Pain after thoracotomy: Conquered or to be conquered?

The post-thoracotomy pain is severe in intensity, and chest movements during breathing further aggravate it. The inadequate control of post-thoracotomy pain leads to splinting effect on chest, which prevents deep breathing efforts and coughing. The cumulative effect results in accumulation of secretions, which is responsible for atelectasis and pulmonary infections. These post-operative pulmonary complications (PPCs) increase the morbidity and mortality of patients.[1] Inadequate control of post-thoracotomy pain in post-operative period may lead to development of chronic pain in up to 68% of patients.[2] Multiple mechanisms are responsible for post-thoracotomy pain; hence, treatment of acute post-thoracotomy pain and preventing development of post-thoracotomy pain syndrome (PTPS) are the significant challenges.

The aetiology of post-thoracotomy pain may be involvement of intercostal, sympathetic, vagus or phrenic nerves. The nociceptive pain arises due to somatic and visceral tissue damage, while neuropathic component is due to stretching or damage of intercostal nerve by application of rib retractor during the surgical procedure.[3] The shoulder pain following thoracotomy is also a common entity described in literature in the range varying from 21 to 97%.[4] The provision of adequate analgesia improves the outcome of surgical procedure.[5] In the era of fast tracking, best modality for providing adequate analgesia is still debatable, and the strive continues. The multimodal pain management strategy should be the mainstay of treatment. The analgesia can be provided with the help of parenteral or oral analgesic agents, regional blocks and adjuvant analgesic agents.[6] The specific enhanced recovery after surgery (ERAS) pathways for thoracic surgery advocating regional nerve block have demonstrated benefits such as reduced opiate usage, minimisation of fluid overload, reduced length of stay, decreased hospital costs and reduced pulmonary and cardiac complications.[7]

The regional blocks are providing superior quality of analgesia compared to intravenous analgesia technique.[8] Among regional blocks, the thoracic epidural analgesia (TEA) is considered as gold standard for post-thoracotomy pain management, but due to more invasive nature, it is not very popular nowadays.[9] Besides, pain from involvement of phrenic nerve and cervical nerves (C4–C6) is also not covered with TEA.[4] In cases with involvement of hemithorax in thoracotomy, the thoracic paravertebral block (PVB) and mid-transverse process to pleura (MTP) approach PVB are used for pain management and are also considered as equally efficacious modality.[10,11] However, due to the proximity to the central neuraxial structures, associated complications and contraindications in patients taking anticoagulation medications, the strive for safer blocks still continues.

A systematic review by the procedure-specific post-operative pain management working group (PROSPECT) stated that TEA and PVB are comparable in terms of analgesic efficacy, and PVB is associated with less respiratory complications and hypotension.[12] Cochrane review also established that PVB is associated with lower rate of chest infection and acute confusion. The minor complications such as low blood pressure, nausea and vomiting, itching and urinary retention are also less in PVB compared to TEA.[11]

The intrathecal administration of morphine provides analgesia for 12–24 hours. Delayed onset respiratory depression and sedation are the common side effects. It is recommended that these patients should be observed for at least 24 hours in hospital setting and early discharge prevented.[13] Interpleural analgesia, interscalene block and intercostal nerve block are the other treatment modalities used for the post-thoracotomy pain management.[14]

With the advancement of surgical instruments and surgical expertise, most of the thoracic surgeries can be performed with video-assisted thoracoscopic (VATS) approach. The minimally invasive techniques create less tissue injury and induce less pain. The pain can be managed with truncal blocks and parenteral administration of analgesic agents. The studies reported that VATS decreases the development of chronic pain and neuropathic pain.[15]

With the availability of ultrasound (US) in the armamentarium of anaesthesiologists, fascial plane blocks can be placed accurately by real-time visualisation of drug deposition, and it also minimises the complications. These blocks can be part of multimodal analgesic techniques. The most studied and efficacious fascial plane block for post-thoracotomy pain is erector spinae plane (ESP) block due to its advantage of blocking the dorsal rami of spinal nerves, which in turn provide the visceral analgesia. The ESP block is far away from the central neuraxial structures, and it is considered a relatively safe procedure. The risk of spinal haematoma in anticoagulated patients is relatively less with ESP; hence, it can be placed in patients taking anticoagulant medications.[16] Various other fascial plane blocks like serratus anterior plane block and pectoralis block are also mentioned in literature for the chest surgery.[17] The limitations of various fascial blocks are that they cannot be used as sole analgesic techniques, and continuous block placement is technically difficult. The role of adjuvants in fascial plane blocks is still controversial; hence, long-acting local anaesthetics are the need of the hour.

The opioid intravenous analgesia was the only available modality practised in the past in those whom regional blocks were contraindicated. The sole use of opioid analgesic medications increases the side effects and hampers the fast tracking, both of which made this technique less popular.[18] The availability of short-acting opioid analgesic agents and availability of patient-controlled analgesic delivery equipment reduces the complications of opioid medications.

As a part of multimodal and opioid sparing technique, the low-dose infusion of non-opioid analgesic agents like lignocaine, ketamine and use of pre-emptive analgesics like gabapentine or pregabalin are also mentioned in literature in various surgical procedures.[19] These agents are shown to reduce the need of opioid analgesic agents, but a multicentric study with large sample size is warranted.

An article being published in this issue of the Indian Journal of Anaesthesia explores the use of gabapentinoids for producing analgesia following thoracic onco-surgeries. The authors report that gabapentinoids result in a significant reduction in the use of non-steroidal inflammatory drugs and opioids. However, the authors have put in a word of caution about the associated side effects such as dizziness.[20] In another randomised double blinded study being published in this issue, intraoperative lignocaine and ketamine infusion was found to reduce the mean fentanyl consumption in the first 24 hours postoperatively.[21]

To summarise, no single technique for analgesia is ideal for thoracic surgeries. Currently with the ERAS protocol, the best technique to follow is multimodal approach to analgesia consisting of pharmacological management in combination with the regional techniques.