Pulmonary microvascular fat: the significance?

OBJECTIVE

To determine the effects of fat emboli on cardiopulmonary function in critically ill patients.

DESIGN

A prospective study.

SETTING

Tertiary referral medical/surgical shock/trauma intensive care unit (ICU).

PATIENTS

A total of 51 critically ill medical and surgical (including acute trauma) patients who required supplemental oxygen (FIO2 of > or = 0.35) to maintain arterial blood oxyhemoglobin saturation of > or = 90% and who had 62 pulmonary artery catheters placed for patient care reasons.

INTERVENTIONS

Pulmonary capillary blood samples were obtained via the pulmonary artery catheters in the "wedged position" at insertion and postinsertion at 8, 24, 48, and 72 hrs. Cytospun smears of the buffy coat aspirates of these samples were made and were stained with Oil Red-O for fat.

MEASUREMENTS AND MAIN RESULTS

One investigator, without knowledge of the patients' cardiopulmonary function, examined all smears and graded them 0 to 4+ for amount of fat. Fat scores were correlated with chest radiograph appearance, hemodynamic and respiratory parameters, complete blood cell counts with differential white blood cell counts, whether the patient was receiving lipid-containing parenteral nutrition, principal organ system failure, and reason for ICU admission. Samples from 27 pulmonary artery catheter insertions had no fat, 13 samples had low-grade (1+) episodic fat, and 22 samples had repeated episodes of > or = 2+ fat or isolated episodes of 4+ fat. There was a significant association between the amount of pulmonary microvascular fat and trauma as the reason for ICU admission. Of the other parameters, only chest compliance and body temperature showed unequivocal significant associations. These associations were opposite to the expected findings, but would support a conclusion that fat emboli did not cause the observed cardiopulmonary dysfunction. The inconsistent associations for the FIO2, PCO2, and mixed venous blood oxyhemoglobin saturation may be random events.

CONCLUSION

Cardiopulmonary dysfunction commonly attributed to fat emboli is likely due to other causes.