Compressibility Index vs Distensibility Index in BiPAP Patients

Understanding IVC Indices Under Positive Pressure

The American College of Chest Physicians recommends using Compressibility Index (CI) and Distensibility Index (DI) to evaluate volume status and right atrial pressure in mechanically ventilated patients, with CI = (IVC diameter max - IVC diameter min) / IVC diameter max × 100% and DI = (IVC diameter max - IVC diameter min) / IVC diameter min × 100% 1
BiPAP fundamentally reverses the normal relationship between intrathoracic pressure and IVC diameter, with positive pressure during inspiration increasing intrathoracic pressure and compressing the IVC, opposite to spontaneous breathing 2

The American Thoracic Society suggests not relying on standard IVC collapsibility/distensibility indices for volume status assessment in patients on BiPAP with IPAP >15 cmH2O or EPAP >8 cmH2O 1
The Society of Critical Care Medicine recommends monitoring arterial blood pressure, heart rate, urine output, and lactate for volume status rather than IVC indices in BiPAP patients 1

The American Heart Association recommends continuous monitoring of arterial oxygen saturation, blood pressure, respiratory rate, heart rate, and mental status when using BiPAP 1
BiPAP's hemodynamic effects are pressure-dependent, with settings of IPAP 14-20 cmH2O and EPAP 4-8 cmH2O representing typical therapeutic ranges with manageable cardiovascular impact 1, 2

The European Society of Cardiology suggests using extreme caution with BiPAP in hypotensive patients, as positive pressure further reduces blood pressure regardless of IVC measurements 1
Recent myocardial infarction represents a relative contraindication for BiPAP, with some evidence suggesting BiPAP may be associated with higher MI rates compared to CPAP in acute cardiogenic pulmonary edema 3, 1, 2