Letter to the Editor: “Ultrasound-guided single thoracic paravertebral nerve block and erector spinae plane block for perioperative analgesia in thoracoscopic pulmonary lobectomy: a randomized controlled trial”
Authors: Zhong Feng, Fu-Shan Xue and Liu-Jia-Zi Shao
Affiliations: Department of Anesthesiology, Beijing Friendship Hospital, Capital Medical University, Beijing, People’s Republic of China
Email: firstname.lastname@example.org; email@example.com
By a randomized controlled trial with 67 patients undergoing thoracoscopic lobectomy, Zhang et al  assessed the efficacy of a single preoperative ultrasound-guided thoracic paravertebral block (TPVB) and erector spinae plane block (ESPB) for perioperative analgesia by comparing with the control intervention. They showed that both TPVB and ESPB reduced postoperative pain and doses of perioperative sufentanil and postoperative remedial analgesics. A valuable clinical trial has been carried out, but there are several issues in methodology and results of this study that deserve further clarification and discussion.
First, the postoperative pain Visual Analog Scale (VAS) score was used as primary outcome and the results of pre-experiment including 5 patients in each group were used for sample size estimation. We noted that the net between-group diffenences in means of resting pain VAS scores at 1 h after surgery for sample size estimation were only 0.5-0.6. As the authors did not provide the expected minimal clinically important difference of primary endpoint between groups, we were concerned that a small sample of 22-23 patients in each group was no enough powered to show the between-group differences in postoperative pain VAS scores . In fact, the recommended minimal clinically important differences of postoperative pain score in available literature are 1.5 at rest state and 1.8 during motion on a 0-10 pain VAS .
Second, early postoperative pain VAS scores at rest state and during motion were significantly decreased in patients receiving the TPVB and ESPB compared with those receiving the control intervention. However, all net between-group diffenences in means of pain VAS scores at rest state and during motion within 48 h after surgery were about 1 or less, which does not achieve the recommended minimal clinically important difference . In the method, moreover, the authors provides the classification of postoperative pain severity, i.e., VAS score < 4 for mild pain; 4-7 for moderate and > 7 pain for severe pain. In addition, rescue analgesia was administered with 50 mg of flurbiprofen ester, if pain VAS score at rest or during motion was ≥ 4. However, they did not observe and compare the incidence of moderate to severe postoperative pain needing rescue analgesia and patient satisfaction with postoperative pain control, as performed in other studies assessing efficacy of nerve blocks for postoperative pain control in patients undergoing thoracoscopic surgery [4-6]. In this case, it is difficult for readers to determine whether early postoperative pain control improved by the TPVB and ESPB compared with the control intervention should be considered as being clinically important.
Third, by directly comparing sufentanil consumption in the analgesic pump and dose of flurbiprofen ester for rescue analgesia within 48 h after operation, the authors concluded that both the TPVB and ESPB significantly decreased sufentanil consumption, but did not significantly affect the dosage of flurbiprofen for rescue analgesia. When comparing analgesic consumption of postoperative pain control, however, doses of all analgesics including opioid and non-opioid drugs should be converted to morphine milligram equivalents (MME) for between-group comparison . In available literature, the recommended minimal clinically important difference of total opioid consumption for postoperative pain control is an absolute reduction of 10 mg intravenous morphine in the MME for 24 h . Given that opioid sparing is one of main benefits of using nerve blocks for postoperative pain control , we are very interested in knowing whether total MME of all analgesic consumptions in each 24 h after operation was significantly different among the three groups and if net between-group difference in the total MME exceeds the recommended minimal clinically important difference.
Finally, this study observed the occurrence of postoperative adverse events, but did not assess the quality of postoperative recovery, as performed in previous studies [9,10]. In fact, the quality of postoperative recovery is very important for determining efficacy and clinical availability of a pain intervention and is easily measured using by a QoR-15 score ranging from 0 to 150, with a higher score indicating an improved quality of postoperative recovery . Furthermore, the recommended minimal clinically important difference of QoR-15 score is an absolute difference of 8 points between groups . We believe that this study would have provided more useful data regarding efficacy and clinical values of TPVB and ESPB for early postoperative analgesia in patients undergoing thoracoscopic lobectomy, if the design had included the assessment on the quality of postoperative recovery.
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