Acute Hypoxemic Respiratory Failure (AHRF) is very common in the ED/ICU. In this multicenter cohort of 21,714 patients in a Canadian ICU registry (iCORE) receiving oxygen or respiratory support, 50% met criteria for acute hypoxemic respiratory failure within 24 hours of ICU admission, and 76% of those patients required invasive mechanical ventilation.
- AHRF severity was categorized using the same Pao2/Fio2 thresholds as the Berlin definition for ARDS: mild (201–300), moderate (101–200), and severe (<100).
- When Pao2/Fio2 ratios were unavailable, severity was assigned using Spo2/Fio2 thresholds: mild (236–315), moderate (149–235), and severe (< 148). One-third of patients were actually classified this way.
PaO2/FiO2 remains the conventional standard and is important for ARDS severity/prognosis, but SpO2/FiO2 is noninvasive, continuous, inexpensive, and showed good agreement with PaO2/FiO2-based severity classification. According to these authors, SpO2/FiO2 can be a practical substitute for PaO2/FiO2 when an ABG is unavailable.
- Important limitations are the reduced accuracy of SpO2 at high saturations and potential pulse-oximetry bias, including overestimation of oxygenation in patients with darker skin tones.
Worsened hypoxemia strongly tracked with worse outcomes. ICU mortality increased from 17% in mild AHRF to 26% in moderate and 44% in severe AHRF; severe disease was also associated with fewer ventilator-free days and a lower probability of ICU discharge.
- AHRF patients were often treated using ARDS-style lung-protective ventilation. Median tidal volume was about 6.5 mL/kg predicted body weight, and most measured plateau/driving pressures were within protective ranges. However, plateau pressure was infrequently documented.
- Among patients with severe AHRF, 26% received neuromuscular blockade, 13% received prone positioning, 12% received iNO, and 12% received ECLS within the first 30 days of ICU admission..
References
https://journals.lww.com/ccmjournal/fulltext/10.1097/ccm.0000000000007284
https://jamanetwork.com/journals/jama/article-abstract/1160659