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Analgesic effect of supplemental intracameral lidocaine during phacoemulsification under topical anaesthesia: a randomised controlled trial
  1. Colin S H Tan1,2,
  2. Han-Bor Fam1,2,
  3. Wee-Jin Heng1,2,
  4. Hung-Ming Lee1,2,
  5. Seang-Mei Saw3,
  6. Kah-Guan Au Eong4
  1. 1Department of Ophthalmology, Tan Tock Seng Hospital, Singapore
  2. 2National Healthcare Group Eye Institute, Singapore
  3. 3Department of Epidemiology and Public Health, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  4. 4Singapore International Eye Cataract Retina Center, Singapore
  1. Correspondence to Dr Colin S H Tan, Department of Opthalmology, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore; colintan_eye{at}yahoo.com.sg

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Introduction

The use of topical anaesthesia during routine phacoemulsification is becoming increasingly common. In a series of annual surveys of members of the American Society of Cataract and Refractive Surgery,1–3 the proportion of respondents who used topical anaesthesia during cataract surgery increased from 8% in 19951 to 61% in 2003.3 In the latter survey, 73% of respondents who used topical anaesthesia supplemented its effect with intracameral lidocaine.3 In the UK, surveys have reported that topical anaesthesia is practiced by 9.9–22.3% of ophthalmologists4 5 and topical anaesthesia combined with intracameral anaesthesia is practiced by 4.7–11.0% opthalmologists.4 5

Topical anaesthesia has several advantages compared to injection (retrobulbar and peribulbar) anaesthesia. It allows rapid visual recovery and avoids rare but potentially serious complications such as globe perforation and retrobulbar haemorrhage.4 5

While it has been reported that the use of supplemental intracameral lidocaine as an adjunct to topical anaesthetic drops may further reduce pain experienced during cataract surgery,6 7 the results of randomised controlled trials (RCTs) have been mixed. Several RCTs have demonstrated that intracameral lidocaine decreases pain and discomfort experienced by patients during phacoemulsification,6–12 while others showed no significant analgesic effect.13–18 In some of these RCTs, sample size estimation was not reported,10 11 16–18 hence it is uncertain if the studies were adequately powered to detect a difference in pain experienced.

In addition, many previous studies did not perform multivariate analysis10 11 16–18 to account for possible confounders such as age and gender. The current RCTs on intracameral lidocaine have not described the effect of age, gender or ethnicity on the experience of pain during cataract surgery, either using univariate or multivariate analysis.

Studies have suggested that intracameral lidocaine may have adverse effects on intraocular structures such as the corneal endothelium and retina.19–26 Therefore, it is important to assess whether the use of intracameral lidocaine during cataract surgery affords any additional pain relief to the patient in order to balance the potential risks and benefits of this intervention.

Our study aimed to investigate if supplemental intracameral lidocaine reduces pain experienced during phacoemulsification and intraocular lens implantation under topical anaesthesia, using a study design that is adequately powered to detect a difference in the pain experienced, and to assess the risk factors associated with a painful experience.

Materials and methods

This two-centre, prospective, double-masked, randomised, placebo-controlled trial (registration number DSRB-A/00/011) was conducted at Tan Tock Seng Hospital and Alexandra Hospital in Singapore from 2003 to 2004. Both hospitals are public hospitals within the National Healthcare Group Eye Institute, and manage patients of all socioeconomic backgrounds in similar proportions. The institutional review boards of both institutions approved the study and written, informed consent was obtained from the participants. This study had two major outcome measures with regard to the effect of supplemental intracameral lidocaine during phacoemulsification under topical anaesthesia: (1) pain and (2) fear caused by intraoperative visual experiences (to be reported separately).

This study was powered to detect a difference in the proportion of patients who experienced fear (the study's other main outcome measure) during phacoemulsification. The sample size was estimated at 462 and since this was larger than the sample size of 366 required to detect a 25% reduction in pain score between the two groups at a power of 90% at the 5% confidence level, the larger of the two possible sample sizes was used.

Consecutive patients undergoing routine phacoemulsification under topical anaesthesia, who met the inclusion criteria and gave informed consent were randomised by the study coordinator. Topical anaesthesia was the method of choice of the four surgeons and was used routinely unless the patient was very anxious or it was anticipated that extensive tissue manipulation might be required during the surgery, in which case they were excluded.

Sequentially numbered envelopes were prepared for the surgeries. Each envelope contained a random number which was generated from a random number table. Based on the random number, patients were assigned to two groups: (1) the intracameral lidocaine group (n=277) received an intracameral injection of 0.5 cc preservative-free 1% lidocaine and (2) the balanced salt solution (BSS) group (n=229) received an intracameral injection of 0.5 cc BSS. The CONSORT 2010 flow diagram is shown in figure 1. All investigators and subjects were masked to the randomisation. The intracameral injections were prepared in a syringe according to randomisation by a circulating nurse and the content was not revealed to the surgeon, the nurse assisting the surgery, the patient or the investigator who performed the postoperative interview.

Figure 1

CONSORT 2010 flow diagram.

Sedation was not administered to most of the study patients and, if required, was administered by the attending anaesthetist based on standard anaesthesia protocols in the hospitals.

The exclusion criteria in this study were patients with severe co-existing ocular pathology such as Fuchs' endothelial dystrophy, end-stage glaucoma, severe diabetic maculopathy and proliferative diabetic retinopathy; patients unsuitable for topical anaesthesia; patients who were unable or unwilling to give consent for the study and patients with intraoperative complications such as posterior capsule rupture.

All protocols used, including randomisation techniques, as well as the inclusion and exclusion criteria were the same in both hospitals.

Five minutes prior to surgery, a standardised volume of lidocaine gel was instilled into the conjunctival sac. During the surgery, a clear corneal incision was made with a keratome. No toothed or fixation forceps was used to grasp the conjunctiva at any time. Immediately after the corneal incision (prior to capsulorrhexis), the contents of the marked syringe was injected into the anterior chamber via a Rycroft canula (Maersk Medical Ltd., Redditch, England). The solution was then left in the eye for a standard 1 min. After this, viscoelastic was injected to fill the anterior chamber to displace the injected solution which was allowed to escape externally, and the surgeon proceeded with the remainder of the surgery—capsulorrhexis, hydrodissection, phacoemulsification, aspiration of cortical material and insertion of an intraocular lens. The wounds were not sutured at the end of the surgery.

The intraoperative pain score was assessed using a visual analogue scale which has previous been described,27 where 0 represents no pain and 10 represents unbearable pain. This was administered in the recovery room by a trained interviewer using standardised phrasing for all patients. The patient was asked, “Did you experience any pain during the surgery? This diagram represents pain. Zero means no pain, and 10 means unbearable pain. Would you please make a mark on the line to show us how much pain you experienced?” The interviews lasted approximately 10 min and were administered by the same interviewer to all patients. When necessary, the questions were translated into the language the patient was most conversant with. The surgeon was not present in the recovery room during the interview.

All statistical analyses were carried out using SPSS version 12.0 (SPSS Inc., Chicago, Illinois, USA), with p values less than 0.05 considered statistically significant. The differences between categorical variables were examined using the Pearson's χ2 test. The Mann–Whitney U test was used to analyse the difference between the pain scores of the two groups.

Results

Of the 506 patients enrolled in the study, 277 (54.7%) were randomised to the intracameral lidocaine group and 229 (45.3%) to the BSS group. The characteristics of the two groups are compared in table 1, showing no significant differences between the two groups except for the proportion of patients undergoing cataract surgery for the first time. Comparing the characteristics of patients from both centres, there was no significant difference between the groups in terms of age, gender, race or operated eye.

Table 1

Characteristics of patients in the intracameral lidocaine 1% and balanced salt solution (BSS) groups

There were no adverse effects and no patients were withdrawn from the study.

A total of 248 patients (49.0%) experienced pain during the surgery, 125 of 277 (45.1%) in the lidocaine group and 123 of 229 (53.7%) in the BSS group. The univariate OR for lidocaine group was 0.71 compared with BSS group (95% CI 0.50 to 1.00; p=0.055). The median pain score (range) was 0.0 (range, 0–10) for intracameral lidocaine compared with 1.0 (range, 0–10) for BSS (p=0.039). In the intracameral lidocaine group, 193 of 277 (69.7%) had a pain score of 0 to 1 compared with 132 of 229 (57.6%) in the BSS group (p=0.005).

Using univariate analysis, a painful experience was significantly associated with non-Chinese race (62.3% vs 46.9%, p=0.020), female gender (54.3% vs 43.6%, p=0.017), previous cataract surgery (55.3% vs 45.0%, p=0.029) and a longer duration of surgery (15.8 min vs 13.3 min, p<0.001). For both the lidocaine and BSS groups, there was no significant difference in the pain score between those who had received sedation and those without.

Using logistic regression, the proportion of patients who experienced pain was significantly lower in the intracameral lidocaine group compared with the BSS group (multivariate OR 0.68; 95% CI 0.47 to 0.97; p=0.034) (table 2). Females were 1.56 times more likely to experience pain compared with males (p=0.016). The ethnic group also affected the likelihood of pain—non-Chinese (Malays, Indians and Eurasians) were 2.13 times more likely to experience pain compared with Chinese (p=0.005). Patients who had previous cataract surgery were more likely to experience pain compared with those undergoing surgery for the first time (multivariate OR 1.61; 95% CI 1.11 to 2.32, p=0.012) However, the age of the patient and the use of sedation did not affect the pain experienced.

Table 2

Multivariate OR of patients who experienced pain compared with those who did not

Discussion

Our study demonstrates that supplemental intracameral lidocaine significantly reduces both the proportion of patients experiencing pain as well as the median grade of pain experienced. These findings are consistent with the results of a meta-analysis of earlier RCTs.6–12 26 Reducing pain during cataract surgery is beneficial as it improves patients' cooperation during the surgery and increases their satisfaction with the surgery.

The strength of our study is that we performed logistic regression analysis and computed multivariate OR, thus accounting for possible confounders such as race, gender and age. Millodot previously demonstrated the effects of demographic factors such as age, race and gender on corneal sensitivity.28 However, our study shows the actual effect of these factors on pain experienced by patients undergoing cataract surgery. We are aware of one other study on intracameral lidocaine that has performed logistic regression analysis,15 although that study did not report any difference in the pain scores and did not report the effect of demographic factors. The earlier study by Gillow et al15 differed from our study in that 30 patients (15%) were operated on by residents, which may have affected the final outcomes. It was reported that the intraoperative and postoperative pain scores were significantly higher for cases performed by residents.15 By contrast, all surgeries in our study were performed by experienced consultant ophthalmologists.

Our study showed that females and non-Chinese were more likely to experience pain, both on univariate and multivariate analyses (table 2). The role of gender has not previously been reported and warrants further investigation. An advantage of our multi-ethnic population is that we were able to study the effects of ethnicity on pain experienced. Most other studies did not report ethnicity as a factor in their respective studies.10 11 14–18

This study has one of the largest sample sizes,10 11 14–18 and is one of a few14 15 that has estimated the sample size required to show a difference. It is not known whether some of the earlier studies that have reported no significant difference between the treatment groups were adequately powered to show a difference.

Our study used the visual analogue scale because it has previously been validated27 and was also used in many earlier studies on the effect of intracameral lidocaine on pain.11 14–18 This allows direct comparison of our results with these earlier studies.6 The visual analogue scale is also easy to use on most adult patients.

We found that 57.6% of patients given topical anaesthesia alone had low pain scores of 0 or 1, indicating that pain experienced was minimal. However, with the addition of supplemental intracameral lidocaine, the proportion of patients with pain scores of 0 or 1 increased to 69.7% (p=0.005). We also found a significant difference in the median pain score between the two groups. By contrast, a study in Chennai, India,18 of 75 patients who were randomised to receive no anaesthesia, topical anaesthesia alone or topical anaesthesia supplemented by intracameral anaesthesia, showed no significant difference in the pain score between the three groups. Similarly, a study of 96 patients in Finland13 showed no relationship between pain scores and intracameral lidocaine. Lofoco et al8 reported significant reduction in the number of patients reporting pain with intracameral lidocaine, but no difference in the mean postoperative pain score.

Several factors may account for the mixed results from different studies, including differences in the choice of topical anaesthetic, the presence of preservatives in the lidocaine solution,18 use of preoperative or intraoperative sedation, the volume of anaesthetic injected intracamerally, the stage of the surgery (before or after capsulorrhexis) when lidocaine was injected and the duration it remained in the eye. The differences may also be explained by the surgical technique and the degree of conjunctival manipulation by the surgeon. For example, in a study by Pandey et al,18 no toothed or fixation forceps was used to grasp the conjunctiva at any time, whereas a Thornton-Fine fixation ring was used to stabilise the eye in Tseng and Chen study.11 In some of the smaller studies, the sample size may have been inadequate to detect a small but significant difference in pain.

An interesting finding in our study is that patients who had previously undergone cataract surgery to the fellow eye were more likely to experience pain compared with those undergoing it for the first time (55.3% vs 44.7% experienced pain, p=0.012). This finding was significant in both univariate and multivariate analysis. To the best of our knowledge, this has not previously been reported in cataract surgery and should be further investigated. A study of pain during vitreoretinal surgery reported previous intraocular surgery under local anaesthesia as a risk factor for elevated pain.29

Some believe that lidocaine has effects on intraocular structures such as the corneal endothelium and retina.23–26 The postulated effects on the endothelium have been demonstrated in animal studies.19–21 However, clinical studies on human patients have shown no significant difference.30–34 It is likely that this controversy will require additional studies to reach a definitive conclusion.

In summary, our study shows that supplemental intracameral preservative-free 1% lidocaine, at the volume (0.5 cc) and duration (1 min) used, significantly reduces the pain experienced during cataract surgery under topical anaesthesia. Females, non-Chinese and those with previous cataract surgery were more likely to experience pain. Reduced pain improves patients' comfort and satisfaction and is a factor that surgeons should consider in their choice of anaesthesia for cataract surgery.

References

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Footnotes

  • This paper was presented at the American Academy of Ophthalmology Annual Meeting, 10–14 November 2006, Las Vegas, Nevada, USA.

  • Funding This study was funded by a Tan Tock Seng Hospital small project research grant.

  • Competing interests None.

  • Ethics approval This study was conducted with the approval of the National Healthcare Group, Singapore.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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