Lipid-laden macrophages in the tracheal aspirate of ventilated neonates receiving Intralipid: A pilot study

Lipid-laden macrophages (LLM) in tracheal aspirates are reported to be pathognomonic findings in exo- and endogenous lipoid pneumonia in adults. A pilot study was carried out to evaluate the effect of lipid infusion on the LLM index of the tracheal aspirates from ventilated neonates. All intubated infants were eligible for the study. Infants receiving parenteral nutrition had intravenous (IV) lipid introduced by 4-7 days of age; most samples after 7 days were from infants receiving IV lipid. Four infants received minimal gastric feeding; none had evidence of aspiration pneumonia. Tracheal aspirates from 28 infants were analyzed for the LLM index. Alveolar macrophages were graded 0-4 in direct relation to the amount of lipid per cell. One hundred macrophages were graded; the maximum possible LLM index was 400. Two hundred forty-five of 387 tracheal aspirate samples were acceptable for analysis. LLM indices increased during the first week after birth; the mean LLM index then continued in the same range, but with a wide distribution of individual values. The mean LLM index from infants receiving an IV lipid infusion during days 4-7 was 87.9 (SD = 44.8), and was significantly higher compared to 58.7 (SD = 40.8) in infants receiving no IV lipid (P < 0. 003). Tracheal aspirates from infants with and without IV lipid infusion yielded many LLM index values >100. These observations invalidate the use of the LLM index >100 as proof of aspiration pneumonia in this group of infants.