Ultrasonographic Mapping of the Median Cubital Vein: Tourniquet-Induced Changes and Demographic Variation Relevant to Safe Venipuncture

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Purpose The median cubital vein (MCV) is frequently used for venipuncture, but anatomical variation and tourniquet application can alter its relationship to the brachial artery and median nerve. This study used ultrasonography to characterise these effects across sex and ethnicity. Methods Sixty healthy adults (28 men, 32 women; aged 18–46 years) from South Asian, Middle Eastern and North African (MENA), Sub-Saharan African (SSA), and other backgrounds underwent ultrasonographic assessment (GE LOGIQ system, 12 MHz linear transducer) of MCV diameter and its distance from the brachial artery, median nerve, and skin surface, before and after tourniquet application. Results Tourniquet application significantly increased MCV diameter and its distance from the brachial artery and median nerve (p<0.05), with no significant change in skin depth. MCV diameter did not differ significantly by sex; however, after tourniquet application, males showed significantly greater distance from the brachial artery and median nerve than females (p<0.05). MCV diameter differed significantly across ethnic groups after tourniquet application (one-way ANOVA, p=0.037), with MENA participants having the largest and SSA participants the smallest mean diameter; no other parameter differed by ethnicity. Anatomical variants included MCV absence (8.3%), MCV coursing deep to the bicipital aponeurosis (3.6% of visualized veins), and the brachial artery or median nerve lying directly beneath the MCV (5.5%). Conclusion Tourniquet application, sex, and ethnicity significantly influence MCV anatomy and its neurovascular relationships. Ultrasonography reliably detects clinically important variants that could compromise venipuncture safety, supporting its selective use before vascular access in high-risk patients.