Estimation of Anterolateral Thigh Muscle Thickness by High Frequency Sonography in Newborns to Ensure Safe Intramuscular Injections

Introduction: Use of same length needle for intramuscularly administered vaccines can cause under and over penetration among newborns due to varying body weights and fat/muscle thickness. The injection technique and needle size both determine how deep a substance is injected. Injection technique involves stretching the skin flat before inserting the needle or pinching a fold of skin before injection, which may necessitate the use of longer needles. Objectives: 1. To measure the depth of subcutaneous tissue layer (STMD) and skin to bone distance (STBD) and muscle thickness (STBD-STMD) over the anterolateral thigh of newborns using high-frequency sonography and suggest appropriate needle length for safe intramuscular injections. 2. To estimate the risk of over penetration and under penetration with standard size needle being used in newborn vaccinations and intramuscular injections. Methodology: A cross-sectional analytical study was done among 150 newborns in four different weight bands of <7 days of life using convenient sampling at a tertiary teaching institute People’s College of Medical Sciences and Research Centre Bhopal Madhya Pradesh in central part of India. Those newborns who were sick and admitted to the NICU, had limb anomalies, or whose parents did not provide consent were excluded from the study. Results: Mean STBD was 14.69 mm, mean STMD was 4.01mm, and mean muscle thickness was 10.71mm. Significant correlations found between weight, STBD, STMD, and muscle thickness. Under penetration and over-penetration risk with 16mm and 25mm needles varied by weight band. Based on needle penetration, with results showing that none of the subjects (0%) experienced under-penetration. However, a significant proportion of subjects experienced over-penetration, with 107 subjects (71.33%) experiencing over-penetration using a 16mm needle and all 150 subjects (100%) experiencing over-penetration using a 25mm needle at a 90-degree angle to the skin surface. Conclusion: Customized needle length based on newborn weight is necessary to ensure safe intramuscular injections. This study provides estimates of thigh muscle thickness to inform appropriate needle size selection. Further large-scale studies are needed to inform future recommendations.