Pulmonary oxygen consumption: a hypothesis to explain the increase in oxygen consumption of low birth weight infants with lung disease
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OBJECTIVE: We determined pulmonary oxygen consumption (VO2lung) in low-birthweight infants with acute lung disease to help explain the greater whole-body oxygen consumption (VO2wb) in these infants with than in those without lung disease. METHODS AND MATERIALS: Eleven infants (birth weight 1,076+/-364 g; gestational age 28+/-3 weeks) undergoing mechanical ventilation for respiratory distress syndrome were studied in their first week of life. We measured VO2wb by indirect calorimetry and simultaneously determined systemic oxygen uptake (VO2Fick) as the product of cardiac output (echocardiography) and the arterial-mixed venous oxygen content difference (cooximetry) assuming that VO2wb-VO2Fick accounts for VO2lung. Right atrial blood samples were used to determine mixed venous oxygenation, and infants were excluded if samples returned saturations greater than 89%. RESULTS: VO2lung was 1.92+/-1.74 ml x kg(-1) x min(-1), representing 25% of their VO2wb (7.58+/-1.48 ml x kg(-1) x min(-1)). VO2lung was not correlated with clinical measures of acute disease severity. However, infants with the most severe changes on follow-up radiography (Edwards score 5 as assessed by radiologist blinded for VO2 data) all had a VO2lung level greater than 2.0 ml x kg(-1) x min(-1). CONCLUSION: VO2lung can account for the elevated metabolic rate in low-birthweight infants with lung injury. We speculate that this reflects in part inflammatory pulmonary processes and may herald chronic lung disease.