DISCUSSION This study shows that experienced metabolic bariatric surgeons estimate laparoscopic small bowel length with on average less than 10% deviation from the goal lengths. However, this still resulted in 51% of the estimated bowel lengths with more than 10% deviation and 30% with more than 15% deviation from the goal lengths. There were considerable inter-individual differences between the metabolic bariatric surgeons. Furthermore, surgical residents inaccurately estimated the small bowel length by structurally underestimating the limb lengths. Acceptable variation in bowel length measurement was defined as less than 10% deviation from the goal limb length. Due to lack of literature, it is unknown which percentage deviation is still acceptable without causing clinical consequences in terms of weight loss and nutritional deficiencies. A deviation of 10% was used as acceptable cut-off value, because a higher deviation would result in an overlap of the different limb lengths used in MBS (Figure 2). A more liberal margin still resulted in 30% of measurements outside 15% deviation. These percentages outside the margins can partially be explained by the inter-individual difference between the metabolic bariatric surgeons, as one of the metabolic bariatric surgeons structurally underestimated the small bowel length with more than 10% deviation. With regard to the structural underestimation, this is probably due to repeatedly estimating the steps too small. Nevertheless, the other three surgeons estimated 22% of the bowel segments with more than 15% deviation. With the hand-over-hand technique, the estimated steps can easily be affected by multiple factors as the flexible structure of the small bowel with limited stretch due to the mesentery, two-dimensional imaging of a three-dimensional bowel, counting error, or error of judgement, which all can result in outlying measurements. In daily practice, these deviations can result in metabolic bariatric patients with considerable difference between the goal and actual limb length. Nevertheless, the actual clinical consequences of these variations remain as yet unknown. Comparable studies show deviations which are considerably higher compared to our results. The study of Gazer et al. assessed the reliability of laparoscopic bowel length measurement in 14 surgeons using an in vivo porcine model. They found measured lengths were 36% shorter than the actual length, concluding that the assessment during laparoscopy was inaccurate.13 However, the measurements were not performed by metabolic bariatric surgeons, which may 6 123 Laparoscopic small bowel length measurement using a hand-over-hand technique
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