Is the intravenous giving set a reliable alternative to the spinal manometer in measuring cerebrospinal fluid opening pressure?

Background. Measurement of the cerebrospinal fluid (CSF) opening pressure (OP) during lumbar puncture (LP) should be routine practice. In resource-limited centres, spinal manometers are seldom available and alternative procedures to measure CSF OP are undertaken. Objectives. To investigate whether the intravenous giving set (IVGS) with a measuring tape is a reliable alternative to the spinal manometer. Methods. One hundred patients requiring CM; examination by LP were consecutively recruited in the Department of Medicine at Edendale Hospital, Pietermaritzburg, South Africa. A three-way stopcock was attached to the end of a 22G spinal needle and the IVGS and spinal manometer were attached to the other two openings of the stopcock. CSF OP was consecutively recorded between the two techniques with 50 patients in each group. Results. The mean (standard deviation (SD)) CSF OP of the 100 patients was 22.7 (10.0) cm CM; measured with the manometer v. 16.2 (9.3) cm CSF measured with the IVGS (p<0.001). Subgroup analysis showed similarly significant findings of consistently lower CSF OP with the IVGS, regardless of whether the IVGS reading was done first or second. The manometer detected 34 cases of elevated CSF OP of >25 cm CSF, hut the IVGS detected 11 cases only (p<0.001, McNeniar's chi(2) test). Similar differences were noted for the subgroups of manometer first and IVGS first. Despite this, linear correlation showed very good correlation (r=0.78) and a 75% agreement between the two techniques. The relationship between the manometer reading and the IVGS reading was M = 0.85V + 8.9 in cm CSF, where M was the manometer reading and V the IVGS reading. Conclusions. The IVGS consistently underestimated the CSF OP against the tried-and-tested spinal manometer, which should be the preferred method of measuring CSF OP. Based on the equation that describes the relationship between the spinal manometer and IVGS reading, the upper limit of normal CSF OP of 25 cm CSF on the manometer is equivalent to 19 cm CSF on the IVGS.