Is There Still Any Indication for Application of Volatile Anesthetics During Induction of Hypotension in Neurosurgery?
Deliberately induced hypotension is quite a useful and widespread technique in neuroanesthesia. It is widely used in the surgical treatment of arterial aneurysms and arteriovenous malformations, sometimes also in cases of meningeoms or other vascularized tumors. The decision to use induced hypotension is a surgical one, the degree of hypotension should be agreed on jointly by the neurosurgeon and anesthetist, each putting forward his arguments. The importance of induced hypotension is well documented: diminished blood loss and reduced brain swelling and intracranial pressure in the presence of impaired autoregulation. Hypotension is the method of preference in aneurysm surgery. It’s influence on the incidence of rupture, however, is not as well established as one might expect from the wide application of this technique. Reports on the correlation between systemic arterial pressure and the incidence of rupture of an aneurysm are somewhat conflicting (Gordon 1975). Some other factors such as configuration of the aneurysm sack, condition of the cerebral arteries and time of foregoing bleeding also seem to be involved. Very often it is not the aneurysm itself that ruptures but a surrounding vessel. The neurosurgeon expects that hypotension produces a somewhat softer aneurysmal sack, and that the blood vessels in the vicinity of the aneurysm are less tortuous. The discussion about the adequate level of hypotension also contributes to this uncertainty: some hospitals use very low limits, e.g. 65 mm Hg systolic pressure or less (Hunter, 1975; Niedermeyer, 1977), other hospitals work quite successfully with higher pressure limits. We lower BP only in a moderate way: at the moment of clipping the aneurysm or wrapping it in a piece of muscle BP is held at about 80 mm Hg systolic pressure (a mean of 60). The safe individual level, however, is chosen during the surgical procedure and depends on well-known factors such as the state of the cardiovascular system, location of the aneurysm and cerebral perfusion.
KeywordsIntracranial Pressure Sodium Nitroprusside Cerebral Perfusion Pressure Cerebral Blood Volume Volatile Anesthetic
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