The use of intravenous lidocaine for postoperative pain and recovery: a reply

Abstract

We thank Dubowitz et al. [1] and Moyano et al. [2] for their interest in our safety statement [3]. The purpose of the guidelines was to provide a safe and pragmatic way of delivering intravenous lidocaine for practising clinicians outside a research context. As it stands, it has successfully delivered a set of recommendations written by a group of clinicians recruited for their expertise, one of whom has experience of more than 3400 intravenous lidocaine infusions in his institution. Theguidelines placedan upperdose limit on the infusion as an additional safety precaution to reduce the risk of adverse events, rather than havingan upper doseper kgbody weight limit. As there are many patient factors as well as drug interactions which may influence the likelihood of lidocaine adverse events, it is prudent to be cautious. This is borne out by clinical experience where, with an upper limit in place, no serious adverse events were encountered in more than 3400 patient infusions of 12 h duration (data fromWesternGeneral Hospital, Edinburgh, UK). Furthermore, the assertion by Dubowitz et al. that there is little difference between reported mean lidocaine plasma levels during infusion rates between 1.5 and3.0 mg.kg.h is not strictly true, as the sampling time becomes important. Brysonet al. gave their patients abolusof 1.5 mg.kg followed by 3 mg.kg.h, and achieved a plasma concentration of 2.6 lg.ml after only an hour (highest mean plasma concentration achieved in the studies summarised); this is unlikely to reflect the achievement of a steady state plasma concentration [4]. This implies that had further sampling taken place at 4 h, the plasma concentration is likely to have been higher. Of course, in a research setting, upper limits may not be necessary as patients tend to be better monitored and adverse effects actively sought. Moyano et al. also touch on infusion rates in their letter, and in response to their suggestion that 2 mg.kg.h be administered, we would point out that our recommendations are designed to be circumspect, as they were the result of the death of apatientwhowas receiving intravenous lidocaine. Detailed recommendations 12 and 13 in our guidelines deal with infusions of intravenous lidocaine outside the operating theatre/recovery room, so we would question the assertion from Dubowitz et al. that postoperative infusions were omitted from the document. Even in the abbreviated recommendations, point 6 covers this. We are pleased that there are three further planned studies assessing the usefulness of intravenous lidocaine in different clinical settings. We believe our guidelines themselves do not deter investigators from taking part in such trials, as the research setting is the best environment to assess the usefulness and safety of lidocaine. The accompanying editorial may deter clinicians from using intravenous lidocaine; however, the guidelines offer a safe and practical way forward for practitioners wanting to use intravenous lidocaine in their own practice currently. These guidelines will be amended once large multicentre randomised controlled trials report their findings. Clinical recommendations are always a balance of evidence and opinion, and we respect the opinion of Dubowitz et al. and their clinical experience. We note, however, that they do not appear to fundamentally disagree withmost of what we have suggested.