Perioperative Detection of Cerebral Fat Emboli From Bone Using High-Frequency Doppler Ultrasound.

Objective: Fat embolism syndrome and cerebral fat emboli are rare yet serious conditions arising from systemic distribution of bone marrow emboli. Emboli are known to produce high-intensity transient signals (HITS) in a Doppler signal. We hypothesized that both intramedullary nailing in pigs and median sternotomy in human infants cause bone marrow release, that some of these cause cerebral emboli, and that these were detectable by a new cerebral doppler ultrasound monitoring system (NeoDoppler). We also aimed to describe the intensity of HITS generated during these procedures.

Methods: Specific pathogen-free Norwegian landrace pigs were allocated to either bilateral femoral nailing or injection of autologous bone marrow (positive controls). Testing was carried out under continuous Doppler monitoring. Presence of cerebral emboli was confirmed with histology. NeoDoppler data from infants undergoing sternotomy prior to cardiac surgery were investigated for comparison.

Results: Eleven of twelve pigs were monitored with cerebral Doppler ultrasound during femoral surgery. HITS were seen in five (45%). Brain biopsies demonstrated bone marrow emboli in 11 of the 12 (92%). Four positive control pigs received intraarterial injections of bone marrow, saline, or contrast, and strong HITS were detected in all pigs (100%). Median sternotomy in eight human infants was associated with a significant increase in embolic burden; the HITS intensity was lower than HITS in pigs.

Conclusion: High-frequency cerebral Doppler ultrasound is a valuable tool for perioperative monitoring that can detect emboli in real-time, but sensitivity and specificity for bone marrow emboli may be limited and size-dependent.