SAN FRANCISCO The use of moderate to large volumes of dilute lidocaine for tumescent anesthesia during Mohs surgery on the face and neck was free of signs of lidocaine toxicity in a prospective single-center study.
Of 19 patients who underwent Mohs surgery for medium to large tumors on the face, scalp, or neck, none had a plasma lidocaine level anywhere close to the 5-mcg/mL threshold above which early signs of systemic lidocaine toxicity can occur, Dr. Murad Alam reported at the annual meeting of the American Academy of Dermatology.
The patients received injections totaling 548 mL of 1% lidocaine with 1:100,000 epinephrine and 1:10 sodium bicarbonate. Each patient had six blood draws for measurement of lidocaine levels; they were obtained before the first anesthetic injection and again immediately before and after each surgical stage, with the final draw an average of 4.4 hours following the first. In addition, active inquiry was repeatedly made of patients regarding any possible signs or symptoms of lidocaine toxicity.
Plasma lidocaine levels remained undetectablebelow 0.1 mcg/mLat all time points in three-quarters of the patients and never exceeded the 3.0-mcg/mL mark in the rest, according to Dr. Alam, chief of cutaneous and aesthetic surgery at Northwestern University, Chicago.
He explained that this study was undertaken because large volumes of tumescent anesthesia, akin to those widely utilized in liposuction, are increasingly being employed for excision of large skin cancers. Lidocaine injections to the face, neck, and scalp result in faster systemic absorption and higher peak levels than elsewhere in the body.
At plasma lidocaine levels above 5 mcg/mL, patients show the early signs of lidocaine toxicity, including tinnitus, muscle twitches, tongue numbness, a metallic taste, dizziness, diplopia, and visual halos. Levels above 10 mcg/mL put patients at risk for seizures, respiratory and cardiac arrest, and coma, Dr. Alam noted.
The pattern of rising plasma lidocaine levels over time documented in this study suggests that peak levels in patients undergoing Mohs surgery above-the-shoulders occur 35 hours after the start of surgery, he added.