NIPPV success revolves around selection of the appropriate patient and early initiation of therapy. Once the decision is initiated, the physician must choose from a variety of delivery modalities and settings. Face mask delivery shows no difference in outcomes when compared with nasal delivery. However, because of excessive air leaks in the mouth, nasal delivery is not tolerated as well as face mask delivery.35 Of note, BiPAP has shown no difference in treatment success when compared to CPAP.24,36
While there is no standard setting to initiate, most studies have a mean NIPPV setting of an inspiratory pressure of 10-15 cm of water and maximum expiratory pressure of 5 cm of water.24,37 Expert guidance from emergency physicians and critical care physicians suggests that starting at an inspiratory pressure of 15 cm of water and a maximum expiratory pressure of 5 cm of water leads to more successful therapy than titrating up from lower settings. Once NIPPV is initiated, the emergency physician must continue to monitor the patient to assess need for escalation or discontinuation of therapy.
The patient’s progress should be measured every 30 minutes to 2 hours to determine treatment success or failure. As an adjunct to clinical exam, serial arterial blood gases may be helpful. If tolerated and needed, then increasing the inspiratory pressure by 2 cm of water every 20-30 minutes may increase the pressure support to a maximum inspiratory pressure of 20-25 cm of water and a maximum expiratory pressure of 15 cm of water. The expiratory pressure should be adjusted in patients with persistent hypoxemia or diffuse lung parenchyma involvement.38
Patient tolerance of BiPAP is variable and can be improved by efficient troubleshooting by the emergency physician (Table 3).
Discontinuation of therapy should not be the initial option if the patient has difficulty tolerating the treatment. If the patient does not tolerate NIPPV, then the first step is to assess for air leaks within the unit. As the default pressure support system is flow limited, any air leaks will prevent the machine from reaching the preprogrammed flow rate/pressure limit, thereby prolonging the inspiratory time.