Causes of Failure of Noninvasive Mechanical Ventilation

Abstract

With selected patients noninvasive positive-pressure ventilation (NPPV) can obviate endotracheal intubation and thus avoid the airway trauma and infection associated with intubation. With patients who can cooperate, NPPV is the first-line treatment for mild-to-severe acute hypercapnic respiratory failure. NPPV is also used for hypercapnic ventilatory failure and to assist weaning from mechanical ventilation, by allowing earlier extubation. Some patients do not obtain adequate ventilation with NPPV and therefore require intubation. Also, some patients will initially benefit from NPPV (for one-to-several days) but will then deteriorate and require intubation. It is not always apparent which patients will initially benefit from NPPV, so researchers have been looking for variables that predict NPPV success/failure. The reported NPPV failure rate is 5-40%, so the necessary staff and equipment for prompt intubation should be readily available. Absolute contraindications to NPPV are: cardiac or respiratory arrest; nonrespiratory organ failure (eg, severe encephalopathy, severe gastrointestinal bleeding, hemodynamic instability with or without unstable cardiac angina); facial surgery or trauma; upper-airway obstruction; inability to protect the airway and/or high risk of aspiration; and inability to clear secretions. The NPPV training and experience of the clinician team partly determines whether the patient will succeed with NPPV or, instead, require intubation. Greater clinician-team NPPV experience and expertise are associated with a higher percentage of patients succeeding on NPPV and with NPPV success with sicker patients (than will succeed with a less-experienced clinician team). With patients suffering hypercapnic respiratory failure the best NPPV success/failure predictor is the degree of acidosis/acidemia (pH and P_aCO2 at admission and after 1 hour on NPPV), whereas mental status and severity of illness are less reliable predictors. With patients suffering hypoxic respiratory failure the likelihood of NPPV success seems to be related to the underlying disease rather than to the degree of hypoxia. For example, the presence of acute respiratory distress syndrome or community-acquired pneumonia portends NPPV failure, as does lack of oxygenation improvement after an hour on NPPV. All the proposed NPPV success/failure predictors should be used cautiously and need further study. We predict that further study and team experience will improve the NPPV success rate and allow successful NPPV-treatment of sicker patients.