Use of intravenous lidocaine for postoperative pain and recovery

Abstract

Intravenous lidocaine after abdominal, orthopaedic, otolaryngological, cardiovascular surgery or caesarean section delivery, among others, is one of the multimodal schemes for the treatment of acute pain. The guideline by Foo et al. [1] makes a relevant contribution to the knowledge on the safety of its administration; however, we believe that the recommendations on the dose of intravenous lidocaine should be revisited based on the preceding literature. Firstly, the fifth recommendation of the guideline states that the dose of lidocaine should not exceed 1.5 mg.kg.h, a claim that is not supported and contradicts previous studies. For example, themeta-analysis conducted byWeibel et al. [2] concluded that continuous intravenous infusion of 2 mg.kg..h within the first 24 h after surgery was not associated with significant adverse effects (n = 4525 randomised patients). Furthermore, in a 2015 Cochrane meta-analysis review by Kranke et al. [3], intravenous doses ≥ 2 mg.kg.h showed evidence of pain reduction when compared with placebo, in contrast to lower doses (n = 2802). Secondly, it is important to note that, although some studies have found levels in plasma greater than 5 mg.ml, these levels do not correlate directly with the dose received, nor with evidence of toxicity in most cases [4]; moreover, plasma concentrations do not correlate linearly with infusion dose. For that reason, it is striking that Table 1 in the article itself states that doses of 3 mg.kg.h do not reach plasma concentrations that exceed the range of toxicity, reaching only 2.6 mg.ml. It has been found that the factor that contributes to a higher or lower concentration of serum lidocaine is the use of a loading dose before infusion; in other words, the use of previousboluses is related tohigherplasmaconcentrations [5]. In conclusion, while we acknowledge the contributions of Foo et al. [1] to improve the care of patients with acute postoperative pain, to achieve analgesic efficacy and to be within the safety margin, the recommended dose of at least 2 mg.kg.h reported in the literature should be considered. This recommendation could provide greater certainty to clinicians using this relatively new, and still investigational, treatmentmodality.