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Non-invasive Ventilation in Acute Respiratory Failure: Importance of the Interface
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert.
Synopsis: When 4 different interfaces with varying internal dead space were randomly applied during non-invasive ventilation in 14 patients with acute respiratory failure, there were no significant differences in gas exchange, minute ventilation, or work of breathing, but patient tolerance of the different devices varied substantially.
Source: Fraticelli AT, et al. Physiological effects of different interfaces during noninvasive ventilation for acute respiratory failure. Crit Care Med 2009;37:939-945.
In the application of non-invasive ventilation (NIV) in the management of patients with acute respiratory failure, Fraticelli and colleagues at Henri Mondor Hospital in Créteil, France, sought to determine the clinical effects of using interfaces with varying dead space and other features. They randomly applied 4 different interfaces for periods of 20 minutes each (with intervening 15-minute rest periods). The interfaces were a whole-face mask with internal volume of approximately 1000 mL, an oronasal mask with an internal volume of 163 mL, a second oronasal mask with a smaller internal volume (84 mL), and a mouthpiece with essentially no internal volume. Pressure-targeted NIV was administered according to usual clinical practice in the authors' institution, with slightly higher pressures used with the largest-volume mask to account for greater gas compression, and slightly lower pressures with the mouthpiece to minimize leaks. Measured variables with the different interfaces were minute ventilation, arterial blood gases, patient-ventilator synchrony, inspiratory work of breathing (using an esophageal probe), air leaks, and patient comfort (using a visual analog scale).
Fourteen alert and cooperative patients were studied, 7 each with hypoxemic and hypercapnic acute respiratory failure. The pressures used during NIV were a pressure support of 11 ± 3 cm H2O above the positive end-expiratory pressure (PEEP); PEEP was 6 ± 2 cm H2O in the hypoxemic patients and 4 ± 3 cm H2O in the hypercapnic patients. NIV was effective in reducing the pressure-time product of the respiratory muscles (an index of the work of breathing) using all 4 interfaces, with no differences among them. Arterial PO2 improved in all patients but there were no differences in minute ventilation or in PCO2 or pH with any of the interfaces. Air leaks and patient-ventilator asynchrony were higher with the mouthpiece, but there were no other differences among the interfaces. Using the visual analog scale, comfort was significantly less with the mouthpiece, with no other differences. The authors concluded that the internal volume of the masks had no apparent short-term dead-space effect, and that the different interfaces were essentially interchangeable in clinical practice.
Used effectively and in the right patients who present with acute respiratory failure, NIV reduces mortality, avoids the need for intubation in many instances, prevents hospital-acquired pneumonia, shortens ICU length of stay, and saves money.1 However, NIV is not like some new antibiotic that the patient's physician simply needs to know when to prescribe. To implement NIV effectively, and achieve improved outcomes, requires that a whole program be set up in the institution, involving not only new policies and procedures, but also increased staff knowledge and training, the right equipment, and availability in every area of the hospital in which the need may exist.2
This study has two important findings that relate to the effective implementation of NIV in treating patients with acute respiratory failure. First, although there are a number of key considerations with respect to the interface,3 the effects of varying mask dead space do not seem to be clinically important. Second, different interfaces may vary considerably with respect to patient tolerance and comfort. This latter finding is consistent with clinical experience at institutions where NIV is done really well. There is no "one-size-fits-all" with respect to NIV masks. Application of NIV according to a fixed protocol that applies the same brand and size of mask to all patients is sure to fail in many patients who would be successfully managed with appropriate individualization of the interface. The successful implementation and clinical application of NIV in treating patients with acute respiratory failure has a solid scientific underpinning but remains an art as well. This modality of respiratory care illustrates the importance of interdisciplinary collaboration and institutional systems integration in achieving the best patient outcomes.