Needle Length and Injection Technique for Efficient Intramuscular Vaccine Delivery in Infants and Children Evaluated Through an Ultrasonographic Determination of Subcutaneous and Muscle Layer Thickness
The relationship between resulting reactogenicity and immunogenicity with route and site of vaccine injection is well documented.1-5 Preference for intramuscular injection is given for aluminum-adsorbed vaccines (eg, diphtheria, tetanus, pertussis, and inactivated poliovirus [DTP-IPV], hepatitis A, and hepatitis B vaccines), because superficial administration leads to increased incidence of local reactions.6 A better immune response for intramuscular compared with subcutaneous injection has been seen with several vaccines, such as the hepatitis B,1,5 rabies,3 and influenza2vaccines. Both the injection technique and the needle length are crucial for ensuring proper intramuscular delivery and thus are directly related to vaccine safety and immuno-genicity.
Guidelines concerning the choice of the injection technique and needle length have been presented. Two injection techniques are currently recommended. The first, widely used in the United States, requires bunching the thigh muscle at the injection site to increase muscle mass and to minimize the chance of striking bone.6 The second, recommended by the World Health Organization (WHO), suggests stretching the skin flat between the finger and thumb, and pushing the needle down at a 90° angle through the skin.7 With respect to needle length, both the WHO and the Committee on Infectious Diseases of the American Academy of Pediatrics support the use of 7/8-inch (22-mm) or longer needles for intramuscular delivery.7,8
Some unidose vaccines are supplied in disposable syringes, equipped with 5/8-inch (16-mm) sealed needles that have been designed to provide an efficient, precise, and user-friendly tool for intramuscular injection. Nevertheless, the adequacy of this shorter needle (compared with the 7/8-inch needle) has been questioned.6 To determine the optimum needle size for intramuscular injection and eventually to make a correlation between needle length and appropriate injection technique, one must have accurate data on the morphometric characteristics of healthy people with respect to subcutaneous tissue (SCT) and muscular layer (ML) thickness. Relatively few such data have been published.8-10 A recent study involving 40 adults showed that the mean SCT thickness in the deltoid region averaged 7 mm.11 The aim of our study was to obtain SCT tissue and ML thickness values at the two sites recommended for vaccine injection, ie, the thigh and the deltoid,6 in infants and children at the age of primary or subsequent booster immunizations.
MATERIALS AND METHODS
A total of 58 patients from different departments of the Queen Fabiola University Children's Hospital (Brussels, Belgium) were included in this open study conducted during a 1-year period beginning in May 1995.
Tissue thickness was measured using a high-frequency, real-time ultrasonograph (ALOKA 2000 SSD) with a 6-cm-long, 7.5 Hz transducer. For the quadriceps, the anterolateral aspect of the thigh at the junction of the upper third and lower two thirds of the muscle was examined at a 45° angle to the horizontal plan. For the deltoid, the external aspect of the median part of the muscle (ie, between the acromial point and the deltoid tuberosity) was studied. The transducer was applied lightly to the skin to avoid tissue compression. Two concordant measurements were performed, at a 90° angle both to the skin and to the long axis of the leg or arm; an image taken at each point provided an automatic measurement in millimeters of the morphometric parameters. Two operators performed the experiments, each doing approximately half of all measurements.
The study protocol had been approved by the hospital ethics committee, and informed oral consent was obtained from all parents.
Descriptive analysis of the evaluation criteria, including mean, median, standard deviation (SD), and range, was performed using SPSS Software, version 5.01 (SPSS, Inc, Chicago, IL).
Forty infants, median age 12 weeks (range, 9 to 27) and 18 toddlers, median age 79 weeks (range, 68 to 88) have been investigated. All were in apparent good health and without a history of upper or lower limb injury or any neurological or muscular disease.
Morphometric characteristics of infants and children included in the present study generally fell between the 10th and 50th percentiles, according to age and gender, of the Belgian normal growth curves. Among infants, these curves are similar to those currently in use in the United States12 and France.13 In 18-month-old children, the median weight corresponded to the 25th percentile of the US curve, and the median height corresponded to the 50th percentile of the US and French curves.
In the deltoid region, evaluated only in toddlers, the SCT thickness was ∼5 mm and never >6.9 mm. The mean ML thickness of the deltoid was 5.8 ± 0.3 mm (range, 3.4 to 7.5 mm) and was similar on the right and left sides. The average skin-to-bone depth was 10 mm and was never >14.2 mm.
Several studies examined the SCT and ML. Our data are consistent with those obtained in an ultrasonographic evaluation conducted in Malmö, Sweden (C.-E. Flodmark, personal communication) of the subcutaneous adipose tissue in 3-, 6-, and 12-month-old children. The fat-fold thickness over the middle of the left thigh averaged 5.4 ± 1.7, 4.9 ± 1.6, and 5.0 ± 1.7 mm, respectively, in the three age groups. No child had a SCT thickness >10.4 mm at 3 months or 9.0 mm at 13 months (C.-E. Flodmark, personal communication). However, Hick et al,9 studying the depth of the fat layer over the thigh by ultrasonography with a transducer oriented at a 45° angle to the long axis of the leg in 24 infants aged 3½ to 4½ months, found the skin-to-muscle depth to be 14.0 ± 2.4 mm in boys and 13.0 ± 2.8 mm in girls. The skin-to-bone depth varied from 32.0 ± 4.5 mm for boys to 28.0 ± 4.7 mm for girls.9 Lack of agreement with the results obtained in our study may be attributed, in part, to a difference in transducer orientation. If the transducer had been applied at a right angle to the leg, the skin-to-muscle depth obtained on extrapolation of the data would be 9.9 mm, close to the value obtained in the present study.
The difference in SCT thickness between infants and children is minimal. Only for infants did a significant correlation between weight and SCT thickness appear. This is consistent with the data obtained in a 1974 US Nutritional Survey that indicated that the arm circumference showed only a small change during childhood.10Nevertheless, because obesity is becoming common in a number of Western countries,14,15 data from overweight children, beyond the 95th percentile, will be useful to complement our findings.
The ultrasonographic measurements demonstrate that the use of the technique recommended by WHO, ie, stretching the skin flat between the finger and thumb, followed by pushing the needle down at a 90° angle through the skin,7 should allow perfect intramuscular vaccine delivery using 16-mm (5/8-inch) needles. Using 25-mm needles with this injection technique could present a real danger of damaging neurovascular structures or bone. On the other hand, 25-mm needles suit the injection technique widely used in the United States, ie, bunching of the tissue at the injection site. The use of 16-mm needles with the injection technique recommended in the US should be avoided, especially for adsorbed vaccines, to minimize the risk of subcutaneous delivery. The injection technique is as important as the needle length itself for ensuring proper intramuscular penetration. The effect of needle length on vaccine reactogenicity was examined by Ipp et al4 in 18-month-old children receiving DTP-IPV vaccine by injection either into the deltoid muscle with a 16-mm needle or into the thigh muscle with a 16- or 25-mm needle. The use of a 16-mm needle causes more redness and swelling than use of a 25-mm needle, but the incidence of pain or systemic symptoms was independent of needle length. The implication of these results are difficult to analyze because, as in most vaccine trials,16 the injection technique was not described.
We conclude that the injection technique is the most important parameter in ensuring efficient intramuscular vaccine delivery. Consequently, the injection technique chosen determines the appropriate needle size. It should be stressed, however, that optimizing factors such as injection route, site, technique, and needle size will not eliminate reactions completely. As stressed by Bergeson and the American Academy of Pediatrics, practitioners should exercise clinical judgment about where and how to inject and adjust needle size appropriately.6,17 If problems are encountered with a particular injection technique or needle size, a change of either should be considered.
We thank Dr. Carl-Erik Flodmark for helpful discussion and for providing unpublished data, and Inna Furman for editorial assistance during the preparation of this manuscript.
- Received January 29, 1997.
- Accepted April 28, 1997.
Reprint requests to (J.G.) Department of Pediatrics, Queen Fabiola Children's Hospital, 15 Av JJ CROCQ, 1020 Brussels, Belgium.
- DTP-IPV =
- diphtheria, tetanus, pertussis, and inactivated poliovirus vaccine •
- WHO =
- World Health Organization •
- SCT =
- subcutaneous tissue •
- ML =
- muscle layer •
- SD =
- standard deviation
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- Copyright © 1997 American Academy of Pediatrics