Prospective study on ultrasonographic measurement of the spinal canal depth in very low birth weight infants

Abstract

Background: Lumbar punctures (LP) in very low birth weight (VLBW) infants often have low success rates. Point-of-care ultrasound (POCUS)-based spinal canal depth (SCD) measurements may provide better outcomes.

Aim: To provide POCUS-based SCD measurement values for VLBW infants using different calculation methods at the L4/5 and L3/4 levels.

Methods: This prospective observational study involved 31 VLBW infants in the neonatal intensive care unit at Women's Wellness and Research Center, Doha, Qatar, from March 2022 to September 2023. The outcome measures included anterior (ASCD), mid (MSCD) and posterior spinal canal depth (PSCD) measurements. The study compared results from different calculation methods at the L4/5 and L3/4 levels.

Results: A total of 63 ultrasound examinations were performed on 31 infants. The median gestational age was 25.0 weeks (IQR 24-27), with a birth weight of 817.9±170.2 g and a birth height of 31.6±2.8 cm. The MSCD at L4/5 was 7.1±0.5 mm and 6.9±0.5 mm at L3/4, with a mean difference (MD) of 0.20 (95% CI 0.15 to 0.24; p<0.001). The mean SC anteroposterior diameter at L4/5 was 3.8 mm versus 4.2 mm at L3/4 (MD -0.334, 95% CI -0.45 to 0.22; p<0.001). Weight-based and body surface area (BSA) calculations correlated best with MSCD at both levels. The MSCD in millimetres was determined by the equations 2×weight (kg)+6 (R²=0.71) at L4/5 and (R²=0.70) at L3/4 and 25×BSA (m²)+5 (R²=0.71) at L4/5 and (R²=0.73) at L3/4 levels. Moreover, body weight and BSA showed a slightly stronger correlation with ASCD measurements compared with PSCD. All SCD measurements demonstrated a poor linear correlation with body length (cm) and body mass index (kg/m²).

Conclusion: This study offers reference data for POCUS-based SCD measurements in VLBW infants, demonstrating that body weight and BSA effectively predict SCD. These findings could enhance the accuracy of LPs in this population when ultrasound guidance is unavailable, supporting personalised care.

Keywords: Data Collection; Infant; Neonatology; Qualitative research; Technology.

Figure 1. Schematic and ultrasound representation of spinal canal depth measurements. (A) Point-of-care ultrasound (POCUS) image demonstrating the actual measurements of posterior spinal canal depth (PSCD) and anterior spinal canal depth (ASCD) at the L4/L5 (Lines 1 and 2, respectively) and L3/L4 (Lines 3 and 4, respectively) vertebral levels. The mid-spinal canal depth (MSCD) was determined as the average of PSCD and ASCD (ASCD + PSCD)/2. (B) Schematic diagram illustrating the anatomical relationships of the PSCD (short dotted yellow line) and ASCD (long dotted yellow line) at both L3/L4 and L4/L5 levels. The solid white line represents the anteroposterior diameter of the spinal canal (SC). Key anatomical structures are labeled, including the spinal canal and cerebrospinal fluid (CSF) (indicated by asterisks), conus medullaris (CM), cauda equina (CE), filar cyst (FC), and spinous process (SP).

Figure 2. Scatterplot of spinal canal depth measurement values at L4/5 levels with body weight (kg). ASCD, anterior spinal canal depth; MSCD, mid spinal canal depth; PSCD, posterior spinal canal depth.

Figure 3. Scatterplot of spinal canal depth measurement values at L4/5 levels with body surface area (m²). ASCD, anterior spinal canal depth; MSCD, mid spinal canal depth; PSCD, posterior spinal canal depth.

Figure 4. Scatterplot of spinal canal depth measurement values at L3/4 levels with body weight (kg). ASCD, anterior spinal canal depth; MSCD, mid spinal canal depth; PSCD, posterior spinal canal depth.

Figure 5. Scatterplot of spinal canal depth measurement values at L3/4 levels with body surface area (m²). ASCD, anterior spinal canal depth; MSCD, mid spinal canal depth; PSCD, posterior spinal canal depth.