Dermatomal spread in lateral quadratus lumborum blocks versus transversus abdominus plane blocks after laparoscopic colorectal surgery: a randomized clinical trial

INTRODUCTION: Postoperative pain after laparoscopic abdominal surgery remains complex. While lateral quadratus lumborum (QL) block and transversus abdominus plane (TAP) block are similar techniques, no studies have examined if one technique has greater dermatomal spread. METHODS: Laparoscopic colorectal surgical patients were randomized to lateral QL or TAP blocks. Dermatomal anesthetic spread, as measured by loss of sensation to temperature in the postanesthesia care unit, was the primary outcome. If a clear level of dermatomal anesthesia could not be defined, the block was categorized as "indeterminate." Secondary outcomes included opioid consumption, pain scores, and opioid-related side effects. RESULTS: 153 patients completed the study (75 QL and 78 TAP). Mean (95% CI) number of dermatomes with loss of sensation to ice was greater in subjects randomized to QL (4.2 (3.7 to 4.8)) versus TAP (2.7 (2.2 to 3.2); p=0.0001), and the QL group was more likely to have loss of sensation above T8 (p=0.01) and T10 (p=0.02). Indeterminate block was more often noted with TAP blocks (p<0.0001). Opioid consumption at 24 hours, pain scores, and opioid-related side effects did not differ. DISCUSSION: Compared with TAP blocks, QL blocks had greater dermatomal anesthesia spread and lower rates of an indeterminate block. However, differences in pain and opioid consumption were not noted. The clinical importance of these findings should be investigated in future trials. TRIAL REGISTRATION NUMBER: NCT03490357.