Does estimating the mid-spinal canal depth improve lumbar puncture success rates? a single centre tertiary neonatal care audit

Abstract

Introduction Lumbar puncture (LP) is part of the neonatal septic screen. A cerebro-spinal fluid (CSF) red blood cell (RBC) count of <500 is required to accurately interpret the CSF white cell count.1 Up to 50% of neonatal CSF samples are blood-stained, with increasing incidence in pre-term infants.2 Mid spinal canal depth (MSCD) varies significantly between neonates of different weights.3 In adults ultrasonically determining the MSCD increases success rates.4 A recent study described a formula to estimate MSCD in neonates.3 Aim To determine if calculated MSCD improves LP success rates. Methods A prospective audit. LPs were performed without and with prior calculation of MSCD. In our primary analysis, a successful tap was defined as CSF obtained with <500 RBCs on cell count. Secondary analysis defined success as obtaining a sample suitable for culture. A multiple regression logistic model was used. We report OR (95% CI). Independent variables were gestational age, weight, operator seniority and whether MSCD was estimated. A 5% level of significance was used. Results Results summarized in table 1; OR compare chance of success with new technique to chance of success without. Abstract PF.20 Table 1Details of results by technique and outcome measure MSCD Total LPs Successful LPs Primary outcome OR (95% CI) Samples for culture Secondary outcome OR (95% CI) No 25 13 0.25 (0.06 to 1.05; p=0.06) 22 0.34 (0.07 to 1.61; p=0.17) Yes 19 5 14 MSCD, mid spinal canal depth; LP, lumbar puncture. Discussion Although neither primary nor secondary results were significant, both showed a trend to decreasing success rates. We show no evidence that estimating MSCD improves success rates, but suggest it may be detrimental. The reason for this is unclear. A randomized trial is required.