EFFECTS OF POSITIVE PRESSURE VENTILATION AND INSPIRED OXYGEN ON PULMONARY VASCULAR-RESISTANCE AND TISSUE OXYGEN DELIVERY IN NEONATAL PIGS

Management of pulmonary-vascular resistance in neonates with congenita l heart disease is important for stabilization before and after surgic al interventions. Thus, we determined which combination of positive en d-expiratory pressure ventilation and fraction of oxygen in the inspir ed air increases pulmonary vascular resistance without compromising de livery of oxygen to the tissue. Eight piglets were anesthetized, incub ated and ventilated. Pulmonary flow and pulmonary arterial and left at rial pressures were monitored continuously. At all levels of inspired oxygen (1.00, 0.21 and 0.15), ventilation at a pressure of 15 cm of wa ter increased pulmonary vascular resistance. At all levels of positive pressure ventilation, a fraction of 0.15 of inspired oxygen increased pulmonary vascular resistance. The combination of a ventilatory press ure of 15 cm of water and inspired oxygen of 1.00, or ventilatory pres sure at 5 cm of water and oxygen delivery of 0.15, produced similar ch anges in pulmonary vascular resistance (19.1 +/- 2.8 vs. 20.0 +/- 3.8 mmHg/(L/min)) and cardiac output (0.78 +/- 0.07 vs. 0.93 +/- 0.10 L/mi n) but, the higher level of positive pressure plus 1.00 inspired oxyge n gave a significantly higher arterial oxygen saturation (0.99 +/- 0.0 3 vs. 0.72 +/- 0.19%) and delivery of oxygen to the tissues (13.7 +/- 2.9 vs 7.4 +/- 1.5 ml O-2/min, p < 0.05). Thus, both high positive pre ssure ventilation and hypoxia increase pulmonary Vascular resistance. Only high pressure ventilation plus high concentrations of inspired ox ygen, however, increased pulmonary vascular resistance without comprom ising delivery of oxygen, suggesting that this combination is a superi or means of increasing pulmonary vascular resistance.