The primary objective of the study is to measure plasma levels of bupivacaine following a pecto-intercostal fascial plane block (PIFB) in patients undergoing sternotomy for cardiac surgery.

Heart disease such as ischemic cardiomyopathy and heart failure are the second leading cause of death and a leading cause of hospitalization in Canada. Approximately 35,000 heart valve or coronary artery revascularization procedures involving median sternotomy, an important component in the treatment of these diseases, are performed annually. Median sternotomy is associated with acute pain that decreases patient satisfaction, increases the risk of delirium, arrhythmias and respiratory complications. It also contributes to the development of postoperative chronic pain that can affect up to 31% of patients in the first year after surgery. Multimodal analgesia, combining drug therapy and regional anesthesia, can help in preventing acute and perhaps chronic pain in patients undergoing sternotomy for cardiac surgery.

The pecto-intercostal fascial plane block (PIFB) is a new locoregional anesthesia technique that has emerged to treat pain following cardiac surgery including sternotomy, breast surgeries and sternal fractures. It consists of injecting local anesthetics in the space located between the major pectoralis muscle and the intercostal muscles using ultrasound guidance, allowing to obtain anesthesia of the territory innervated by the anterior cutaneous intercostal branches, i.e. the medial aspect of the breast and the sternum.

The dose of local anesthetic injected after a PIFB should aim to maximize analgesia while minimizing the chance of toxic systemic concentrations. Defining the rate of absorption of local anesthetics into the blood after a PIFB will therefore help anesthesiologists to determinate optimal analgesic doses, in terms of both safety and effectiveness.

This observational study will determine bupivacaine pharmacokinetics after a PIFB with bupivacaine, to further define the right dose and duration of surveillance in post-anesthesia care.

Methods: Anesthesia and cardiac surgery will be initiated as usual. The use of bupivacaine by the anesthesiologist or surgeon will be prohibited. Following closure of the sternum, while the patient remains intubated and ventilated under general anesthesia with monitoring, including invasive blood pressure, oxygen saturation, respiratory rate and ECG, the PIFB will be done before application of sternal dressing and removal of sterile fields. Using an ultrasound machine with a high frequency linear probe (Sonosite, HFL50 15-6MHz) placed in the parasagittal plane, 3cm away from the midline, the fascia between the major pectoralis muscle and the internal intercostal muscle will be visualized. Subsequently, four injection sites, defined by the space between the fascia of the pectoral and intercostal muscles at the third and sixth intercostal spaces on each side of the patient, will be reached with an insulated hyperechoic needle (50-80 mm, 22 gauge, SonoPlex STIM, Nanoline, Pajunk, Germany) inserted cephalically and positioned in-plane.

Following negative aspiration, the anesthesiologist will confirm the correct position of the needle with the fluid spread of 1 mL of 5% dextrose. Then, he will inject bupivacaine 0.25% with epinephrine 5 mcg/mL in 5 ml aliquots for a total dose of 2mg/kg of ideal body weight (maximum of 150mg or 60 mL).

The end of injection will be considered as T0. Collection of 4.5mL of blood will be performed at T10min, T20min, T30min, T45min, T60min, T90min, T120min, T180min, and T240min.

Blood tubes will be immediately placed on ice to be ultimately sent to the laboratory for centrifugation and measurement of bupivacaine level using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for each of the samples.

After the block, the patient will be transferred to the Intensive Care Unit. At T240min, if the patient is extubated, the level of the sensory block will be identified by the pinprick test.

The time between ICU arrival and extubation, as well as the total consumption of opioids and co-analgesics for the first 24 hours will be recorded for each patient.

Inclusion Criteria:

• ASA l-lll
• Undergoing sternotomy for cardiac surgery under a PIFB and general anesthesia

Exclusion Criteria:

• Patient's refusal or inability to consent
• Allergy, hypersensibility or resistance to local anesthetic
• Contraindication to regional anesthesia: infection in the designated area, severe congenital coagulopathy or inadequate hemostasis before PIFB
• Severe hepatic (Child B and C) or renal insufficiency (GFR<30 mL/min)

Patients requiring a pecto-intercostal fascial block following cardiac surgery