This prospective, randomized, double-blind, placebo-controlled study showed that USG parasternal intercostal nerve block, following bolus initiation, reduces opioid requirements and adjunctive analgesia within the first 24 hours after mediastinal mass resection by median sternotomy, with less postoperative adverse events. Patients administered USG parasternal intercostal nerve block reported significantly lower pain scores and higher satisfaction toward analgesia compared with those treated with sufentanil PCIA alone. Parasternal intercostal nerve block with ropivacaine has been successfully employed for pain management in cardiac surgery and our previous study(7–10, 15, 22), consistent with the present results. However, inconsistent results have been reported regarding the use of liposomal bupivacaine for parasternal intercostal nerve block(23). Regardless, evaluating the analgesic efficacy of USG parasternal intercostal nerve block with ropivacaine in patients undergoing mediastinal mass resection by median sternotomy was firstly performed in this study.
While mediastinal mass resection by thoracoscopy or robot-assisted surgery as a minimally invasive approach is widely used, median sternotomy as the traditional standard approach remains irreplaceable(24). However, a significant adverse effect of the latter technique is the intense chest wall pain major originating from the median sternal wound. Meanwhile, ineffective postoperative pain management leads to reduced pulmonary function caused by atelectasis and pneumonia, coronary ischemia, poor wound healing, fatigue, insomnia, depression and the transition from acute pain to chronic pain(3, 4). The intercostal nerve originates from the intervertebral foramen, branching into the lateral cutaneous branch and the anterior cutaneous branch at the mid-axillary line, which separates into the medial-branch that runs across the sternum and the lateral branch running in the breast tissue. Parasternal intercostal nerve block aims to neutralize anterior cutaneous intercostal nerves with the goal of reducing sternal nociception which may exert preemptive analgesic effects, and restraining the establishment of altered central processing of afferent input which may amplify postoperative pain(13, 14). This technique is considered a good modality for adjuvant analgesia. However, parasternal intercostal nerve block does not neutralize the lateral intercostal nerves or other somatic and visceral nerves, both of which are sources of musculoskeletal nociceptive pain in the chest wall area post-median sternotomy(11, 25).
Adjuvant nonsteroidal anti-inflammatory drugs are often employed to reduce opioid requirements(6). Opioids used as the sole agent carry risks of excessive sedation, respiratory depression and gastrointestinal reaction(26, 27). This study adopted a multimodal analgesia regimen, including opioids, nonopioid analgesics and a nerve block for optimal pain relief, and was successful in achieving good patient satisfaction with low postoperative adverse events. The USG parasternal intercostal nerve block averted the negative side effects observed with other postoperative analgesia modalities, and epidural analgesia and paravertebral block, in cardiac surgery patients. Furthermore, these modalities are operator-dependent and require experienced professionals for safe and quick application(28–30). In this study, parasternal intercostal nerve block under real-time ultrasound guidance was performed near the sternum by injecting ropivacaine between the external intercostal and pectoralis major muscles, resulting in a larger area of sensory deprivation in comparison with transversus thoracic muscle plane block(31). In the latter approach, the injected analgesic flows anteriorly to the transversus thoracic muscle, making USG application difficult. Anatomical experiments have found that the plane between the pectoralis major muscle and the external intercostal muscle is the same as that between the pectoralis major muscle and the ribs because the pectoralis minor muscle originates from the middle of the third(32), fourth and fifth ribs, while the hard ribs act as fences to prevent the needle from going deeper. Therefore, we implemented parasternal intercostal nerve block only in the 3rd and 5th parasternal intercostal spaces, which would result in 2nd to 6th parasternal intercostal nerve block after diffusion. Meanwhile, there were no technique- or drug-related complications such as pneumothorax and deep sternal wound infection invading the mediastinum, muscle and bone in this study at 1 week after surgery. We also believe that USG parasternal intercostal nerve block may be applied for chest wall keloid scar resection.
This study had several limitations. Firstly, a short-term follow up of patients was performed, limiting the ability to assess long-term chest wall pain. Although patients administered USG parasternal intercostal nerve block had lower pain scores, formal sensory block assays were not carried out. Meanwhile the significant reduction in opioid use in the PSI group is a strong indication that analgesia was present. Paravertebral block with 0.5% ropivacaine or 0.5% bupivacaine imparts pain relief lasting between 6 and 8 hours post-thoracoscopy(33). However, this time frame was not assessed in this study, whose goal was to evaluate the reduction in adjuvant opioid use. In addition, it remains unclear whether reduced adjunctive analgesia and opioid requirements in the PSI group compared with control patients within the first 24 hours after surgery are only associated with the early postoperative period. USG parasternal intercostal nerve block may not be ideal in the ward setting and in case of more extensive surgical incisions, for which continuously infused local anesthetics for postoperative analgesia after median sternotomy is more advantageous(34). Therefore, modifications to the continuous parasternal intercostal nerve block protocol for pain management warrant further investigation. Pathological diagnosis of mediastinal masses after resection was also not taken into consideration. Given the limited demographic profile of the study population, additional larger investigations are required to confirm these findings, thereby advocating this technique for application in the general population.