Oxygen delivery and oxygen tension in cerebral tissue during global cerebral ischaemia: a swine model.
Interest in tissue oxygen (PtiO2) monitoring is increasing. However the exact interactions between ptiO2, systemic and cerebral variables are a matter of debate. Particularly, the relationship between ptiO2, cerebral oxygen supply and consumption needs to be clarified. We designed a model to achieve progressive Cerebral Blood Flow (CBF) reduction through 3 steps: 1. baseline, 2. CBF between 50-60% of the baseline, 3. CBF < 30% of the baseline. In 7 pigs, under general anaesthesia, Cerebral Perfusion Pressure (CPP) and CBF were reduced through the infusion of saline in a lateral ventricle. PtiO2 and CBF were monitored respectively through a Clark electrode (Licox, GMS) and laser doppler (Peri-Flux). Blood from superior sagittal sinus and from an arterial line was simultaneously drawn to calculate the artero-venous difference of oxygen (AVDO2). Brain oxygen supply was calculated by multiplying relative CBF change and arterial oxygen content. PtiO2 reflected CBF reductions, as it was 27.95 (+/- 10.15) mmHg during the first stage of intact CBF, declined to 14.77 (+/- 3.58) mmHg during the first CBF reduction, declined to 3.45 (+/- 2.89) mmHg during the second CBF reduction and finally fell to 0 mmHg when CBF was completely abolished. CBF changes were also followed by a decline in O2 supply and a parallel increase in AVDO2.


CONCLUSIONS
This model allows stable and reproducible steps of progressive CBF reduction in which ptiO2 changes can be studied together with oxygen supply and consumption.
Rossi
S
S
Department of Anaesthesia and Intensive Care, Ospedale Maggiore, Policlinico IRCCS, Milano, Italy.
Balestreri
M
M
Spagnoli
D
D
Bellinzona
G
G
Valeriani
V
V
Bruzzone
P
P
Maestri
M
M
Stocchetti
N
N
D000818:Animals; D001921:Brain / Q000098:blood supply / Q000503:physiopathology; D001929:Brain Edema / Q000503:physiopathology*; D002545:Brain Ischemia / Q000503:physiopathology*; D002245:Carbon Dioxide / Q000097:blood; D002534:Hypoxia, Brain / Q000503:physiopathology; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D013552:Swine
D002245:Carbon Dioxide; D010100:Oxygen