Non-invasive ventilation for acute hypoxemic respiratory failure: intubation rate and risk factors

Abstract

Introduction: We assessed rates and predictive factors of non-invasive ventilation (NIV) failure in patients admitted to the intensive care unit (ICU) for non-hypercapnic acute hypoxemic respiratory failure (AHRF).

Methods: This is an observational cohort study using data prospectively collected over a three-year period in a medical ICU of a university hospital.

Results: Among 113 patients receiving NIV for AHRF, 82 had acute respiratory distress syndrome (ARDS) and 31 had non-ARDS. Intubation rates significantly differed between ARDS and non-ARDS patients (61% versus 35%, P = 0.015) and according to clinical severity of ARDS: 31% in mild, 62% in moderate, and 84% in severe ARDS (P = 0.0016). In-ICU mortality rates were 13% in non-ARDS, and, respectively, 19%, 32% and 32% in mild, moderate and severe ARDS (P = 0.22). Among patients with moderate ARDS, NIV failure was lower among those having a PaO2/FiO2 >150 mmHg (45% vs. 74%, p = 0.04). NIV failure was associated with active cancer, shock, moderate/severe ARDS, lower Glasgow coma score and lower positive end-expiratory pressure level at NIV initiation. Among intubated patients, ICU mortality rate was 46% overall and did not differ according to the time to intubation.

Conclusions: With intubation rates below 35% in non-ARDS and mild ARDS, NIV stands as the first-line approach; NIV may be attempted in ARDS patients with a PaO2/FiO2 > 150. By contrast, 84% of severe ARDS required intubation and NIV did not appear beneficial in this subset of patients. However, the time to intubation had no influence on mortality.

Figure 1

Flow-chart of the study. Among the 1,163 patients admitted for acute respiratory failure, 465 patients received NIV over a three-year period. After excluding 35 patients who received NIV with a “do not intubate” order, 430 received NIV of which 242 had acute hypercapnic respiratory failure and 188 had acute hypoxemic respiratory failure. After excluding 69 patients who received NIV for cardiogenic pulmonary edema and 6 patients without pulmonary infiltrates, 113 patients had non-hypercapnic acute hypoxemic respiratory failure. (ARDS, acute respiratory distress syndrome; NIV, Non-invasive ventilation).

Figure 2

Rates of NIV failure and in-ICU mortality (expressed in %) according to clinical criteria for acute respiratory distress syndrome (ARDS) and clinical severity of ARDS using the Berlin definition. Intubation rate was significantly different between the four groups (P = 0.001) but not the mortality rate (P = 0.22). Intubation and mortality rates were higher in patients with moderate or severe ARDS than in patients with mild or without clinical criteria for ARDS.

Figure 3

Kaplan-Meier estimate of survival without intubation according to presence of ARDS and its severity at presentation, stratified as no ARDS or mild ARDS (solid line) or moderate or severe ARDS (dashed line). The difference between the two groups was highly significant (P <0.0001, log-rank test). (ARDS, acute respiratory distress syndrome).

Figure 4

Box-plots indicating the median delay (25^th to 75^th percentiles) between NIV initiation and intubation in patients intubated within the first 96 h. The time to intubation was similar in survivors (at left) and non-survivors (at right). Only five patients (three survivors and two non-survivors) were intubated beyond 96 hours.

Figure 5

Rate of in-ICU mortality in patients with moderate or severe ARDS. No difference was found in patients who were intubated after NIV failure as compared to those who were directly intubated for acute respiratory failure without prior NIV (at right).