Cardiopulmonary response of the rat to gram-negative bacteremia

Hemodynamic and respiratory effects of a continuous 5-h intravenous infusion of live Escherichia coli were studied in rats. Control animals were infused with saline. Rats infused with 1.8 +/- 0.4 X 10(10) bacteria/h did not survive a 5-h infusion. These animals developed early hypotension and reduced cardiac output (CO) measured by thermal dilution technique. Rats infused with 8.0 +/- 0.4 X 10(9) bacteria/h survived a 5-h infusion with hypotension and reduced CO occurring later in the course of bacteremia. Heart rate was markedly elevated in both septic groups. Arterial blood gas measurements revealed that partial pressure of O2 was not affected by bacteremia, but partial pressure of CO2 was significantly decreased. Arterial pH remained within the normal range indicating respiratory compensation of a metabolic acidosis. Since hypotension and reduced CO were accompanied by a fall in right atrial pressure (RAP) during bacteremia, a third septic group was studied to evaluate cardiac performance during volume loading. After 3-5 h of bacteremia, a 40% reduction in CO was associated with a significant drop in arterial pressure and RAP. Despite volume loading, ventricular stroke work and arterial pressure were significantly reduced compared with control animals. The results indicate that severe gram-negative bacteremia produces myocardial depression in the rat. This model can be useful for further studies of cardiac dysfunction during sepsis.