Experimental investigation of lumbar epidural pressure measurement.

To evaluate the usefulness of lumbar intraspinal epidural pressure (ISEDP) measurements for the estimation of intracranial pressure, we studied the relationship between ISEDP and intracranial epidural pressure (ICEDP) in 25 adult mongrel dogs. ICEDP and ISEDP were measured simultaneously with Gaeltec catheter-tip pressure transducers placed in the parietal epidural space and in the lumbar epidural space. Groups 1 and 2 dogs served as normal cerebrospinal fluid condition models. Group 1 received sequential steady-state normal saline infusions (0.5, 1.0, and 1.5 ml/min) into the cisterna magna. ISEDP and ICEDP measurements exhibited a linear correlation, and ISEDP was 80 to 90% of ICEDP at any pressure level. There was no significant difference in the pressure curves obtained at the different infusion rates. Group 2 dogs were subjected to rapid pressure changes by a cisternal bolus injection. Although compliance calculated from the change in ISEDP was slightly greater than that from ICEDP at resting pressure, the compliance calculated from both ISEDP and ICEDP decreased at 20 and 30 mm Hg of ICEDP and the values became almost equivalent. Groups 3 and 4 dogs were mild and severe experimental subarachnoid models, respectively. The ISEDP and ICEDP measurements also showed a linear correlation; however, ISEDP was about 70% of ICEDP in Group 3 and about 50% of ICEDP in Group 4. Although there are varying degrees of discrepancy between ISEDP and ICEDP in the normal or subnormal pressure range and in the presence of severe spinal block, our findings suggest that ISEDP measurements can be used to estimate intracranial pressure in a clinical practice.