Intertransverse Process Block to Improve Quality of Recovery After Cardiac Surgery With Sternotomy

BACKGROUND Acute postoperative pain is common among cardiac surgical patients, particularly within the first 2 days after surgery, with reported at least moderate intensity. Pain is mainly caused by sternotomy incision, surgical dissection, sternal and ribs fracture, injury to intercostal nerves, and also from sites of drainage cannulas and chest tubes. Poorly controlled acute postoperative pain is associated with adverse physiological outcomes that impair the recovery of cardiac surgical patients. It reduced patient satisfaction, delayed postoperative ambulation, and was associated with development of chronic postsurgical pain (CPSP). The association between sternotomy pain and pulmonary complications has been observed, and the sympathetic activation secondary to pain can induce myocardial ischemia and arrhythmias. Pain control has also been pointed out as one of the major concerns to cardiac surgical patients in intensive care unit (ICU).

Opioid-based technique is commonly used in cardiac anaesthesia to blunt the sympathetic response to surgical pain and maintain hemodynamic stability. However, opioids have dose-dependent side effects and excessive use can prolong mechanical ventilation and time spent in intensive care unit. In modern years that fast-track cardiac anaesthesis is being practiced, opioid-sparing techniques and incorporation of regional anaesthesia into cardiac surgical pain management would enable early extubation, mobilization and discharge from ICU. While neuraxial techniques such as spinal and epidural anaesthesia are possible, there are concerns on hemodynamic instability and the potential for neuraxial hematoma after systemic heparinization in cardiac surgery. Thoracic paraspinal blocks such as paravertebral (PVB) and erector spinae plane block (ESPB) seem to be better alternatives to neuraxial techniques. Paravertebral block has more stable hemodynamic profile and was shown to reduce time on mechanical ventilation and improved intraoperative and postoperative opioid consumption. However, there are concerns on pleural puncture and pneumothorax. The close proximity to vascular structures also raise concerns in systemic heparinization in cardiac surgery. ESPB was reported to decrease perioperative morphine consumption and pain score.However, the sensory block was inconsistent. A systematic review reported no difference in postoperative pain intensity. The spread of local anaesthetics in ESPB was unpredictable, resulting in variable anaesthesia and analgesia over anterior hemithorax. Parasternal fascial plane blocks such as superficial and deep parasternal intercostal blocks can avoid the complications associated with neuraxial and paravertebral techniques with favourable outcomes. However, they only cover anterior cutaneous branches of intercostal nerves T2-6 which may not relieve the visceral pain from mediastinum and the pain from chest tubes inserted beyond the dermatomes. Moreover, due to the close proximity of deep parasternal intercostal plane to internal mammary artery (LIMA) and pleura, there are risks of pneumothorax, LIMA injury or hematoma which are considered undesirable in cardiac surgical patients.

Intertransverse process block (ITPB) is a collective name for several reported paraspinal block techniques such as midpoint transverse process block, costotransverse process block or costotransverse foramen block. The nomenclature was standardized through international consensus. ITPB targets paravertebral space by extra-paravertebral injection of local anaesthetics (LA) within the intertransverse tissue complex (ITTC), posterior to the superior costotransverse ligament (SCTL). ITPB anaesthetizes the ventral rami of spinal nerves, the sympathetic trunk, the communicating rami, and demonstrated LA spread into the thoracic paravertebral space with effective analgesia after breast and video-assisted thoracoscopic surgeries. Compared to other regional techniques for pain management in cardiac surgery, ITPB can be technically simpler and safer to avoid pleural puncture, less bleeding concerns in systemic heparinization, yet provides both somatic and visceral analgesia. Randomized controlled trials (RCT) for ITPB in cardiac surgery are sparse. To date, this is the first RCT to evaluate the analgesic efficacy of ITPB in adult cardiac surgical patients. The investigators hypothesized that bilateral ITPB can provide better perioperative analgesia by blunting sympathetic response of sternotomy, achieving perioperative opioid-sparing and improving quality of recovery.

METHODS

Study population and design This is a single-centre, prospective, randomized, double-blinded, placebo-controlled trial at the Prince of Wales Hospital, a university teaching hospital in Hong Kong.

The investigators include adult patients aged 18 or older, undergoing elective coronary artery bypass graft (CABG), valve repair/replacement, or combined CABG/valve procedure via sternotomy. The investigators exclude emergency surgery, redo surgery, history of thoracotomy or mastectomy, patients with history of chronic pain or on chronic opioids or sedatives, renal failure with estimated glomerular filtration rate <30ml/min (calculated by Cockcroft-Gault formula), intraoperative use of remifentanil and unable to provide informed consent.

Randomization and concealment Patients are randomly assigned into two groups by drawing sequentially numbered, coded sealed, opaque envelops each containing the group assignment of either interventional or control group. The sealed envelopes are prepared by a third party who took no further part in the study. The study drug syringes are prepared under strict aseptic techniques by a nurse not involved in the study. ITPB will be performed by a single anaesthesiologist who was blinded to group allocation. The primary care team, blinded to group allocation, performs all surgical procedures using standardized techniques. Anaesthesiologists, nurses and research team, blinded to group allocation, record data intraoperatively, in ICU, and at regular intervals in the cardiac wards.

Ultrasound block placement Patients receive ITPB prior to anaesthesia induction in a lateral decubitus position. All blocks will be done by a single anaesthesiologists who had performed more than 50 successful ITPBs, using a low-frequency curved array transducer (6-1 MHz), and a 80mm echogenic nerve block needle (SonoTAP; PAJUNK, Germany). Ultrasound-guided bilateral ITPB is performed at T4/5 level by counting from cephalad to caudad direction starting from the most prominent spinous process at C7. The transducer is placed transversely to delineate several bony landmarks associated with paravertebral region: the rib, transverse process, inferior articular process and SCLT that are collectively known as the ITTP. Nerve block needle is introduced in-plane and advanced from lateral-to-medical direction until tip is visualized within the retro-SCLT space lateral to the inferior articular process. After negative aspiration of blood, 25ml 0.25% levobupivacaine will be injected on each side in intervention group while sham block with equal volume of normal saline will be injected in the control. During injection, the investigators observe for distension of retro-SCLT space, distension of thoracic paravertebral space and increased echogenicity of SCLT. All patients are tested for anaesthesia (reduced sensation to ice) at bilateral anterior hemithorax 15 minutes after the block. Surgical incision and sternotomy are performed more than 30 minutes after block placement.

Anaesthesia and interventions All patients receive general anaesthesia for the cardiac surgery, which include midazolam 0.01-0.05mg/kg, fentanyl 2-5mcg/kg and rocuronium 0.5-1mg/kg to facilitate intubation with single-lumen cuffed endotracheal tube. Anaesthesia is maintained with sevoflurane and propofol infusion that targeted Bispectral Index 40 to 60. No vasoactive agents are used to lower the blood pressure except fentanyl and morphine that blunt sympathetic response to pain. Administration of opioids will be left to the discretion of the attending anaesthetist. No other analgesics will be used intraoperatively. Patient-controlled analgesia (PCA) morphine is prescribed for 72 hours after operation for postoperative analgesia (1mg bolus, 5 minute lockout time and a safety maximum of 20mg per 4 hour interval). Information about the PCA pump and instructions to use only if the Numeric Rating Scale (NRS) pain score ≥4 will be given to the patient before surgery and repeated in ICU. Oral analgesics including paracetamol 1g and dihydrocodeine 30mg every 6 hours are prescribed by parent surgical team. At the end of the operation, patients are kept sedated with propofol infusion to ICU. It is stopped upon admission to ICU to facilitate weaning from ventilator. Adaptive support ventilation (ASV) is used for weaning. It adjusts the ventilatory parameters depending on lung mechanics and breathing effort.

Data collection Patients are screened the day before operation. Eligible patients are given information sheets regarding the main aspects of the trial and information is discussed with the research nurse before informed consent can be obtained. All data are collected by research team members blinded to group assignment. Patient demographics and body mass index are recorded. Cumulated opioid consumption data and time to first morphine rescue are extracted from PCA pump. At 15 minutes after tracheal extubation and at 2h, 4h, 6h, 8h, 12h, 24h, 48h and 72h post-extubation, pain score at rest and on coughing will be quantified using NRS from 0 to 10. Zero represents no pain at all while 10 points represents the worst pain ever. The patients are asked to rate the overall satisfaction to pain management on a verbal analogue scale (0 = worst possible, 100 = best possible) at the predefined points. The level of sedation is measured using the Ramsay Sedation Scale (1 = anxious, agitated or restless, or both; 2 = co-operative, oriented and tranquil; 3= respond to command only; 4 = exhibit brisk response to light glabellar tap or loud auditory stimulus; 5 = exhibit sluggish response to light glabellar tap or loud auditory stimulus; 6 = exhibits no response). Any nausea and vomiting, and use of rescue antiemetics are documented. The Chinese validated version of the Quality of Recovery Questionnaire (QoR-15) is completed at baseline (preoperatively) and postoperatively at 24 hours and 72 hours after extubation.

Outcome measures Primary outcome is QoR-15 score at 24 and 72 hours after extubation. Secondary outcomes include intraoperative opioid consumption, morphine consumption within 24 and 72 hours after surgery, percentage changes in hemodynamic parameters from baseline within the first 10 minutes of skin incision for sternotomy, postoperative pain score, time of first morphine rescue, patients' satisfaction to pain, time weaned to spontaneous breathing on ASV, time to extubation, side effects from opioids (level of sedation, nausea and vomiting), length of ICU and hospital stay, and neuropathic pain assessment at 3 and 6 months after surgery.

Intraoperative opioids other than morphine are converted into intravenous morphine equivalent dose, and dose of fentanyl used at anaesthesia induction is recorded. Hemodynamic changes following sternotomy are defined as percentage increase in systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and heart rate (HR) between the baseline and their peaks within 10 minutes of skin incision for sternotomy. All hemodynamic parameters are automatically recorded using the Anaesthesia Clinical Information System at one-minute interval.

Neuropathic pain at 3 and 6 months after surgery will be assessed using the Douleur Neuropathique en 4 questionnaire (DN4). It is a 10 items questionnaire and the Mandarin Chinese version has been validated in previous study. Each item of DN4 is assigned a score of 0 when the participant answered 'no' and a score of 1 when the participant answered 'yes'. The total DN4 score ranges from 0 to 10, and a score ≥4 indicates a diagnosis of neuropathic pain.

Sample size and statistics Sample size is calculated using G*Power software version 3.1.9.3 (Kiel University, Kiel, Germany) and based on the QoR-15 score at 24 and 72 hours after surgery, which is the primary outcome variable. The minimum clinically important difference (MCID) for the QoR-15 score at 24 hours is 8 and the typical standard deviation (SD) of QoR-15 in the postoperative period ranges between 10-16. Based on these data, for a two-sided test, assuming a type I error of 0.05 and type II error of 0.2, population variance of 144 (SD was assumed to be 12), the investigators calculate a sample size of 36 in each group. Considering a 10% dropout rate, a total of 80 patients (40 patients in each group) will provide 80% power to detect a different in the mean QoR-15 score at 24 hours.

The primary analyses are performed on a modified intention-to-treat basis. Patients are analysed according to their randomized allocated groups but are excluded from the analysis if they do not adhere to the protocol after randomisation. Categorical data is reported as numbers and percentages. Continuous variables are reported as mean (standard deviation) or median (interquartile range) as appropriate after checking for normality using the Shapiro-Wilk's test. Comparison of continuous data is performed by Student's t test and by Mann-Whitney U test for non-normally distributed data. Chi-square test is used to compare groups with categorical variables. Level of significance is set at P<0.05. SPSS 27.0 software (IBM Corp, Armonk, NY) is used for data analysis.