Cerebral arterial gas embolism in swine. Comparison of two sites for air injection

Cerebral arterial gas embolism is a risk in diving and occurs as a complication in surgery and interventional radiology. Swine models for cerebral arterial gas embolism have been used in the past. However, injection of air into the main artery feeding the pig brain - the ascending pharyngeal artery - might be complicated by the presence of the carotid rete, an arteriolar network at the base of the brain. On the other hand, anastomoses between external and internal carotid territories are present in the pig. In order to determine the most appropriate vessel for air injection, we performed experiments in which air was injected into either the ascending pharyngeal artery or the external carotid artery. We injected 0.25 ml/kg of room air selectively into the ascending pharyngeal artery or the external carotid artery of 35-40 kg Landrace pigs (n=8). We assessed the effect on cerebral metabolism by measuring intracranial pressure, brain oxygen tension and brain glucose and lactate concentrations using cerebral microdialysis. Intracranial pressure and brain oxygen tension changed significantly in both groups, but did not differ between groups. Brain lactate increased significantly more in pigs in which air was injected into the ascending pharyngeal artery. Intracranial pressure, brain oxygen tension and brain lactate correlated after injection of air into the ascending pharyngeal artery, but not after injection into the external carotid artery. Our model is suitable for investigation of cerebral arterial gas embolism. The ascending pharyngeal artery is the most appropriate vessel for air injection.