The Effect of Parasternal Block on Postoperative Pain in Patients Undergoing Coronary Artery Bypass Graft Surgery

Objective: This study aims to investigate the effects of intraoperative parasternal block on postoperative analgesia in patients undergoing elective coronary artery bypass graft surgery.

Materials and Methods: This prospective, randomized, double-blind study included 78 patients aged 30-80 years with an ASA (American Society of Anesthesiologists) risk score of III-IV, who were scheduled for elective coronary artery bypass graft surgery. Patients were randomly assigned into two groups: the parasternal block group (n = 39), receiving parasternal block with 2.5% bupivacaine, and the saline group (n = 39), receiving parasternal block with 0.9% NaCl. All patients were administered a standard anesthesia protocol, and routine care and analgesia practices during the postoperative period were not interfered with. Patients in the intensive care unit received intravenous paracetamol every 8 hours for analgesia. If postoperative 24-hour pain scores in the intensive care unit , assessed using the Behavioral Pain Scale while intubated and the Numeric Rating Scale while extubated, exceeded 4, 1 mg/kg tramadol was administered. The timing and doses of the first tramadol administration, as well as extubation times, intensive care unit stay durations, and discharge times, were recorded.

Results: In the postoperative period, Behavioral Pain Scale scores at the 8th hour and Numeric Rating Scale scores at the 4th and 12th hours were significantly lower in the parasternal block group compared to the saline group (p \< 0.005). The average extubation time was 8.76 hours in the parasternal block group and 14.76 hours in the saline group (p \< 0.001). Among patients with pain scores of 4 or higher, the total tramadol consumption in the parasternal block group was 150 ± 64.72 mg, with the first tramadol administration occurring at 17.26 ± 4.78 hours. In the saline group, total tramadol consumption was 212.5 ± 82.23 mg, and the first administration occurred at 12.35 ± 5.75 hours.

Conclusion: Our study demonstrated that parasternal block, as a component of multimodal analgesia, improved postoperative analgesia levels in coronary artery bypass graft surgery. Therefore, the investigators consider parasternal block to be effective in pain management following median sternotomy.

INTRODUCTION Worldwide, more than 800,000 coronary artery bypass graft surgeries are performed annually. Coronary artery bypass graft surgery is traditionally conducted via median sternotomy, a procedure that can cause damage to both bone and soft tissues. Pain levels are particularly high during the first days following cardiac surgery . Between 30% and 75% of patients report moderate to severe chronic pain after cardiac surgery, and it is known that 4% to 10% develop chronic pain syndrome associated with sternotomy .

Improved pain management reduces surgery-related complications, shortens hospital stays, and enhances patient satisfaction. Traditionally, opioid-based analgesics have been the primary method for postoperative pain control in cardiac surgeries for many years . However, high-dose opioid use is associated with numerous side effects, including sedation, respiratory depression, delayed extubation, urinary retention, itching, nausea, and vomiting . Additionally, intravenous opioid therapy is commonly preferred for postoperative pain management in patients undergoing cardiac surgery.

Thoracic epidural analgesia is a method capable of providing excellent "opioid-free" analgesia following cardiac surgery. Thoracic epidural analgesia has been recognized as an effective alternative due to its ability to reduce respiratory complications, arrhythmias, and mortality rates.

Regional anesthesia, as an essential component of multimodal analgesia approaches, allows cardiac anesthesiologists to minimize opioid consumption. Thoracic epidural and paravertebral blocks are effective methods for continuous pain management; however, their widespread use in cardiac surgery patients is restricted due to the increased risk of epidural hematoma, particularly after cardiac surgery, where coagulopathy, anticoagulation, and antiplatelet drug use are prevalent.

Perioperative analgesic management has become a crucial component of fast-track cardiac anesthesia practices, with the potential to facilitate early tracheal extubation and shorter hospital stays . However, cases where existing pain control methods are insufficient are still observed. In such patients, the use of intravenous opioids during the intraoperative and postoperative periods may lead to undesirable effects such as nausea, vomiting, respiratory depression, and sedation . In this context, parasternal intercostal blocks performed with local anesthetics have been shown to provide adequate analgesia and reduce opioid requirements.

Materials and Methods Ethical Approval This study was approved by the Clinical Research Ethics Committee of Aydın Adnan Menderes University (Ethics Committee Approval Date: January 16, 2020, Decision No: 97479326-050.04.04). The study was conducted in the operating room of Aydın Adnan Menderes University Hospital between February 1, 2020, and February 1, 2021. A total of 80 patients scheduled for elective coronary artery bypass graft surgery and classified as ASA III-IV were included in the study after being appropriately informed and providing verbal and written consent. The study was designed as a prospective, randomized, and double-blind trial.

Randomization

The patients included in the study (n = 80) were divided into two groups according to a randomization sequence prepared in advance by an independent statistician and assigned by the researcher:

1. Parasternal block (PSB) group (n=40)
2. Saline group (n=40) Patients in both groups who were on regular medication for cardiovascular or other systemic diseases continued their usual treatment regimens. The saline group received a block with 0.9% NaCl solution, and paracetamol was administered at 10 mg/kg every eight hours as per the hospital's routine analgesia protocol. In cases of inadequate analgesia, an intravenous infusion of 0.5-1 mg/kg tramadol was added.

In the bupivacaine group, bilateral parasternal block was performed using 0.25% bupivacaine, while in the saline group. The solution used for the parasternal block (local anesthetic or saline) was colorless and indistinguishable. All patients, surgeons, intensive care unit nurses, and outcome assessors were blinded to the treatment allocation Anesthesia Management The patients' age, height, weight, gender, comorbidities, and American Society of Anesthesiologists scores were recorded. Prior to induction in the operating room, a five-lead electrocardiography was used to evaluate heart rhythm, ST-segment changes, and heart rate. Arterial blood pressure was measured via a 20G invasive arterial catheter placed in the radial artery. Peripheral oxygen saturation values were monitored using a pulse oximeter. All these parameters were monitored using a Datex-Ohmeda S/5 anesthesia machine.

All patients received a standard anesthesia protocol. Anesthesia induction for all patients was achieved with 1-1.5 mg/kg propofol, 0.03-0.05 mg/kg midazolam, 3-4 μg/kg fentanyl, 1 mg/kg lidocaine, and 1 mg/kg rocuronium. Following endotracheal intubation, anesthesia maintenance was provided with a 3 L/min flow of a 50/50 O₂/air mixture and 1.5-2% sevoflurane. Using the Seldinger technique under ultrasound guidance, a triple-lumen catheter and a 7F introducer were placed in the right internal jugular vein, and central venous pressure was measured. Body temperature was monitored with an esophageal temperature probe.

Before pericardium incision, patients were administered 300-400 U/kg heparin, and ACT was checked 3 minutes later. The heparin dose was adjusted to maintain an ACT \> 480. Intraoperative analgesia was provided with a continuous infusion of fentanyl at a dose of 0.1-0.2 μg/kg/min. Coronary anastomoses were completed under moderate hypothermia (28°C-30°C). After the anastomoses were completed, protamine was administered to antagonize heparin.

At the end of the surgical procedure, just before the closure of the sternotomy, if the patient was in the PSB group according to the randomization, the surgeon administered the prepared 0.25% bupivacaine solution bilaterally into the 2nd to 6th intercostal spaces, 2 cm lateral to the mid-sternal line, beneath the pectoralis major muscle and over the internal intercostal muscle. For the parasternal block, a 20 mL solution was prepared by mixing 10 mL of 0.5% bupivacaine with 10 mL of 0.9% NaCl. From this prepared solution, 2 ml of 0.25% bupivacaine was injected into the parasternal area at each intercostal space, and the procedure was repeated sequentially for 5 levels. The same procedure was performed on the opposite parasternal area. No local anesthetic was applied around the thoracic tube insertion sites. In the saline group, the same procedures were performed using 0.9% NaCl solution.

Postoperative Period After the surgery, the patient was transferred to the intensive care unit while intubated. In the intensive care unit, respiratory support was set to the pressure-controlled synchronized intermittent mandatory ventilation mode. Monitoring of electrocardiogram, peripheral oxygen saturation, invasive arterial pressure, and central venous pressure continued in the intensive care unit. Patients' follow-up in the intensive care unit, extubation times, analgesic use, and transfer from the intensive care unit to the ward were managed according to routine practices. Pain assessment in the intensive care unit was performed and recorded by the intensive care unit nurse responsible for the patient's care. Pain assessment began upon the patient's admission to the intensive care unit and was conducted using the Behavioral Pain Scale at the 1st, 2nd, 4th, and 8th hours while intubated. After extubation, pain was assessed using the Numeric Rating Scale at the 1st, 4th, and 12th hours. During follow-up, if the Behavioral Pain Scale or Numeric Rating Scale scores were 4 or higher and adequate analgesia was not achieved despite the routine administration of 1000 mg paracetamol every eight hours, intravenous tramadol at a dose of 0.5-1 mg/kg was administered.

Paracetamol doses routinely administered every eight hours were not recorded for either group. However, the timing of the first tramadol dose and the total tramadol doses administered were documented from the intensive care unit monitoring charts. Extubation time was defined as the duration between the patient's admission to the intensive care unit and the removal of the endotracheal tube. After extubation, patients' triflo exercise performance, specifically the level of ball elevation (Level 1, 2, 3, or 4), was recorded at the 1st, 4th, and 12th hours. Routine postoperative parameters, including heart rate, cardiac rhythm, SPO₂, blood pressure, and arterial blood gas levels, were recorded. Intensive care unit length of stay and ward length of stay were also documented. Patient satisfaction was assessed in the first postoperative month using the Short Form-36 (SF-36), and the collected data were statistically analyzed.

Statistical Analysis The data were analyzed using the SPSS 19.0 software (IBM, California). An independent samples t-test was used for variables with a normal distribution, while the Mann-Whitney U test was applied for variables not showing a normal distribution. The Pearson Chi-Square test was used for the comparison of categorical data. Statistical significance was defined as p \< 0.05.

Eligibility Criteria:
Inclusion Criteria:

* Study included patients aged 30-80 years
* American Society of Anesthesiologists risk score of III-IV,
* Who were scheduled for elective Coronary Artery Bypass Graft Surgery.

Exclusion Criteria:

* In this study, patients with hypersensitivity to the medications used,
* Patients under 30 years or over 80 years of age,
* Patients with chronic opioid use or severe psychiatric disorders,
* Patients who did not provide informed consent, patients with infection at the injection site,
* Patients with preoperative left ventricular ejection fraction \<30%,
* Patients with a history of previous sternotomy,
* Patients with severe renal or liver diseases,
* Patients unable to communicate.