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NEUROSURGICAL ANESTHESIA

Dynamic Characteristics of Cerebral Lipid Microemboli: Videomicroscopy Studies in Rats

Robert J. Byrick, MD^*, J. Colin Kay, C. David Mazer, MD^*, Zhilan Wang, MSc, and J. Brendan Mullen, MD

*Department of Anaesthesia and the Anesthesia Research Laboratory, St. Michael’s Hospital, University of Toronto, and the Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, University of Toronto, Toronto, Ontario

Address correspondence and reprint requests to Dr. Robert J. Byrick MD, Department of Anesthesia, Room 132 FitzGerald Building, 150 College Street, Toronto, ON, M5S 3E2. Address email to robert.byrick{at}utoronto.ca

Cerebral lipid microemboli (LME) may cause postoperative cognitive dysfunction after orthopedic and cardiovascular surgery. In 13 anesthetized rats, we created a cranial window to study LME using orthogonal polarization spectral imaging videomicroscopy. All rats received 0.2 mL of human marrow fat, obtained from surgical waste during arthroplasty, injected into the superior vena cava. Five rats died within seconds of this injection, despite resuscitation efforts. Seven minutes later, we injected an additional 0.1 mL in 6 of the 8 surviving rats. We observed the videomicroscopy for 1 h in all 8 rats. Arterial blood pressure (BP) was continuously measured. No LME were observed in the first 7 min (n = 8); however, within seconds of the additional 0.1 mL injection, mean BP decreased from 79 ± 31 mm Hg to 28 ± 12 mm Hg (n = 6; P < 0.02). Epinephrine and crystalloid infusion increased BP to 161 ± 9 mm Hg and 20–100 LME were seen within 5 min. LME changed shape and fragmentation, erosion, and streaming patterns were noted, with transient arteriolar occlusion (10–220 s). Increasing BP resulted in reperfusion of occluded arterioles. No venous LME were noted. Postmortem, brain and lung LME were found with no patent foramen ovale. This model may be useful in studying cerebral LME.

IMPLICATIONS: Marrow lipid may pass through the lung during orthopedic surgery, creating cerebral lipid microemboli (LME). We created a cranial window in rats to study LME flowing through pial-cortical vessels. Cerebral LME appeared after resuscitation from hypotension and vessel occlusion was transient. This model may be useful in studying cerebral LME.

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