By Betty Tran, MD, MSc

Assistant Professor of Medicine, Pulmonary and Critical Care Medicine, Rush University Medical Center, Chicago

Dr. Tran reports no financial relationships relevant to this field of study.

SYNOPSIS: In this large, retrospective cohort study, the use of noninvasive ventilation (NIV) as an initial mode of ventilation for patients with asthma exacerbation was common; those successfully treated with NIV experienced lower inpatient mortality and shorter lengths of stay, but were likely a carefully selected population.

SOURCE: Stefan MS, Nathanson BH, Lagu T, et al. Outcomes of noninvasive and invasive ventilation in patients hospitalized with asthma exacerbation. Ann Am Thorac Soc 2016;13:1096-1104.

Despite limited evidence for the use of noninvasive ventilation (NIV) in acute exacerbation of asthma, rates of NIV use for patients suffering from asthma have increased recently.1 In this retrospective cohort study, Stefan et al used an electronic medical record database comprised of ICD-9 diagnoses, medication, laboratory, and clinical data from 125 hospitals to examine factors associated with the choice of ventilation in patients hospitalized with acute asthma exacerbation and the outcomes of NIV vs. invasive mechanical ventilation (IMV) in this patient population. The primary outcomes of the study were in-hospital case fatality and length of stay. Secondary outcomes included initial method of ventilation and rates and outcomes of NIV failure (defined as use of IMV after NIV).

A total of 13,930 admissions at 97 hospitals were included in the study, with 1,254 of the patients requiring mechanical ventilation; 556 (44.3% of ventilated patients) were given NIV initially, and 698 (55.7% of ventilated patients) were initiated on IMV. NIV failure was reported in 26 patients (4.7% of those treated with NIV initially). Compared to those initially ventilated with IMV, those treated initially with NIV demonstrated lower in-hospital case fatality rates (2.3% vs. 14.5%) and shorter median lengths of stay (4.1 days vs. 6.7 days). However, those who experienced NIV failure demonstrated the highest in-hospital case fatality rate at 15.4% and longest length of stay at 10.9 days. Patients who were older, those who previously received NIV, and those who had more than two prior admissions in the past 12 months were more likely to receive NIV initially. In contrast, higher acuity patients (based on the Laboratory Acute Physiology Score), those with concomitant pneumonia, status asthmaticus, prior IMV use, comorbid weight loss, and neurological disorders, were less likely to receive NIV. In addition, the hospital in which the patient was treated had a major association with the type of ventilation received.

Overall, use of NIV was associated with lower inpatient mortality (relative risk, 0.12; 95% confidence interval [CI], 0.03-0.51) and shorter length of stay (4.3 days less; 95% CI, 2.9-5.8). However, patients with NIV failure had slightly higher (albeit statistically not significant) mortality rates than patients treated with IMV initially (15.4% vs. 14.7%; P = 0.92) and longer median lengths of stay (10.9 days vs. 6.7 days; P = 0.007). Factors associated with NIV failure included admission for asthma within the prior 12 months, diabetes, and coexisting pneumonia.

COMMENTARY

This is the largest cohort of patients with asthma treated with mechanical ventilation to date. Although it is retrospective in design and much of the data are subject to limitations of ICD-9 coding, selection bias, and propensity matching in only 38% of patients treated with NIV, this study reveals that NIV is used in > 40% of patients suffering from asthma who are started on some form of ventilation, despite limited evidence for its use. Although the reasons for this are not explored in this study, the authors hypothesized that physicians may be more likely to use NIV in asthma patients because of the similarities in the pathophysiology of asthma vs. COPD exacerbations, given evidence favoring use of NIV in the latter and increasing familiarity and comfort with the use of NIV in general.

The rate of NIV failure was low at 4.7%, suggesting that NIV use across hospitals likely was in a very selected group of patients with asthma, probably an overall low-acuity, low-risk group. The fact that patients who failed NIV had higher rates of in-hospital death and longer lengths of stay suggests these patients probably should not have been started on NIV to begin with, and this may have delayed intubation when it was warranted. Overall, this study is enlightening with regard to current practice patterns surrounding NIV in asthma, but its findings that NIV is associated with improved outcomes in patients with asthma should be regarded as hypothesis-generating rather than conclusive. For now, patients with more severe asthma exacerbations who have a history of prior asthma admission within the past 12 months, diabetes, or concomittant pneumonia should not be considered for NIV given the higher risk of NIV failure with subsequent increased mortality.”

REFERENCE

  1. Nanchal R, Kumar G, Majumdar T, et al. Utilization of mechanical ventilation for asthma exacerbations: Analysis of a national database. Respir Care 2014;59:644-653.