Trojan horse anaesthesia: A novel method of anaesthesia for pars plana vitrectomy.

CONTEXT: Topical anesthesia has been used for pars plana vitrectomy (PPV) with limited patient comfort. Thus, augmenting topical anesthesia with intracameral anesthesia (Trojan horse anesthesia) will provide pain-free experience during PPV. AIMS: This study was undertaken to evaluate the patient comfort and surgical safety using 2% lignocaine jelly augmented with intracameral 1.0% lignocaine solution for anesthetizing the eyes undergoing PPV. SETTINGS AND
DESIGN: This was a prospective interventional case series at tertiary care hospital. SUBJECTS AND METHODS: Patients planned for PPV for indications other than retinal detachment were included in the study. The pain perception of the participants undergoing PPV under Trojan horse anesthesia was evaluated using visual analog scale (VAS). STATISTICAL ANALYSIS USED: Data analysis was done using descriptive statistics and nonparametric analysis with level of significance at P < 0.05.
RESULTS: There were 114 eyes of 114 patients in the study out of which 68.4% (n = 78) were males. The mean age was 42.31 years (range 14-80 years, standard deviation [SD] 18.7). The mean surgical time was 34.0 min (range 13-80 min, SD 14.2). The pain perception on VAS scale averaged 3.0 (range 0-8, SD 1.59, median 3.0). Pain scores were not affected by the age (Pearson correlation = 0.098, P = 0.3), gender (P = 0.44), or the educational status of the participant (P = 0.28). The pain scores were not affected by the indications of surgery (P = 0.58) or the use of silicone oil (P = 0.07).
CONCLUSIONS: Trojan horse anesthesia provides adequate analgesia for comfortable and safe 23-gauge PPV with high patient acceptability.

Introduction

Topical anesthesia has been in use for anterior segment surgeries routinely, with acceptable patient comfort and surgical safety. Pars plana vitrectomy (PPV) is one of the posterior segment surgeries being done under topical anesthesia since the advent of 23- and 25-gauge vitrectomy systems.[12] Reports of vitrectomy under topical anesthesia for various diseases including rhegmatogenous retinal detachment, epiretinal membrane, macular hole, dislocated crystalline lens or intraocular lens, giant retinal tear, intraocular foreign body, trauma, endophthalmitis, subfoveal choroidal neovascular membrane, and neovascular glaucoma are available in the literature.[3]

All the studies to evaluate the patient's pain during PPV under topical anesthesia alone or with sedation using 20 g, 23 g, or 25 g have demonstrated that although the pain is acceptable, there is moderate-to-severe pain during specific surgical steps of PPV including sclerostomy (trocar cannula placement or withdrawal),[124] endolaser,[3] and scleral indentation.[35] Thus, going by the present evidence, there is still need to improve the technique and explore other modalities to alleviate pain experienced by the patients while undergoing PPV under topical anesthesia.

In this effort to reduce the pain during PPV under topical anesthesia, we have adopted two enhancements.

Use of lignocaine 2% jelly in place of lignocaine/proparacaine eye drops

Trojan horse anesthesia (intracameral lignocaine irrigation).

In anterior segment surgeries under topical anesthesia, the use of lignocaine jelly has been demonstrated to provide better anesthesia when compared to drop formulations.[5] Lignocaine jelly 2% has been used to provide adequate analgesia to perform sutureless vitrectomy as well.[3]

In anterior segment surgeries (phacoemulsification,[67] manual small-incision cataract surgery,[8] and trabeculectomy),[9] addition of intracameral lignocaine significantly enhances the effects of topical anesthesia in reducing the pain during surgery.

The Trojan horse is a tale from the Trojan War about the subterfuge that the Greeks used to enter the city of Troy and win the war. In nutshell, the expression indicates an easily deliverable tool inside a closed perimeter which can be used to gain unobstructed access by disarming the guarding element. In our technique of anesthesia for PPV, this is relevant as we deliver intracameral anesthesia (through clear corneal incision under topical anesthesia) to anesthetize the ciliary body from inside so that the incision for sclerotomies is painless, thus the use of “Trojan horse anesthesia” for our technique. This is in contrast to peribulbar or retrobulbar infiltration anesthesia where an infiltrating injection is given to anesthetize the ciliary ganglion and related nerves to achieve anesthesia and akinesia of the eye.

In the described technique, the delivery of anesthesia is nearly painless and the eyelid and eye movements are preserved (no anesthesia to ciliary ganglion) so that there is no need to patch the eye after the surgery.

Going by this present evidence, using lignocaine jelly 2% for topical application with intracameral lignocaine may be a better option to perform painless PPV without using injection anesthesia.

This study was undertaken to evaluate the patient comfort, surgical safety, and outcome using 2% lignocaine jelly augmented with intracameral 1.0% lignocaine solution for anesthetizing the eye undergoing PPV for various indications.

Subjects and Methods

This prospective case series study was approved by the institutional ethics committee and followed the tenets of the Declaration of Helsinki. This was a prospective interventional study at tertiary care hospital including patients planned for PPV for media opacity at the level of vitreous. Consecutive patients presenting in the outpatient department were screened for exclusion criteria [Table 1] and were included in the study after taking their informed consent. A sample size of 107 patients was reached upon using confidence interval of 10% confidence level 99% for the population size of 300 participants (average number of patients undergoing vitrectomy surgery in a year).

Table 1

Exclusion criteria screening participants for the study

Surgical technique

Lignocaine jelly 2% (Oculan 2% jelly, Sunways pharmaceuticals, India) was instilled in the planned eye in the waiting room 5–10 min before surgery. After draping the patient and insertion of speculum lignocaine jelly 2% was re-instilled to cover the exposed ocular surface. A 1.8 mm keratome was used to enter the anterior chamber, and intracameral irrigation solution (lignocaine 1.0% solution, prepared by mixing 1 ml of 2% preservative-free lignocaine with 1 ml of balanced salt solution) was injected in the anterior chamber with intent to replace aqueous humor. After a wait of 120 seconds, transconjunctival one-step sclerotomies were constructed at standard sites, using 23 g trocar cannula set from Synergetics © USA. Standard three-port PPV was done using 23-gauge system, and silicone oil was instilled as if needed/indicated. At the end of surgery, the sclerotomies were inspected for proper sealing and sutured with buried knot with 8-0 vicryl suture if there was leak detected.

Patients were instructed to communicate verbally whenever they had pain or discomfort and this was noted with the ongoing surgical step. At the end of surgery, antibiotic-steroid combination eye drop was instilled in the operated eye. The operated eye was not patched and patients were provided with postoperative care instructions and medications or posturing as and when indicated. Patients were counseled for the pain experience using visual analog scale (VAS) to grade their pain during the surgery. Preference for topical anesthesia for any future such surgery was also recorded.

Data analysis was done using descriptive statistics and nonparametric analysis as applicable.

Results

There were 114 eyes of 114 patients in the study out of which 68.4% (n = 78) were males. The mean age was 42.31 years (range 14–80 years, SD 18.7) with nonnormal distribution (Shapiro–Wilk test for normal distribution, P ≤ 0.05).

Table 2 shows the distribution of participants according to the education status. The surgical procedure and the frequency distribution are shown in Table 3. Silicone oil was injected in 48 eyes of 114 eyes for internal tamponade as required (42.1%).

Table 2

Education status distribution of the participants undergoing pars plana vitrectomy under topical anesthesia

Table 3

The surgical procedure and the frequency distribution

Total surgical time measured from draping the patient to the removal of drape after completion of the surgery averaged 34.0 min (range 13–80 min, SD 14.2).

The pain perception of the patients undergoing PPV under topical anesthesia on 10 cm VAS scale averaged 3.0 (range 0–8, SD 1.59, median 3.0). Figure 1 depicts the frequency distribution of VAS scores among the participants. Majority of the patients (86.8%) had VAS scores ≤4.

Figure 1

Histogram of visual analog scale scores awarded by the participants undergoing vitrectomy under topical anesthesia

There was a favorable tilt toward topical anesthesia among the patients for selection of anesthesia technique for similar future surgery. One hundred out of 114 patients (87.7%) opted for topical anesthesia to be used again as compared to 14 patients (12.3%), who opted alternative technique. Those patients who rejected topical anesthesia for future had a higher average pain scores (5.77 on VAS scale) as compared to the patients preferring topical anesthesia (mean VAS score 2.66) and this difference was statistically significant (P = 0.006), and this is depicted visually in the box plot graph in Figure 2.

Figure 2

Chart showing visual analog scale scores versus preference for future anesthesia technique

Pain scores had statistically insignificant weak positive correlation to the duration of surgery on analysis with Spearman's rho (r = 0.10, P = 0.2).

Age of the patients and the pain scores had weak positive correlation which was statistically insignificant (r = 0.098, P = 0.3). Pain scores were not affected by the educational status of the participant as shown by the Kruskal–Wallis test (P = 0.28).

Variation in surgical procedure and pain perception was analyzed using independent samples Kruskal–Wallis test (P = 0.58) which showed that the pain scores were the same across all indications of surgery. Pain scores were unaffected by the use of silicone oil as revealed by Mann–Whitney U-test (P = 0.07).

Pain perception was unaffected by the gender of the patients (Mann–Whitney U-test, P = 0.44).

Discussion

Ideal anesthesia technique for ocular surgery may be judged by its painless and safe delivery, effective analgesia, not interfering with surgery, comfortable for surgeon, and fast and complication-free recovery. When local injectable anesthesia techniques for eye surgery (peribulbar/retrobulbar) are weighted against these parameters, these techniques fall short from ideal.[101112] Thus, the need for topical anesthesia provides painless safe delivery of anesthesia and fast and complication-free recovery with safe surgery and comfortable surgeon as concluded by number of studies on cataract surgery.[713]

This study done, to evaluate the pain experiences of the patients undergoing PPV under topical anesthesia, using 2% lignocaine jelly and intracameral 1.0% lignocaine (silicone oil instillation or anterior segment surgery as and when needed) shows that more than 85% of patients had only mild pain. More than 85% patients were willing to select topical anesthesia for any such future similar surgery. In contrast to other similar studies, we have used lignocaine jelly instead of anesthetic pledgets or drops because lignocaine jelly has been proved to be more effective, safe, and acceptable for use as topical anesthetic agent for ocular surgery.[14]

The pain experience is not affected by the educational status of the patients or the gender as seen in our study patients. Additional procedures such as phacoemulsification, intraocular lens implantation, or instillation of silicone oil did not affect the pain as experienced by the patients in our study.

Duration of the surgical procedure was positively correlated to pain but was statistically insignificant. It can be expected that the increased duration of surgical procedure should cause more pain because the effect of local anesthesia gradually reduces with time. In our study, the duration of surgery ranged from 13 to 80 min which was well within the duration of action of lignocaine (1.5–2 h); hence, the duration of procedure did not have any effect on the pain scores.

In addition to the topical lignocaine jelly, we have also used supplemental anesthesia in the form of Trojan horse anesthesia (intracameral 1.0% lignocaine). Intracameral anesthesia as supplement to topical anesthesia is used routinely in the patients undergoing cataract surgery under topical anesthesia and provides additional analgesia by anesthetizing the pain-sensitive uveal tissue.[6] This addition may be even more important for PPV because the pain-sensitive uveal tissue is punctured through during sclerostomy creation as a routine step.

Pain perception during PPV under local anesthesia has been reported by Yu et al. and they have reported postsurgery pain perception averaged 1.30 (SD: 1.60), but this was 1 day after the procedure during recuperation period.[15]

Topical anesthesia for vitrectomy has been evaluated by few studies. An study done by Theocharis et al. compared the anesthesia effect of topical 2% lignocaine jelly to peribulbar anesthesia in patients undergoing vitrectomy using 23 g and 25 g systems and concluded that 2% lignocaine jelly provided enough analgesia for the procedure and the akinesia was not a problem for the operating surgeon.[3] Similar studies using lignocaine drops with systemic sedation and analgesia also concluded that with appropriate case selection, topical anesthesia is a safe and effective alternative to peribulbar or retrobulbar anesthesia in three-port PPV procedures.[1617] In both the above studies, every patient was given systemic sedative and analgesics to supplement the topical anesthesia. We, however, have not used any systemic sedation or analgesic before the procedure. Deka et al. evaluated the efficacy of pledgets soaked in 0.5% proparacaine hydrochloride for PPV in a pilot project and concluded that with appropriate case selection, topical anesthesia is a safe and effective alternative to infiltrative anesthesia for 25-gauge vitrectomy.[1]

All the mentioned studies have used 25 g or 23 g vitrectomy systems with topical anesthesia, and all but last one have used systemic sedation and analgesics. In contrast to those studies, we have not added any systemic sedation or analgesia.

In our Trojan horse anesthesia technique, we have supplemented topical anesthesia with intracameral anesthesia. Although this necessitated the need to make an additional 1.8 mm self-sealing incision at the clear cornea, this aided in providing analgesia to pain sensitive uveal tissue which otherwise would have caused significant pain to the patients.

As ours is not a comparative study, hence comparative studies will be needed to establish the indications and limitations of our technique (topical anesthesia augmented with intracameral anesthesia) over local anesthesia for PPV.

Conclusions

Trojan horse anesthesia (topical 2% lignocaine jelly with intracameral anesthesia) provides adequate analgesia for comfortable and safe 23-gauge PPV with high patient acceptability. The pain experience is not affected by the educational status of the patients or the gender or duration of surgery as seen in our study patients. Additional procedures such as phacoemulsification, intraocular lens implantation, or instillation of silicone oil did not affect the pain as experienced by the patients in our study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.