Evaluation of the right atrial venous oxygen saturation as a physiologic monitor in a neonatal model

Abstract

Pulmonary artery (PA) mixed venous saturation (SO2) has become a crucial monitor in the adult intensive care unit, but is not used in neonates because of the difficulty in PA catheterization. We evaluated the possibility of utilizing the right atrial venous oxygen saturation (RAO2), which is easily accessed in the neonate, as a monitor of the effects of mechanical ventilation and intravascular volume in an animal model selected to be the size of the human neonate. A continuous RAO2 monitoring catheter was placed into the right atrium of 16 normal rabbits (2.2 to 4.1 kg). Oxygen delivery was manipulated by alterations in peak inspiratory pressure (PIP) (n = 6), positive end-expiratory pressure (PEEP) (n = 6), or by progressive hypovolemia (n = 4). RAO2 decreased with onset of mechanical ventilation alone from 69% +/- 6% to 61% +/- 5% (P 2O, the RAO2 progressively decreased from 59% +/- 4% to 49% +/- 6% (P 2O, the RAO2 progressively decreased from 64% +/- 5% to 33% +/- 16% (P 2 approached baseline after return to continuous positive airway pressure (CPAP) of 3 cm H2O. Progressive phlebotomy to a total of 10 mL/kg resulted in a decrease in RAO2 from 70% +/- 6% to 27% +/- 5% (P 2 to near baseline. Peripheral arterial oxygen saturation remained at a constant 100% throughout each protocol. With oxygen consumption stable, the RAO2 is an excellent monitor of the effect of airway pressure or of hypovolemia on oxygen delivery. Use of the peripheral arterial oxygen saturation alone as a parameter for monitoring ventilator or intravascular volume effect is not adequate. RAO2 monitoring may be a powerful tool in the management of the critically ill neonates.