Changes in ventilation and oxygen consumption during acute hypoxia in sedated newborn piglets

The purpose of this study was to evaluate the relationship between changes in minute ventilation (VE) and oxygen consumption (VO2) in response to acute hypoxia in the newborn piglet. Twenty-five (mean +/- SD; age, 4.7 +/- 1.1 d; weight, 1451 +/- 320 g) sedated, spontaneously breathing newborn piglets were studied. VE was measured by pneumotachography, and VO2 was measured by the open-circuit technique. Measurements were performed while the animals breathed room air and repeated after 10 min of hypoxia, which was induced by breathing 10% oxygen. Although the mean VE values during hypoxia displayed a typical biphasic ventilatory response, the individual pattern of this ventilatory response to hypoxia was variable. Thirteen animals sustained VE above baseline after 10 min of hypoxia, whereas the 12 remaining animals decreased VE after 10 min of hypoxia to values below their room air baseline. The VO2 values did not differ between groups during normoxia, and a similar decrease in VO2 occurred in both groups after 10 min of hypoxia. Furthermore, no correlation was observed between changes in VE and VO2 during hypoxia either in absolute values or in the percent change from room air baseline. Arterial PO2 decreased similarly in both groups, but PACO2 decreased significantly only in the group that sustained VE above baseline after 10 min of hypoxia. These data demonstrate that in this animal model the hypoxic ventilatory depression is not determined by the decrease in VO2 that occurs during hypoxia.