Effects of Hypoxic-hyperoxic Preconditioning in Cardio-surgical Patients

Overview

Coronary artery bypass grafting (CABG) with cardiopulmonary bypass is a common surgical therapy for patients suffering from coronary artery diseases. The heart is subjected to a long period of ischemia due to the occlusion of the aorta. The heavy burden of myocardial ischemia-reperfusion injury (IRI) thus induces cardiomyocyte death, which can paradoxically reduce the beneficial effect of CABG. Preconditioning by moderate hypoxia or hyperoxia serves as an effective drug-free method to increase the organism's resistance to negative effects, including IRI.

It has been firmly established that the diminished oxygen delivery to the tissues in response to hypoxia is countered by a combination of the increased regional blood flow and the enhanced functional capillary density in the microcirculation. In experimental studies, exposure to hyperoxia for a limited time before ischemia induces a low-grade systemic oxidative stress evokes a preconditioning-like effect on the myocardium and reduces the infarction area by 20%, and the number of arrhythmias after ischemia-reperfusion. One hundred twenty patients were randomly assigned into two equal groups: hypoxic-hyperoxic preconditioning before the surgery (HHP group) and the control group (without preconditioning). Safety control of the preconditioning procedure included ECG monitoring, invasive blood pressure, cardiac output, pulse oximetry, capnography, cerebral oximetry, measurement of anaerobic threshold; acid-base status and metabolic state of arterial and venous blood were assessed once every 10 min during the preconditioning procedure; oxygen balance parameters were calculated. Seventy-two hours before the surgery, an anaerobic threshold was determined to establish a safe oxygen concentration in the respiratory gas mixture during the hypoxic preconditioning phase from 10 to 14%, followed by 75-80% oxygen concentration during the hyperoxic phase. The hypoxic-hyperoxic preconditioning with individual parameters selection based on the anaerobic threshold in patients with coronary artery diseases before the main stage of cardiac surgery with a cardiopulmonary bypass should reduce the duration of mechanical ventilation, catecholamine support, and frequency of perioperative complications.