Effect of the arterial oxygenation level on cardiac output, oxygen extraction, and oxygen consumption in low birth weight infants receiving mechanical ventilation

Objective: To investigate the effects on oxygenation of targeting the higher versus the lower end of the currently recommended range for pulse oximetry (Sp o ₂ ). Design: Nonrandomized crossover trial with the use of within-subject comparisons (two-tailed paired t test). Setting: Level III neonatal intensive care unit of a university hospital. Patients: Twenty infants whose lungs were mechanically ventilated (mean ± SD: birth weight, 1192 ± 396 gm; gestational age, 28.7 ± 2.7 weeks; age at time of study, 42 ± 26 hours). Interventions: The inspired oxygen concentration was adjusted to achieve Sp o ₂ readings of 93% to 96% versus 89% to 92% (Ohmeda pulse oximeter) or 95% to 98% versus 91% to 94% (Nellcor oximeter). Measurements: Cardiac output was measured by echocardiography, oxygen content of arterial blood samples by cooximetry, and oxygen consumption by indirect calorimetry. Results: The inspired oxygen concentrations required to achieve the Sp o ₂ target ranges were 39.8% ± 8.3% versus 28.7% ± 6.1% ( p <0.001). The respective arterial oxygen contents were 18.0 ± 2.6 ml/dl versus 16.9 ± 2.5 ml/dl ( p <0.001). Oxygen consumption was unchanged. In the lower-oxygen condition no compensatory increase in cardiac output was detected; thus the estimated mixed venous oxygen tension decreased and the oxygen extraction ratio increased. Venous admixture increased from 15% ± 6% to 31% ± 9% in the lower-oxygen condition ( p <0.001). Conclusions: The "low normal" Sp o ₂ target range allowed for less oxygen exposure. No signs of mismatch between systemic oxygen delivery and demand could be detected. (J P EDIATR 1995;126:777-84).