Acute respiratory insufficiency is a frequent complication in critically ill surgical patients. Support of optimal alveolar-capillary oxygen exchange becomes a primary consideration for survival. Despite the frequent occurrence of hypoxia, controversy still exists regarding its hemodynamic effects. This study was designed to determine the circulatory effects of prolonged hypoxia in dogs prior to and following acute hemorrhage. Respiration was carefully controlled throughout these experiments to prevent any change in pH or arterial carbon dioxide pressure (Pco2) not directly attributable to hypoxia. The moderate hemorrhage (2% of body weight) employed in this study served as a challenge to test the integrity of cardiovascular function following the prolonged hypoxia.
The majority of studies reporting the circulatory effects of hypoxia have involved experimental animals subjected to severe hypoxia for brief periods of time. Under these circumstances, blood pressure rises and there is an increase in cardiac output and heart rate. Little
Hayashi T, Veragut UP, Bailey LL, Smith LL. Circulatory Effects of Prolonged Hypoxia in Normal and Hemorrhaged Dogs. Arch Surg. 1969;99(5):645-648. doi:10.1001/archsurg.1969.01340170097023