bronchoscopy (FOB). It has been suggested that the total dose of lidocaine should be limited to 300-400 mg (or < 8.2 mg/kg). Lidocaine toxicity is directly correlated with its concentration in the blood and a threshold above which the side effects become more likely has been put at a plasma level of 5 microg/ml. The aim of our study was to determine plasmatic lidocaine concentrations (PLC), how often the PLC fall into the potentially toxic range and its correlation with adverse reactions. PLC were recorded in 30 patients undergoing FOB. Lidocaine was administered as a 2% gel, 10% spray and 2% solution. Venous blood samples were taken before the beginning of local anesthesia and at 20, 30 and 40 min thereafter. The mean total amount of lidocaine administered was 746.3 +/- 159.5 mg (11.6 +/- 3.1 mg/kg). Before the beginning of anesthesia, no significant levels of lidocaine were measurable in the patients. PLC were 3.2 +/- 1.7 (g/ml at 20 min., 3.3 +/- 1.7 microg/ml at 30 min. and 3.0 +/- 1.5 microg/ml at 40 min. The PLC exceeded toxic levels in 6 patients, but no complications were observed. Our data show that although the amount of lidocaine used in this study exceeded the recommended highest dose, no subjects had signs of toxicity. A maximum dose of lidocaine for topical anesthesia should be determined despite the fact that an average total dose superior to 400 mg appears to be safe in patients undergoing FOB.