Comparison of Olive Tipped and Conventional Steven's Cannula for Sub-Tenon Ophthalmic Anesthesia.

PURPOSE: To compare the efficacy of the olive tipped (OT) cannula to the conventional Steven's cannula for sub-Tenon block (STB) before cataract surgery.
METHODS: This prospective, randomized, double-masked compared STB delivered in cataract surgery patients with an OT cannula or a conventional Steven's cannula (ST). Outcome variables included the akinesia score and lid movement scores at 5 and 10 min. The patient perception of pain during delivery of the STB and surgery were also compared between groups. Surgeon satisfaction with anesthesia was compared between groups. P <0.05 was statistically significant.
RESULTS: There were sixty patients in each group. The age between groups was not statistically different (P = 0.4). The body mass index was higher in the ST group compared to the OT group (P < 0.001). The akinesia score at 5 and 10 min did not differ between groups (P = 0.07 and P = 0.6, respectively). The patient perception of pain during STB and surgery were similar between groups (P = 0.1 and P = 0.06, respectively). There were six patients with mild chemosis and redness in the OT group and 15 patients in the ST group.
CONCLUSION: An OT cannula is equally effective as the conventional Steven's cannula for delivering STB anesthesia before cataract surgery.

RCT Entities:   Population Interventions Outcomes

Introduction

Retrobulbar and peribulbar anesthesia for ocular surgery can cause serious ocular and systemic complications.[1] Hence, the use of sub-Tenon block (STB) has become more common for ocular surgery.[2] However, some complications of STB have also been reported including, rectus muscle paresis, diplopia, central spread, orbital cellulitis, and/or other vascular damage.[3] Globe perforation after STB is a rare but catastrophic complication.[45] The risk factor is higher with an inexperienced user, poor technique and in a previously operated eye due to adhesions.[6]

The conventional Steven's cannula (ST) is commonly used for STB. ST is a 19-gauge cannula and 25.5 mm long. It is metallic and has a curved shaft and flattened tip [Figure 1]. The olive tip (OT) cannula is primarily used to free the intraocular adhesions secondary to previous inflammation or adhesions over the capsular bag during cataract surgery.[7] This cannula has a smooth oval tip and a malleable shaft compared to the ST cannula. It also has a smaller gauge (25) but comparable length (26 mm) to the ST cannula [Figure 2]. We assumed that OT cannula can be used for STB, due to the very similar design to the ST cannula. In addition, the OT cannula may be less traumatic due to the smoother bulbous tip and smaller gauge, especially in patients with sclerotic vessels or in eyes with adhesions from a previous surgery. This prospective, randomized study compared the efficacy of OT cannula to the ST cannula for the delivery of STB for cataract surgery.

Figure 1

Standard Steven's cannula

Figure 2

Olive tip cannula

Methods

A total of 120 patients, scheduled for phacoemulsification cataract surgery under local anesthesia having the American Society of Anesthesiologist physical status I-III were enrolled in this study. Patients were randomly allocated into two groups using a sealed envelope technique to receive STB with ST cannula (ST group) or an OT cannula (OT group). After approval from Institutional Review Board, written informed consent was obtained from all patients. No pilot study was performed as STB is a routine procedure at our institution.

Patients with a known allergy to local anesthetics, previous retinal surgery with a scleral buckle in place, previous strabismus surgery, localized infection, previous STB in the same quadrant, and those on anticoagulant therapy or nonsteroidal anti-inflammatory drugs were excluded from the trial. Patients were also excluded if they declined to consent or had any communication difficulties.

To calculate sample size, we assumed that pain during delivery of anesthesia and surgery will occur in 20% of the ST group and 5% of the OT group. To achieve 95% confidence interval (CI) and 90% power to the study with 1:1 ratio in two study arms, at least 51 patients were required in each group. To compensate for patient dropout and introduction of an additional anesthetic agent, we increased the sample size to sixty patients in each arm.

The technique of STB for both groups involved the instillation of three drops of 0.4% oxybuprocaine (benoxinate) followed by two drops of 1% tetracaine and one drop of 5% iodine. A lid speculum was inserted and the conjunctiva and Tenon's capsule were incised with Westcott scissors in the inferonasal quadrant, approximately, 5 mm from the limbus. The cannula was slowly advanced through the incision in the infero-posterior direction in a sliding pattern. The cannula was gently moved right and left while advancing to separate the tissue and 4–6 ml of a mixture of local anesthetic solution (bupivacaine 0.5%, lidocaine 2% in a 3:2 volume ratio and hyaluronidase 5 unit/ml) was slowly injected. The cannula was withdrawn, and the incision site was compressed with a sterile cotton-tipped applicator for 2 min for hemostasis. To decrease the chance of postoperative endophthalmitis, the second drop of 5% Iodine was instilled on the ocular surface prior to removal of the speculum.[8]

Ocular movements were assessed at 5 and 10 min after the block. A simple akinesia score (globe movement-inferior, superior, medial, and lateral) was used for assessment of STB. Normal movement graded as two and reduced movement as one while a flicker to no movement was graded as zero.[9] Similarly, eyelid movement was separately scored as 0 for complete ptosis, 1 for partial ptosis and 2 for no ptosis.

The purpose of study and procedure of STB block was explained to every patient. The patients were masked to the type of cannula used. A primary anesthesiologist performed the block in the holding area while a second anesthesiologist assessed the block, once the patient was moved into the operating room. The surgeon was assigned to check the patient's pain and akinesia score. The surgeon was also asked to rate his own satisfaction level about the quality of block using a subjective score with a verbal scale, from 0 (total dissatisfaction) to 10 (total satisfaction).[10] A visual analog scale (0–10) was used to assess the level of patient pain during the block and at the end of the procedure.[11] Chemosis and subconjunctival hemorrhage were noted in each eye before starting surgery. The amount of supplementary local anesthetic (if required) was also recorded for the study.

Statistical Package for Social Studies 22 (IBM Corp., New York, NY, USA) was used for statistical analysis. Numbers and percentages were calculated for qualitative outcome variables. The relative risk and 95% CI with a two-sided P value were used to compare outcomes between groups. Quantitative outcome variables were plotted to determine the distribution pattern. If they were normally distributed, the mean and standard deviation was calculated. To compare the outcomes between groups, we calculated the difference of mean, the 95% CI and a two-sided P value. A P < 0.05 was considered statistically significant.

Results

Sixty patients were included in each of the group, and there were no dropouts from either group. The mean age of participants was 64.7 ± 12.0 years in the OT group and 63.0 ± 11.2 years in ST group (difference of mean = 1.65; 95% CI − 2.5–5.8; P = 0.6). The mean BMI was statistically significantly lower in the OT group at 29.9 ± 14.8 kg/m2 compared to 32.3 ± 6.5 kg/m2 for the ST group (difference of mean = 2.4; 95% CI − 1.7–6.5; P < 0.001). The duration of anesthesia with STB was 72.8 ± 24 min in the OT group and 72.5 ± 29.5 min in the ST group (P = 0.96). The volume of injected anesthetic was 6.4 ± 0.6 ml in the OT group and 6.6 ± 0.6 ml in the ST group (P = 0.07).

There were 6 patients with mild chemosis and redness in the OT group and 15 patients in the ST group. The pain scores during delivery of the STB was 0.65 ± 0.92 in the OT group and 0.95 ± 0.98 in the ST group (P = 0.6). The akinesia scores at 5 and 10 min after STB in each group is presented in Figure 3. Although the akinesia score was higher at 5 min compared to 10 min in both groups, there was no statistically significant difference in STB using the different cannulas (P > 0.05 all comparisons).

Figure 3

Akinesia scores

The lid movement score at 5 and 10 min following delivery of STB in both groups is presented in Figure 4. The lid score was not significantly different between the groups at both time points (P > 0.05, all comparisons). The lid at 5 and 10 min after STB did not statistically differ in each group (P > 0.05, all comparisons).

Figure 4

Lid scores

Surgeon perception of the ability to perform surgery due to good anesthesia was 9.28 ± 1.64 for the OT group and 9.53 ± 1.27 for the ST group (P = 0.35).

Patient feedback regarding intraoperative pain varied widely between groups. The pain score was 0.53 ± 0.93 in the OT group and 0.23 ± 0.7 in the ST group (P = 0.05).

Discussion

Ophthalmic regional anesthesia has been traditionally performed with sharp needles for peribulbar and/or retrobulbar blocks. Patients with myopic globes, thin sclera and staphyloma, pose a higher risk of hemorrhage and globe perforation during insertion of a sharp needle.[12] STB is a safer alternative technique that not only avoid to penetrate a more vascular peribulbar area but also uses a blunt cannula instead of a sharp needle to avoid this complication. Different types of cannulas are currently used for STB, but ST cannula is considered the gold standard.[1314] Hence, the efficacy of all other cannulas is compared to the ST cannula. Mather compared a simple 20-gauge intravenous cannula to ST and has found it equally effective.[15] Better akinesia scores have been reported with the Jacob cannula because of its shape has a definite endpoint compared to the standard cannula, which does not have a well-defined end point.[16]

We compared the OT cannula, which is basically a surgical cannula and is meant to free the intraocular and the capsular bag adhesions during cataract surgery.[17] We used it for the first time for STB because of its similarity in shape and size with the standard ST cannula.

The primary outcome of our study suggests that the OT cannula is as effective as the conventional ST cannula for STB. In the current study, the overall quality of blocks was similar in both groups, irrespective of the type of cannula used. The lower number of patients with complications such as chemosis and hemorrhage in the OT group (a secondary outcome of our study), suggests that the OT cannula may also mitigate ocular damage compared to the ST cannula during STB.

We assumed that the oval bulb at the end of the OT cannula during insertion into the sub-Tenon's space may have separated the tissues and fibrous bands (if present) more gently, compared to the ST cannula, despite the similar outcome in both groups. In addition, the smaller gauge of the OT cannula may have added another safety factor because needle gauge has been associated to the risk of trauma during peribulbar anesthesia in patients who were at higher risk for hemorrhage.[6] However, currently, there is no such comparison for STB.[18] Hence, we speculate that in addition to the equal efficacy, an OT cannula may also be safer than the ST cannula because of the smaller gauge.

The main limitation of our study is the type of patient population that is referred to our hospital. The majority of the patients have systemic and ocular comorbidities. Simple cataract cases usually undergo surgery at local hospitals in the Kingdom of Saudi Arabia, but complicated cases are referred to our hospital. Based on this observation, the ease of access to sub-Tenon's space at the inferotemporal quadrant could vary in eyes that had undergone previous surgeries. In this study, information on previous ocular surgery was limited, and the effect of this variable could not be evaluated. However, the randomized, prospective, double-masked nature of this study does mitigate some of the drawbacks of this study.

Conclusion

The OT cannula seems equivalent to the gold standard Steven's cannula (ST) for STB during cataract surgery. Both patient and physician perceptions were similar regardless of the type of cannula used. There were greater complications such as chemosis with the ST cannula compared to the OT cannula. Further studies on larger patient groups are warranted before the recommending switching to the OT cannula for Sub-Tenon's ocular anesthesia.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.