Effect of arterial PCO₂ on local HbO₂ and relative Hb concentration in the human brain-a study with the Erlangen micro-lightguide spectrophotometer (EMPHO)

Intraoperative investigations of local intracapillary haemoglobin oxygenation have been performed in 5 patients during neurosurgical interventions using the Erlangen micro-lightguide spectrophotometer (EMPHO). As the measurements can be performed in a very short period of time (approximately 60 s) the EMPHO enables rapid monitoring of local haemoglobin oxygenation in the brain. All patients received thiopental anaesthesia and were mechanically ventilated. The local measurements were performed during normoventilation (arterial PCO₂-PaCO₂ 37.8+or-0.7 mm Hg) and hyperventilation (PaCO₂ 31+or-0.5 mm Hg). Hyperventilation caused a decrease in the mean SO₂ from 47.8% to 41.1%. The number of SO₂ values <50% increased from 58% to 77.8%. The possible significance of the low local SO₂ values is discussed.