Minimum local analgesic concentration of local anaesthetics

Abstract

The minimum local analgesic concentration (MLAC) model was first described in 1995. The idea was to develop a clinical model for local anaesthetic drugs, similar to that which was in routine use for inhalation anaesthetics, the minimum alveolar concentration (MAC). Before this much of the clinical research into local anaesthetic drugs involved comparisons of fixed doses or combinations with other adjuvants. Most of these studies used supramaximal doses with the resulting conclusions of similar efficacy being difficult to interpret correctly, more commonly the problem was that researchers were not yet really appreciating the issue. It was becoming clear that to be able to distinguish marginal differences in treatments, we would learn more from ‘ineffective’ outcomes rather than ubiquitous or universal analgesia. Epidural analgesia in labour presented a most pragmatic clinical area to develop this approach. Since it was first described, the MLAC model has been adapted to a variety of clinical scenarios and utilized extensively in regional anaesthesia research. In this article, we will explain the principles underlying the MLAC model, some of the areas of research in which the MLAC methodology has been used and the understanding that has emerged.