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Physiological changes during acute obstruction of the superior vena cava, azygos, and internal thoracic veins in dogs.

PURPOSE
In the surgery for superior vena cava (SVC) reconstruction, the cross-clamping of the SVC may cause brain damage. Experimental study was performed to clarify the safe limit of the clamping time and the appropriate monitoring method during the surgery.


METHODS
In anesthetized dogs, the internal thoracic and azygos veins were ligated, and the SVC was clamped for 120 min. Arterial blood pressure, intracranial venous pressure, regional cerebral blood flow, and electroencephalogram were monitored in six dogs. Somatosensory evoked potentials were recorded in one other dog, and in another dog postoperative neurological changes were evaluated for 3 weeks. The brains of the dogs were subjected to the histological examination including tetrazolium stain.


RESULTS
The arterial blood pressure decreased and the intracranial venous pressure increased during the clamping. Oscillation of the pressure was noted at 45 to 74 min after clamping. The regional cerebral blood flow was 57.4 ml/100 g/min on average before clamping, and decreased to 15.5 ml/100 g/min at 105 min after clamping. The electroencephalogram demonstrated no pronounced change during clamping, but the amplitude of the somatosensory evoked potentials decreased and the latency was prolonged during clamping. No neurological defect was noted in the dog observed for 3 weeks. All areas of the brain showed staining with the tetrazolium, indicating intact mitochondria. The microscopic findings for the brains included no marked changes.


CONCLUSION
The SVC clamping for 120 min was tolerated by the dogs, and the most reliable monitoring method was concluded to be the recording of somatosensory evoked potentials.