This study aims to compare the efficacy and quality of pain relief provided by the high-dose serratus anterior plane (SAP) block with the standard SAP block in preventing and treating acute postoperative pain after total endoscopic aortic or mitral valve surgery.

During the last two decades, cardiac surgical techniques have changed dramatically. Evidence for good short and long-term outcomes after endovascular and minimally invasive procedures is rising. This shift made it possible to avoid sternotomy and thus facilitating earlier patient recovery without compromising safety. Therefore, enhanced recovery after surgery (ERAS) protocols have been implemented to aim for early extubation and ambulation. While policies for early extubation and discharge from the hospital have been implemented, the analgesic regimen has not been modified. Opioids remain the standard treatment in the postoperative setting after cardiac surgery despite known side effects such as nausea, constipation and the risk of addiction. Neuraxial anaesthesia techniques, which require fewer opioids in cardiac surgery, have been studied and validated but not yet implemented.

In 2013, the serratus anterior plane (SAP) block was described as a pain relief option for chest surgery. This anaesthesia technique injects local anaesthetics under the serratus muscle and between the latissimus dorsi and serratus anterior using ultrasound. Successful pain relief with this SAP block has been reported in thoracotomy, chest surgery, and rib fractures. In our previous study, we demonstrated a 40% reduction in morphine consumption during the first 24 hours after total endoscopic aortic valve replacement with an SAP block compared to a control group without an SAP block. Lower pain scores were also observed in the SAP group

As such, in this proposed study, we aim to optimise the intensity of the Serratus anterior plane block (SAPB) to decrease opioid requirements further and to encounter more favourable secondary clinical outcome parameters. One strategy to increase the duration of action of plane blocks is injecting higher doses of local anaesthetics. A meta-analysis by De Oliveira et al. on transabdominal plane (TAP)-blocks for abdominal surgery showed a correlation between the local anaesthetic dose and the late block effect, impacting both pain scores and opioid consumption. In a randomised controlled trial by Suresh, a TAP block with bupivacaine 1.25 mcg/kg was compared to a TAP block with bupivacaine 2.5 mcg/kg, revealing a longer duration of analgesia and a lower need for additional analgesics up to 24 hours post-surgery. Moreover, loading doses up to 2mg/kg body weight are recommended for truncal blocks in general, but the mean injected dose in our intervention group was 1.25mg/kg, considering a mean patient body weight of 79.2kg. Notably, a pharmacokinetic study by Maximos and colleagues on an adrenalised bupivacaine mixture after pectointercostal fascial plane block (PIFB) after cardiac surgery showed that, despite injecting 2mcg/kg adrenalised bupivacain, both total and free arterial serum bupivacaine levels were 10-20 times lower than levels associated with neurologic or cardiovascular toxicity in the literature.

In conclusion, we are convinced we can safely improve the late effects of our SAPB compared to our first study by increasing the dose of the local anesthetic injectate.

Inclusion Criteria:

• Scheduled for elective aortic valve surgery or elective mitral valve surgery via right anterolateral thoracotomy
• Adult patients (minimally 18 years old)
• Bodyweight > 50kg
• EuroScore ii < 3%

Exclusion Criteria:

• Refusal to participate
• Inability to communicate due to language or neurologic barriers
• Inability to control and self-administer opioids with PCIA or to comprehend the NRS pain score due to confusion or learning difficulties
• Chronic use of opioids
• Chronic use of analgesic antidepressants and/or antiepileptics
• Use of prohibited medication which possibly interacts with bupivacaine-epinephrine or opioids (mexiletine, ketoconazole, theophylline, IMAO, Digitalis and cimetidine)
• History of major trauma or surgery to right chest wall
• History of chronic pain at right chest wall
• Allergy to opioids and/or local anesthetics
• Allergy to paracetamol
• Class 3 obesity (BMI 40 or more)
• Pregnancy
• Intraoperative events compromising early postoperative recovery (aortic dissection, systolic anterior motion of the mitral valve, cardiac tamponade, brady-arrhytmias requiring external pacing,...)