Material and methods
A retrospective observational study was conducted in the Medical Intensive Care Unit (MICU) of University-affiliated hospital during the pandemic period. Twenty-nine adult patients fulfilling the Berlin criteria of definition of ARDS [15] admitted to MICU were included in the study. The patients’ clinical histories were taken and routine blood and urine investigations including complete hemogram, renal function tests, serum electrolytes, liver function tests, urine routine, chest X‐ray, arterial blood gas analysis, and electrocardiogram were performed in every patient and were later repeated depending on clinical profile. SAPS II and APACHE II scoring were calculated on day 1. The study included all mechanically ventilated patients with a diagnosis of Influenza A (H1N1) pneumonia complicated by ARDS. During the Influenza A (H1N1) pandemic period, most patients admitted with ARDS were Influenza A (H1N1) positive (> 90%). The diagnosis of Influenza A (H1N1) infection in all patients was confirmed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) of nasopharyngeal swab specimens and respiratory secretions at the time of hospital admission. Based on death end-point within 28 days after diagnosis or admission, the patients were divided into survivor or non-survivor groups. All patients with ARDS caused by Influenza A (H1N1) pneumonia were treated using the same principle of mechanical ventilation - volume control ventilation with appropriate positive end-expiratory pressure (PEEP) according to the fraction of inspired oxygen (FiO2) (lung protective ventilation strategies). This study was approved by the Institutional Ethical Committee.