HVNI vs Noninvasive Ventilation for Acute Hypercapnic Respiratory Failure

Dyspnea and acute respiratory failure are among the top 5 reasons for patients to present to the emergency department (ED)(1).Supplemental oxygen therapy forms the cornerstone of resuscitation of the acutely unwell patient.Under normal circumstances, tissue hypoxia occurs within 4 min of inadequate tissue oxygenation (2). Oxygen delivery to the peripheral tissues depends upon the product of cardiac output and the arterial oxygen content (3), which is partly dependent on FIO2. In intensive care unit (ICU) patients with acute respiratory failure, non-invasive strategies of oxygenation are mainly used to avoid invasive mechanical ventilation (4). In such situations, the goal of treatment should not only be survival, but also improved respiratory condition and avoidance of inappropriate discomforts. Since the 90's, noninvasive ventilation (NIV) has been largely used with strong level of evidence in cardiogenic pulmonary edema and chronic obstructive pulmonary disease (COPD) exacerbation. NIV improves gas exchange and reduces inspiratory effort through positive pressure. However, good tolerance to NIV is sometimes difficult to achieve due to frequent leaks around the mask, possibly leading to patientventilator asynchrony and even to intubation. It may have other deleterious effects such as delayed intubation by masking signs of respiratory distress, or barotrauma by the high tidal volume potentially generated under positive pressure (5). High-velocity nasal insufflation (Hi-VNI), a viable alternative to NiPPV in treating adults in undifferentiated respiratory distress. It provides both oxygenation and ventilatory support to reduce hypercapnia(6).It focuses on optimum efficiency of the deadspace purge to augment ventilation (7,8), in addition to delivering up to 100% oxygen by nasal cannula(9,10) This is accomplished by use of small-bore nasal cannulae (typically 2.7-mm internal diameter for adult patients) to produce high velocity flow that is approximately 360% greater than that of the larger bore cannulae. It requires a flow of 25 to 35 L/min in adults to accomplish a complete purge of the extrathoracic anatomic reservoir between breaths (8,11).