To the Editor:
This interesting article adds to the literature confirming the analgesic effects of lidocaine but leaves several questions unanswered.1 The hypothesis is plausible, but there is insufficient evidence to prove an effect in this population group. It is a small trial comprising only 116 patients, and even with randomization, mismatches in patient characteristics may occur which the authors acknowledge.
One important problem with this trial concerns the chronic use of opioids, with 32.8% in the control group compared with 15.8% in the treatment group. Chronic average opioid use seems higher in the lidocaine group although there were fewer users. There is no clear statement whether the authors controlled for the intraoperative opiate used or whether the preoperative opioid dose was subtracted from the postoperative dose in making the final calculation. There is no subgroup analysis looking at the opioid-naive group alone or the opioid-tolerant group alone. It would be interesting to know how many patients and in which grouping received the full 8 h of lidocaine infusion allowed in the protocol.
We would suggest that the use of opiate dose as an endpoint is inappropriate unless subanalysis is performed on the opioid naive versus the opioid tolerant. It is possible that the difference in opioid use is due to the patients’ need for their regular opioid medication, tolerance, or even opioid-induced hyperalgesia; an effect that might be greater in the control group. If as the authors suggest many centers have a higher incidence of patients on chronic opiates, a larger study should possibly include only patients on opiates and look at total opiate dose required for adequate pain control looking at the change in pre- to postoperative dose requirements.
There are possibly other similar other unmeasured confounders due to the small number of participants, but the study does provide data for sample size selection for a large clinical trial.
The authors declare no competing interests.