Comparing Analgesic Efficacy of Nerve Blocks after Thoracoscopic Surgery: Methodology Is Important

Reply to Letter to Editor titled “Comparing Analgesic Efficacy of Nerve Blocks after Thoracoscopic Surgery: Methodology Is Important”

By a prospective randomized controlled trial of 50 patients with primary spontaneous pneumothorax and undergoing single port video-assisted thoracoscopic surgery, Kim et al[1] compared efficacy of serratus anterior plane block (SAPB) and intercostal nerve block (INB) for postoperative analgesia. They showed that compared with INB, the SAPB provided similar postoperative pain relief with reduced analgesic consumption. A valuable clinical trial has been performed, but we noted several issues in methodology and results of this study that deserved further clarification and discussion.

First, the SAPB was performed with ultrasound guidance just before the initiation of surgery after anesthetic induction, while the INB was performed by a surgeon just before the closure of surgical incision. In this way, the SAPB actually is a modality of preemptive analgesia, which can provide an improved efficacy of postoperative pain control by preventing the establishment of central sensitization.[2] However, the INB performed at the end of operation is a modality of nonpreemptive analgesia. Although the randomized controlled trial is an accepted gold standard method to compare the effect-difference of different interventions, all of confounders that affect assessment of primary endpoint must be standardized to avoid potential bias. Thus, we are concerned that imbalance in intervention times between groups would have biased the main findings of this study.

Second, other than SAPB and INB, postoperative pain control strategy of this study also included the scheduled acetaminophen 650 mg three times per day. Furthermore, rescue analgesia was performed with intravenous (IV) ketorolac 30 mg when postoperative numeric rating scale (NRS) score was 4 or 5, and IV fentanyl 50 μg when NRS score was more than 6. We noted that during 12 hours after surgery in the two groups, mean postoperative pain NRS scores at rest state were more than 3 and mean NRS scores with coughing were 4 or more, with large standard deviations. These results indicate that some of patients in the two groups experienced moderate-to-severe pain in early postoperative period, especially on coughing state at 3 hours after surgery. In patients undergoing single port video-assisted thoracoscopic surgery, this is evidently unsatisfied postoperative analgesia for successful use of enhanced recovery after surgery protocols, in which multimodal analgesia regimen is recommended and analgesics should be universally titrated to achieve patient comfort and minimal pain, that is, a NRS score of 3 or less.[3] We are very interested in knowing why the designed goal of postoperative pain control in this study is not achieved, if rescue analgesia was given on demand.

Third, the number and amount of ketorolac consumption for rescue analgesia before removal of chest tube were significantly lower in patients receiving the SAPB compared with those receiving the INB. In clinical trial, however, postoperative analgesic consumption is often normalized to morphine milligram equivalents (MME) for comparison. Furthermore, available literature recommends that the minimal clinically important difference of MME is an absolute reduction of 10 mg IV morphine in the 24 hours.[4] As 30 mg IV ketorolac is equivalent to 10 mg IV morphine,[5] we are concerned that the absolute reduction in IV MME during postoperative first 24 hours in patients receiving SAPB compared with patients receiving INB does not exceed the recommended minimal clinically important difference.

Finally, this study did not assess the quality of postoperative recovery and patients' satisfaction for postoperative analgesia, as performed in previous studies.[6] [7] In fact, these variables are very important for determining efficacy and clinical availability of interventions and are easily measured using by a quality of recovery-15 score ranging from 0 to 150 (a higher score indicating an improved quality of postoperative recovery)[5] and a visual analog score (0 = least satisfied, 100 = most satisfied),[6] respectively. We believe that this study would have provided more useful data comparing efficacy and clinical values of SAPB and INB for postoperative analgesia after single port video-assisted thoracoscopic surgery.

Authors' Contributions

All authors had carefully read the manuscript of Kim et al, analyzed their methods and data. XL suggested comment points and drafted this manuscript, and is the author responsible for this manuscript. FSX critically revised comment points and this manuscript, and is the author responsible for this manuscript. LJZS and NH revised comment points and this manuscript. All authors had seen and approved the final manuscript.

Publication History

Received: 12 December 2021

Accepted: 08 February 2022

Article published online:
29 May 2022

• References

• 1 Kim S, Bae CM, Do YW, Moon S, Baek SI, Lee DH. Serratus anterior plane block and intercostal nerve block after thoracoscopic surgery. Thorac Cardiovasc Surg 2021; 69 (06) 564-569
• 2 Woolf CJ, Chong MS. Preemptive analgesia–treating postoperative pain by preventing the establishment of central sensitization. Anesth Analg 1993; 77 (02) 362-379
• 3 Mancel L, Van Loon K, Lopez AM. Role of regional anesthesia in enhanced recovery after surgery (ERAS) protocols. Curr Opin Anaesthesiol 2021; 34 (05) 616-625
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• 6 Finnerty DT, McMahon A, McNamara JR, Hartigan SD, Griffin M, Buggy DJ. Comparing erector spinae plane block with serratus anterior plane block for minimally invasive thoracic surgery: a randomised clinical trial. Br J Anaesth 2020; 125 (05) 802-810
• 7 Zhang Y, Yan W, Chen Y, Fan Z, Chen J. Lower background infusion of oxycodone for patient-controlled intravenous analgesia, combined with ropivacaine intercostal nerve block, in patients undergoing thoracoscopic lobectomy for lung cancer: a randomized, double-blind, controlled clinical trial. Drug Des Devel Ther 2021; 15: 3535-3542