The rapid shallow breathing index as a predictor of failure of noninvasive ventilation for patients with acute respiratory failure.

BACKGROUND Noninvasive ventilation (NIV) may reduce the need for intubation in acute respiratory failure (ARF). However, there is no standard method to predict success or failure with NIV. The rapid shallow breathing index (RSBI) is a validated tool for predicting readiness for extubation. We evaluated the ability of the RSBI to predict failure of NIV and mortality in ARF. METHODS Prospective, observational trial of patients with ARF treated with NIV. NIV was initiated at the discretion of the clinicians, and an RSBI was recorded on the initial level of support (designated as assisted RSBI [aRSBI]). Patients were categorized by initial aRSBI value as either high (aRSBI > 105) or low (aRSBI ≤ 105). The primary end point was need for intubation, and the secondary end point was in-hospital mortality. Patients in the low and high aRSBI groups were compared using univariate analysis, followed by multivariable logistic regression to determine the association between aRSBI groups and outcome. RESULTS A total of 101 patients were included. The majority of patients had an inspiratory pressure of 5-10 cm H(2)O in addition to an expiratory pressure of 5-8 cm H(2)O. Of 83 patients with an aRSBI ≤ 105, 26 (31%) required intubation, compared to 10/18 (55%) with an aRSBI > 105 (multivariate odds ratio 3.70, 95% CI 1.14-11.99, P = .03). When comparing mortality, 7/83 patients (8.4%) with an aRSBI ≤ 105 died, compared to 6/18 (33%) patients in the group with an aRSBI > 105 (multivariate odds ratio 4.51, 95% CI 1.19-17.11, P = .03). CONCLUSIONS An aRSBI of > 105 is associated with need for intubation and increased in-hospital mortality. Whether patients with an elevated aRSBI could also have benefitted from an increase in NIV settings remains unclear. Validation of this concept in a larger patient population is warranted.