Brain tissue oxygenation during transnasal endoscopic skull base procedures.

Purpose: We aimed to study brain tissue oxygenation during the period of controlled reduction of arterial blood pressure - a maneuver often used in extended endoscopic skull base surgery for bloodless operative field.

Methods: Intracranial pressure, arterial blood pressure and the resultant cerebral perfusion pressure were measured during extended endoscopic skull base surgery in 5 patients with diagnosed tumors of the skull base and arterial hypertension. Simultaneously, in those patients, we measured partial pressure of oxygen in the brain parenchyma (PbtO).

Results: Values of PbtO lower than 15 mm Hg (risk of brain ischemia) were observed in 3 patients for periods of 40 min, 110 min and 123 min, respectively. In 2 of these patients, no hypotension (mean arterial pressure <65 mm Hg) was necessary for bloodless operative field. Another 2 patients had PbtO above 30 mm Hg at the time when their mean arterial pressure was below 65 mm Hg. The time course of PbtO followed that of cerebral perfusion pressure with a time lag of 40-60 s in all patients.

Conclusion: Moderate reduction of arterial pressure, often used to obtain bloodless operative field during extended endoscopic skull base surgery, may in patients with the medical history of arterial hypertension be associated with critically low values of partial oxygen pressure in brain tissue.