Effects of hyperoxia on brain tissue oxygen tension in cerebral focal lesions.
We evaluated the systemic and cerebral effects induced by an increase to 100% of the inspired oxygen fraction (FiO2) on 20 comatose patients with head injury (9 patients) and SAH (11 patients). Brain tissue oxygen tension (PtiO2) was measured through a Clark electrode inserted in penumbra-like areas. We performed 55 hyperoxia tests by increasing FiO2 from 35 +/- 8% to 100% in one second and calculating the PtiO2 index as: PtiO2 variation from baseline at 1 minute/arterial oxygen tension (PaO2) variation from baseline at 1 minute x 100. One hundred percent FiO2 caused an increase of both arterial (from 139 +/- 28 to 396 +/- 77 mmHg) and cerebral (from 22.6 +/- 14 to 65.4 +/- 60 mmHg) oxygenation after 1 minute. The range of the PtiO2 response was not uniform and two groups were identified. The change was small, 0.8 mmHg/min/100 mmHg PaO2 (+/- 0.7; range 0-2) when mean PtiO2 was 19.7 +/- 13.1 mmHg, while a stronger response, 8 mmHg/min/100 mmHg PaO2 (+/- 5; range 3-18) (p < 0.01) was found when mean PtiO2 was 31.7 +/- 14.3 mmHg. Since O2 diffusion should follow the gas diffusion law, the increase in diffusion distance due to a reduction of capillary density in focal lesions may explain this relationship.
Longhi
L
L
Department of Anesthesia and Intensive Care, Ospedale Maggiore Policlinico IRCCS, Milano, Italy.
Valeriani
V
V
Rossi
S
S
De Marchi
M
M
Egidi
M
M
Stocchetti
N
N
D001921:Brain / Q000378:metabolism*; D001930:Brain Injuries / Q000378:metabolism*; D004563:Electrochemistry; D005260:Female; D007839:Functional Laterality; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism*; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D010313:Partial Pressure; D013345:Subarachnoid Hemorrhage / Q000150:complications / Q000378:metabolism
D010100:Oxygen