Pulmonary oedema

A 35-year-old male presents to the intensive care unit with respiratory failure requiring mechanical ventilation. His chest X-ray shows bilateral pulmonary infiltrates. Which of the following statements makes a diagnosis of non-cardiogenic pulmonary oedema MOST LIKELY?

a) The presence of peribronchial cuffing

b) Even or central radiographic distribution of the pulmonary oedema

c) The presence of septal lines

d) The presence of an air bronchogram

e) The presence of pleural effusions

Answer: d

Explanation

While pulmonary oedema may be relatively easy to diagnose, clinically elucidating the underlying cause is often far more taxing. These causes may be divided into cardiogenic and non-cardiogenic. The former is caused by a rapid increase in hydrostatic pressure in the pulmonary capillaries leading to increased transvascular fluid filtration. This in turn develops secondary to elevated pulmonary venous pressure from increased left ventricular end-diastolic pressure and left atrial pressure. The latter develops secondary to an increase in the vascular permeability of the lung leading to an increase in movement of fluid and protein into the lung interstitium and air spaces. Differentiation into non-cardiogenic and cardiogenic is based on a combination of history, physical examination, radiography, echocardiography and data from invasive cardiac output devices. Chest radiography is simple and used ubiquitously in this group of patients, but oedema may not even be visible until the amount of lung water increases by 30%. In addition other radiolucent material, such

as pus and blood, may give a similar radiographic image and there are many technical problems associated with chest radiography in the critically ill that reduce both the sensitivity and specificity, e.g. incorrect penetration, rotation, degree of inspiration and PEEP. Radiographic features supporting a non-cardiogenic cause of pulmonary oedema are: normal heart size; normal or balanced vascular distribution; a patchy or peripheral distribution of the oedema; the absence of peribronchial cuffing; septal lines; pleural effusions and lastly the presence of air bronchograms. It is the presence of air bronchograms that is the MOST suggestive and thus the best answer here.

Reference

Ware LB, Matthay MA. Clinical practice: acute pulmonary edema. New Engl J Med

2005; 353(26): 2788–96.