Association between the PaO2 /FiO2 Ratio and Pneumonia Severity Index in Pneumonia Patients with ARDS: A Cross-sectional Study from a Critical Care Unit

Introduction: Pneumonia is a major concern in patients in critical care units. Severe pneumonia can lead to hypoxaemia and Acute Respiratory Distress Syndrome (ARDS). The Partial pressure of arterial Oxygen (PaO2 ), Fraction of inspired Oxygen (FiO2 ) ratio and Pneumonia Severity Index (PSI) are helpful in assessing the severity of pneumonia and ARDS. Identifying the correlation between the PaO2 /FiO2 ratio and PSI can improve patient management strategies and outcomes in cases of pneumonia. Aim: To analyse the PaO2 /FiO2 ratio and the PSI in pneumonia patients with ARDS and examine their association. Materials and Methods: A cross-sectional study was conducted in the Critical Care Unit, Smt. B.K. Shah Medical Institute and Research Hospital, Sumandeep Vidyapeeth Deemed to be University, Piparia, Waghodia, Gujarat, India, from October 2024 to November 2024. Study involved 67 pneumonia patients with ARDS, aged over 18 years, who were admitted to the Critical Care Unit. Following informed consent, detailed history taking and clinical examinations were performed. Routine investigations, including Arterial Blood Gas (ABG), blood urea nitrogen, serum sodium, serum glucose, haematocrit and chest X-ray, were conducted. The PSI score and PaO2 /FiO2 ratio were calculated at the time of pneumonia diagnosis. Statistical tests for prevalence and associations within the data were applied, with the Chi-square test used and a p-value of less than 0.05 considered statistically significant. Results: The mean±Standard Deviation (SD) age of the study participants was 49±9.79 years, with 34 (50.7%) females and 33 (49.3%) males. The majority of the study subjects resided in rural areas (83.6%). The mean±SD PaO2 /FiO2 ratio among the study subjects was 218.55±60.98 and the mean±SD PSI score was 117.97±39.80. A PaO2 /FiO2 ratio of 201-300 mmHg was observed in 39 (58.2%) patients, 101-200 mmHg in 24 (35.8%) patients and ≤100 mmHg in 4 (6%) patients. Patients classified in higher-risk categories included 32.84% in class IV and 35.82% in class V, reflecting an increased risk of mortality. Statistical analysis revealed a highly significant association between PSI class and the PaO2 / FiO2 ratio (p-value <0.001), indicating that patients with higher PSI class severity are more likely to develop severe ARDS. Conclusion: The study emphasises the strong association between the PaO2 /FiO2 ratio and the PSI in pneumonia patients with ARDS. A decline in the PaO2 /FiO2 ratio is linked to higher PSI classes, reflecting greater disease severity and a higher risk of mortality. These findings highlight the value of both metrics in assessing patient risk and guiding clinical management. By incorporating the PaO2 /FiO2 ratio and PSI into their evaluations, healthcare providers can better prioritise care and potentially reduce mortality in critical care settings.