Intracranial Hypertension

Chapter 100 Intracranial Hypertension





PHYSIOLOGY OF INTRACRANIAL PRESSURE







INTRACRANIAL PRESSURE


Intracranial pressure ICP is the pressure inside the cranial vault exerted by the tissues and fluids against the encasing bone. Normal ICP in the dog is 5 to 12 mm Hg, similar to that of humans for whom 20 mm Hg is an arbitrary upper limit beyond which treatment for ICH may be instituted1,3 (see Chapter 209, Intracranial Pressure Monitoring). The upper limit of ICP above which treatment is indicated for ICH has not been defined in dogs and cats. It seems reasonable to utilize the human guidelines for ICH until species-specific information is available.



Homeostatic Responses of the Brain


Three primary homeostatic mechanisms exist to maintain ICP within a range where the brain is functional. These include volume buffering, autoregulation, and the Cushing response.1,4-6



Volume Buffering


The brain is relatively noncompressible and is encased in bone, causing the volume of the intracranial contents to be fixed. Increase in the volume of one component requires a compensatory decrease in one or more of the others if ICP is to remain unchanged (Monroe-Kellie doctrine). Sources of added volume include hemorrhage, CSF accumulation, vascular congestion, cerebral edema, and decreases in venous outflow (Figure 100-1). Immediate volume buffering responses, specifically displacement of blood and CSF extracranially, are reflected by the pressure-volume curve that relates the temporal change in ICP to expanding intracranial volume.




Autoregulatory Mechanisms




Chemical Autoregulation


Chemical regulation of cerebral vascular resistance is influenced by three factors: partial pressure of arterial carbon dioxide (PaCO2), partial pressure of arterial oxygen (PaO2), and cerebral metabolic rate of oxygen consumption.1,4,5







Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Intracranial Hypertension
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