Exploring the best predictors of fluid responsiveness in patients with septic shock

Abstract

Objective

To evaluate respiratory variations in carotid and brachial peak velocity and other hemodynamic parameters to predict responsiveness to fluid challenge.

Methods

A prospective observational study was performed on mechanically ventilated patients with septic shock. Outcomes included the measurements of central venous pressure, intrathoracic blood volume index, stroke volume variation (SVV), pleth variability index(PVI), and ultrasound assessments of respiratory variations in inferior vena cava diameter (ΔIVC), carotid Doppler peak velocity (ΔCDPV), and brachial artery peak velocity (ΔVpeak brach).

Results

All patients received 200 mL normal saline challenge. There were 27 responders and 22 non-responders. Responders had higher SVV, PVI, ΔIVC, ΔCDPV, and ΔVpeak brach measurements. In addition, all these measurements had statistically significant linear correlations with changes in cardiac index (CI).When responders were defined by ΔCI ≥ 10%, receiver operating characteristics (ROC) curve analysis showed that fluid responsiveness could be predicted:11.5% optimal cut-off 1evels of SVV with sensitivity of 75% and specificity of 85%, 15.5% optimal cut-off 1evels of PVI with sensitivity of 65% and specificity of 80%, 20.5% optimal cut-off 1evels of ΔIVC with sensitivity of 67% and specificity of 77%, 13% optimal cut-off 1evels of ΔCDPV with sensitivity of 78%% and specificity of 90%, 11.7% optimal cut-off 1evels of ΔVpeak brach with sensitivity of 70% and specificity of 80%.

Conclusion

Ultrasound assessment of ΔIVC and ΔVpeak brach, especially ΔCDPV, could predict fluid responsiveness and might be recommended as a continuous and noninvasive method to monitor functional hemodynamic parameter in mechanically ventilated patients with septic shock.

Introduction

Septic shock is a serious infectious condition characterized by low blood pressure and multiple organ damage. One of the traditional recommendations is to administer intravenous fluids as the first step to improve blood pressure [1], [2]. However, studies have shown that not every patient benefits from aggressive intravenous hydration [3], [4]. Only about 40% of hypotensive patients with sepsis respond to fluid infusion with improvement in blood pressure and outcomes [5], [6]. Those who do not respond to fluid infusion are liable to develop high intravascular pressure, pulmonary edema, heart failure with a high associated mortality [7], [8], [9]. Therefore, it is crucial to develop a hemodynamically-guided approach to evaluate volume status and to identify patients who are likely to benefit from fluid administration.

Previous studies have shown that certain parameters may correlate with volume status. The traditional static parameters, such as central venous pressure (CVP), pulmonary wedge pressure, and intrathoracic blood volume index (ITBVI), have been shown not to correlate with patient volume status [10], [11]. Hemodynamic parameters, such as stroke volume variation (SVV) and pleth variability index (PVI) may better predict fluid responsiveness. However, assessments of these parameters require invasive procedures and special monitoring equipment, which limits their clinical application [12].

In recent years, ultrasound has been proposed as a tool to help guide fluid resuscitation [13], [14]. According to the Frank-Starling curve, when patients are in the low volume status, the cardiac preload is low and the curve is in the rising phase,therefore intrathoracic pressure fluctuations by breathing could have a greater impact on cardiac stroke volume(SV) [15], [16]. The variation of SV may be assessed by variation of arterial blood peak velocity on the Doppler ultrasound. At last, it leads the higher variation of SV and arterial blood peak velocity. Studies have shown that respiratory variation in aortic blood peak velocity had high sensitivity and specificity to predict fluid responsiveness [17], [18], [19]. However, measurements of aortic blood flow velocity require transesophageal ultrasound which is an invasive procedure. Measurements of femoral artery blood flow are frequently affected by changes in intra-abdominal pressure. Measures of carotid or brachial artery flow were recently shown to predict fluid responsiveness [18], [19], [20], [21]. Both these peripheral arteries are relatively superficial large vessels which can provide easy ultrasound evaluation and high-quality images. However, assessment of respiratory variation in artery peak velocity in these two arteries in ventilated patients with septic shock has not been studied.

In the current study, we measured the respiratory variation in arterial blood peak velocity in carotid and brachial arteries and compared their use against that of other static and hemodynamic parameters for predicting fluid responsiveness in ventilated patients with septic shock. Clinical application of these measures is discussed.