Prone Position and Lung Ventilation and Perfusion Matching in Acute Respiratory Failure due to COVID-19.

A 70-year-old man (body mass index = 29 kg/m2) was admitted for acute respiratory failure consequent to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. He had no disease in his past medical history and received no medication. He was intubated and mechanically ventilated with a Vt of 6 ml/kg of ideal body weight, a respiratory rate of 25 breaths/min, positive end-expiratory pressure of 12 cm H2O, and an FiO of 0.6. Because of severe hypoxemia (PaO/FiO = 118 mm Hg), the patient underwent prone positioning, which resulted in PaO/FiO improvement (263 mm Hg) after 1 hour (1). As previously attempted (2), we recorded images of lung ventilation and perfusion at the fifth intercostal space by using electrical impedance tomography (Pulmovista 500; Dräger Medical), with the patient supine and after 1 hour of pronation, maintaining the ventilator settings unchanged. Both ventilation and perfusion changed from the supine to the prone position (Figure 1). Ventilation increased in the dorsal half of the thorax (+20%), whereas perfusion decreased (−11%) in the same area, moving toward the ventral areas. However, the global inhomogeneity index (3) decreased for both ventilation and perfusion, overall increasing ventilation and perfusion matching in the lung, which may help explain the observed improvement in oxygenation with prone positioning in patients with acute respiratory failure secondary to SARS-CoV-2.

Figure 1.

(A) Transverse thoracic electrical impedance tomography images illustrating (from top to bottom) the distribution of tidal ventilation (blue–white gradient area), lung perfusion (red–yellow gradient area), and the two overlaid. Images were acquired with the patient in a supine position and 1 hour after prone positioning. (B) Plot illustrating the variations in the ventilation and perfusion distribution, as recorded with electrical impedance tomography. GI = global inhomogeneity index.