Hemodynamic effects of aortic occlusion during hemorrhagic shock and cardiac arrest

To determine the hemodynamic consequences of aortic occlusion during controlled hemorrhagic arrest.

Ten anesthetized, hemodynamically monitored swine were subjected to a 40 mL/kg hemorrhage over 10 minutes, followed by a 5-minute period of apnea. At this time (T15), they were randomized into an UP group (n = 5) in which the thoracic aorta was occluded or a DOWN group (n = 5) in which the aorta was not occluded. Simultaneously, volume resuscitation with shed blood plus 20 mL/kg of normal saline was performed over a 10-minute period. Cardiac massage was performed until return of spontaneous circulation (ROSC), which was defined as a sustained systolic blood pressure > 60 mm Hg. After 30 minutes of occlusion (T45), the aortic occlusion was released. Parameters measured include mixed venous and arterial blood gases, serum lactic acid levels, cardiac index, mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), coronary perfusion pressure (CoPP), and left ventricular stroke work index (LVSWI). Oxygen delivery index (DO2I) was measured using a pulmonary artery catheter, and oxygen consumption index (VO2I) was measured by direct calorimetry (Delta Trac metabolic monitor).

Four animals in each group achieved ROSC after 3.0 +/- 1.8 and 2.2 +/- 1.8 minutes in the occluded and nonoccluded groups, respectively. During cardiac compressions and volume resuscitation, the CoPP, MAP, and MPAP were greater in the UP group, although the differences did not achieve statistical significance. After volume resuscitation was complete and during the period of aortic occlusion (T25-T45), the UP group had significantly greater MAP (mm Hg), with a difference of 42.5 +/- 20.75 mm Hg at T25 and 44.7 +/- 19 mm Hg at T35 (p < 0.03). Despite no difference in DO2I, VO2I (mL/min/kg) was significantly lower in the UP group than in the DOWN group, 4.28 +/- 0.48 versus 8.33 +/- 0.85 at T25 (p = 0.0002) and 4.62 +/- 0.9 versus 7.09 +/- 0.72 at T35 (p = 0.0005). After release of aortic occlusion at T45, the UP group had significantly lower CoPP (mm Hg) than the DOWN group (20.5 +/- 17.3 versus 66.5 +/- 28.2 at T45, p = 0.03). LVSWI (g/kg) was also lower in the UP than in the DOWN group (18.6 +/- 8.28 versus 36.5 +/- 10.2 at T60 [p = 0.031 and 23.6 +/- 6.48 versus 48.8 +/- 15.3 at T240 [p = 0.021). After release of the occlusion, there were trends toward increased acidosis and lactic acid levels in the UP group.

Aortic occlusion in this controlled hemorrhagic arrest model does not result in improved salvage but is associated with impaired left ventricular function, systemic oxygen utilization, and coronary perfusion pressure in the postresuscitation period.