High-Flow Oxygen as Noninvasive Ventilation May Complicate Timely Intubation in Patients With Acute Respiratory Distress Syndrome

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In a recent issue of Critical Care Medicine, Kangelaris et al (1) demonstrated that nonintubated patients (including noninvasive positive pressure ventilation [NIPPV]) had similar mortality at 60 days to intubated patients in a retrospective analysis of a previously conducted large multi-ICU prospective cohort study of intubated and nonintubated patients with acute respiratory distress syndrome (ARDS). Most interestingly, although the authors observed that 12% of their patients who met criteria for ARDS never required either NIPPV or intubation, they noted that those patients requiring late intubation have a 1.5 times significantly higher mortality (56%) than those intubated on day 1 (36%) of ARDS onset.
With recent trends demonstrating a declining mortality in ARDS to 26%, we find this higher mortality in the late intubation group and likewise in the NIPPV arm (55%) especially concerning (2). Of note, one study has demonstrated a similar hospital mortality (64%) although among a higher percentage of patients requiring intubation after NIPPV (60%) (3). This raises the question of whether an initial attempt of NIPPV obscures recognition of acute respiratory failure and delays endotracheal intubation, without a measured interaction between intubation and mortality as the authors have shown? Perhaps, other modalities such as high-flow (HF) oxygen via nasal cannula contribute to this delay as there is confusion of what constitutes NIPPV and whether patients with this movadality should be included in a NIPPV group or not. For instance, it remains to be defined whether HF oxygen delivers significant enough levels of positive end-expiratory pressure to be considered true NIPPV as one study demonstrated with 40, 50, and 60 L/min of oxygen that upper airway pressures were approximated at 1.52 ± 0.7, 2.21 ± 0.8, and 3.1 ± 1.2 cm H2O, respectively (4). Additionally, further delay in appropriate management may occur as some patients are incrementally advanced in therapy from HF oxygen to NIPPV (continuous positive airway pressure or bilevel positive airway pressure), and then ultimately endotracheal intubation.
Likewise, NIPPV has been a successful therapy in acute chronic obstructive pulmonary disease exacerbation and acute cardiogenic pulmonary edema but studies in hypoxemic respiratory failure have had conflicting results. Similarly, one HF study did demonstrate similar intubation rates compared with NIPPV with improved 90-day mortality in hypoxemic respiratory failure without a mixed disturbance of hypercapnia (5). In this study (and others), the presence of combined type I and II respiratory failure with hypoxemia and hypercarbia is associated with increased mortality and NIPPV failure. Thus, including initial acid-base balance, PaCO2, respiratory rate, and ETCO2 levels may be helpful as potential indicators of success for NIPPV.
If noninvasive approaches may be viable adjuncts to invasive ventilation in ARDS, understanding definitions of NIPPV with key data components in ventilation in addition to oxygenation may be paramount to understanding timing of intubation and determining its utility.

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