Comparison of Bolus and Constant Infusion Techniques for Determining the Resistance of the Absorption of CSF

Abstract

Two techniques are generally used to determine the resistance to the absorption of CSF (Ro) in clinical settings: constant infusion techniques (Katzman and Hussey 1970) and the bolus injection utilizing the Pressure Volume Index (Marmarou et al. 1976). In previous communications this laboratory measured Ro using the bolus injection technique in normal patients. These studies showed that Ro in normal patients was 2.8 mm Hg/ml/min which differed from the accepted normal range of Ro of 5–9 mm Hg/ml/min reported by others using infusion techniques (Ekstedt 1978). This discrepancy between the two techniques has led some to question the validity of the bolus injection technique in clinical settings (Sullivan et al. 1978). However, the simpliCity of the bolus injection technique and its utility in cases where steady State dynamics are precarious makes it a useful clinical tool. For this reason we have been reluctant to abandon this rapid method for determining Ro and have attempted to understand the differences between the two methods of determining Ro by the following experiments.