CARDIOVASCULAR EFFECTS OF HYPOXIA/HYPERCARBIA AND TENSION PNEUMOTHORAX IN NEWBORN PIGLETS

Objectives: To test the hypothesis that, in newborn piglets, the presence of a tension pneumothorax modifies the cardiovascular responses to hypoxia/hypercarbia. Design: Prospective laboratory study. Setting: Perinatal cardiovascular research laboratory at a university school of medicine. Subjects: Seven newborn piglets. Interventions: We sequentially exposed the piglets to a baseline (control I) measure, hypoxia/hypercarbia, tension pneumothorax with normoxia/normocarbia, and tension pneumothorax with hypoxia/hypercarbia added. Measurements and Main Results: Brain and systemic blood pressures and blood now (radionuclide-microspheres) were measured. Hypoxia/ hypercarbia resulted in increased brain perfusion (207 +/- 61% of control, mean +/- SEM, P < .05) and heart perfusion (176 +/- 58% of control, p < .05) and decreased gastrointestinal perfusion (37 +/- 9% of control, p <. 05). Tension pneumothorax with normoxia/normocarbia reduced the cardiac output (-70 +/- 8% of control, p < .05), which was redistributed toward the brain (p < .05) at the expense of the gastrointestinal tract (p < .05). Although this redistribution in cardiac output persisted during tension pneumothorax with hypoxia/hypercarbia added, sustained reductions in cardiac output (-57 +/- 11%, of control, p < .01) were associated with smaller increases in perfusion to brain (55 +/- 54 vs. 207 +/- 61% of control, tension pneumothorax with hypoxia/hypercarbia added, and hypoxia/hypercarbia time periods, respectively, p < .05) and heart (65 +/- 49 vs. 176 +/- 58% of control, tension pneumothorax with hypoxia/hypercarbia added, and hypoxia/hypercarbia time periods, respectively, p < .05) and larger decreases in blood flow to gastrointestinal tract, pancreas, and kidneys (p < .05) than with hypoxia/hypercarbia alone. Conclusions: Tension pneumothorax-induced reductions in cardiac output Limit the hypoxia/hypercarbia-mediated increases in perfusion to brain and heart and accentuate the hypoxia/ hypercarbia-related decreases in perfusion to kidneys and splanchnic organs.