Intrapulmonary Shunt and Alveolar Dead Space in a Cohort of Patients with Acute COVID-19 Pneumonitis and Early Recovery.

BACKGROUND: Pathological evidence suggests that COVID-19 pulmonary infection involves both alveolar damage (causing shunt) and diffuse micro-vascular thrombus formation (causing alveolar dead space). We propose that measuring respiratory gas exchange enables detection and quantification of these abnormalities. We aimed to measure shunt and alveolar deadspace in moderate COVID-19 during acute illness and recovery. METHODS: We studied 30 patients (22 males, age: 49.9±13.5 years) 3-15 days from symptom onset and again during recovery, 55±10 days later (n=17). Arterial blood (breathing ambient air) was collected while exhaled O2 and CO2 concentrations were measured, yielding alveolar-arterial differences for each gas (AaPO2, aAPCO2) from which shunt and alveolar dead space were computed. MEASUREMENTS AND MAIN RESULTS: For acute COVID-19 patients, group mean (range) for AaPO2 was 41.4 (-3.5 to 69.3) mmHg; aAPCO2 was 6.0 (-2.3 to 13.4) mmHg. Both shunt (% cardiac output) at 10.4 (0 to 22.0)%, and alveolar dead space (% tidal volume) at 14.9 (0 to 32.3)% were elevated (normal: <5% and <10%, respectively), but not correlated (p=0.27). At recovery, shunt was 2.4 (0 to 6.1)% and alveolar dead space was 8.5 (0 to 22.4)% (both p<0.05 versus acute); shunt was marginally elevated for 2 patients, however, 5 (30%) had elevated alveolar dead space. CONCLUSIONS: We speculate impaired pulmonary gas exchange in early COVID-19 pneumonitis arises from two concurrent, independent and variable processes (alveolar filling and pulmonary vascular obstruction). For most patients these resolve within weeks, however, high alveolar dead space in ∼30% of recovered patients suggests persistent pulmonary vascular pathology.

Pulmonary function testing during SARS-CoV-2: An ANZSRS/TSANZ position statement.

The Thoracic Society of Australia and New Zealand (TSANZ) and the Australian and New Zealand Society of Respiratory Science (ANZSRS) commissioned a joint position paper on pulmonary function testing during coronavirus disease 2019 (COVID-19) in July 2021. A working group was formed via an expression of interest to members of both organizations and commenced work in September 2021. A rapid review of the literature was undertaken, with a 'best evidence synthesis' approach taken to answer the research questions formed. This allowed the working group to accept findings of prior relevant reviews or societal document where appropriate. The advice provided is for providers of pulmonary function tests across all settings. The advice is intended to supplement local infection prevention and state, territory or national directives. The working group's key messages reflect a precautionary approach to protect the safety of both healthcare workers (HCWs) and patients in a rapidly changing environment. The decision on strategies employed may vary depending on local transmission and practice environment. The advice is likely to require review as evidence grows and the COVID-19 pandemic evolves. While this position statement was contextualized specifically to the COVID-19 pandemic, the working group strongly advocates that any changes to clinical/laboratory practice, made in the interest of optimizing the safety and well-being of HCWs and patients involved in pulmonary function testing, are carefully considered in light of their potential for ongoing use to reduce transmission of other droplet and/or aerosol borne diseases.