Patient selection: trauma patient being mechanically ventilated
The BAL is performed within the first 3 days following the trauma.
Method of Corwin and Irwin for counting lipid-laden macrophages (see Chapter 08):
(1) Fluid from a bronchoalveolar lavage is processed with smears prepared for cytology.
(2) The slides are stained for lipid using the oil red O stain.
(3) 100 alveolar macrophages are graded using the following scheme.
|
Amount of Lipid in the Alveolar Macrophage
|
Grade
|
|
none
|
0
|
|
one or few intracellular droplets
|
1
|
|
many distinct intracellular droplets
|
2
|
|
many confluent intracellular droplets with the nucleus still visible
|
3
|
|
many confluent intracellular droplets with the nucleus obscured
|
4
|
percent of lipid-laden cells =
= ((number of Grade 3 cells) + (number of Grade 4 cells)) / (number of cells counted) * 100%
Interpretation:
• minimum percent of lipid-laden macrophages: 0%
• maximum percent of lipid-laden macrophages: 100%
• Surgical patients without ARDS have a percent <= 5%.
• A percent > 30% supports the diagnosis of the pulmonary fat embolism syndrome.
Differential diagnosis:
(1) Aspiration pneumonia.
Performance:
• The index has a high negative predictive value (98%) but low positive predictive value (53%). The sensitivity was 89% and specificity 85% (page 978).
