DETERMINATION OF DELTOID FAT PAD THICKNESS - IMPLICATIONS FOR NEEDLE LENGTH IN ADULT IMMUNIZATION

Objective.-To measure deltoid fat pad thickness and determine the opti mal needle length for deltoid intramuscular immunization in healthy ad ults. Design, Setting, and Participants.-Prospective study of 220 heal thy health care workers (126 women, 94 men) at the Mayo Medical Center , Rochester, Minn. Main Outcome Measures.-Deltoid fat pad thickness de termined by high-resolution ultrasound scanning, weight, height, and m id-deltoid arm circumference. Results.-We found a highly significant d ifference between women and men in deltoid fat pad thickness, with wom en having a thicker deltoid fat pad (11.7 vs 8.3 mm; P<.001), Women ha d a greater deltoid skin-fold thickness than men (34.7 vs 17.2 mm, P<. 001) and an equal body mass index, According to the ultrasound finding s, a standard 16-mm (5/8-in) needle would not have reached 5 mm into m uscle in 17% (16/94) of men and 48.4% (61/126) of women in this study. Conclusions.-Among healthy adults of the age range we studied, the fo llowing needle lengths appear to be appropriate for true deltoid intra muscular immunization: For men across the weight ranges we studied (59 -118 kg), use of a 25-mm (1-in) needle would result in at least 5 mm o f muscle penetration in all subjects. For women who weighed less than 60 kg, a 16-mm (5/8-in) needle would be sufficient to achieve muscle p enetration of 5 mm. For women between 60 and 90 kg, a 25-mm (1-in) nee dle would be sufficient, and women greater than 90 kg would require a 38-mm (1.5-in) needle to ensure intramuscular administration.