The covid-19 crisis has placed extraordinary pressures on the health service. Public health measures have been implemented to reduce community spread and ease pressures on the NHS and these have shown benefits with a reduction in hospital admissions and daily death rates.¹ However, a concerning unintended side effect of this campaign may have been the observed delayed presentation of severely unwell patients, who have attempted to cope at home. Patients with severe covid infections are often falsely reassured by an unusual lack of dyspnoea despite severe hypoxaemia—so called “silent (or happy) hypoxia.” In our hospitals we have recorded patients attending the emergency department (ED) with saturations as low as 43% on room air.

While the majority of patients infected with SARS-Cov-19 will experience mild illness, up to 20% will develop more severe illness requiring acute admission, frequently in association with respiratory failure, necessitating consideration of intubation and ventilation.² The natural history of the disease is such, that deterioration, when it occurs, may happen after several days of apparently stable illness.³ Although there are patient risk factors which can identify those at increased risk, there currently are no validated markers with which to distinguish patients initially who will progress to respiratory failure from those who recover with just mild illness, while there appears to be a narrow window in which to identify deterioration. Many of the patients in critical care within NHS Lothian have presented in the emergency department in extremis, often requiring immediate transfer to intensive care. Chest radiology at presentation typically shows extensive multi-lobar disease. 

Many patients who require mechanical ventilation have poor outcomes⁴ and the UK has a higher in-hospital mortality than countries such as Germany which may be attributable to less aggressive testing, tracking, and observation in the community and reduced mitigation of spread to the vulnerable.⁵

As the UK continues to ease lockdown, without a validated means of predicting prognosis, it is not feasible to hospitalise all patients from the community. But when symptoms occur, they are late, and patients progress rapidly to respiratory failure. Within our cohort of ventilated ICU patients it is notable that 45% had healthcare contact in the community before admission, highlighting that active monitoring of higher-risk patients remotely at home has the potential to detect deterioration early and prevent late presentation.

The observation of silent hypoxia and associated physiological changes gives a signal which could be monitored to identify those at risk of progression to respiratory failure. It is our opinion that with the continued relaxation of lockdown, there is an urgent need for community identification and monitoring of patients to facilitate research into the natural history of covid-19 infection alongside earlier admission to hospital for patients who deteriorate at home and to identify those whom therapies can be tested and evaluated before they “crash into the ICU”. This could be facilitated with the use of telemedicine, SpO2 monitors, and remote monitoring by trained medical and nursing staff.

Tom Quinn, clinical research fellow and specialist respiratory registrar, University of Edinburgh, Centre for Inflammation Research & NHS Lothian Department of Respiratory Medicine. 

Tom Craven, consultant in anaesthesia and critical care and honorary senior clinical lecturer, NHS Lothian, Department of Intensive Care and University of Edinburgh, Centre for Inflammation Research.

David Dockrell, professor of infection medicine, University of Edinburgh Centre for Inflammation Research.

Tim Walsh, professor of anaesthesia, critical care and pain medicine, University of Edinburgh Centre for Population Health Sciences (Usher Institute). 

Bruce Guthrie, professor of general practice, University of Edinburgh Centre for Population Health Sciences (Usher Institute).

Brian McKinstry, professor of primary care e-health, University of Edinburgh Centre for Medical Informatics (Usher Institute).

Kevin Dhaliwal, professor of molecular imaging and healthcare technology, University of Edinburgh Centre for Inflammation Research & NHS Lothian Department of Respiratory Medicine. 

References:

1. COVID-19 Daily Death Summary, NHS England. [Accessed 28/4/2020].
2. Guan WJ, Ni ZY, Hu Y, et al. Clinical Characteristics of Coronavirus Disease 2019 in China [published online ahead of print, 2020 Feb 28]. N Engl J Med. 2020;NEJMoa2002032. doi:10.1056/NEJMoa2002032
3. Chen T, Wu D, Chen H, et al. Clinical characteristics of 113 deceased patients with coronavirus disease 2019: retrospective study [published correction appears in BMJ. 2020 Mar 31;368:m1295]. BMJ. 2020;368:m1091. Published 2020 Mar 26. doi:10.1136/bmj.m1091
4. ICNARC report on COVID-19 in critical care, published 27 March 2020. Intensive Care National Audit and Research Centre.
5. COVID-19: Why Germany’s case fatality rate seems so low. Stafford. BMJ 2020; 369:m1395 doi: 10.1136/bmj.m1395