[Intra-macrophage lipid particles collected by bronchoalveolar lavage: incidence and diagnostic value]

Testing for lipid-laden macrophages in bronchoalveolar lavage fluid to diagnose vaping-associated pulmonary injury. Are we there yet?

Vaping-associated pulmonary injury (VAPI) is a severe respiratory disorder associated with the inhalation of nicotine, tetrahydrocannabinol, cannabidiol, or other active substances through a personal vaporizer ("vaping"). Within 2 months after its description, the disease has reached epidemic proportion, affecting over 2000 people and resulting in a number of fatalities. The substance(s) responsible for the lung injury are still unknown, and the pathophysiology of the disease is still incompletely understood. The manifestations of the disease are protean, and the insidiously starting respiratory, gastrointestinal, and constitutional symptoms may initially resemble a viral flu-like illness. The disease may increase in severity, requiring hospitalization, and in more severe cases, mechanical ventilation. The diagnosis of VAPI currently relies on the identification of pulmonary infiltrates on imaging studies in patients who have used vaping products, after excluding infections and other plausible alternative diagnoses. Because VAPI is currently a diagnosis of exclusion, some authors have suggested the use of lipid-laden macrophages (LLM) as a diagnostic test to confirm the disease. We review the current state of the knowledge about the pathologic basis of VAPI, and the literature on the analytic performance of the LLM test to better understand the potential utility of this test in the diagnosis of VAPI. Our review finds little evidence to suggest the use of LLM in the diagnosis of VAPI, since its underlying pathology is acute lung injury, which is unrelated to LLM, and the frequency of their detection varies greatly in different reported series.

Toxic alveolitis after inhalation of a water repellent

Inhalation of fluorocarbon polymers can cause pulmonary toxicity. Although multiple cases of lung injury have been reported, cellular characterization of the associated alveolitis occurring acutely after inhalation is limited. We report the case of a previously healthy woman who presented at our Emergency Department with an acute pneumonitis following inhalation of a fluorocarbon polymer-based rain-proofing spray. Bronchoalveolar lavage (BAL) performed shortly after the presentation showed an elevated total cell count, with a high proportion of neutrophils (58%) and eosinophils (9%). In addition, a lipid stain (Oil-Red-O-stain) showed a high level of lipid laden macrophages, a marker that could reflect a direct toxic effect of the spray on alveolar cells. The patient made a full recovery after four days of in-hospital observation with supportive care.

Lipid-laden macrophages in bronchoalveolar lavage fluid as a marker for pulmonary aspiration

An increased lipid content in alveolar macrophages of bronchoalveolar lavage (BAL) fluid is thought to be a useful indicator for recurrent pulmonary aspiration. To assess whether pulmonary diseases unrelated to aspiration can raise the lipid content in alveolar macrophages, we evaluated Oil-Red-O-stained smears of BAL fluid in 18 children aged 3-15 years undergoing elective surgery for nonpulmonary illnesses under general anesthesia and in 18 children aged 1-16 years who had pulmonary diseases without clinical evidence of aspiration (pneumonia, exogenous allergic alveolitis, or cystic fibrosis). A semiquantitative lipid-laden macrophage (LLM) index was determined for each patient. LLM indices in children without pulmonary disease were higher than those published for healthy adults. In children with pulmonary diseases but without evidence of aspiration, a significantly higher LLM index was observed compared to controls. The LLM indices of children with pulmonary diseases were similar to those published by other authors for children with pulmonary aspiration. We conclude that an elevated LLM index in alveolar macrophages of BAL can be found in a variety of pulmonary diseases in which there is no clinical evidence of aspiration and is therefore unlikely to be a specific parameter for silent pulmonary aspiration.

[From fat emboli to fat embolism syndrome]

The occurrence of a fat embolism syndrome (FES) can be explained by two hypothetic mechanisms. In the mechanical hypothesis, bone marrow enters into the cardiovascular system during an intramedullary peak pressure. This peak could occur during either long bone fracture and/or intramedullary nailing or cemented or noncemented arthroplasty. According to the biochemical hypothesis, the FES could occur in nontraumatic conditions such as lipid emulsion infusion or sickle cell disease. The C-reactive protein is a possible factor for destabilizing plasma fat (chylomicrons or Intralipid liposomes). Treatment with heparin has been reported to interfere with lipid metabolism through a "creaming" phenomenon. Plasma fatty acids increase lipid peroxidation, with potential severe oxidative stress of lung. Vascular lung injury is increased by granulocytes and the clotting cascade is activated by neutral fat. After a symptom-free period, the full clinical picture is characterized by pulmonary insufficiency with hypoxaemia, neurological impairment, pyrexia and petechial haemorrhages. The accurate incidence cannot be assessed as many subclinical forms remain unrecognized. Transoesophageal echocardiography with color-flow Doppler allows considerable insight into the sequence of embolic events and patent foramen ovale (PFO). A PFO induces an increase in right-to-left shunt in case of an elevated intrapulmonary pressure. PFO might elicit systemic manifestations of the FES, particularly with neurological impairment. Carotid ultrasonography helps to visualize embolism. Magnetic resonance imaging of cerebral fat emboli is a better diagnostic tool for detecting brain embolism than computerized tomography. Quantification of cells containing fat droplets in bronchoalveolar lavage material could also be helpful. Pulmonary microvascular cytology analysis of capillary blood samples obtained through a pulmonary artery catheter in combination with blood gas changes are of value for earlier stage FES. Prophylactic and therapeutic measures are aimed to counteract the various mechanisms leading to FES. The decrease in time delay of fracture management is probably the most effective prophylactic means. A reaming procedure can be noxious, particularly in a patient with a severe thoracic trauma. The insertion without reaming of a small diameter nail, plating or external fixation have several advantages. Albumin infusion is recommended for restoration of blood volume and binding of fatty acids. Among pharmacologic measures, only corticosteroids have a proven benefit, not only for prophylaxis but also for therapy. Aprotinin and heparin are beneficial in counteracting blood cell aggregation. A prophylactic use of vena cava filters has been advocated. Prevention or early treatment of hypovolaemia and hypoxaemia are essential.