Remote Ischemic Preconditioning in High Risk Cardiovascular Surgery Patients

Remote Ischemic Preconditioning in High Risk Cardiovascular Surgery Patients: A Randomized Controlled Trial

Remote ischemic preconditioning (RIPC) occurs when a tissue (ex. heart) becomes less vulnerable to an ischemic insult if a remote tissue (ex. arm) has had previous exposure to a period of ischemia and reperfusion. A beneficial effect of RIPC has been demonstrated in several randomized studies in patients undergoing cardiac and vascular surgery, as well as interventional cardiac procedures such as angioplasty. They have shown improvements in cardiac, renal, neurologic and respiratory function. Most have focused on surrogate outcomes, such as biochemical markers of cardiac and renal function in low-risk patients. No trials have investigated only high-risk patients or been designed to detect clinical outcomes. This study is a randomized-controlled trial powered to detect clinical events in a high-risk cohort undergoing cardiovascular surgery. Patients will be randomized to RIPC (exposed to cycles of inflation of a blood pressure cuff on the upper arm prior to undergoing surgery) or control (no ischemic stimulus). The investigators hypothesize this population will demonstrate lower rates of adverse ischemic events. The investigators also intend to sample biochemical markers to better elucidate the mechanism of RIPC and generate hypotheses for future studies and interventions. Post-operatively the investigators will monitor for adverse clinical outcomes including cardiac, renal, pulmonary and neurologic injury. RIPC is simple, inexpensive and easily reproducible and there have been no reports of adverse consequences. Post-operative ischemic events such as stroke, myocardial infarction, cardiac, renal and respiratory failure affect patient survival and quality of life, and represent a sizeable financial burden to health care. If beneficial effects of RIPC are demonstrated, it will be widely applicable to the entire population of cardiac and vascular patients resulting in a widely-implemented change in practice.

The intervention will consist of 3 cycles of 5 minutes of upper limb ischemia. The RIPC stimulus will be performed using a blood pressure cuff placed on the upper arm inflated above systemic pressure to 200 mmHg for 5 minutes, then deflated for 5 minutes. Ischemia will be assured with the use of a saturation probe on the digit of the involved arm.

The primary outcome measure will be a composite of clinical MACE (Multiple Adverse Cardiovascular Events), incorporating all-cause mortality, myocardial infarction, stroke, respiratory failure, acute renal failure and low cardiac output syndrome

Inclusion Criteria: Undergoing either cardiac or vascular surgical procedures and are deemed to be at increased risk of suffering adverse ischemia-related events (judged by pre-operative evidence of clinical ischemic conditions, pre-operative screening indicating cardiovascular disease or undergoing higher-risk surgery). Exclusion Criteria: Will not include emergency cases, patients with known vascular disease (ex. arterial occlusive disease, arterio-venous shunts) or neurologic disease affecting the upper limb and patients unable to give informed consent.