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

[La distance entre la peau et l’espace sous-arachnoïdien peut être prédite chez les enfants prématurés et les anciens prématurés]

Ze’ev Shenkman, MD^*, Valeria Rathaus, MD, Robert Jedeikin, BSc MB CHB FFA^*, Osnat Konen, MD, David Hoppenstein, MB BCH DA(SA)^*, Mitchell Snyder, PhD and Enrique Freud, MD

^* From the Departments of Anesthesia and Critical Care Medicine,
Radiology, and
Pediatric Surgery, Meir Hospital, Kfar Saba; and the Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv; and the
Department of Mathematics and Statistics, Bar Ilan University, Ramat-Gan, Israel.

Address correspondence to: Dr. Ze’ev Shenkman, Department of Anesthesia and Intensive Care, Meir Hospital, Tshernichovsky Street, Kfar Saba 44281, Israel. Phone: 972-9-747-1545; Fax: 972-9-747-1298; E-mail: shlomsh1{at}netvision.net.il

Purpose: Spinal 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.

Methods: The 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.

Results: Thirty-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 x W - 0.12 x 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.

Conclusion: The 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.