The -Blocker Esmolol Restores the Vascular Waterfall Phenomenon After Acute Endotoxemia*

Background: A vascular waterfall occurs when the critical closing pressure is greater than the mean systemic filling pressure. Because the waterfall phenomenon likely exists in the microcirculation, 1-receptor blockers such as esmolol could have some effect on microcirculation and vascular waterfall. Objectives: To determine whether a vascular waterfall exists during septic shock and to assess the effects of vasopressors and -blockers on vascular waterfall. Design: Sixteen mongrel dogs were mounted with ultrasonic flow probes to measure renal blood flow. The hemodynamic variables of 16 animals were measured at baseline, after induction of acute endotoxemia; then, they underwent volume expansion, and norepinephrine was used to achieve baseline. After achieving septic myocardial depression, the animals were randomly divided into two groups (esmolol vs control groups) after reaching septic myocardial depression. Measurements and Main Results: There was a pressure gap of 41.913.9mm Hg between the arterial critical closing pressure and the mean systemic filling pressure, indicating that a vascular waterfall was present under baseline conditions. Endotoxemia caused a decrease in cardiac output, mean arterial pressure, and critical closing pressure. Endotoxemia also caused the vascular waterfall to disappear. Neither volume expansion nor norepinephrine had any effect on the vascular waterfall. Esmolol infusion restored the vascular waterfall effect following endotoxemia and resuscitation. The 24-hour survival was 75% in the esmolol group versus 12.5% in controls (p = 0.041). Conclusions: Vascular pressure gradients in renal vasculature suggest the presence of a vascular waterfall at baseline. Although this phenomenon disappeared in endotoxemic dogs, it could be restored with -blocker therapy (esmolol).