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Effect of ligation on internal carotid artery blood pressure in horses
D E Freeman1, W J Donawick, L V Klein
1Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square.
Insights
Internal carotid artery ligation in horses did not significantly alter blood pressure due to collateral circulation. This suggests ligation alone may not prevent hemorrhage in guttural pouch mycosis until thrombosis occurs.
Area of Science:
- Veterinary Surgery
- Equine Internal Medicine
- Cerebrovascular Anatomy
Background:
- Guttural pouch mycosis can cause severe internal carotid artery hemorrhage in horses.
- Surgical ligation is a common treatment, but its efficacy in maintaining adequate blood pressure is debated.
- Understanding collateral circulation is crucial for assessing ligation's effectiveness.
Purpose of the Study:
- To evaluate the immediate and short-term effects of internal carotid artery ligation on blood pressure in horses.
- To identify potential collateral pathways that may maintain cerebral perfusion after ligation.
- To determine the clinical implications of ligation for managing hemorrhage associated with guttural pouch mycosis.
Main Methods:
- Nine anesthetized horses underwent internal carotid artery catheterization and continuous blood pressure monitoring.
- Ligation of the internal carotid artery was performed in six horses; a loose ligature was used in three horses that recovered from anesthesia.
- Post-ligation blood pressure was recorded, and cerebral arterial anatomy was examined post-mortem.
Main Results:
- Blood pressure in the internal carotid arteries remained unchanged immediately after ligation.
- Collateral channels, including the caudal intercarotid artery and cerebral arterial circle, were subjectively identified as potential pressure maintainers.
- No significant immediate hemodynamic changes were observed following acute ligation.
Conclusions:
- Ligation of the equine internal carotid artery does not acutely prevent hemorrhage.
- Effective prevention of hemorrhage requires thrombosis of the internal carotid artery distal to the lesion site.
- This finding has implications for surgical management strategies in horses with guttural pouch mycosis.
Abstract:
The effect of a single ligature on back pressure in the internal carotid artery was studied in nine horses. In six anesthetized horses, one internal carotid artery was catheterized 2 cm from its origin and blood pressure was recorded continuously. Then the artery was ligated, pressure was recorded again, and the horses were euthanatized. In another three anesthetized horses, indwelling catheters were placed in both internal carotid arteries and a loose ligature was placed proximal to one catheter. After horses recovered from anesthesia, the ligature was tied and blood pressure was recorded in both arteries on that day and 3 days later, then these horses were euthanatized. The anatomy of the cerebral arteries was examined in all nine horses. Blood pressure in the internal carotid arteries did not change after ligation. Subjectively, collateral channels considered most likely to maintain blood pressure in the ligated internal carotid artery were the caudal intercarotid artery and the cerebral arterial circle. We concluded that ligation of the internal carotid artery would not prevent severe hemorrhage from the internal carotid artery in horses with guttural pouch mycosis until the ligated artery thrombosed to the level of the lesion.