This is a pilot study to assess the feasibility of a full study. The purpose is to assess the analgesic effectiveness of the serratus anterior plane (SAP) block following cardiac surgery.

Patients will be randomized to receive either Ropivacaine 0.2% or placebo via bilateral SAP block catheters for 72 hours postoperatively.

Inadequate pain relief following cardiac surgery increases morbidity, length of stay in the intensive care unit, persistent pain, and costs. Moderate to severe pain is common after cardiac surgery, peaking during the first and second postoperative day, then decreasing after the third day.

Regional anesthesia as part of a multimodal pain management strategy has become a key feature of cardiac surgery enhanced recovery after surgery (ERAS) protocols. A technique consolidating the pectoralis nerve block (PECS) and serratus anterior plane block (SAPB) into a single injection has been described, also called the serratus anterior plane (SAP) block. Given the relative paucity of evidence assessing the utility of continuous serratus anterior plane block (cSAP) in cardiac surgery, we decided to assess the feasibility of a placebo controlled randomized controlled trial (RCT) with a pilot study.

Primary Pilot Study Objective To assess feasibility of a larger intervention study by measuring recruitment rate, adherence rate, retention rates and continuous serratus anterior plane block (cSAP)-related adverse events following cardiac surgery via median sternotomy.

Methods This study will include patients undergoing valvular replacement/repair and/or coronary artery bypass grafting (CABG) at the QEII Health Sciences Center in Halifax, Nova Scotia. The study will include a maximum of 50 participants, randomly assigned to 2 study arms of 25 participants. A computer-generated random number will be assigned by the central pharmacy to randomize patients on a 1:1 basis to the Ropivacaine and placebo groups.

cSAP block procedure - Study Intervention A member of the cardiac anesthesia or regional anesthesia team will place bilateral serratus anterior catheters under ultrasound guidance within 2 hours of arrival to the cardiovascular intensive care unit. A bolus of study drug 20ml (either ropivacaine 0.2% or normal saline) will be delivered at the time of the block. A 18g multiholed catheter will be inserted and secured to the patients' skin. The same procedure will be followed on the contralateral side. The study drug will be administered by programmed intermittent bolus (PIB) 10ml every 2 hours to each side in a staggered, alternating fashion. The PIB study drug will to be continued for 72 hours post-insertion.

Feasibility endpoints The study will be deemed feasible if it meets the following predetermined endpoints: 1. Recruitment of 4 patients per month; 2. The adherence rate to protocols is >90%; 3. Primary outcome measurement rate is >90%; 4. Combined major catheter-related adverse event rate (pneumothorax + LAST + allergic reaction) is <2%.

Inclusion Criteria:

• Adult (aged >18 years) patients at time of screening
• Undergoing valvular replacement/repair and/or coronary artery bypass grafting (CABG)
• via median sternotomy

Exclusion Criteria:

• Surgery on an emergency basis (level 1 or 2, <2 hours)
• An ejection fraction <30%
• Patient on extracorporeal membrane oxygenator (ECMO),
• Presence of an intra-aortic balloon pump (IABP)
• Preoperative vasopressors or inotropes
• Severe pre-existing liver disease (Child B or C)
• Severe kidney disease (Glomerular filtration rate (GFR) <30 (mL/min/1·73m²))
• An allergy to ropivacaine
• Planned circulatory arrest
• BMI >35
• Weight <50 kg
• Opioid tolerant (oral morphine equivalent >60mg per day for >1 week prior to admission)
• Unable to provide valid consent to study prior to surgery

The Nova Scotia Health (NSH) pharmacy will prepare either Ropivacaine 0.2% (2mg/ml) or normal saline in identical bags labelled as "study drug" such that the patient, clinical staff and the researchers are blinded to assigned group. The pharmacy will maintain the assignment list, only unmasking assignment in cases of suspected local anesthetic systemic toxicity (LAST) or allergic reactions.