In the United States today there are two different codes that can be used in putting patients on home-based NIV (as described by Dr Wolfe in a separate discussion).  There is a respiratory assist device [RAD] device, which can billed under the HCPCS Code E0471, and a noninvasive positive pressure ventilator [NIPPV], which can be billed under the Code E0464.  Guidelines for both of these are shown here.^[3] (Dr Wolfe also described some of the variations in these codes.)  One version of the model that we developed compares patients who received no NIV or NIPPV with patients who received AVAPS-AE support; the other version of the model looks at patients who received either a RAD device or NIPPV with AVAPS-AE.