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% O 2 on cardiac troponin I (cTnI), cardiac output (CO), and pulmonary artery pressure (PAP) in newborn pigs. Design: Twenty anaesthetised pigs (12-30 hours; 1.7-2.7 kg) were subjected to hypoxaemia by ventilation with 8% O 2. 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) O 2 for 30 minutes, then ventilation with 21% O 2 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% O 2 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% O 2 showed no benefits compared with 21% O 2 in normalising myocardial function and PAP. The important issue may be resuscitation and reoxygenation without hyperoxygenation.