COVID-19 controversy: when to intubate?

Today we publish correspondence [1, 2] concerning a heated debate on when to institute mechanical ventilation in patients with hypoxaemic respiratory failure due to COVID-19. The decision, of course, rests on the definition of respiratory failure and how to measure it. An almost universal tool is oximetry, which provides us with the percentage of haemoglobin saturated with oxygen in arterial blood. However, this metric is not linearly related to...