Metabolic and developmental responses of the calf to a chronic hypoxic episode in the immediate newborn period.
While there is an extensive bank of literature on hypoxia and anoxia in the neonate, the primary focus of previous research has been pulmonary responses to acute hypoxia. Furthermore, no research on the metabolic effects of chronic hypoxia in the immediate newborn period has been published to our knowledge. Given the dynamic state of the newborn in the first hours of life, the relevance of previous observations to the results of the present study is questionable. Previous studies on calves subjected to periods of acute hypoxia have reported decreased PO2, decreased PCO2 and increased pH (Reeves and Leathers, 1964). Thus, it is clear that newborn calves respond differently to chronic hypoxia than they do to acute hypoxia. Much of this difference is due to the biphasic ventilatory response previously discussed. Past reports of acid-base changes in newborn calves utilized venous blood (Moore, 1969; Schlerka et al., 1979; Eigenmann et al., 1981; Maurer-Schweitzer et al., 1977) and are therefore subject to criticism given the variability inherent in venous blood values. Waizenhoffer and Mulling (1978) compared arterial and venous blood gases, but only drew a limited number of arterial samples at 12 and 24 hours. These values were comparable to 12- and 24-hour values in the present experiment. In conclusion, the metabolic effects of a 24-hour hypoxic episode in the newborn calf are relatively mild, consisting primarily of the development of a primary metabolic acidosis due in large part to accumulation of lactate. A relatively large base deficit was incurred concurrently. Most values returned to normal following return of PO2 to normal levels at 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)