The ideal local anaesthesia should have a quick anaesthetic effect, long duration time, cause little pain on injection, and have little effect on the surgical procedure. There have been numerous studies examining which anaesthetic protocol provides an optimal anaesthesia in eyelid surgery. Recently, a systematic review including 23 randomised controlled trials investigated local anaesthesia in periocular procedures.22 Only one of these studies examined the needle type as an equipment factor.21 Forty four patients (mean age=31) undergoing blepharoplasty used a blunt 27-gauge needle, which has the same thickness as a conventional sharp needle, to compare pain, bruising, and hematoma formation. Blunt needle use led to a significantly lower pain score than conventional sharp needle use (VAS score 5.48 vs 4.64), and the incidence of hematoma was also significantly lower.
Theoretically, the blunt tip needle may be an alternative choice as an anaesthetic injection tool, because it can lower the probability of direct blood vessel puncture. However, there are some points to be considered for its use in ptosis surgery. First, it is not easily obtainable because it is used in other procedures (interventional radiology, procedures on spinal lesions, etc.) to avoid penetrating blood vessels or vital organs. Second, unlike in the young or middle-aged patients undergoing blepharoplasty, the age of the patients undergoing ptosis surgery is usually higher (average age in this study, 68.35±13.24 years).The penetration of blunt tip needles through the relatively thin, inelastic, and dry skin of the eyelids of older patients may not be as easy as in younger patients.
In this study, we tried an insulin syringe, which is relatively easy to obtain, as an anaesthetic injection tool for ptosis operations. Compared with the 27–30-gauge needles commonly used for inducing local anaesthesia in the eyelids, the insulin syringe needle is thinner (31-gauge) and shorter (6–8 mm), making it more suitable for subcutaneous injection; in this study, a 6 mm needle was used. In addition, the sharpness of the needle tip is blunt compared to that of the conventional 30-gauge needle (Figure 1). Therefore, the insulin syringe was expected to reduce injection pain relative to the use of the conventional 30-gauge needle, and reduce haemorrhage and oedema by reducing tissue damage and vascular penetration. However, there was no statistically significant difference in the pain score between the insulin syringe and the 30-gauge needle groups (VAS 5.17 and 5.35, respectively). The insulin syringe group did show significantly lower scores for haemorrhage and oedema than the 30-gauge needle group.
The similarity in pain scores may simply be because the needle thickness (1 gauge) and needle tip bluntness did not differ significantly between the two needle groups. Another possible explanation is that elderly patients are less sensitive to pain stimuli; therefore, the pain caused by the two needles may not be distinguished.25 26 It is important to note that haemorrhage and oedema, which are indicators of tissue damage caused by needle injury, were significantly lower in the insulin syringe group. This may be because the insulin syringe needle is thinner and the needle tip is blunt, but, above all, the main factor is thought to be the shorter needle length of the insulin syringe than that of the conventional 30-gauge needle (6 mm vs 13 mm). In a study with diabetic children who used insulin injections using 8 mm and 12.7 mm needles with various insulin syringes, 8 mm needles significantly lowered the incidence of intramuscular penetration compared to 12.7 mm long needles.20 Insulin injection in diabetic patients and anaesthetic injection in eyelid surgery require different depths and angles of penetration making direct comparison difficult. However, the length of the 30-gauge needle is much longer; therefore, there is a greater tissue damage caused by the long subcutaneous or intramuscular tract created in the skin. Furthermore, as the skin, subcutaneous tissue, and muscle layers become thinner with age, the chance of the needle penetrating deeper tissues after skin penetration increases. For this reason, it is believed that the scores of haemorrhage and oedema in the 30-gauge needle group were significantly higher than those in the insulin syringe group.
As insulin syringes are shorter in length, the effect of anaesthesia may not be sufficient, because the spread of anaesthetic solution is relatively limited, even if the same amount of anaesthetic is injected. However, the anaesthetic solution could spread evenly during mild compression of the eyelids for 1 min after injection, and an initial anaesthetic effect was found sufficient. We also found that the duration of the anaesthesia and amount of anaesthetic solution added after the initial anaesthetic injection did not differ between the two groups.
Some swelling will inevitably occur after injection because the injected anaesthetic agent is delivered to the subcutaneous or deeper tissue layer. In this study, since the subjects were elderly with an average age of 68 years, it is necessary to consider that dermatochalasis is usually present. After the injection of 2 mL or less of anaesthetic solution, mild compression was done for approximately 1 min for haemostasis. When the degree of eyelid oedema was observed 10 min after injection, it varied from grade 1 (minimal) to grade 4 (very severe) depending on the degree of dermatochalasis. In general, when the bleeding was severe, the degree of oedema worsened; however, in some cases, eyelid oedema was found to be relatively severe compared to the degree of haemorrhage. In contrast, in some patients with diffuse haemorrhage without hematoma, the degree of eyelid oedema was observed to be relatively less severe. For this reason, haemorrhage and eyelid oedema after anaesthesia injection were scored separately for analyses. Factors driving oedema include patient-related factors, such as patient age and underlying comorbidities, and treatment factors, such as the injection technique, rate and amount of injected anaesthetic agent, and degree of tissue damage caused by needle penetration.27 Since the anaesthesia was performed on the two eyelids of the same patient by one operator using the same injection technique and same volume of anaesthetic agent, the degree of eyelid oedema reflected the degree of penetrative tissue damage caused by the difference in the instrument (needle) factor.
Subgroup analysis was performed to determine whether there were differences in pain, haemorrhage, and oedema according to patient factors, such as the underlying systemic disease or medication history. The insulin syringe group showed lower pain, bleeding, and oedema scores. In the insulin syringe group, there was no significant difference in pain, haemorrhage, or oedema scores according to comorbidities such as diabetes or hypertension, or history of medication that increases bleeding risk. However, the subgroup of patients using medications increasing bleeding tendency in the 30-gauge needle group had significantly higher haemorrhage and oedema scores than the patients who did not take the drugs. This may be an evidence of the reduction in haemorrhage and oedema of the eyelids when anaesthesia is performed using an insulin syringe rather than the conventional 30-gauge needle, especially in patients who use medication that increase bleeding risk. Since insulin syringe needles are thinner and shorter and the needle tip is relatively blunt, it can be useful in patients with increased bleeding risk because it can reduce the penetrative tissue damage caused by needle injection. It is known that oedema is associated with medications such as aspirin, NSAIDs, hormone treatments, calcium channel blockers, and certain vitamin supplements (vitamin E, ginger, ginseng, ginkgo biloba and garlic).27 28 Although this study did not include and analyse all of these medications, patients undergoing ptosis surgery are typically older than other patients in the oculoplasty field; therefore, there is a greater likelihood of using these medications. Given that it is not always possible to confirm the use of all these medications and complementary medicines, an insulin syringe provides a good option for performing injections during ptosis surgery.
A limitation of this study is that eyelid oedema was scored according to the subjective judgment of the observer; thus, there may be some intra-observer variation between individual patients. However, since the main analysis of this study compares the difference between the two different needle groups in the same patient, we can conclude that comparing oedema in the two eyes of one patient sufficiently reflects the objective difference. Also, the evaluation of haemorrhage and oedema, which reflects the degree of penetrative tissue injury after anaesthetic infiltration, was not assessed serially over a long time. In this study, the time from anaesthetic agent injection to skin incision was 10 minutes; therefore, only haemorrhage and oedema 10 minutes after injection, just before skin incision, were evaluated. Bleeding or oedema inevitably occurs during the operation after the skin incision step; therefore, haemorrhage and oedema after skin incision are related to other factors in addition to the anaesthetic effect. As a result, haemorrhage and oedema after skin incision procedures were not evaluated in this study. The reason for setting the 10-minute time period in this study is that this is the time it takes for the surgeon to disinfect and drape after the actual anaesthesia injection. This is also a reflection of previous research that found that waiting 7 minutes before skin incision in eyelid surgery is enough to achieve a maximal haemostatic effect following the induction of local anaesthesia using epinephrine.29