Can Ventilatory Strategies in COVID-19 Have an Impact on Outcomes?

The rapidly evolving understanding of Coronavirus Disease 2019 (COVID-19) respiratory failure pathogenesis, limited disease-specific evidence and demand-resource imbalances have posed significant challenges for intensive care clinicians. In this single-centre retrospective cohort study we describe the outcomes of COVID-19 patients admitted to Guy’s and St. Thomas’ NHS Foundation Trust (GSTT) critical care service. Patients were managed according to a local respiratory failure management pathway that was predicated on timely invasive ventilation when indicated and tailored ventilatory strategies according to pulmonary mechanics. Between 2nd March and 25th May 2020 GSTT critical care service admitted 316 patients with confirmed COVID-19. Of the 201 patients admitted directly through the Emergency Department with a completed critical care outcome, 71.1% survived to critical care discharge. These favourable outcomes may serve to inform the wider debate on the optimal ventilatory management in COVID-19.


Abstract:
The rapidly evolving understanding of Coronavirus Disease 2019  respiratory failure pathogenesis, limited disease-specific evidence and demand-resource imbalances have posed significant challenges for intensive care clinicians. In this singlecentre retrospective cohort study we describe the outcomes of COVID-19 patients admitted to Guy's and St. Thomas' NHS Foundation Trust (GSTT) critical care service. Patients were managed according to a local respiratory failure management pathway that was predicated on timely invasive ventilation when indicated and tailored ventilatory strategies according to pulmonary mechanics. Between  Distress Syndrome (ARDS), as this is influenced by the timing of presentation and may be affected by the treatments received. [1] The uncertainties generated by this new disease have engendered a debate on the optimal strategy for respiratory support and highlighted the need for data to help design clinical trials. However, in the context of a pandemic, institutions needed to develop pragmatic clinical pathways to meet the excess critical care demand and consider how best to use the available local resources -such as ventilators, staffing and oxygen supplies.
The objective of this study was to evaluate the impact of a locally derived respiratory failure management pathway on the outcomes of critically ill COVID-19 patients admitted to a high volume severe respiratory failure centre in the United Kingdom (UK).

Methods
This was a retrospective single-centre cohort study of all RT-PCR confirmed COVID-19 patients admitted to the critical care service at Guy's and St. Thomas' NHS Foundation Trust Briefly, after an initial triage assessment performed on oxygen alone and an assessment of the work of breathing, patients were considered for a time-limited trial of awake proning or non-invasive respiratory support, or otherwise for endotracheal intubation. The overarching objective was the avoidance of delayed invasive mechanical ventilation in patients with increased work of breathing or severe hypoxemia. Subsequent ventilation and positive end expiratory pressure (PEEP) selection were based on categories of static compliance and driving pressure. Preference was given to prone position rather than higher PEEP. This is consistent with emerging phenotypes identified using international observational data. [1] The definition of a priori parameters based on a pathophysiological construct, together with a substantial increase in our resources, allowed us to provide the required respiratory support for an individual patient, according to an egalitarian, rather than utilitarian perspective.
The primary outcome was critical care mortality in patients admitted directly to GSTT. Given the wide range of mortality reported in the literature, it is useful to consider our singlecentre outcomes in the context of the UK data reported by Intensive Care National Audit and Research Centre (ICNARC).

Results
During the study period, our critical care service admitted 316 confirmed COVID-19 patients, including 52 mobile ECMO retrievals and 51 non-ECMO critical care transfers from other institutions ( Figure 2 received it primarily for humidification purposes with flow rates ≤ 15 litres-per-minute. Only one patient originally admitted to GSTT required ECMO initiation for AHRF due to a concurrent massive pulmonary embolism. Our critical care mortality was 28.9%.

Discussion
This is one of the largest single-centre studies describing outcomes of critically ill COVID-19 patients managed according to a local respiratory failure management pathway. The survival to critical care discharge of 71.1% provides reassurance that a strategy predicated on timely invasive ventilation and personalised ventilatory strategies can confer favourable outcomes. This strategy and outcomes are similar to the one adopted and described by Ziehr et al, where in a smaller cohort of 66 patients, the authors report a mortality of 16.7%. [2] When comparing to the contemporaneous ICNARC report of 9,026 COVID-19 patients admitted to critical care in the UK, our cohort had comparable baseline characteristics (age, sex, BMI and APACHE II scores) but with higher rates of advanced respiratory support (82.6% versus 72.5%), lower use of basic respiratory support (30.3% versus 63.3%) and a lower mortality (28.9% versus 44.3%). [3] COVID-19 is an inflammatory vasculopathy that is initially associated with minimal parenchymal edema and atelectasis but significant pulmonary shunt, dead space and hypoxemia.  . ECMO -Extracorporeal Membrane Oxygenation, BMI -Body Mass Index, BAME -Black, Asian and Minority Ethnic, APACHE -Acute Physiology And Chronic Health Evaluation, NIV -Non-Invasive Ventilation, and HFNO -High Flow Nasal Oxygen. *Of the 48 patients coded as receiving 'High flow nasal oxygen', 28 (58.3%) received it primarily for humidification purposes with flow rates ≤ 15 litres-per-minute.