Cardiovascular responses to arterial and venous hemorrhage in neonatal swine

The cardiovascular effects of graded arterial or venous hemorrhage were evaluated in developing swine (less than or equal to 1 day, 2-5 days, 1 wk, and 2 wk of age) anesthetized with halothane in 50% N2O-50% O2. Serial 5-ml/kg aliquots of arterial or venous blood were removed at 3- to 4-min intervals to a cumulative total of 20 ml/kg. Tachycardia occurred in most animals. Decreases in aortic pressure to arterial, but not to venous, hemorrhage were age dependent. Renal, femoral, and carotid arterial flows decreased with hemorrhage in all animals; the decreases in blood flow did not differ among the three circulations and were not age dependent. Increases in femoral resistance were obtained to both arterial and venous hemorrhage only in the 2-wk-old group. As the degree of hemorrhage was increased, aortic pressure, regional blood flow, and femoral resistance (2 wk olds) responses were larger in magnitude. Aortic pressure in piglets 1-5 days of age could not be restored to within 20% of the prehemorrhage level at a smaller bleeding volume with arterial than with venous hemorrhage. Pressor responses to norepinephrine (0.5 micrograms/kg) and to bilateral common carotid occlusion were still present after 20-ml/kg hemorrhage. These responses indicate the presence of a progressive maturation-related compensation to the stress of arterial but not venous hemorrhage.