Regional blood flows in newborn lambs during endotracheal continuous airway pressure and continuous negative pressure breathing.

Cardiovascular changes resulting from continuous distending alveolar pressure during endotracheal intubation (CPAP) and continuous negative pressure (CNP) were studied in two groups of healthy newborn lambs at 6 and 11 mm Hg and -6 and -11 mm Hg, respectively. Heart rate, left ventricular pressure, and arterial blood gases were unchanged in each group. Cardiac output decreased 16 and 15% at 6 and 11 mm Hg CPAP (P less than 0.05), respectively, whereas a fall of 9% occurred at both -6 and -11 mm Hg CNP (P greater than 0.05). Central venous pressure (mm Hg) rose from a control value of 7.0 +/- 1.4 (mean +/- S.E.) to 11 +/- 3.1 and 12 +/- 2.7 at 6 and 11 mm Hg CPAP (P less than 0.025), respectively, and decreased from a control of 7.7 +/- 0.7 to 5.8 +/- 0.5 at -6 mm Hg CNP and 4.8 +/- 1.3 at -11 mm Hg CNP (P less than 0.05). Jugular venous pressure also rose progressively with increasing CPAP (P less than 0.05), but was unchanged during CNP. Regional blood flow to the liver fell at both 6 and 11 mm Hg CPAP, whereas renal and gastrointestinal blood flows showed a tendency to decrease at 11 mm Hg CPAP. The removal of CPAP resulted in a prompt return of venous pressure, cardiac output, and regional blood flows to control values. Reductions in blood flows to the gastrointestinal tract at -6 mm Hg CNP and spleen at -11 mm Hg CNP were observed; blood flows returned toward control values when CNP was removed.