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ABSTRACT & COMMENTARY
By Richard H. Kallet, MS, RRT, FAARC, FCCM
Director of Quality Assurance, Respiratory Care Services, San Francisco General Hospital
Mr. Kallet reports no financial relationships relevant to this field of study.
This article originally appeared in the July 2014 issue of Critical Care Alert. It was edited by David J. Pierson, MD, and peer reviewed by William Thompson, MD. Dr. Pierson is Professor Emeritus, Pulmonary and Critical Care Medicine, University of Washington, Seattle, and Dr. Thompson is Associate Professor of Medicine, University of Washington, Seattle. Drs. Pierson and Thompson report no financial relationships relevant to this field of study.
SYNOPSIS: Patients on mechanical ventilation who were managed with both conservative fluid administration and aggressive diuresis weaned faster, had significantly more ventilator-free days, and experienced reduced incidences of both ventilator-associated complications and ventilator-associated pneumonia.
SOURCE: Mekontso Dessap A, et al. Ventilator-associated pneumonia during weaning from mechanical ventilation: Role of fluid management. Chest 2014; Mar 20. doi: 10.1378/chest.13-2564. [Epub ahead of print.]
This article reports a secondary analysis of patients enrolled into a multicenter, randomized, controlled trial that examined the impact of B-type natriuretic peptide (BNP)-directed fluid management ("fluid-depletion strategy") vs. "usual care."1 The relationship between fluid balance and the incidence of ventilator-associated pneumonia (VAP) over the first 14 study days was analyzed in patients who met weaning-readiness criteria. Weaning was standardized using an automated pressure-support titration algorithm. When daily BNP values were ≥ 200 pg/mL, patients in the fluid-depletion arm had fluid restriction (baseline infusion ≤ 0.5 L/day; parental nutrition ≤ 1 L/day) along with aggressive diuresis (furoseminde: 10-30 mg boluses, Q-3h), targeting a urine output of 4.5-9 mL/kg over 3 hours. In the usual care group, clinicians were blinded to the BNP results, and both fluids and diuretics were administered per clinician practice. VAP diagnosis was standardized and required positive quantitative cultures from distal pulmonary sampling.
The 304 medical-surgical patients studied (152 in each group) were not different in terms of baseline characteristics and risk factors for VAP, and they had been receiving mechanical ventilation (MV) for approximately 4-5 days at randomization. There was a significantly lower incidence of VAP in the BNP-managed group (8.6%) vs. the usual care group (17.8%, P = 0.03). This also coincided with a more negative daily fluid balance, faster weaning time, and more ventilator-free days.
Both the parent trial1 and the seminal NIH FACTT study2 have validated the emerging concept that "keeping the lungs dry" during critical illness improves outcomes, in part by reducing the need for MV. The current study augments these findings by showing that reducing the need for MV provides an additional benefit of decreasing the incidence of VAP. Patients in the BNP group were successfully weaned approximately 1 day earlier (27 hours) than those in the usual care group, and on average were successfully extubated < 48 hours of enrollment into the trial. The most obvious explanation is that the lower incidence of VAP stems from reduced risk exposure related to the presence of the endotracheal tube.
Because the duration of MV is a risk for VAP (and VAP increases the duration of MV), the investigators used a competing risk model to analyze the effects of the fluid-depletion strategy while controlling for weaning outcome. They found that the fluid-depletion strategy itself significantly reduced the risk of both ventilator-associated complications and VAP (sub-hazard ratios of 0.44 (P = 0.02) and 0.50 (P = 0.03), respectively). These findings lead the authors to speculate that pulmonary edema may increase the risk for developing VAP by two mechanisms: 1) the long-recognized impairment of pulmonary host-defense mechanisms, and 2) an interesting hypothesis of enhanced growth and virulence of Pseudomonadaceae because these bacteria characteristically thrive in wet conditions. In this study, Pseudomonadaceae accounted for 44% of all positive bronchoalveolar lavage fluid cultures. The independent effect of pulmonary edema on VAP is an enticing explanation as some of the highest at-risk patients are those suffering from acute respiratory distress syndrome, traumatic injuries, and massive burns, conditions commonly associated with large fluid requirements and pulmonary edema formation.
This study underscores the beneficial effects of fluid restriction and aggressive diuresis in critically ill patients once they have achieved hemodynamic stability. Despite the growing body of evidence supporting this approach, it has not been enthusiastically embraced, particularly in the management of trauma patients. Unarguably, persistent hypotension caused by sustained capillary leak is a daunting problem. But overzealous crystalloid therapy also has been a well-recognized problem for more than 70 years, and one that "every generation of surgeons must discover for themselves."3 However, with mandatory public reporting of ventilator-associated complications looming in the near future, complacency toward managing "correctable" risk factors leading to avoidable patient complications will not be tolerated by society. The cumulative evidence clearly suggests that much more can be done to improve this aspect of patient care.