Abstract

Cerebrospinal fluid (CSF) pressure measurements in animals demonstrated an increase in cardiorespiratory pressure oscillations after administration of local anesthetic into the CSF. This increase was still present even when CSF pressure had returned to the preinjection level. There are two possible explanations for this phenomenon: impairment of cerebrospinal blood flow autoregulation and/or alteration in the pressure-volume relationships within the CSF. In six goats a 17-gauge cannula was inserted permanently into the third ventricle as a future pressure measurement device. Cerebrospinal blood flow autoregulation was tested by measuring and comparing the pressure increases respectively of the mean CSF pressure in the third ventricle and the mean systemic arterial blood pressure after adminstration of 4 mg of metaraminol intravenously. During spinal anesthesia with 10 mg of tetracaine in 12.5% glucose solution, 4 mg of intravenous metaraminol was administered. The increase in the mean CSF pressure in the third ventricle relative to the simultaneous mean blood pressure increase during spinal anesthesia due to the metaraminol was significantly higher ( P < 0.001) than before spinal anesthesia. This suggests impairment of cerebrospinal blood flow autoregulation. Pressure-volume relationship was tested before and during spinal anesthesia by measuring the pressure volume index (PVI). The PVI remained unchanged. Spinal anesthesia in goats with 10 mg of tetracaine in 12.5% glucose results in impairment of cerebrospinal blood flow autoregulation, whereas the pressure volume relationship remains unchanged.