The distance from the skin to the subarachnoid space can be predicted in premature and formerpremature infants

PurposeSpinal anesthesia can be technically challenging in young infants. We studied whether the distance between the skin and the lumbar subarachnoid space in premature and former-premature young infants could be predicted prior to lumbar puncture.MethodsThe distance from skin entry point to tip of the spinal needle was measured using a caliper after lumbar spinal anesthesia at the L4–5 interspace. This distance was correlated to the patient’s weight, postconceptual age and lumbar ultrasonographic measurement of the skin-to-subarachnoid space and predictive statistical models were sought.ResultsThirty-five premature or former-premature infants were studied. Three models were examined: all three independent variables, weight and postconceptual age only, and weight only. The model selected contained the weight and postconceptual age, because it had the highest value for adjusted R squared, as well as the lowest value for the mean squared error. Adding the ultrasonic measurement to the model worsened the results. The statistical model that described the depth of the subarachnoid space at the L4–5 level was Y = 13.19 + 0.0026 × W −0.12 × PCA, where Y is the distance (mm) from the skin to the subarachnoid space, W is the patient’s weight (g) and PCA is the postconceptual age (weeks). Adjusted R squared was 0.72, mean square error was 2.63 and P< 10−9.ConclusionThe distance between the skin and the subarachnoid space at the level of L4–5 interspace can be predicted using a statistical model based on the infant’s weight and postconceptual age. Spinal ultrasound has no value in L4–5 subarachnoid space depth prediction.