In normal perfusion pressure breakthrough (NPPB) it is assumed that following arteriovenous malformation (AVM) resection, vasoparalysis persists in the margins of the lesion and that a sudden increase in cerebral blood flow (CBF) after AVM exclusion leads to brain swelling and postsurgical complications. However, the pathophysiology NPPB remains controversial.
The aim of our study was to investigate the oxygenation status in tissue surrounding AVMs and in the distant brain using intraoperative monitoring of cerebral partial pressure of oxygen (PtiO2) to achieve a better understanding of NPPB pathophysiology.
Patients with supratentorial AVMs were monitored intraoperatively using 2 polarographic Clark-type electrodes. To establish reference values, we also studied PtiO2 in a group of patients who underwent surgery to treat incidental aneurysms.
Twenty-two patients with supratentorial AVMs and 16 patients with incidentally found aneurysms were included. Hypoxic pattern was defined as PtiO2≤15 mm Hg and/or PtiO2/PaO2 ratio ≤0.10. Tissue hypoxia was detected in 63.6% of the catheters placed in the perinidal area and in 43.8% of catheters placed in a distant area. AVM excision significantly improved oxygenation both around the AVM and in the distant area.
The PtiO2/PaO2 ratio is a better indicator than absolute PtiO2 in detecting tissue hypoxia in mechanically ventilated patients. Intraoperative monitoring showed tissue hypoxia in the margins of AVMs and in the distant ipsilateral brain as the most common finding. Surgical removal of AVMs induces a significant improvement in the oxygenation status in both areas.