NIV for Hypercapnic Respiratory Failure: AVAPS vs S/T BIPAP

1\. Overall Study Design and Plan This is a single center, randomized trial that will include a total of 100 adult subjects aged 18 or older with hypercapnic respiratory failure of all etiologies (i.e. "all comers"). The investigators will randomize patients in a single-blinded (patient blinded) fashion to BIPAP S/T or AVAPS during the duration of their hospitalization. The investigators will assess ABG at baseline, 1 hour after initial placement on BIPAP S/T or AVAPS, and between hours 24-48 of use. The investigators will record the pre-NIV pH and PaCO2, post-NIV pH and PaCO2, length of hospital stay in the medical ICU or telemetry unit, days on NIV, need for intubation (if occurred), transition to medical ICU care in patients who were initially admitted to telemetry, and in-hospital mortality. All collected laboratory data are already done as part of usual care for all patients placed on NIV when a patient is on the telemetry unit or medical ICU. The groups will undergo stratified randomization based on whether they are initially admitted to medical ICU or medical telemetry. Patients from medical ICU or telemetry units will be randomized to one of the following arms: Arm 1: AVAPS mode Arm 2 2: BIPAP S/T mode