To the Editor:—
We read the article of Stevens et al. 1with interest and would like to congratulate the authors on their effort in investigating some advantages of regional anesthesia. However, we have some concerns regarding the methodology of the study.
One important outcome investigated by Stevens et al. 1in this trial is to evaluate whether a lumbar plexus block could reduce preoperative and postoperative blood loss. Because this question is crucial and may have important clinical implications, all means to evaluate blood loss as precisely as possible have to be used. Unfortunately, in our opinion, these conditions were not fulfilled in the current trial. We agree that intraoperative estimation of blood loss is difficult. Indeed, we are surprised that the authors only make a rough estimation of 40 ml blood per dressing. First, it is well-known that the amount of blood absorbed by operative swabs is variable, usually from 20 to 150 ml. The minimal condition to ascertain the validity of these results would have been to weigh the swabs before and after their use. Second, in addition to blood collected in suction canisters and swabs, there is also a considerable portion in the operative surroundings. Unfortunately, this was neither mentioned nor evaluated by the authors.
We also have some concerns regarding the statistical analysis. Looking at the results in detail, great interindividual variation in Visual Analogue Scale scores is evident, which may imply a non-Gaussian distribution. Therefore, we believe that the use of a nonparametric test would have been more accurate for the analysis of Visual Analogue Scale scores. Furthermore, a post hoc test for repeated measurements would have been necessary but does not seem to have been performed.
To evaluate the quality of two different postoperative analgesia techniques, Visual Analogue Scale scores have to be compared at certain points during the course of the study. In our opinion, these time points have to be exactly defined and, for this reason, a reference point, the time point zero (t = 0) is necessary. The lack of a time point (t = o) may introduce bias in the interpretation of the results.
There is little information given on exclusion criteria. Were patients with diabetes mellitus, peripheral neuropathy, or steroid intake included? In part, these pathologies may influence the results of the study.
Finally, we were surprised to read that the lumbar plexus block was performed after induction of general anesthesia. At our institution, we perform all nerve blocks with the patient awake or, if necessary, with light sedation. The safety of performing nerve blocks in patients during general anesthesia or heavy sedation has been questioned. 2The counter argument is that by excluding verbal contact with the patient, the most useful warning of impending nerve contact is lost and that no potential benefit to the patient is worth the risk of serious nerve damage.
*Orthopedic University Hospital of Zurich/Balgrist, Switzerland. firstname.lastname@example.org