A Randomized Study to Validate a Midspinal Canal Depth Nomogram in Neonates

Abstract

Improving the accuracy of lumbar puncture (LP) in neonates should reduce the incidence of hemorrhagic contamination of cerebrospinal fluid (CSF) samples. We have previously demonstrated a linear correlation between neonatal weight and midspinal canal depth (MSCD), generating a nomogram and simple formula to allow MSCD estimation. In this study, we attempted to validate the nomogram by improving the quality of the CSF samples obtained. We consecutively randomized 99 infants in whom LP was clinically warranted to receive either a standard, "blind" ( N = 48) or "measured" ( N = 51) procedure. If allocated to the measured technique, the operator marked the LP needle with a Steri-Strip (TM) at the predicted depth of insertion (i.e., MSCD) derived from the weight-based nomogram. CSF samples were classified as clear (<500 red blood cells [rbc]/mL), mildly bloodstained (500 to 10,000 rbc/mL), heavily bloodstained (>10,000 rbc/mL or clotted), or failed procedures. Clear and mildly bloodstained LPs were "successful." Heavily bloodstained or failed procedures were considered "unsuccessful." We also recorded the number of attempts required to obtain a CSF sample. The overall success rate (<or=10,000 rbc/mL) in this study was 56/99 (56.6%). There was no significant difference in success rates in the measured group (32/51, 62.7%) when compared with the blind group (24/48, 50%; chi-square = 1.143, P = 0.072). Success rates were higher for less experienced (Resident) doctors (62.8% versus 45.0%; chi-square = 0.51, P = 0.047) and in the premature (28 to 37 weeks' gestation) group (80.0% versus 37.5%; chi-square = 2.66, P = 0.007). Overall success rates dropped with each consecutive LP attempt (first, 39/52, 75.0%; second, 11/22, 50.0%; third, 5/16, 31.3%), and no fourth or fifth attempts were successful. The nomogram did not significantly improve OVERALL LP success rates in this cohort of patients. However, using the measured technique, LPs performed by less experienced doctors and those performed in the premature (28 to 37 weeks' gestation) group were more successful than those performed using the blind technique. The measured technique has the potential to be a useful tool for doctors in the early stages of their training. Furthermore, we advocate no more than three LP attempts in this population to avoid prolonging discomfort and increasing the risk of physiological compromise to the neonate.