Deep Neuromuscular Block and Surgical Conditions During Bariatric Surgery

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We read with interest the article by Baete et al1 about the influence of deep versus moderate neuromuscular block (NMB) on surgical conditions in patients undergoing laparoscopic bariatric surgery. The authors found no difference in their primary outcome measure, the overall quality of the surgical field as rated on a 5-point surgical rating scale (SRS, 4.2 for deep NMB versus 3.9 for moderate NMB, P = .16). However, several studies observed that deep NMB significantly improves surgical conditions during various laparoscopic procedures2–4 and reduces postoperative pain.5 More specifically, the recent publication by Torensma et al5 with a similar research question and design as that of Baete et al produced different results. Torensma et al5 investigated the effect of deep NMB (posttetanic count 2–3 twitches) versus moderate NMB (train of four 1–2 twitches) on surgical conditions in 100 obese patients (body mass index >30 kg/m2) during laparoscopic gastric bypass surgery. In this study, the surgeons scored the surgical conditions during deep NMB significantly better compared to the moderate block (4.3 vs 4.8, P < .001) as assessed on the 5-point Leiden SRS.4 Moreover, Leiden SRS scores <4 did not occur during the deep NMB, and the variability of the scores was much lower during deep than moderate NMB (4% vs 17%). We wonder how the differences between the studies of Baete et al and Torensma et al can be explained.
The primary outcome used by Baete et al was the overall SRS obtained only after the surgeon had finalized the procedure. While this may give an indication of the overall surgical conditions, subtle and short intraoperative fluctuations in surgical conditions may not be reflected. In contrast, Torensma et al assessed intraoperative conditions at 10-minute intervals. Multiple scoring moments increased the resolution of the score and resulted in 412 scorings in 100 patients. Thus, the study by Torensma et al had a stronger power to detect a smaller difference in SRS.
Finally, we were somewhat surprised by the observation in the study of Baete et al that overall scores of 1 or 2, which represent extremely poor or poor conditions, occurred in approximately 10% of the patients. This would suggest that the surgeon is unable to complete his procedure. Additionally, the low scorings were only partly reflected in the incidence of intra-abdominal pressure rises >18 mm Hg, which occurred in equal amounts in both groups. Pressure rises are usually evoked by sudden involuntary muscle contractions. In this respect, it remains speculative what conditions caused the occurrences of overall scores of 1 or 2.
In conclusion, the effect of deep NMB on surgical conditions is a new field of research, only recently being explored. It is our task to identify which procedures and which patients may benefit from deep NMB and ultimately whether the implementation of a deep NMB affects patient outcome. We agree with Baete et al that more studies are needed to definitely answer these questions. However, when assessing the quality of the surgical field, we strongly feel that repeated ratings of the surgical field during a procedure are superior to 1 overall rating. Ideally, more than 1 surgeon should be involved in the scoring and ideally video snippets should be taken during the ratings, to compare scorings between surgeons.
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