We conducted an observation sub-study of the prospective randomized controlled trial "High Dose Inhaled Nitric Oxide in Acute Hypoxemic Respiratory Failure", in which we analysed the echocardiographic data collected both at baseline when patients where included and 3-5 days later for followup.

We conducted an observation sub-study of the prospective randomized controlled trial "High Dose Inhaled Nitric Oxide in Acute Hypoxemic Respiratory Failure" which was conducted in 2020/2021 during the COVID-19 pandemic on patients with ARDS due to COVID and requiring mechanical ventialtion. Patients underwent echocardiography at baseline, and were then randomized either to control, or treatment with inhaled nitric oxide, starting at 80ppm and then 40ppm. Followup echocardiography was performed 3-5 days later, and all echocardiographies were conducted by highly experienced sonographeres certified by the European Association of Cardiovascular Imaging. Analysis of these cardiac ultrasounds focused on the amount of patients showing signs of pulmonary hypertension, right ventricular failure and left ventricular failure. Several parameters were used to estimate these, and we also aimed to evalute the utility of more novel measures such as RV and LV GLS for this use in the ICU.

Inclusion Criteria:

• Age ≥18.
• Positive PCR for COVID-19.
• Admission to the ICU.
• Endotracheal intubation and mechanical ventilation.
• Severe hypoxemia, defined by PaO2/FiO2 < 300 mmHg.
• Inclusion in the trial "High Dose Inhaled Nitric Oxide in Acute Hypoxemic Respiratory Failure"

Exclusion Criteria:

• Endotracheal intubation for >72h before inclusion.
• Do not resuscitate order or other limitation of care.
• Known pregnancy.
• Cases where the treating physician opposes inclusion due to safety concerns or considerations that renders inclusion unfeasible.
• Not having had echocardiography performed during the trial period (exclusion criteria for this sub-study).

A population studied in the trial "High Dose Inhaled Nitric Oxide in Acute Hypoxemic Respiratory Failure", consisting of 40 patients recruited in the ICU at Danderyds Hospital at the height of the COVID-19 pandemic. The study population consisted of critically ill patients requiring mechanical ventilation suffering from verified COVID-19 with ARDS.