Needle injections are administered for a myriad of reasons to millions of people worldwide. Pain experienced upon injection may influence adherence for patients who must receive injections for therapeutic or diagnostic reasons. Additionally, pain may affect a patient's willingness to receive injections for elective procedures. Thinner needles may cause less pain and discomfort.1 The role that needle size plays in pain perception has been a subject of controversy. Arendt-Nielsen and colleagues2 have shown that, by decreasing the outer diameter of a needle, insertional pain is reduced, which may increase adherence to injection regimens, but many groups have found that thinner needles do not influence injection pain.3–8 Although patients receiving cosmetic botulinum toxin type A (BTX-A) are choosing to undergo an elective injection, the amount of pain experienced may affect their willingness to receive treatment again. Currently, 30-gauge needles are the standard needle size employed for giving BOTOX Cosmetic (Allergan, Irvine, CA) to the face (as recommended by the package insert). Although 32-gauge needles are thinner, they are more expensive than 30-gauge needles. However, if patient care is improved by reducing pain and bruising, using the thinner needle might be worth the additional cost.
BACKGROUND Patients often complain of pain and bruising from needle injections. Some clinicians believe smaller gauge needles cause less pain. Thirty-gauge needles are currently the standard needles employed for administering botulinum toxin type A (BTX-A).
OBJECTIVE This study sought to determine whether patients receiving BTX-A have a preference for 30-gauge or 32-gauge needles based on the amount of pain and bruising experienced.
METHODS Thirty-seven subjects received BTX-A on the right side of the face using a 30-gauge needle and on the left side using a 32-gauge needle. Subjects were masked to needle size. They were then asked to rate injection pain on an 11-point numerical rating scale and to note any bruising. Physician preference was also evaluated.
RESULTS There were no statistically significant differences in the amount of intra-procedural pain (p=.37) or the level of post-procedural pain and discomfort (p=.76) experienced. Twenty-seven percent of subjects reported greater bruising with the 32-gauge needle, versus 29.7% with the 30-gauge needle. The physician injector did not have a preference. Lastly, 83.8% of subjects did not detect a difference in BTX-A paralysis effect.
CONCLUSION We do not recommend using 32-gauge needles in place of 30-gauge needles for administering BTX-A.
The authors have indicated no significant interest with commercial supporters.
Thirty-seven subjects already scheduled to receive BTX-A for cosmetic purposes were recruited from the Duke Aesthetic Center. Subjects were excluded if they had any condition that could affect the perception of pain, including paralysis, injury to the frontal and maxillary branches of the fifth cranial nerve, or other conditions that may cause hypoesthesia in the areas to be injected. Subjects taking anticoagulant medication or subjects with medical or social conditions (e.g., alcohol abuse) that could affect blood clotting were also excluded. Informed, written consent was obtained from the subjects in compliance with the Duke Institutional Review Board. The subjects then received BTX-A facial injections. Thirty-gauge needles (30 G by 1/2 inch Precision Glide, Becton Dickinson & Co., Franklin Lakes, NJ) delivered BTX-A to the right side of the face and 32-gauge needles (32 G by 1/2 inch TSK Steriject, Air-tite, Tochigi, Japan) to the left side. The side of the face injected first was randomized, ensuring that desensitization and hypersensitization factors were not confounders. The subjects were masked to needle size. Approximately the same number of injections and units of BTX-A were given to each side of the face. One physician (JW) administered the injections to all the subjects so that technique and skill of delivery was not a confounding factor. The physician was not blinded to needle gauge. Immediately after the injections, patients were asked to rate the pain of injection on an 11-point numerical rating scale (0 indicating no pain and 10 indicating severe pain). The physician injector was also asked to note needle preference based on ease of injection and any complications encountered, including needle dysfunction and subject bruising. One week after injection, the subjects were asked to rate the level of post-injection pain or discomfort on each side (using the same 11-point scale) and which side bruised more. Lastly, they were asked whether the paralysis effect of the BTX-A was the same on both sides. The Wilcoxon signed rank test was used to evaluate the median differences in pain scores between the two needles for each subject. Statistical significance was achieved if p<.05.
There was no significant difference in the average pain scores between the 32-gauge and 30-gauge needles during the injection (4.30±1.59 vs 4.57±1.69; p=.37) and 1 week post-injection (0.57±1.28 vs 0.54±1.26; p=.76) (Figure 1). Twenty-seven percent of subjects reported greater bruising with the 32-gauge needle, versus 29.7% with the 30-gauge needle. The physician injector found no difference in ease of injection in 91.9% of injections and did not encounter any needle dysfunction for either needle. The physician injector also noted immediate bruising in only 10.8% of subjects from the 32-gauge needle and 8.1% of subjects from the 30-gauge needle. Lastly, six subjects (16.2%) experienced a difference in paralysis effect between sides. Of those, 100% reported that the left side (32-gauge needle) had greater paralysis. Data are depicted in Table 1.
|Greater Discomfort After|
|1||32||=||=||Bruise with 30||—||=||NA|
|2||30||=||=||Bruise with 32||—||32||NA|
|3||=||=||=||Bruise with 32||—||32||NA|
|26||30||=||=||Bruise with 30||—||=||NA|
|32||32||=||=||Bruise with 32||—||=||NA|
|36||30||=||=||Bruise with 30||—||30||32|
|37||30||=||=||Bruise with 32||—||32||NA|
There have been a number of studies, most derived from the dental and diabetic literature, that have examined differences in pain perception experienced by needle injections. Most of the patients studied required injections for treatment, anesthesia, or diagnostic purposes. In the majority of these studies, no difference in perceived pain was found based on needle size.1–9 Some authors have examined bruising or hematoma formation, needle deflection, needle breakage, and aspiration ability to determine whether needle gauge is consequential. Overall, these studies have not found significant differences between needles sizes with regard to these various parameters.3,9–15 Additionally, smaller-diameter needles are more expensive. The cost would not be a significant factor if the smaller-gauge needle improved patient care, and the larger number of patients undergoing the less painful injection procedure would probably offset the extra cost.
Of the few subjects who experienced a difference in BTX-A paralysis effect, all reported a greater paralysis effect with the 32-gauge needle, but because the 32-gauge needle was always injected on the left side of the face, this finding could be secondary to the technique applied to the two sides of the face. For example, because the physician injector is right-handed, it might have been easier for her to inject the left side of the face; thus the placement of the needle bevel, the depth of penetration, or the general stability of the needle may have affected the overall BTX-A infusion. There is also a chance that the smaller needle allows BTX-A aliquots to infuse more slowly, perhaps diffusing through the muscle more effectively, but this hypothesis necessitates further investigation. Additionally, a quantitative difference would need to be obtained and analyzed to evaluate whether the difference is clinically significant or relevant.
We found no significant differences in pain perception between needles. We also found that subjects bruised with similar frequency, that the physician injector did not have a needle preference, and that the majority of subjects felt that there was no difference in BTX-A paralysis effect. Therefore, because cost is the only difference between the two needles, we do not suggest changing to the smaller 32-gauge needle for administration of BTX-A for cosmetic purposes.
Acknowledgments We would like to thank Sandra S. Stinnett, PhD, for her contribution to the statistical analysis of this study.