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Published on: February 17, 2013
Dynamic characteristics of cerebral lipid microemboli: videomicroscopy studies in rats
Robert J Byrick1, J Colin Kay, C David Mazer
1*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.
Unlabelled:
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.
Insights
Lipid microemboli from bone marrow can cause brain issues after surgery. This rat study shows these microemboli appear after blood pressure drops and can temporarily block brain vessels.
Area of Science:
- Neuroscience
- Cardiovascular Science
- Surgical Research
Background:
- Cerebral lipid microemboli (LME) are implicated in postoperative cognitive dysfunction following orthopedic and cardiovascular procedures.
- Understanding the mechanisms of LME formation and their impact on cerebral circulation is crucial for patient outcomes.
Purpose of the Study:
- To investigate the behavior of lipid microemboli in cerebral circulation using an in vivo rat model.
- To characterize the dynamic changes and effects of LME on pial-cortical vessels.
Main Methods:
- Anesthetized rats underwent cranial window surgery for direct videomicroscopy of pial-cortical vessels.
- Human marrow fat was injected intravenously, and arterial blood pressure was continuously monitored.
- Orthogonal polarization spectral imaging videomicroscopy was used to observe LME dynamics for 1 hour.
Main Results:
- Injection of marrow fat led to significant hypotension and the appearance of cerebral LME.
- LME exhibited dynamic changes including fragmentation and streaming, causing transient arteriolar occlusion.
- Increasing blood pressure promoted reperfusion of occluded arterioles, and no venous LME were observed.
Conclusions:
- Marrow lipids can form cerebral lipid microemboli, potentially contributing to neurological deficits after surgery.
- The developed rat model provides a platform for studying cerebral LME and their transient effects on brain vasculature.
- Transient vessel occlusion by LME can be reversed with increased blood pressure, suggesting potential therapeutic targets.
