Restoration of cardiopulmonary function with 21% versus 100% oxygen after hypoxaemia in newborn pigs

Abstract

Objective: To assess the consequences of hypoxaemia and resuscitation with room air versus 100% O₂ on cardiac troponin I (cTnI), cardiac output (CO), and pulmonary artery pressure (PAP) in newborn pigs.

Design: Twenty anaesthetised pigs (12–36 hours; 1.7–2.7 kg) were subjected to hypoxaemia by ventilation with 8% O₂. When mean arterial blood pressure fell to 15 mm Hg, or arterial base excess was ≤ −20 mmol/l, resuscitation was performed with 21% (n  =  10) or 100% (n  =  10) O₂ for 30 minutes, then ventilation with 21% O₂ for 120 minutes. Blood was analysed for cTnI. Ultrasound examinations of CO and PAP (estimated from tricuspid regurgitation velocity (TR-Vmax)) were performed at baseline, during hypoxia, and at the start of and during reoxygenation.

Results: cTnI increased from baseline to the end point (p<0.001), confirming a serious myocardial injury, with no differences between the 21% and 100% O₂ group (p  =  0.12). TR-Vmax increased during the insult and returned towards baseline values during reoxygenation, with no differences between the groups (p  =  0.11) or between cTnI concentrations (p  =  0.31). An inverse relation was found between increasing age and TR-Vmax during hypoxaemia (p  =  0.034). CO per kg body weight increased during the early phase of hypoxaemia (p<0.001), then decreased. Changes in CO per kg were mainly due to changes in heart rate, with no differences between the groups during reoxygenation (p  =  0.298).

Conclusion: Hypoxaemia affects the myocardium and PAP. During this limited period of observation, reoxygenation with 100% O₂ showed no benefits compared with 21% O₂ in normalising myocardial function and PAP. The important issue may be resuscitation and reoxygenation without hyperoxygenation.