The role of alveolo-arterial oxygen gradient and pneumonia severity index in predicting mortality in patients with COVID-19 pneumonia

Abstract

IntroductionThe new coronavirus disease-19 , also known as the new coronavirus pneumonia, first appeared in Wuhan Province of China during early December and spread almost all over the world within two months which also caused a pandemic. COVID-19 disease is caused by the virus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). 80% of COVID-19 patients have mild illness whereas 20% require hospitalization. Some of these cases need to be followed under the intensive care units (ICU). The cases that need to be followed up in intensive care refer to the patients with severe pneumonia and acute respiratory distress syndrome (ARDS) requiring invasive or non-invasive respiratory support. This rate is between 5% and 10% for the patients requiring hospitalization (1-3).In general, pneumonia is ranked 6th among all causes of death in the United Kingdom and the USA. Pneumonia is also ranked 1st among the deaths caused by infections. The mortality rate ranges between 1-5% for the ambulatory patients diagnosed with pneumonia whereas it reaches up to 12% for the hospitalized patients and 40% for the patients in the ICUs. In our country, the mortality rate ranges between 30% and 87% for the hospital-acquired pneumonia (4). Several scoring systems are used to predict mortality in pneumonia. The most popular ones are the pneumonia severity index (PSI) and CURB-65. The patient's demographic data, concomitant diseases, physical examination findings and laboratory values are used in calculating PSI (5-7).The fatal disease incidents appear as severe pneumonia and ARDS in COVID-19 patients. The PaO2/FiO2 (arterial oxygen pressure/fraction of inspired oxygen) and the alveolar-arterial oxygen gradient (AaDO2) are the indicators of oxygenation status in critical ill patients and stand as the diagnostic criteria for ARDS in adults. Low PaO2/FiO2 value has been associated with the increased mortality and hospitalization period for the patients admitted to the ICUs. The PaO2/FiO2 rate provides quick and easy data on the oxygenation status of critical ill