Hemodynamic Effects of Different Fluid Volumes for a Fluid Challenge in Septic Shock Patients

Fluid therapy is a cornerstone in the management of septic shock, aiming to restore adequate tissue perfusion by optimizing cardiac output (CO) and arterial pressure. However, the optimal volume of fluid required to predict fluid responsiveness remains a subject of debate. This study sought to determine the minimal infusion volume needed to effectively predict fluid responsiveness in septic shock patients, while also exploring the hemodynamic effects of fluid administration on arterial load and the predictive value of effective arterial elastance (Ea) during fluid resuscitation.

The study was conducted in the Medical Intensive Care Unit (MICU) of Peking Union Medical College Hospital, involving 47 patients diagnosed with septic shock according to the Sepsis 3.0 criteria. Patients were included if they required fluid resuscitation and had an indwelling pulmonary artery catheter (PAC) for hemodynamic monitoring. Exclusion criteria included other types of shock, chronic cardiac dysfunction, known allergy to colloid fluids, pregnancy, or participation in another biomedical study.

The fluid challenge (FC) protocol involved administering five sequential intravenous boluses of 100 mL 4% gelatin, with CO measured before and after each bolus using the thermodilution technique via PAC. Fluid responsiveness was defined as an increase in CO greater than 10% after a total of 500 mL fluid infusion. Hemodynamic parameters, including CO, stroke volume (SV), systolic arterial pressure (SAP), mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), and pulmonary artery wedge pressure (PAWP), were recorded at each stage. Additionally, arterial load parameters such as Ea, systemic vascular resistance (SVR), net arterial compliance, and arterial time constant (Tau) were calculated.

Of the 47 patients, 35 (74.5%) were identified as fluid responders. The study found that an increase in CO greater than 5.2% after a 200 mL fluid challenge provided an improved detection of fluid responsiveness, with a specificity of 80.0% and a sensitivity of 91.7%. The area under the receiver operating characteristic (ROC) curve (AUC) for the 200 mL volume was 0.93, indicating excellent predictive ability. In contrast, a 100 mL volume had a poor predictive ability (AUC = 0.76). The predictive abilities of 300 mL and 400 mL volumes were also strong, with AUCs of 1.00 and 0.97, respectively. However, the 200 mL volume was deemed sufficient to reliably detect fluid responders, as it provided comparable predictive accuracy to larger volumes.

Fluid administration induced a significant decrease in Ea from 2.23 mmHg/mL to 1.83 mmHg/mL, particularly in fluid responders who did not exhibit an increase in arterial pressure. This reduction in Ea suggests a loss of arterial load, which may explain why some patients experienced an increase in CO without a corresponding rise in arterial pressure. Baseline Ea was found to predict fluid responsiveness with an AUC of 0.74, but it failed to predict the pressure response to fluid challenge (AUC = 0.50).

The study also highlighted the reproducibility of CO measurements, with a coefficient of variation (CV) of 1.4%, precision of 2.7%, and least significant change (LSC) of 3.8%. These findings underscore the reliability of the thermodilution technique via PAC for assessing fluid responsiveness.

The hemodynamic effects of fluid administration were further analyzed in terms of arterial load. In fluid responders, fluid infusion led to a decrease in Ea, SVR, and Tau, while net arterial compliance increased. These changes were more pronounced in fluid responders who were pressure non-responders, indicating that the reduction in arterial load may be a key factor in the absence of a pressure response despite an increase in CO. Notably, baseline Ea was significantly higher in fluid responders than in non-responders, suggesting that a high Ea before fluid challenge may be predictive of fluid responsiveness.

The study’s findings have important implications for clinical practice. The use of a minimal volume of 200 mL gelatin for fluid challenge can effectively detect fluid responders in septic shock patients, reducing the risk of fluid overload while ensuring adequate resuscitation. Additionally, the assessment of Ea provides valuable insights into the hemodynamic effects of fluid administration, helping clinicians optimize fluid therapy and avoid unnecessary fluid loading.

The study also addressed the limitations of previous research, which often used varying fluid types, volumes, and infusion rates, leading to inconsistent results. By employing a standardized protocol with PAC-based CO monitoring, this study provides robust evidence for the use of a 200 mL fluid challenge in septic shock patients. Furthermore, the study contributes to the understanding of arterial load dynamics during fluid resuscitation, highlighting the importance of Ea in predicting fluid responsiveness and guiding therapy.

In conclusion, this study demonstrates that a minimal volume of 200 mL gelatin can reliably detect fluid responders in septic shock patients using thermodilution via PAC. Fluid administration reduces Ea, particularly in patients who increase CO without a corresponding rise in arterial pressure, suggesting a loss of arterial load. Baseline Ea may predict fluid responsiveness but not the pressure response to fluid challenge. These findings underscore the importance of individualized fluid therapy and the need for further research to optimize fluid resuscitation strategies in septic shock and other forms of acute circulatory failure.

doi.org/10.1097/CM9.0000000000001919

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