Redefining pain management after cardiac surgery to improve intensive care and hospital length of stay: a randomised pilot trial.

Prior to the closeure of the sternotomy wound post coronary artery graft surgery (CAGS), eligible participants will be randomly allocated to receive either 1: usual care, 2: saline (placebo) via On-Q Pain Buster device or 3: continuous infusions via the On-Q Pain Buster device. Treatment assignment of the infusion solution will remain blinded to study personnel. An un-blinded pharmacist will phone the NHMRC Clinical Trials Centre remote telephone randomisation service. A computer generated programme makes treatment assignment based on stratification by minimisation. The placebo and active agent pre-loaded bags are stored in the clinical trials refridgerator with a 3 month expiry. A log is kept in the pharmacy with access only by the trial pharmacist. The bag is then blinded and sent to theatre. If treatment assignment is to the trial device, the pharmacist will prepare the appropriate solution (400ml of normal saline or 0.5% ropivacaine solution in the On-Q Pain Buster device plus a 10ml syringe of matched solution which is a part of the 400ml solution) to the operating theatre labeled as "Ropivacaine/Placebo:PAINLESS TRIAL". The blinded, scrubbed, surgical registered nurse will load the On-Q Pain Buster device which will be tunnelled parasternally in a subpectoral position by one of the investigating surgeons. The On-Q Pain Buster system utilises a balloon-type elastomeric pump filled with a local anaesthetic that is automatically delivered to the surgical site by the On-Q soaker catheter. Dual catheters have a flow restrictor, one on each catheter side after the bifurcation above the luer lock connection just before the soaker catheters. This ensures that the flow rate to both catheters is equal and prevents the fluid taking the least path of resistance or the lowest catheter port. A small dressing will be placed over the catheter. Arm1(usual care) will receive standard pain therapies with patient controlled analgesia (PCA), intravenous (IV) morphine or fentanyl, at the discretion of the ICU or pain teams, and oral analgesia Arm2 will receive normal saline through the On-Q device and usual care Arm 3 (experimental group) will receive ropivacaine by the delivery system and usual care as needed. The recommended maximum daily dose of ropivacaine will not be exceeded and will be administered within the recommended standard. The 400ml elastomeric pump will be filled with ropivacaine 10x20ml 1% Naropin ampoules and normal saline (200ml) yielding a ropivacaine concentration of 5mg/ml (0.5%). The On-Q pump will deliver 5mg/ml of ropivacaine 0.5% via the two tunnelled catheters at a total rate of 4ml/hr. Therefore the total hourly dose is 20mg resulting in a total 24hr dosage of 480mg of ropivacaine. For arm 2 and arm 3, prior to the commencement of the infusion, a 10ml bolus dose of the solution (50mg if the solution is ropivacaine or 10ml of saline if placebo) will be given by the cardiothoracic surgeon through the catheters. The infusion will commence at a total rate of 4mls/hr. The catheters will stay in place until the 400ml elastomeric pump is emptied. This will take approximately 4 days (96 hours) at which point the On-Q Pain Buster device will be removed by trained registered nurses (RN) on the cardiothoracic ward. Surgeons, intensive care specialists, registrars, junior medical officers and nursing staff will be responsible for monitoring signs of toxicity. Premonitory signs of toxicity will be documented in the data sheet. Such symptoms include: dysarthria, muscular rigidity or twitching, unconsciousness, convulsions, hypoxia, hypercapnia, apnoea, severe hypotension or tachycardia, paraesthesia, temperature elevation, rigors (chills), headache and dizziness, vomitting, urinary retention, hypothermia, back pain, dyspnoea, insomnia, chest pain, pain and oliguria (more than 1% risk) In the event of toxicity, the catheters will be clamped immediately. Subsequently treatment will require securing a patent airway and ventilating with 100% oxygen. In the event of cardiac toxicity, sodium bicarbonate intravenous 1-2meq/kg will be required to treat cardiac toxicity due to sodium channel blockade. The Lipid Rescue Protocol will be observed in the operating theatre (OT) and copies of the rescue protocol will be made available in ICU, cardiothoracic ward and in the OT. Further management will be decided by the intensivist and the cardiothoracic surgeons. Intravenous access will be maintained until the Pain Buster is removed. The use of the continuous ropivacaine infusion will compliment, not replace existing pain therapies hence patients will have the use of standard intravenous PCA and oral pain medication once the PCA narcotics are ceased as per curent standard practice. The pain team will review this post-operatively. PCA requirements will be monitored for the purpose of this study. Post operative period Suitability for extubation and clearance from intensive care will be assessed and documented by the study intensivist and surgeon using standardised criteria. Visual analogue scores (VAS) for pain will be measured every 12 hours for the duration of the local anesthetic infusion or for 4 days (whichever is longer) and before and after physiotherapy treatment sessions. Data on PCA, intravenous and oral analgesia requirements will be collected. The distance participants walk with the physiotherapist in each post operative day will be recorded. The pulmonary function test (forced expiratory volume in 1 second, functional vital capacity and peak expiratory flow) will be conducted pre operatively and on post operative day 3 prior to removal of the device. The discharge date from ICU and hospital will also be recorded. Preoperatively and at 3 and 6 months participants who agreed to chronic pain substudy will be contacted to complete a chronic pain assessment survey.