Optimum needle length for DPT inoculation of indian infants

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Abstract
Correct placement of the injected DPT vaccine into the deep muscular layers decreases the local reactions, including the sterile abscess formation. However, recommendations on size of the needle to be used and the angle of injection are not easily available, are not uniform and are based on case reports. The only study based on scientific data of ultra-sonographic measurement of fat layer and muscle layer thickness of thigh of only 24 infants of 4 months age covers only American children. (Hick et al,Pediatrics 1989; 84: 136–37). In the present study, we have produced similar data on 215 Indian children belonging to all those age groups in which DPT vaccinations are given. Mean thickness of skin + fat layer in the middle one-third of the anterolateral aspect of thigh was 1.03±0.23 cm, 1.04±0.21 cm, 0.95±0.19 cm and 1.06±0.27 cm in the age groups of 6–12 weeks (Groups I), 13–18 weeks (Group II), 19–24 weeks (Groups III) and 18±1 month (Group IV) respectively. These age groups correspond to the timings of first 3 primary doses and the first booster dose of the DPT vaccine in our immunization clinic. Mean thickness of all the soft tissues together at the same site were 1.87±0.35, 2.17±0.38, 2.07±0.39 and 2.07±0.26 cm respectively for the groups I to IV. Calculations with 25, 20 and 15 mm long needles injected at an angle of 45° and 90° to the thigh surface show that success rates would be best with 15 mm needle injected at 90° angle (actual depth of penetration 15 mm) or a 20 mm needle injected at 45° angle (actual depth of penetration 14.1 mm). Success rates in the four groups with 15 mm needle at 90° angle would be 88.5%, 93.2%, 90.5% and 90.5% respectively, and with 20 mm needle at 45° angle would be 92.3%, 93.1%, 90.5% and 90.5% respectively. Thus, 20 mm needle at 45° or 15 mm needle at 90° inserted to their full length at the mid anterolateral thigh of the child are recommended for field trials to confirm that they indeed reduce the incidence of subcutaneous sterile abscess formation and other local reactions.