Abstract
The effects of elevated intracranial pressure (ICP) on intracellular oxygenation and cerebrocortical blood volume (CBV) were studied in rabbits. Intracellular oxygen (O2) concentration was assessed as the level of pyridine nucleotide concentration ([NADH])) oxidation/reduction balance and relative cerebrocortical blood volume (CBV) were measured with a fibreoptic fluororeflectometer probe placed on the cerebrocortical surface. Experiments were conducted in six urethane anaesthetized, normocarbic animals at different fractions of inspired O2 (FlC2). During gradual increases in ICP, [NADH] began to increase (representing decreased intracellular mitochondrial PO2)for all values of FlO2 as ICP exceeded a threshold of 18± 2.2 cmH2O (P < 0.05). The decline in intracellular oxygenation with elevated ICP was inversely related to FlO2 (P < 0.05). With ICP greater than 18 ± 2.2 cmH2O, intracellular mitochondrial oxygenation showed an improvement between an FlO2 of 0.21 and 0.5 (P < 0.05) but increasing FlO2 from 0.5 to 1.0 resulted in no statistically significant improvement in tissue redox balance. The CBV, largely representing tissue capillary blood, increased when ICP reached greater 18 ± 1.2 cmH2O probably reflecting local autoregulation or venous distension (P < 0.05). However, above 30 ± 1.1 cmH2O, CBV decreased (P < 0.05). The results demonstrate the interdependence of inspired oxygen concentration, elevated ICP, and brain intracellular oxygenation, and suggest that brain oxygen utilization deteriorates above an ICP of about 18 cmH2O.
Résumé
Les effets dune pression intracrdnienne elevee (ICP) sur l’oxygenation intracellulaire et le volume sanguin cérébrocortical (CBV) on été étudiés chez les lapins. La concentration en oxygene intracellulaire (O2) a été évaluée alors que le niveau de la balance oxidation/réduction de la concentration de nucleotide pyridine ([NADH]) et le volume sanguin cérébrocortical relatif (CBV) étaient mesurés à l’aide de la sonde d’un fluororéflectomètre à fibre optique placée à la surface cérébrocorticale. Les expériences ont été menées chez six animaux normocarbiques anesthésiés à iurethane et à différentes fractions d’oxygène inspiré (FlO2). Lors des augmentations graduelles de l’ICP, la [NADH] a augmenté pour toutes les valeurs de FlO2 lorsque l’ICP dépassait un seuil de 18 ± 2.2 cm H2O (representant une diminution de la PO2 mitochondriale intracellulaire) (P < 0.05). La diminution de l’oxygénation intracellulaire en relation avec une ICP élevée était inversement proportionnelle à la FlO2 (P < 0.05). Avec une ICP plus grande que 18 ± 2.2 cm H2O, l’oxygénation intracellulaire mitochondriale montrait une amelioration entre une FlO2 de 0.21 et de 0.5 (P < 0.05) mais l’augmentation de la FlO2 0.5 a 1.0 ne provoquait pas une amelioration statistiquement significative de la balance tissulaire réduction-oxydation. La CBV, representant principalement le sang capillaire tissulaire, augmentait lorsque l’ICP atteignait des valeurs de plus de 18 ± 1.2 cm H2O, probablement secondaire à l’autorégulation locale ou à une distension veineuse (P < 0.05). Cependant, à des valeurs au-dessus de 30 ± 1.1 cm H2O, la CBV diminuait (P < 0.05). Les resultats demontrent l’étroite dépendance entre la concentration d’oxygéne inspirée, l’augmentation de l’ICP et l’oxygénation cérébrate intracellulaire, et suggère que l’utilisation cerebrale en oxygène se détériore à des valeurs de l’ICP denviron 18 cm H2O.
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Abbreviations
- CBF:
-
cerebral blood flow
- CBV:
-
cerebrocortical blood volume
- CPP:
-
cerebral perfusion pressure
- CSF:
-
cerebral spinal fluid
- CF:
-
corrected fluorescence
- CVP:
-
central venous pressure
- FlO2 :
-
fraction of inspired oxygen
- ICP:
-
intracranial pressure
- MAP:
-
mean arterial pressure
- [NADH]:
-
pyridine nucleotide, reduced concentration
- [NAD+]:
-
pyridine nucleotide, oxidized concentration
- PaCO2 :
-
arterial carbon dioxide partial pressure
- PaO2 :
-
arterial oxygen partial pressure
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Bissonnette, B., Bidder, P.E., Gregory, G.A. et al. Intracranial pressure and brain redox balance in rabbits. Can J Anaesth 38, 654–659 (1991). https://doi.org/10.1007/BF03008204
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DOI: https://doi.org/10.1007/BF03008204