Fluid management in critically ill patients is a daily dilemma for physicians in particular when it comes to patients with acute respiratory distress syndrome (ARDS). The main study that addressed the issue of fluid management in ARDS patients is the FACTT study (1). The authors reported that a conservative strategy of fluid management improved lung function and shortened the duration of mechanical ventilation and intensive care stay without increasing non pulmonary-organ failures(1).
A decade later, in the article “Impact of Initial Central Venous Pressure on Outcomes of Conservative Versus Liberal Fluid Management in Acute Respiratory Distress Syndrome”, the authors examined the response to fluid management in different groups of patients with a post hoc analysis of the function of the patients’ initial CVP (2). They hypothesised that the initial CVP would modify the effect of fluid management on outcomes. Specifically, patients without shock at enrollment, those with higher initial CVPs would experience lower 60-day mortality when randomised to the conservative strategy.
From the initial 1000 patients enrolled in the FACTT study, 609 ARDS patients were analysed because they fulfilled eligibility criteria: absence of shock and the presence of baseline CVP. The whole group was subdivided into two subgroups according to the baseline value of CVP: 169 patients in the subgroup with CVP≤8mmHg and 440 patients in the subgroup of patients with CVP>8mmHg. Interestingly, the results of the study were not in accordance with what the authors expected. For patients with initial CVP≤8mmHg, conservative fluid management not only increased ventilator-free days (17.1 ± 10.0 vs. 11.1 ± 10.7; p < 0.001) and ICU-free days (14.8 ± 9.7 vs. 9.5 ± 10.1, p < 0.001) but also decreased mortality (17% vs. 36%; p = 0.005; OR, 0.365; 95% CI, 0.178–0.746). The results were confirmed by multivariable logistic regression after accounting for prespecified confounders. The other important result of the study is that no difference in mortality was found for patients with initial CVP > 8 mm Hg in conservative compared with liberal fluid management (18% vs. 18%; p = 0.928; odds ratio [OR], 1.022; 95% CI, 0.630–1.660), in spite of the significant difference between ventilator-free days (15.6 ± 10.2 vs. 13.8 ± 10.2; p = 0.022) and ICU-free days (14.3 ± 9.8 vs. 12.5 ± 9.6; p = 0.020) in conservative and liberal groups, respectively. The authors concluded that the analysis of the FACTT dataset demonstrated a decreased mortality with conservative fluid management among ARDS patients with a low initial CVP.
Two main messages are given in this study: first, maintaining low pulmonary hydrostatic pressures is of real benefit in ARDS patients. Second, attempting to decrease pulmonary hydrostatic pressures when they are already high with a conservative strategy is not efficient. Even if the authors were surprised by the results, they seem logical when referring to pathophysiology. ARDS is a complex disease where the mechanisms implicated in the constitution of pulmonary oedema are different from those implicated in its resorption, explaining the failure of a sole and a simple conservative strategy (mainly diuresis) to reduce the amount of pulmonary oedema when pulmonary hydrostatic pressures are already high.
Moreover, it is now well demonstrated that CVP cannot predict fluid responsiveness (3) since it is a poor marker of ventricular-preload dependency, although it is marker of right ventricular preload. In this regard, patients with high CVP could have still been preload-dependent so that the use of diuretics in the conservative strategy may have induced a decrease in cardiac output and eventually organ hypoperfusion and dysfunction. This might have contributed to the absence of benefit of this strategy in patients with high CVP.
In conclusion, this study suggests that when CVP is measure in ARDS a lower value may be associated to better outcome. On the other hand, CVP does not seem to be a reliable parameter to guide fluid management in ARDS patients.
Article review submitted by ESICM Journal Review Club member Olfa Hamzaoui on behalf of the Cardiovascular Dynamics section.
- National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network. Comparison of two fluid-management strategies in acute lung injury. N Engl J Med. 2006 15;354: 2564-75.
- Semler MW, Wheeler AP, Thompson BT, Bernard GR, Wiedemann HP, Rice TW; National Institutes of Health National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome Network. Impact of Initial Central Venous Pressure on Outcomes of Conservative Versus Liberal Fluid Management in Acute Respiratory Distress Syndrome. Crit Care Med. 2016 (ahead of print)
- Osman D, Monnet X, Castelain V, Anguel N, Warszawski J, Teboul JL, Richard C; French Pulmonary Artery Catheter Study Group. Incidence and prognostic value of right ventricular failure in acute respiratory distress syndrome. Intensive Care Med. 2009;35: 69-76.