Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) is the pathogenic organism leading to COVID-19 disease1. Transmission predominantly occurs through respiratory droplet spread between individuals or direct contact with fomites on contaminated surfaces .
The clinical spectrum of COVID-19 disease is wide, from asymptomatic infection to severe pneumonia and the development of multiple organ failure leading to death. Approximately 5% of patients with confirmed SARS-CoV-2 infection requiring hospital admission become critically ill . Several risk factors for progression to critical illness have been identified, including increasing age , obesity , male gender , Black and Asian ethnicity , low socio-economic status and the presence of chronic co-morbidity .
COVID-19 disease may lead to the development of severe hypoxaemic respiratory failure, with most patients fulfilling the Berlin Criteria8 for diagnosis of Acute Respiratory Distress Syndrome (ARDS). As a new disease, the pathophysiology of COVID-19 is not yet fully understood. Although controversial, two distinct clinical phenotypes of respiratory failure in COVID have been proposed, which may occur in sequence . Early in the disease course, it is proposed that some patients have an atypical viral pneumonitis with severe hypoxaemia with relative preservation of compliance and a low ventilation - perfusion (V: Q) ratio. This subsequently progresses into a more classic "ARDS" phenotype, as defined by the Berlin Criteria , with poor compliance, high lung weight, and the potential for recruitment.
In addition to respiratory failure, multi-system involvement is common in COVID-19 disease, with over 25% of patients developing cardiovascular failure, and over 30 % suffering an acute kidney injury necessitating renal replacement therapy . Patients with COVID-19 disease are also recognised to be at increased risk of arterial, venous and pulmonary thromboembolism, the mechanisms of which are not fully understood . SARS-CoV-2 infection has also been associated with the development of a potentially severe inflammatory syndrome in children called paediatric multisystem inflammatory disorder (PIMS) .
Initial outcome data for the critically ill Scottish Population with confirmed COVID-19 disease indicates a 30-day mortality of 39%, which is increased in those receiving advanced respiratory support, older patients, and those requiring multiple organ support . The long-term sequelae of COVID-19 survivors are currently unknown. Guidance for the longer term recovery needs of COVID-19 survivors is currently being developed and when published will be signposted within this document.