Serum concentrations of lignocaine before, during and after fiberoptic bronchoscopy

Lignocaine is commonly used for local anesthesia during fiberoptic bronchoscopy (FOB). Several studies have reported the peak serum concentration of lignocaine in relation to time, but most of them did not specify the administered dose of lignocaine gel and its possible correlation with peak serum concentration.

The aim of our study was to record the plasma concentrations of lignocaine before, during and after FOB and to evaluate whether the doses for nasal and tracheobronchial anesthesia have any correlation with the peak serum concentrations of the drug.

Twelve patients with no comorbid conditions undergoing FOB were studied. Lignocaine was administered as a 2% solution using a larynx syringe, 2% gel (mean dose 182.5 +/- 15 mg) and finally 2% solution through the bronchoscope (mean dose 339 +/- 12 mg). Total dose was 622 +/- 20 mg. Venous blood samples were taken before the beginning of local anesthesia and then at 5, 10, 20, 60, 90 and 120 min thereafter.

Our results showed that peak plasma concentrations of lignocaine were observed in 8 patients 20 min after the beginning of local anesthesia, in 3 patients 30 min afterwards and in 1 patient 60 min afterwards (2.15 +/- 0.4 microg/ml, 1.9 +/- 0.3 microg/ml, 1. 81 microg/ml, respectively). None of our patients exceeded the critical level of toxicity (5 microg/ml). Both the total and tracheobronchial doses of lignocaine were significantly correlated with peak serum concentration (r = 0.63, p = 0.05 and r = 0.64, p = 0.02, respectively). No correlation was found between the dose for nasal anesthesia and peak serum concentration. No adverse reactions were observed.

In conclusion our data show that although the amount of lignocaine used in this study exceeded the recommended highest dose (400 mg) in all patients, no toxic levels were observed. Peak plasma concentrations were found within 20-30 min from the beginning of local anesthesia. The dose for the anesthesia of nasal mucosa represented a significant percentage of the total dose, but did not correlate with the peak serum concentration of the drug.