Methane inhalation reduces the systemic inflammatory response in a large animal model of extracorporeal circulation

Extracorporeal circulation induces cellular and humoral inflammatory reactions, thus possibly leading to detrimental secondary inflammatory responses. Previous data have demonstrated the bioactive potential of methane and confirmed its anti-inflammatory effects in model experiments. Our goal was to investigate the in vivo consequences of exogenous methane administration on extracorporeal circulation-induced inflammation.

Two groups of anaesthetized Vietnamese minipigs (non-treated and methane treated, n = 5 each) were included. Standard central cannulation was performed, and extracorporeal circulation was maintained for 120 min without cardiac arrest or ischaemia, followed by an additional 120-min observation period with haemodynamic monitoring. In the methane-treated group, 2.5% v/v methane-normoxic air mixture was added to the oxygenator sweep gas. Blood samples through the central venous line and tissue biopsies from the heart, ileum and kidney were taken at the end point to determine the whole blood superoxide production (chemiluminometry) and the activity of xanthine-oxidoreductase and myeloperoxidase, with substrate-specific reactions.

Methane treatment resulted in significantly higher renal blood flow during the extracorporeal circulation period compared to the non-treated group (63.9 ± 16.4 vs 29.0 ± 9.3 ml/min). Whole blood superoxide production (548 ± 179 vs 1283 ± 193 Relative Light Unit (RLU)), ileal myeloperoxidase (2.23 ± 0.2 vs 3.26 ± 0.6 mU/(mg protein)) and cardiac (1.5 ± 0.6 vs 4.7 ± 2.5 pmol/min/mg), ileal (2.2 ± 0.6 vs 7.0 ± 3.4 pmol/min/mg) and renal (1.2 ± 0.8 vs 13.3 ± 8.0 pmol/min/mg) xanthine-oxidoreductase activity were significantly lower in the treated group.

The addition of bioactive gases, such as methane, through the oxygenator of the extracorporeal circuit represents a novel strategy to influence the inflammatory effects of extracorporeal perfusion in cardiac surgical procedures.