OBJECTIVES: The ratio between Pao2 and Fio2 is used as a marker for impaired oxygenation and acute respiratory distress syndrome classification. However, any discrepancy between Fio2 and o2 fraction in the alveolus affects the Pao2/Fio2 ratio. Correcting the Pao2/Fio2 ratios using the alveolar gas equation may result in an improved reflection of the pulmonary situation. This study investigates the difference between standard and corrected Pao2/Fio2 in magnitude, its correlation with the mortality of acute respiratory distress syndrome classification, and trends over time. DESIGN: A register and a retrospective study combined with the development of a mathematical model to determine the difference between standard and corrected Pao2/Fio2 ratio for various levels of Paco2 and atmospheric pressure. SETTING: ICU in a secondary hospital in The Netherlands. PATIENTS: Patients admitted to the ICU for pneumonia or acute respiratory distress syndrome. Register cohort: January 1, 2010, till March 1, 2020 (n = 1008). Retrospective cohort: March 1, 2020, till June 1, 2020 (n = 34). MEASUREMENTS AND MAIN RESULTS: The register was used to determine the 7-day ICU mortality per acute respiratory distress syndrome classification based on the standard and corrected Pao2/Fio2 ratio. The retrospective dataset correlated the Paco2 with Pao2/Fio2 ratio over time in patients with assumed stable oxygenation. The model demonstrated an increased difference between the standard and corrected Pao2/Fio2 ratios by a lower Fio2 and atmospheric pressure and higher Pao2 and Paco2. Reclassification of severe acute respiratory distress syndrome resulted in an increase in mortality from 28.1% for standard Pao2/Fio2 to 30.6% for corrected Pao2/Fio2 ratios. Acute Physiology and Chronic Health Evaluation scores correlated better with 7-day ICU-mortality when corrected Pao2/Fio2 ratio was used for classification. For patients with Fio2 less than 50% (n = 55), change in Paco2 correlated with change in Pao2/Fio2 ratio (r = –0.388; p = 0.003). INTERVENTIONS: A corrected Pao2/Fio2 ratio was calculated. CONCLUSIONS: Correcting the Pao2/Fio2 ratio for the alveolar gas equation predominantly affects patients with high ratios between Pao2 and Fio2 and Paco2 and at low atmospheric pressure. Using the corrected Pao2/Fio2 ratio for acute respiratory distress syndrome classification results in improved correlation with the 7-day ICU mortality and increases generalization among acute respiratory distress syndrome studies. The authors provide a free, web-based tool.

Background Presenting symptoms of COVID-19 patients are unusual compared with many other illnesses. Blood pressure, heart rate, and respiratory rate may stay within acceptable ranges as the disease progresses. Consequently, intermittent monitoring does not detect deterioration as it is happening. We investigated whether continuously monitoring heart rate and respiratory rate enables earlier detection of deterioration compared with intermittent monitoring, or introduces any risks. Methods When available, patients admitted to a COVID-19 ward received a wireless wearable sensor which continuously measured heart rate and respiratory rate. Two intensive care unit (ICU) physicians independently assessed sensor data, indicating when an intervention might be necessary (alarms). A third ICU physician independently extracted clinical events from the electronic medical record (EMR events). The primary outcome was the number of true alarms. Secondary outcomes included the time difference between true alarms and EMR events, interrater agreement for the alarms, and severity of EMR events that were not detected. Results In clinical practice, 48 (EMR) events occurred. None of the 4 ICU admissions were detected with the sensor. Of the 62 sensor events, 13 were true alarms (also EMR events). Of these, two were related to rapid response team calls. The true alarms were detected 39 min (SD = 113) before EMR events, on average. Interrater agreement was 10%. Severity of the 38 non-detected events was similar to the severity of 10 detected events. Conclusion Continuously monitoring heart rate and respiratory rate does not reliably detect deterioration in COVID-19 patients when assessed by ICU physicians.