We have seen significant growth in clinical research in critical care medicine in the last decade. Advances have been made in many important areas in this field; of these, advances in treating septic shock and acute respiratory distress syndrome (ARDS), and also in supportive therapies for critically ill patients (eg, sedatives, insulin), have perhaps received the most attention.
Of note, several once-established therapies in these areas have failed the test of time, as the result of evidence from more-recent clinical trials. For example, recent studies have shown that a pulmonary arterial catheter does not improve outcomes in patients with ARDS. Similarly, what used to be “optimal” fluid management in patients with ARDS is no longer considered appropriate.
In this review, we summarize eight major studies in critical care medicine published in the last 5 years, studies that have contributed to changes in our practice in the intensive care unit (ICU).
FLUID MANAGEMENT IN ARDS
- In patients with acute lung injury (ALI) and ARDS, fluid restriction is associated with better outcomes than a liberal fluid policy.
- A pulmonary arterial catheter is not necessary and, compared with a central venous catheter, may result in more complications in patients with ALI and ARDS.
Fluid management practices in patients with ARDS have been extremely variable. Two different approaches are commonly used: the liberal or “wet” approach to optimize tissue perfusion and the “dry” approach, which focuses on reducing lung edema. Given that most deaths attributed to ARDS result from extrapulmonary organ failure, aggressive fluid restriction has been the less popular approach.
Additionally, although earlier studies and meta-analyses suggested that the use of a pulmonary arterial catheter was not associated with better outcomes in critically ill patients,1 controversy remained regarding the value of a pulmonary arterial catheter compared with a central venous catheter in guiding fluid management in patients with ARDS, and data were insufficient to prove one strategy better than the other.
The Fluids and Catheter Treatment Trial (FACTT)
NATIONAL HEART, LUNG, AND BLOOD INSTITUTE ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS) CLINICAL TRIALS NETWORK; WIEDEMANN HP, WHEELER AP, BERNARD GR, ET AL. COMPARISON OF TWO FLUID-MANAGEMENT STRATEGIES IN ACUTE LUNG INJURY. N ENGL J MED 2006; 354:2564–2575.
NATIONAL HEART, LUNG, AND BLOOD INSTITUTE ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS) CLINICAL TRIALS NETWORK; WHEELER AP, BERNARD GR, THOMPSON BT, ET AL. PULMONARY-ARTERY VERSUS CENTRAL VENOUS CATHETER TO GUIDE TREATMENT OF ACUTE LUNG INJURY. N ENGL J MED 2006; 354:2213–2224.
The Fluids and Catheter Treatment Trial (FACTT) compared two fluid strategies2 and also the utility of a pulmonary arterial catheter vs a central venous catheter3 in patients with ALI or ARDS.
This two-by-two factorial trial randomized 1,000 patients to be treated according to either a conservative (fluid-restrictive or “dry”) or a liberal (“wet”) fluid management strategy for 7 days. Additionally, they were randomly assigned to receive either a central venous catheter or a pulmonary arterial catheter. The trial thus had four treatment groups:
- Fluid-restricted and a central venous catheter, with a goal of keeping the central venous pressure below 4 mm Hg
- Fluid-restricted and a pulmonary arterial catheter: fluids were restricted and diuretics were given to keep the pulmonary artery occlusion pressure below 8 mm Hg
- Fluid-liberal and a central venous catheter: fluids were given to keep the central venous pressure between 10 and 14 mm Hg
- Fluid-liberal and a pulmonary arterial catheter: fluids were given to keep the pulmonary artery occlusion pressure between 14 and 18 mm Hg.
The primary end point was the mortality rate at 60 days. Secondary end points included the number of ventilator-free days and organ-failure-free days and parameters of lung physiology. All patients were managed with a low-tidal-volume strategy.
The ‘dry’ strategy was better
The cumulative fluid balance was −136 mL ± 491 mL in the “dry” group and 6,992 mL ± 502 mL in the “wet” group, a difference of more than 7 L (P < .0001). Of note, before randomization, the patients were already fluid-positive, with a mean total fluid balance of +2,700 mL).2
At 60 days, no statistically significant difference in mortality rate was seen between the fluid-management groups (25.5% in the dry group vs 28.4% in the wet group (P = .30). Nevertheless, patients in the dry group had better oxygenation indices and lung injury scores (including lower plateau airway pressure), resulting in more ventilator-free days (14.6 ± 0.5 vs 12.1 ± 0.5; P = .0002) and ICU-free days (13.4 ± 0.4 vs 11.2 ± 0.4; P = .0003).2
Although those in the dry-strategy group had a slightly lower cardiac index and mean arterial pressure, they did not have a higher incidence of shock.
More importantly, the dry group did not have a higher rate of nonpulmonary organ failure. Serum creatinine and blood urea nitrogen concentrations were slightly higher in this group, but this was not associated with a higher incidence of renal failure or the use of dialysis: 10% in the dry-strategy group vs 14% in the wet-strategy group; P = .0642).2
No advantage with a pulmonary arterial catheter
The mortality rate did not differ between the catheter groups. However, the patients who received a pulmonary arterial catheter stayed in the ICU 0.2 days longer and had twice as many nonfatal cardiac arrhythmias as those who received a central venous catheter.3
The liberal fluid-strategy group had fluid balances similar to those seen in previous National Institutes of Health ARDS Network trials in which fluid management was not controlled. This suggests that the liberal fluid strategy reflects usual clinical practice.
Although the goals used in this study (central venous pressure < 4 mm Hg or pulmonary artery occlusion pressure < 8 mm Hg) could be difficult to achieve in clinical practice, a conservative strategy of fluid management is preferred in patients with ALI or ARDS, given the benefits observed in this trial.
A pulmonary arterial catheter is not indicated to guide hemodynamic management of patients with ARDS.