Lidocaine concentration in blood after topical anaesthesia of the upper respiratory tract.

The venous blood concentration of lidocaine was determined after stepwise application of lidocaine spray (270 mg) to the upper respiratory tract in 10 patients scheduled for bronchography, and after oropharyngeal application (150 mg) to five intubated patients under general anaesthesia. The peak level of lidocaine (about 1 microgram)ml/occurred 20--30 min after spraying in the bronchography group, while there was a level plateau at about 0.5 microgram/ml after oropharyngeal application of the local anaesthetic. There was great variation in the lidocaine concentration in both groups, but the highest observed concentration, 2.7 micrograms/ml, was safely below the toxic level. The mean rise in systolic and diastolic blood pressures at the various stages of spraying and on passing the bronchography tube in the local anaesthesia patients was 14.5--17.5/6.5--11 mmHg (1.9--2.3/0.9--1.5 kPa) compared to preanaesthetic values. In a similar group of patients, also scheduled for diagnostic bronchography, thiopentone anaesthesia, succinylcholine relaxation and laryngotracheal lidocaine spray resulted in a peak blood pressure increase of 36.5/27 mmHg (4.9/3.6 kPa) on passing the tube. The mean increases in pulse rate (21--26/min) were similar in both bronchography patient groups. No serious cardiac arrhythmias were observed in any of the patients.