Serratus Posterior Superior Plane Block in Minimally Invasive Cardiac Surgery

Introduction

Pain in cardiac surgery is of moderate to severe intensity due to factors such as sternotomy, sternal retraction, harvesting of the internal mammary artery, thoracotomy or thoracoscopy in minimally invasive approaches, and chest tube placement. Minimally invasive cardiac surgery (MICS) aims to shorten hospital length of stay and provide optimal postoperative analgesia in order to facilitate early mobilization and recovery. Adequate pain management reduces pain-related systemic and pulmonary complications. Tachycardia and hypertension secondary to pain increase myocardial oxygen consumption and predispose patients to hemodynamic instability.

Enhanced Recovery After Surgery (ERAS) protocols following cardiac surgery aim to reduce opioid consumption and eliminate opioid-related adverse effects. With increasing awareness of opioid overuse, tolerance, and opioid-induced hyperalgesia, opioid-sparing analgesic strategies have been increasingly adopted. The most important component of opioid-sparing analgesia is the use of regional anesthesia techniques. The Procedure-Specific Postoperative Pain Management (PROSPECT) guidelines recommend plane blocks as part of analgesic management in thoracic surgery. The incidence of severe chronic pain after sternotomy has been reported to be approximately 35% within the first postoperative year. Various regional anesthesia techniques, including thoracic epidural, thoracic paravertebral block, and parasternal intercostal block, have been used for postoperative analgesia in cardiac surgery. However, coagulation abnormalities limit the use of central neuraxial blocks. Consequently, ultrasound-guided fascial plane blocks have gained widespread use in cardiac surgery. Commonly used techniques include the erector spinae plane block, serratus anterior plane block, parasternal block, paravertebral block, pectoral nerve blocks (PECS I-II), and serratus posterior superior intercostal plane block (SPSIPB).

The ultrasound-guided SPSIPB was first described in 2023 by Tulgar et al. through cadaveric studies and a case series involving five patients. Due to its extensive local anesthetic spread and broad sensory dermatomal coverage (C3-T10), it has increasingly been used in cervical and thoracic surgical procedures.

The aim of this study is to evaluate the effectiveness of the serratus posterior superior intercostal plane block (SPSIPB) in postoperative analgesic management for minimally invasive cardiac surgery.

Materials and Methods

This prospective randomized controlled study is planned to be conducted between May 2025 and May 2026 at Kartal Koşuyolu High Specialization Training and Research Hospital. Sixty patients aged 18 years or older, classified as ASA III, and scheduled for minimally invasive coronary artery bypass surgery will be included. Exclusion criteria include age under 18 years, ASA classification other than III, pregnancy, emergency surgery, history of trauma within the past 24 hours, neurological or psychiatric disorders affecting consciousness or decision-making capacity, allergy to local anesthetics, skin infection at the puncture site, body mass index >35 kg/m², body weight <42 kg, and coagulation disorders (international normalized ratio >1.25, activated partial thromboplastin time >35 seconds, or platelet count <100,000/µL).

Eligible patients will be randomly allocated into two equal groups (n=30 each) using sealed opaque envelopes: the SPSIPB group and the control group. All patients will be informed about the study, and written informed consent will be obtained after providing detailed information regarding the plane block procedure. In the preoperative holding area, patients will be monitored, intravenous access will be established with a 20-gauge cannula, and premedication will be administered with intravenous midazolam (0.03 mg/kg) and fentanyl (1 µg/kg). All blocks will be performed under full aseptic conditions while patients receive supplemental oxygen via face mask.

No plane block will be performed in the control group. In the SPSIPB group, patients will be positioned laterally with the surgical side up and the upper extremity extended above the head. Under ultrasound guidance, the scapular spine will be identified using a high-frequency linear probe. The third rib will be visualized medial to the scapula at the level corresponding to the third intercostal space. After identifying the ribs, pleura, and overlying serratus posterior superior muscle, the needle will be advanced until contacting the third rib. Following hydrodissection with 5 mL isotonic saline, 30 mL of 0.25% bupivacaine (1 mg/kg) will be injected between the serratus posterior superior muscle and the third rib. Cranio-caudal spread of the local anesthetic will be confirmed by ultrasound.

Standard intraoperative monitoring will include electrocardiography, peripheral oxygen saturation, invasive arterial blood pressure, near-infrared spectroscopy (NIRS), and bispectral index (BIS). Anesthesia induction will be performed with propofol (2-2.5 mg/kg) and rocuronium (1 mg/kg). Patients will be intubated with a double-lumen endotracheal tube, and correct placement will be confirmed by bronchoscopy. Anesthesia maintenance will consist of sevoflurane (0.8-1 MAC) in a 50% oxygen/air mixture and remifentanil infusion (0.01-0.1 µg/kg/min), targeting a BIS value between 40 and 60. If heart rate or arterial blood pressure increases by more than 20% from baseline, remifentanil infusion will be increased up to 0.1-2 µg/kg/min. Lung-protective ventilation strategies will be applied during one-lung ventilation.

Hemodynamic parameters, intraoperative remifentanil consumption, and duration of surgery will be recorded. Thirty minutes before the end of surgery, all patients will receive intravenous tramadol (1 mg/kg) and paracetamol (1000 mg). Time to extubation will be documented. Postoperatively, patient-controlled analgesia (PCA) with tramadol will be initiated in cooperative patients. The PCA device will be programmed with tramadol at a concentration of 4 mg/mL, a bolus dose of 2 mL, a lockout interval of 15 minutes, and a 4-hour limit of 100 mg.

Pain intensity will be assessed using the Numeric Rating Scale (NRS; 0 = no pain, 10 = worst imaginable pain) at postoperative 30 minutes and at 1, 6, 12, 18, and 24 hours, both at rest and during coughing. Time to first rescue analgesic, incidence of postoperative nausea and vomiting, and other adverse effects will be recorded. Patients with NRS ≥4 despite PCA will receive intravenous paracetamol (1000 mg) as rescue analgesia. Lengths of intensive care unit and hospital stay will also be recorded.

Sample Size and Statistical Analysis

Sample size calculation was performed using G*Power version 3.1.9.2. Based on data from a similar study involving plane blocks, postoperative 24-hour total opioid consumption was significantly lower in the erector spinae plane block group compared to the serratus anterior plane block group. With a significance level of 0.05 and a power of 85%, a minimum of 26 patients per group was required. Considering a potential 20% dropout rate, 30 patients per group (total n=60) will be included.

Statistical analyses will be performed using SPSS version 27.0. Continuous variables will be expressed as mean ± standard deviation or median (minimum-maximum), while categorical variables will be presented as frequencies and percentages. Normality will be assessed using the Shapiro-Wilk test and box plots. Student's t-test or Mann-Whitney U test will be used for intergroup comparisons as appropriate. Categorical variables will be analyzed using the chi-square test or Fisher's exact test. A p value <0.05 will be considered statistically significant.

The procedures described are part of routine clinical practice, and no additional interventions outside standard care will be performed. Patients will be randomized using a computer-generated method, and outcomes will be evaluated without bias.

Primary outcome: Postoperative opioid (tramadol) consumption Secondary outcomes: Intraoperative remifentanil consumption, time to first analgesic request, NRS pain scores, time to extubation, length of ICU stay, length of hospital stay, and postoperative complications (nausea, vomiting, atelectasis)

No additional budget beyond routine clinical care will be required, and no study-specific extra parameters will be collected.

Inclusion criteria

• Adults aged 18 years or older
• American Society of Anesthesiologists (ASA) physical status III
• Scheduled for elective minimally invasive coronary artery bypass surgery
• Ability to understand the study procedures and provide written informed consent

Exclusion criteria

• Age under 18 years
• ASA physical status other than III
• Pregnancy
• Emergency surgery
• History of trauma within the previous 24 hours
• Neurological disorders affecting consciousness or decision-making capacity
• Psychiatric disorders affecting decision-making capacity or cooperation
• Known allergy to local anesthetic agents
• Infection or skin disease at the block injection site
• Body mass index greater than 35 kg/m²
• Body weight less than 42 kg
• Coagulation disorders (international normalized ratio >1.25, activated partial thromboplastin time >35 seconds, or platelet count <100,000/µL)