Cardiovascular Response to Endotoxin-Mediated Sepsis: A Dose-Response Study

Abstract

Purpose: Our long-term goal is to advance our understanding and treatment of sepsis, a potentially life-threatening condition that occurs when the response to infection causes tissue and organ damage. Sepsis can be caused by lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria. We used a swine model of LPS-induced sepsis to study the impact of the lymphatic and immune systems on the disease progression. Our first experiments were aimed at determining the optimal dose of Escherichia coli LPS in order to study the effect of sepsis on the cardiovascular system. We hypothesized that 2-hour intravenous infusions of 1- 50 µg/kg LPS would reveal dose- and time-dependent changes in hemodynamic parameters that are consistent with sepsis. Methods: Yorkshire pigs (61 ± 4 kg, n = 4, 2 male) were sedated, intubated, and ventilated. Femoral artery and venous lines were placed to allow measurement of blood pressure, infusion of LPS, and blood gas sampling. A thoracotomy was performed in order to secure a Transonic flow probe around the left anterior descending coronary artery and to insert a sampling catheter in the anterior cardiac vein. A dose of LPS (1, 5, 25, and 50 µg/kg) was given to each pig over 2 hours. Blood samples were collected immediately before LPS infusion and for every 30 minutes during and after LPS infusion for blood gas measurements. Vital signs were recorded as the animals developed sepsis. Results: Only the pig given the lowest dose of LPS (1 µg/kg) survived the full 6 hours (mean survival time in remaining 3 pigs was 180 ± 30 min). At 150 min, a ≈55% decrease in mean arterial pressure was observed (107 ± 4 to 48 ± 13 mmHg), resulting in a ≈60% increase in heart rate (91 ± 9 to 146 ± 14 beats/min). Coronary blood flow and myocardial oxygen consumption decreased ≈28% (0.53 ± 0.06 to 0.38 ± 0.02 ml/min/g) and ≈33% (60 ± 6 to 44 ± 2 µl/min/g), respectively. Ventricular fibrillation was the cause of death in the 3 non-surviving pigs. Conclusion: A dose of 1 µg/kg appears to be an optimal dose for future studies, as this dose was survivable in the desired time frame, while causing hypotension and tachycardia. In future studies, this model will allow us to study the effect of novel therapeutics during acute sepsis.