Tumescent Lidocaine Bioavailability and Absorption Kinetics:Maximum Safe mg/kg Lidocaine Dosage

Background:

Tumescent local anesthesia (TLA) permits a wide variety of therapeutic surgical procedures of subcutaneous tissues and skin to be performed totally by local anesthesia ( ). Infiltration of a sufficient volume of TLA causes the target tissues become temporarily tumescent, or swollen and firm.

TLA is defined as the subcutaneous infiltration of a large volume of a tumescent local anesthetic solution (TLAS). The safe use of TLA requires the safe formulation and safe use of a tumescent local anesthetic solution (TLAS). By definition TLAS contains very dilute lidocaine (≤ 1 gm/liter = 0.1%) and epinephrine (≤ 1 mg/liter = 1:1,000,000) with sodium bicarbonate (10 milliequivalents/liter) in a physiologic crystalloid solution. Bicarbonate, an essential ingredient, neutralizes the acid pH of commercial lidocaine and epinephrine thereby eliminating the intense stinging discomfort which often associated with the infiltration of commercial local anesthetics. Lidocaine which has been infiltrated for TLA is referred to as tumescent lidocaine.

The FDA-approved maximum recommended dosage is 7 mg/kg for lidocaine with epinephrine infiltration local anesthesia. However with TLA much larger mg/kg dosages of lidocaine are used. The safety and efficacy of TLA is based on the unexpected slow lidocaine absorption associated with large volumes of very dilute lidocaine and epinephrine when infiltrated into subcutaneous tissue. Published estimates of a maximum safe mg/kg dosage of tumescent lidocaine are derived from liposuction patients and have ranged from 35 mg/kg to 55 mg/kg ( ) and much higher lidocaine doses without evident toxicity have been reported.

Liposuction, a cosmetic surgical procedure which removes subcutaneous fat, also removes some tumescent lidocaine thereby reducing lidocaine bioavailability. In contrast, therapeutic surgeries usually do not remove subcutaneous lidocaine and therefore the bioavailability of lidocaine is relatively increased as is the peak serum lidocaine concentration (Cmax) and the risk of lidocaine toxicity. Because TLA is now used for surgical procedures unrelated to liposuction, it is desirable to have a reliable estimate of the maximum safe dosage of tumescent lidocaine based on clinical data from subjects not having liposuction.