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.

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.