|Title:||Effects of non-invasive respiratory supports on gas exchange and outcomes in COVID19 outside the ICU Insights from the first wave|
|Author(s):||C Gough M Casey T McCartan A. Franciosi D Nash D Doyle N Hyland G Kavanagh S Toland C Powell R O’Regan R ´O. Conluain G Greene G Murray I Fathi Hussein E Hunt F Gargoum D Curran T Hassan L Cormican R Costello T McEnery.|
|Institution:||University Hospital Galway|
|Poster:||Click to view poster|
|Abstract:||Patients with COVID-19 related acute hypoxemic respiratory failure (AHRF) were frequently outside the intensive care unit (ICU). |
We hypothesised that analysis of gas exchange abnormalities prior to- and post-initiation of non-invasive respiratory supports (NRS) could characterise a phenotype more likely to positive end expiratory pressure (PEEP). Furthermore, we aimed to clarify whether patients requiring NRS could be managed safely without invasive arterial blood gas (ABG) sampling.
We performed an observational cohort study of 169 Irish patients across 6 centres admitted with AHRF attributable to COVID-19 and radiographic diagnosis of pneumonia. NRS modalities included continuous positive airway pressure (CPAP) or nasal high flow (NHF). CPAP was administered via face mask with minimum PEEP of 10cmH2O. Flow rate for NHF was capped at 30L/min, limiting PEEP to <3cmH20. Data from first presentation to time of death, intubation or recovery was collected. We calculated P:F and SpO2:FiO2 (S:F) prior to initiation of CPAP or NHF and within 24hrs.
Transition from low flow oxygen to CPAP was associated with ΔP:F of +79.4 mmHg). Greater improvement in P:F with CPAP did not correlate significantly with BMI, age, symptoms duration or biomarkers. Nadir P:F correlated with intubation rate - 59.3% with P:F ≤ 150 mmHg compared to 15.3% with P:F nadir >150 mmHg. Regarding the need for invasive ABG sampling, the relationship of Sp02:Fi02 (S:F) to P:F was described by the equation SF = 1.167*P:F + 47.99 (p < 0.0001, R2 0.76, Fig. 2A). An S:F cut-off of 225 had 88% sensitivity and specificity of 92% to determine P:F < 150 mmHg (area under the ROC curve 0.9476). S:F correlated well with P:F ratio and permits non-invasive assessment of treatment response.
S:F ratio <225 predicted P:F < 150 mmHg, and was associated with increased risk of intubation and may serve as a useful benchmark for escalation to the ICU.