Effect of fluid bolus triggers and their combination on fluid responsiveness in optimization phase of severe sepasis and septic shock resuscitation

In optimization phase, fluid is usually administered upon clinical signs that suggest of hypovolemia, i.e. fluid triggers. Among these triggers, tachycardia was the most common used in our study. In a mcta-analysis about diagnostic value of vital signs in hypovolemic state, heart rate > 100 bpm had a very high specificity in revealing hypovolemia due to blood loss [16]. Although being considered as a form of hypovolemic shock, unlike hemorrhagic shock, tachycardia in septic shock may be caused by many other etiologies such as hyper-metabolism, effect of cytokines on sinus node and vasopressor use turns it to be a unreliable indicator of hypovolemia [17]. In our study, patients with tachycardia had a higher response rate than patients without tachycardia (38.5% versus 26.3%), but this difference was not statistically significance. CVP is an easily measured and commonly used to predict fluid responsiveness. Using a low cut-off (< 8 mmHg) in Surviving Sepsis Campaign 2012 guidelines we found the response rate to low CVP (48.6%) was highest compared to other triggers with OR 2.81. However, in sensitivity analysis, we did not find higher response rate at lower cut¬offs of CVP which indicated the former cut-off was likely to have been a spurious finding. Our result is consistent with a meta-analysis that demonstrated CVP neither relate to intravascular volume nor predict fluid responsiveness [18]. Besides low filling pressure, low blood pressure also had high response rate (47.4%). In early phase of septic shock, hypotension is a sign hypovolemia but it is mainly due to low vascular tone [1, 19]. Therefore, fluid responsiveness according this trigger was not higher than other triggers. Oliguria is another traditional sign of hypovolemia that is often used to trigger fluid administration. Bihari reported it was the bolus with lowest responsiveness among FB triggers while it was more effective than low filling pressure in ARDS patients [8, 9]. We found oliguria was the least used trigger and its responsiveness was lower than with low CVP and low MAP. It suggested that clinician was aware of the limitation of this parameter in predicting volume status. In fact, ƯOP in septic shock is controlled by renal mechanism more than hemodynamic parameter makes oliguria become a unreliable indicator of hypovolemia [20].