Outcomes/PredictorsOxygen saturation/fraction of inspired oxygen ratio is a simple predictor of noninvasive positive pressure ventilation failure in critically ill patients☆
Introduction
Mechanical ventilation is an essential component of critical care for patients with acute respiratory failure. However, several aspects of invasive mechanical ventilation can detrimentally impact clinical outcomes. Complications of invasive mechanical ventilation include ventilator-associated pneumonia, increased sedation use, and mechanical trauma of the upper airway [1], [2], [3]. Noninvasive positive pressure ventilation (NPPV) has received increasing consideration in the intensive care unit (ICU) because of the potential benefits over invasive ventilatory support. Randomized controlled studies have offered support for the use of NPPV in patients with chronic obstructive pulmonary disease (COPD) [4] and in the immunocompromised hosts [5]; however, the use of NPPV in a more general population of patients with acute respiratory failure is less certain with several reports having suggested that patients with hypoxemic respiratory failure are less likely to benefit from NPPV [1], [6], [7]. Therefore, predictors of NPPV success would be valuable in selecting patients who would more likely benefit from NPPV. Other investigators have identified Pao2/fraction of inspired oxygen (Fio2) ratio, various injury severity scores, acidemia, and temporal changes of physiologic variables as predictors of NPPV outcomes [8], [9], [10]; however, these parameters require invasive and/or extended periods of monitoring and observations. We conducted a prospective observational study to identify noninvasive parameters at the time of NPPV institution that can serve as predictors of NPPV outcomes in the intensive care setting.
Section snippets
Study design
All patients with respiratory failure receiving NPPV support in the medical ICUs at the Brigham & Women's Hospital between May 2007 and March 2009 were included in the study. Routine practice in our ICU is that the respiratory therapists select the mask type or interface, and the initial NPPV settings aiming to provide adequate support. Subsequently, the therapist records respiratory mechanics, including exhaled tidal volumes, and ventilator settings from the ventilator (Vision BiPAP,
Patient characteristics
A total of 133 patients were included in the study. The general characteristics of these patients are summarized in Table 1.
Our study population spent almost half of the initial 24-hour period on NPPV (average, 13 hours) and only 41% of our patients improved on NPPV compared to the 70% NPPV success rate reported by a large multicenter ICU study [9]. The high failure rate in our study was likely reflecting high severity of disease and the relatively high percentage of patients with cancer (43%)
Discussion
Noninvasive positive pressure ventilation can be an essential component for providing respiratory support to critically ill patients. Patient selection is critical in ensuring optimal use of NPPV [6]. We found that patient comorbidity plays a significant role in predicting NPPV success; specifically, patients with malignancy had a dramatically lower chance of improvement on NPPV reflecting generally worse outcomes of critically ill cancer patients with respiratory failure [17], [18].
Conclusions
In conclusion, we propose that a simple index of SF ratio at the time of NPPV initiation could be used to identify patients at high risk of NPPV failure. Avoiding delayed or emergent intubation could potentially improve outcomes of critically ill patients requiring respiratory support. Furthermore, our data suggest lower tidal volume may be protective in at risk patients who required more than 24 hours of NPPV support.
Acknowledgments
We thank the respiratory therapists at the Brigham & Women's Hospital for assisting in patient identification and data gathering, which made this study possible.
Part of the study has been presented by Carol Spada in abstract form at the International Respiratory Congress in Anaheim, Calif, on December 14, 2008.
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This work was supported by the American Heart Association Scientist Development Grant 0735620N (PSL) and National Institute of Health HL081385 (SRP). The funding agency played no role in the study or the manuscript. The authors have no conflicts of interest to declare.