The Role of the Tissue Perfusion Index in Predicting Disease Severity and Prognosis in Patients with Severe and Critical COVID-19

Objectives The study investigated whether percutaneous partial pressure of oxygen (PtcO 2 ), percutaneous partial pressure of carbon dioxide (PtcCO 2 ), and the derived tissue perfusion index (TPI) can predict the severity and short-term outcomes of severe and critical COVID-19. Design Prospective observational study conducted from January 1, 2023 to February 10, 2023. Setting A teaching hospital specializing in tertiary care in Nanjing City, Jiangsu Province, China. Participants Adults (≥18 years) with severe and critical COVID-19. Interventions Not applicable. Main outcome measures The general information and vital signs of the patients were collected. The PtcO 2 and PtcCO 2 were monitored in the left dorsal volar. The ratio of TPI was defined as the ratio of PtcO 2 /fraction of inspired oxygen (FiO 2 ) to PtcCO 2 . Mortality at 28 was recorded. The ability of the TPI to assess disease severity and predict prognosis was determined. Endpoint Severity of the disease on the enrollment and mortality at 28. Results A total of 71 patients with severe and critical COVID-19, including 40 severe and 31 critical cases, according to the COVID-19 treatment guidelines published by WHO, were recruited. Their median age was 70 years, with 56 (79%) males. The median SpO 2 /FiO 2 , PtcO 2 , PtcCO 2 , PtcO 2 / FiO 2 , and TPI values were 237, 61, 42, 143, and 3.6 mm Hg, respectively. Compared with those for severe COVID-19, the TPI, PtcO 2 / FiO 2 , SpO 2 /FiO 2, and PtcO 2 were significantly lower in critical COVID-19, while the PtcCO 2 was significantly higher. After 28 days, 26 (37%) patients had died. TPI values < 3.5 were correlated with more severe disease status (AUC 0.914; 95% CI: 0.847-0.981, P < 0.001), and TPI < 3.3 was associated with poor outcomes (AUC 0.937; 95% CI 0.880-0.994, P < 0.001). Conclusions The tissue perfusion index (TPI), PtcCO 2 , and PtcO 2 / FiO 2 can predict the severity and outcome of severe and critical COVID-19.