Title: Does obesity prevent the needle from reaching muscle in intramuscular injections?
Aim: This paper is a report of a study to measure subcutaneous tissue thickness at the dorsogluteal and ventrogluteal sites and to determine optimal needle length for dorsogluteal and ventrogluteal intramuscular injections in adults with a body mass index of more than 24·9 kg/m2.
Background: Problems can arise if drugs designed to be absorbed from muscle are only delivered into subcutaneous tissue. Increasing obesity in all developed and many developing countries makes this an increasing concern.
Method: Ultrasound measurements were made of the subcutaneous tissue of overweight, obese and extremely obese people at the dorsogluteal and ventrogluteal sites with the probe held at a 90° angle to the plane of the injection site. Subcutaneous tissue thickness was measured in 119 adults whose body mass index was >=25 kg/m2. The data were collected in 2005–2006.
Results: Mean subcutaneous tissue thickness at the dorsogluteal site was 34·5 mm for overweight adults, 40·2 mm for obese adults and 51·4 mm for extremely obese adults, and at the ventrogluteal site was 38·2 mm for overweight adults, 43·1 mm for obese adults and 53·8 mm for extremely obese adults.
Conclusion: Intramuscular injections administered at the dorsogluteal site in 98% of women and 37% of men, and at the ventrogluteal site in 97% of women and 57% of men, would not reach the muscles of the buttock. A needle longer that 1·5 inches should be used in women whose body mass index is more than 24·9 kg/m2, the dorsogluteal site may be used in all overweight and obese men, and the ventrogluteal site may be used in overweight men only.
Problems can arise if drugs designed to be absorbed from muscle are only delivered into subcutaneous tissue (SCT). There is concern and uncertainty about whether standard needle length is able to achieve drug delivery into muscle in larger people. Increasing obesity in all developed and many developing countries makes this an increasing concern. In the study reported here, we set out to establish range of depth of SCT in overweight, obese and extremely obese individuals.
Intramuscular injections are made into the striated muscle fibres that are under the subcutaneous layer of the skin. Intramuscular injections are defined as injections in which the needle tip pierces the muscle by at least 5 mm (Huffman 1997, Cook et al. 2006). Thus needles used for the injections are generally 1–1·5 inches (2·5–3·8 cm) long and generally 19–22 gauge in size (Chan et al. 2006). When administrating intramuscular injections into the gluteus maximus, the length of the needle must be chosen based on the patient's deposits of fat. If a needle is used that is too short to pass all the way through the fat into the muscle, then the injection will be made into the fat (Aggarwal 1998, Morley & Babiar 2005). Therefore, if using a 1·5 inch needle for intramuscular injection, SCT thickness must not be more than 33·1 mm for the medication to be injected into muscle tissue.
Immunogenicity, pain and adverse effects may all be related to the length of needles used for intramuscular injections. If the needle is not long enough to penetrate through the SCT into the muscle mass, the patient may not develop an adequate therapeutic response, will have more pain, and may develop an abscess or granuloma at the injection site (Poland et al. 1997).
The risk of local complications particularly in obese people is also higher. This is due to local complications of the drug along with the length of a needle that is too short (Padhan 2006). In a population that is increasingly overweight, these complications could become more exaggerated, leading overall to less effective intramuscular gluteal injections. Standard available needles may be inappropriate for gluteal intramuscular injections, especially for obese individuals (Nisbet 2006). Studies of intramuscular injections have shown that local complications decreased depending on the length of the needle. Huffman (1997) stated in his study that the deeper the injection, the less likely was abscess formation. In a study conducted by Diggle and Deeks (2000), it was found that redness and swelling were less common when a 1-inch needle was used compared with another group where a 5/8 inch needle was used.
The aim of the study was to measure SCT thickness in the dorsogluteal and ventrogluteal sites and to determine optimal needle length for dorsogluteal and ventrogluteal intramuscular injections in overweight, obese and extremely obese adults. The specific research question addressed was: Is the standard 1·5-inch needle effective in reaching muscle when injecting healthy adults with a body mass index (BMI) of more than 24·9 kg/m2?
This was a descriptive study carried out between April 2005 and February 2006.
The study took place in the province of Izmir, Turkey in 2006. Participants were recruited from a university hospital, and 119 healthy adults were enroled (59 women, 60 men; mean 38·6 years (SD 7·95); range: 21–69 years) with a BMI of more than 24·9 kg/m2. The sample was grouped by BMI into three BMI groups: overweight (BMI: 25–29·9), obese (BMI: 30–34·9) and extremely obese (BMI >=35). Seventeen per cent of participants were in the overweight group, 55% in the obese group and 28% in the extremely obese group.
Data were collected in the hospital, and the following measurements were performed: weight, height and SCT thickness at gluteal sites. Measurements were obtained by a single observer using standard methods (Gibson 1993). Prior to ultrasound measurements, the participants were weighed, measured and had their BMI recalculated.
The thickness of SCT was assessed by ultrasound. SCT thickness was defined as the distance from the skin surface to the muscular fascia as measured by ultrasound. All ultrasound measurements were performed by an experienced radiologist using a 7·5 mHz linear-array transducer (Sonoline Elegra System™, Erlangen, Germany). Ultrasound images were made at the sites of dorsogluteal and ventrogluteal injection. SCT measurement for the dorsogluteal site was made above and outside a line drawn from the posterior superior iliac spine to the greater trochanter of the femur. For the ventrogluteal site, the ball of the opposing hand was placed on the greater trochanter and the index finger on the anterior superior iliac crest, a V was formed with the middle finger, and the injection site was within the V. Gluteus maximus, medius and minimus muscles are used when administering injections at these sites. The probe was inserted between the two fingers. SCT thickness measurements at each site were obtained for each subject. Compression by the ultrasound probe against the skin was avoided, and the probe was held at a 90° angle to the plane of the injection site.
Study approval was obtained from the Ethics Committee of Ege University School of Nursing. Informed written consent was obtained from all participants.
Body mass index was calculated as weight (kg) divided by height (m2), and grouped into three groups graded 1–3 representing BMI: 25–29·9, 30–34·9 and >=35. Differences in tissue thickness between men and women at the dorsogluteal and ventrogluteal sites in relation to BMI were analysed using two-way ANOVA, and these differences by sex were analysed using Student t-test. Relationship between age and SCT thickness was assessed using correlation analysis.
A total of 119 healthy adults (59 women, 60 men) whose BMI was more than 24·9 kg/m2 participated in the study. Their mean age was 38·6 ± 7·9 years, and mean BMI was 32·9 ± 3·7 kg/m2. Table 1 displays the mean (SD) SCT thickness at the dorsogluteal and ventrogluteal sites in men and women grouped according to BMI as overweight, obese and extremely obese participants. SCT thickness measured at the dorsogluteal site for overweight participants was 50·5 mm in women and 27·6 mm in men; for obese participants it was 51·7 mm in women and 30·7 mm in men, and for extremely obese participants it was 55·8 mm in women and 41·2 mm in men. There was no statistically significant difference among BMI groups in SCT thickness at the dorsogluteal site in women (F = 0·708, P > 0·05). However, there was a statistically significant difference among BMI groups in SCT thickness at the dorsogluteal site in men (F = 4·609, P < class="fulltext-IT">F = 2·210 for women, F = 2·982 for men and all P > 0·05).
Table 1 Mean subcutaneous tissue (SCT) at both sites in men and women by body mass index (BMI) groups
Subcutaneous tissue thickness was markedly different in men and women. At the dorsogluteal site, 58 of 59 women (98%, mean 53·2 ± 13·8 mm and range from 32 to 100 mm) had a depth >33·1 mm, whereas 22 of 60 men (37%, mean 31·7 ± 11·9 mm and range from 14 to 68 mm) had a depth of >33·1 mm. There was a significant difference in SCT thickness at the dorsogluteal site between women and men (t = 9·04, d.f. = 117 and P <>33·1 mm, and 34 of 60 men (57%, mean 36·4 ± 10·5 mm and range from 18 to 62 mm) had a depth of >33·1 mm. There was a statistically significant difference in SCT thickness at the ventrogluteal site between women and men (t = 7·35, d.f. = 117 and P < class="fulltext-IT">r = 0·072 in women, r = 0·087 in men for the dorsogluteal site and r = 0·014 in women, r = 0·182 in men for the ventrogluteal site and all P > 0·05).
The non-invasive ultrasound method used in this study gives precise measurements of SCT thickness. The standard 1·5 inch (38·1 mm) needle is not effective in carrying injections to muscle in healthy adults with a BMI of more than 24·9 kg/m2 according to the ultrasound findings. Our study has shown that, when using a 1·5 inch (38·1 mm) needle, an intramuscular injection administered at the dorsogluteal site in 98% of women and 37% of men, and at the ventrogluteal site in 97% of women and 57% of men, will not reach the muscles of the buttock. Women typically have a higher amount of fat in their buttocks than do men. Although neither site should be used in women whose BMI is more than 24·9 kg/m2, the dorsogluteal site may be used in all overweight and obese men, and the ventrogluteal site may be used in overweight men only. In overweight and larger women, the amount of fat tissue overlying the muscle commonly exceeds the length of the needles used for these injections. Therefore a longer needle is required to achieve successful penetration of muscle in injections at these sites.
Our results are consistent with the findings of previous work (Feng & Wu 1994, Huffman 1997, Morley & Babiar 2005, Chan et al. 2006). Compared with men, women have more SCT in the buttocks, and for both sexes SCT is thicker at the ventrogluteal site. According to measurements of SCT thickness made in this study, only 2% of the women in the sample and 63% of the men would have received a proper intramuscular injection at the dorsogluteal site, and only 3% of the women and 43% of the men would have received one at the ventrogluteal site. Cockshott et al. (1982), in analysing over 200 simulated injections to the dorsogluteal region by nurses on normal participants, found through computerized axial tomography scans of the sites that under 5% of the women and under 15% of the men would have actually received an intramuscular injection into the gluteus. Our results are supported by Newton et al. (1992), who assert that for the humanitarian reason of trying to save their patients pain, nurses underestimate the length of needle required to deposit medication into the intended muscle. In another study conducted by Nisbet (2006), it was found that for 16% of women and 5% of men an intramuscular injection at the dorsogluteal site using a 1·5-inch needle would only have reached the SCT. Using a 1-inch needle, the same was true for 36% of women and 10% of men. At the ventrogluteal site, 1·5 inch (38·1 mm) needles of will fail to reach muscle in 57% of women and 21% of men, and 1-inch needles will fail in 90% of women and 44% of men. Although Nisbet (2006) worked with an obese population, there is a lack of information about the BMI of participants, so we were unable to compare the results of all BMI groups.
Our data demonstrate the importance of adequate needle length, particularly for women, in whom SCT thickness in the buttocks is more variable than in men. Based on our data we concluded that needles longer than 1·5 inches would be required to allow at least 5 mm of muscle penetration for women where the needle is inserted at 90° into the gluteus maximus, medius and minimus muscles.
Our study has several limitations. Participants were relatively young and healthy, and their age and weight distributions may have been more limited than those of the general population. They are unlikely to be representative of persons over 65 years of age. Also, we failed to equalize the numbers of people in the BMI groups. Further research is needed to compare the differences in SCT thickness between mid-deltoid, rectus femoris and vastus lateralis in obese individuals.
The efficacy of intramuscular injections is related to sex as well as to SCT thickness. Compared with men, obese women typically have a higher amount of fat in their buttocks. Use of shorter needles (<1·5>
We wish to thank all the people who so willingly participated in this study.
AZ, LK, UYG and IE were responsible for the study conception and design and the UYG, AZ, LK and IE were responsible for the drafting of the manuscript. AZ, UYG and ST performed the data collection and UYG and AZ performed the data analysis. ST provided administrative support. UYG, AZ and LK made critical revisions to the paper. UYG, AZ and ST provided statistical expertise. UYG and AZ supervised the study.
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Keywords: empirical research report; intramuscular injection; needle length; nursing; obesity; subcutaneous tissue; ultrasound