Assessment of severity of methaemoglobinemia following fibreoptic bronchoscopy with lidocaine.

Background. Lidocaine is commonly used for topical anaesthesia during fibreoptic bronchoscopy (FOB) and it can cause methaemoglobinemia. The present study was undertaken to evaluate the severity of post-bronchoscopy methaemoglobinemia while using lidocaine as a topical anaesthetic agent. Methods. We prospectively studied consecutive adult patients who underwent diagnostic FOB in our institution. Blood methaemoglobin levels were estimated by co-oximetry before bronchoscopy and one hour after first instillation of lidocaine. Occurrence of symptoms suggestive of mild methaemoglobinemia (i.e., fatigue, palpitation, dizziness, nausea and headache) were recorded in a severity scale before collection of post-bronchoscopy blood samples. Results. A total of 48 adult patients were enrolled in this study. The mean amount of lidocaine used for bronchoscopy during this study was 7.4±1.4mg/kg body weight. The mean pre- and post-bronchoscopy methaemoglobin levels were 0.44mg/mL and 0.80mg/mL, respectively. After bronchoscopy, severe and very severe symptoms were reported by 2.1% to 10.4% patients. However, severities of the symptoms were unrelated to post-bronchoscopy methaemoglobin level or the amount of lidocaine used during the FOB. Conclusions. Blood methaemoglobin levels following FOB remained within the physiological limits when British Thoracic Society recommended dose of lidocaine was used. However, few patients had symptoms similar to mild methaemoglobinemia after FOB.