VANCOUVER, B.C. A new study finds that the local anesthesia used for Mohs surgery appears to be safe, with serum levels of lidocaine remaining well below the threshold for toxicity and an absence of any drug-related adverse events.
Although Mohs procedures are routinely performed using lidocaine anesthesia without any complications, few studies have looked at lidocaine levels specifically in this context, said study author Dr. Murad Alam, chief of cutaneous and aesthetic surgery at Northwestern University, Chicago.
Research on tumescent anesthesia suggests that a greater vascular supply above the clavicle promotes faster systemic absorption of lidocaine (Plast. Reconstr. Surg. 2005;115:174451). The concentration of lidocaine in the anesthesia used for Mohs surgery is 510 times that of tumescent anesthesia.
The prospective cohort study, reported at the annual meeting of the American College of Mohs Surgery, took place among 20 consecutive adults undergoing Mohs surgery with local anesthesia for nonmelanoma skin cancer. The anesthesia consisted of a lidocaine solution (concentration, 1:100) also containing epinephrine (1:100,000) and 8.4% sodium bicarbonate (1:10); it was injected at the start of each stage of Mohs surgery. Blood was drawn from the patient's arm before and after each of three stages (or two stages plus closure), for a total of six sampling time points over roughly 5 hours.
Serum lidocaine levels were measured by gas chromatography, and both patients and physicians assessed the occurrence of adverse events.
Dr. Alam explained that mild symptoms of lidocaine toxicity occur when the serum level of the drug reaches 3 mcg/mL; moderate symptoms when the level exceeds 5 mcg/mL; and severe and potentially life threatening symptoms when the level exceeds 10 mcg/mL.
Study results indicated that across all time points, lidocaine levels were detectable (greater than 0.1 mcg/mL) in just five (25%) of the patients.
"Even in the worst-case scenariothe sixth and final time point, where you would expect the serum lidocaine level to be the highest because of the cumulated dosage to that pointonly 5 of the 20 patients had a detectable serum lidocaine level," Dr. Alam remarked.
Furthermore, the median level for the cohort was undetectable at all time points.
"Assuming the vast majority of patients did absolutely fine, were there some patients who had very high levels and got into trouble? Again, the answer is no," Dr. Alam asserted.
Of all patients, the highest peak serum lidocaine level observed was 0.3 mcg/mL noted during the last three time points. "That is still one-tenth of the amount for even mild symptoms to occur," he pointed out.
When patients who did and did not have detectable serum lidocaine levels were compared, those with detectable levels had been injected with a significantly greater mean volume of lidocaine solution (30 vs. 9.5 mL). They were also significantly older (68.6 vs. 50.7 years) and somewhat more likely to be male, although Dr. Alam cautioned "this might just mean that older men have larger tumors."
A final analysis showed that peak serum lidocaine levels were well correlated with the total volume of solution injected.
Adverse events were reported by two patientsa 56-year-old man who reported a mild headache and a 42-year-old woman who reported feeling shaky. "Both were after the first Mohs stage, and so they were much more likely to be epinephrine effects than lidocaine effects, which would be expected to happen after a lot of lidocaine was injected," Dr. Alam observed. No adverse events related to the drug were noted.
"There was no case in which serious adverse events or even mild adverse events associated with lidocaine toxicity were seen, which suggests what we already knew to be true based on experiencethat local anesthesia given during Mohs surgery appears to be safe," Dr. Alam concluded.
He reported having no conflicts of interest in association with the study.
No patient in the study experienced adverse events associated with lidocaine toxicity. DR. ALAM