Effects of 60 minutes of hyperoxia followed by normoxia before coronary artery bypass grafting on the inflammatory response profile and myocardial injury

Abstract

BackgroundIschemic preconditioning induces tolerance against ischemia-reperfusion injury prior a sustained ischemic insult. In experimental studies, exposure to hyperoxia for a limited time before ischemia induces a low-grade systemic oxidative stress and evokes an (ischemic) preconditioning-like effect of the myocardium. We hypothesised that pre-treatment by hyperoxia favours enchanced myocardial protection described by decreased release of cTn T in the 1st postoperative morning and reduces the release of inflammatory cytokines.MethodsForty patients with stable coronary artery disease underwent coronary artery bypass grafting with cardiopulmonary bypass. They were ventilated with 40 or >96% oxygen for 60 minutes followed by by 33 (18–59) min normoxia before cardioplegia.ResultsIn the 1st postoperative morning concentrations of cTnT did not differ between groups ((0.44 (0.26-0.55) ng/mL in control and 0.45 (0.37-0.71) ng/mL in hyperoxia group). Sixty minutes after declamping the aorta, ratios of IL-10/IL-6 (0.73 in controls and 1.47 in hyperoxia, p = 0.03) and IL-10/TNF-α (2.91 and 8.81, resp., p = 0.015) were significantly drifted towards anti-inflammatory, whereas interleukins 6, 8and TNF-α and interferon-γ showed marked postoperative rise, but no intergroup differences were found.ConclusionsPre-treatment by 60 minutes of hyperoxia did not reduce postoperative leak of cTn T in patients undergoing coronary artery bypass surgery. In the hyperoxia group higher release of anti-inflammatory IL-10 caused drifting of IL-10/IL-6 and IL-10/TNF-α towards anti-inflammatory.

Cardiovascular effects of hyperoxia during and after cardiac surgery

“…Two other studies showed a non‐significantly lower or similar cardiac index . Pre‐treatment by 60 or 120 min of hyperoxia did not affect cardiac index .…”

“…Animal studies suggest that hyperoxia has favourable effects on myocardial ischaemic injury through a preconditioning effect on cardiac muscle . A similar study in humans, exposing patients to hyperoxia (F I O 2 > 0.96) for 130 and 60 min before coronary artery bypass grafting, had no effect on the cardiac enzymes creatine kinase MB (CK‐MB) and troponin I . However, hyperoxia applied during cardiac surgery, during reperfusion or the entire bypass period increased ischaemia‐reperfusion injury as estimated by troponin T and creatine kinase (Table ).…”

“…The randomised controlled trials investigated the following phases: ‐before cardioplegia, F I O 2 > 0.96 vs 0.4 for 120 and 60 min, respectively , ‐during the entire bypass period, F I O 2 0.4–0.6 during rewarming vs 0.4–0.5, or 0.35–0.45 and P a O 2 53 vs. 19 kPa , ‐during reperfusion after aortic unclamping, P a O 2 60–73 vs 27–33 kPa . …”

“…Of six studies, four suggested impaired cardiovascular function with higher oxygen targets, while two studies showed no difference (Table ). Haemodynamic variables were measured by thermodilution , or lithium dilution technique . Patients with higher oxygen targets during bypass showed increased systemic vascular resistance (by up to 24%) compared with patients with lower targets .…”

The impact of hyperoxia on outcomes after cardiac surgery: a systematic review and narrative synthesis

“…Only five of the reports described how the trials were funded. 1,8,9,26,27 None of these trials were industry supported. The average age of patients included in trial intervention groups ranged from 47 to 68 years ( Table 1).…”