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 (Spo2).

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 Spo2 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 Spo2 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" Spo2 target range allowed for less oxygen exposure. No signs of mismatch between systemic oxygen delivery and demand could be detected.