Noninvasive ventilation via face mask (MPSV) is widely used for respiratory failure. Although the literature demonstrates that adequate support requires at least 15cmH2O of pressure, many patients are treated with lower pressures for fear that higher pressures would be intolerably uncomfortable. This study was conducted in order to asses this concern’s validity.
10 normals and 7 respiratory failure patients were studied. Each was given a series of increasing levels of MPSV and positive end expiratory pressure (PEEP). At each level respiratory rate (RR) and a numerical comfort rating were recorded. Clinical data was obtained from the hospital chart. The patients were followed for 6+/-4 months of daily MPSV. RR and comfort were correlated with support pressures and assessed for patterns. Values were compared using Student’s T test for paired data.
In all subjects discomfort rose with increasing MPSV, but not with use of PEEP. In normals RR decreased significantly at MPSV=15cmH2O, but RR did not decrease in patients until 20cmH2O MPSV was provided. Decreases in RR were associated with discomfort, described as the sensation of loss of control of breathing rather than as pain or dyspnea. All patients adapted to MPSV levels of 15-22cmH2O in less than 2 weeks of daily ventilator use with normalization of PCO2 and expressed comfort .
There is discomfort with MPSV at levels adequate to support respiration. This is described not as noxious, but as a loss of control of respiration and may represent the neuromuscular “capture” described in the early noninvasive ventilation literature. The fact that RR decreased at 15cmH2O in normals but not until 20cmH2O in patients correlates with the need for greater support in the patients, whose respiratory workload is greater. This need probably helped the patients adapt to MPSV levels which were initially perceived as uncomfortable.
MPSV should be used with pressures adequate to support ventilation and assurance that any feelings of loss of control of breathing will resolve with continued use of the treatment.
William Marino, None.