A national retrospective cohort study of mechanical ventilator availability and its association with mortality risk in intensive care patients with COVID-19

Wilde, H. A.; Mellan, T. A.; Hawryluk, I.; Dennis, J.; Denaxas, S.; Pagel, C.; Duncan, A.; Bhatt, S.; Flaxman, S.; Mateen, B. A.; Vollmer, S.

Importance: The virulence of SARS-CoV-2 has provoked concerns about hospitals' ability to effectively care for the vast numbers of people affected. Notably, several countries reported operating near or at their intensive care capacity during the COVID-19 pandemic, although the impact of this on patient outcomes remains unclear. Objectives: To determine if there is an association between survival rates in intensive care units (ICU) and occupancy of the unit on the day of admission. Design: National retrospective observational cohort study spanning the first wave of the COVID-19 pandemic in England. Setting: 114 hospital trusts (groups of hospitals that function as a single operational unit). Participants: 4,032 adults admitted to an ICU in England between 2nd April and 1st June, 2020, with presumed or confirmed COVID-19, for whom data was submitted to the national surveillance programme and met study inclusion criteria. Interventions: N/A Main Outcomes and Measures: A Bayesian hierarchical approach was used to model the association between hospital trust level (mechanical ventilation compatible) bed occupancy, and in-hospital all-cause mortality. Results were adjusted for unit characteristics (pre-pandemic size), individual patient-level demographic characteristics (age, sex, ethnicity, time-to-ICU admission), and recorded comorbidities (obesity, diabetes, chronic respiratory disease, chronic liver disease, chronic heart disease, hypertension, immunosuppression, chronic neurological disease, chronic renal disease). Results: 38.4% (1,548) of patients admitted to an ICU died. Adjusting for patient-level factors, mortality was higher for admissions during periods of high occupancy (>85% occupancy versus the baseline of 45 - 85%) [median odds ratio (OR) 1.19 (95% posterior credible interval (PCI): 1.00 - 1.44)]. In contrast, mortality was decreased for admissions during periods of low occupancy (<45% relative to the baseline) [OR 0.75 (95% PCI: 0.62 - 0.89)]. Conclusion and Relevance: Increasing occupancy of beds compatible with mechanical ventilation, a proxy for operational strain, is associated with a higher mortality risk for individuals admitted to ICU. Public health interventions (such as expeditious vaccination programmes and non-pharmaceutical interventions) to control both incidence and prevalence of COVID-19, and therefore keep ICU occupancy low in the context of the pandemic, are necessary to mitigate the impact of this type of resource saturation.