Comparison of the G and V methods for ventrogluteal site identification: Muscle and subcutaneous fat thicknesses and considerations for successful intramuscular injection

Abstract

The ventrogluteal site is increasingly recommended for long-acting antipsychotic intramuscular injections; however, it remains infrequently utilized due to nurses' lack of confidence in site identification. The more recent G (geometric) method of ventrogluteal site identification is less subjective and likely more reliable than the V method for successful intramuscular injection outcomes. Knowledge of muscle and subcutaneous fat thicknesses, and the influence of sex and anthropometry on theoretical injection outcome, is necessary to support evidence-based use of the ventrogluteal site. In the presents study, we compared the V and G methods for injection site subcutaneous fat, muscle, and total tissue thicknesses, and theoretical injection outcome (bone injury, intramuscular or subcutaneous), and determined anthropometric predictors of injection outcome. Subcutaneous fat and muscle thicknesses were measured via ultrasound, bilaterally at V and G method sites (28 males, 32 females). Muscle and total tissue were significantly thicker, and successful intramuscular injection significantly more likely, using the G versus V method (75% versus 57%). Females had significantly thicker subcutaneous fat than males at both sites. Even using the G method, 92% of males but only 59% of females, would have a successful intramuscular injection, with remaining females at risk of bone injury (16%) or subcutaneous injection (25%). The G method site is more reliable for successful intramuscular injection, with less risk of bone injury than the V method site. Appropriate needle-length selection is essential for females with a body mass index (BMI) <23kgm-2 and weight <60kg (to avoid bone injury), and BMI >30kgm-2 and hip >90cm (to avoid subcutaneous injection).