Focus on acute circulatory failure

Abstract

A task force of the European Society of Intensive Care Medicine published the results of a consensus conference on the definition, diagnosis, monitoring, and treatment of circulatory failure [1]. Circulatory failure was defined as a life-threatening, generalized form of acute circulatory failure with inadequate oxygen utilization by the cells resulting in cellular dysfunction as a result of dysoxia, i.e., the loss of the physiological independence of oxygen delivery and oxygen consumption associated with increased lactate levels.However, the interpretation of increased lactate levels may not be as straightforward as suggested. In many cases lactate levels remain elevated after initial resuscitation. Ospina-Tascón et al. [2] showed that under these circumstances, the use of the venous-arterial CO 2 to arterial-venous O 2 content difference ratio as a surrogate of the respiratory quotient could reveal an increased lactate level as a result of persisting anaerobic metabolism. Increased lactate with an abnormal ratio (suggesting anaerobic metabolism) was associated with an excess mortality of almost 30 % compared to APACHE II expected mortality. Therefore, early resolution of tissue hypoperfusion and oxygen delivery-dependent oxygen consumption might prevent excess mortality. As shown by Gu et al. [3] in their meta-analysis of four studies, the use of early therapy aimed at decreasing lactate levels in patients with sepsis is associated with a significant improvement in mortality [risk ratio 0.65 (95 % CI 0.26-1.95)].Frequently abnormalities in skin perfusion are present in circulatory failure. Coudroy et al. [4] showed that skin mottling was present in 49 % of septic shock patients. Prolonged mottling (more than 6 h) was associated with a 40 % mortality. Similarly, Ait-Oufella et al. [5] showed that persistent abnormal capillary refill time (CRT) after initial resuscitation was related to mortality in septic shock patients. Although these data confirm similar studies in circulatory failure, the effect of using skin perfusion as a goal of therapy on outcome is not yet clear [6].Fluid resuscitation is an important intervention to improve tissue perfusion. In this regard the results of the FENICE study [7] on the use of fluid challenges in intensive care are remarkable. From this study in 2213 patients admitted to 311 ICUs in 46 countries, it was clear that the use of a fluid bolus was mainly aimed at restoring blood pressure. In the majority of cases, central venous pressure (CVP) was used to predict fluid responsiveness and monitor effectiveness. This is most likely based on the misconception of the original Starling experiments where CVP was the dependent variable on venous return and cardiac function instead of an independent variable of preload [8]. The goal of fluid resuscitation should not be an increase in CVP but rather an increase in stressed volume resulting in an increase in mean systemic filling pressure (MSFP) and a rise in the pressure for venous return (Pvr = MSFP − CVP) thus increasing cardiac ou...