• View in gallery

    Mean end-tidal isoflurane concentration recorded 5 minutes after the start of various intraocular surgical stimuli in dogs that received an intracameral injection of 2% lidocaine hydrochloride solution (0.3 mL; white squares; n = 6) or BSS (0.3 mL; black squares; 6). Stimuli included corneal incision (incision), continuous-tear curvilinear capsulorhexis (CCC), phacoemulsification (phaco), irrigation-aspiration (I/A), and corneal suture (suture). *Values differ significantly (P < 0.05) between treatment groups for the indicated stimuls.

  • View in gallery

    Cumulative number of dogs treated with intracameral injection of 2% lidocaine hydrochloride solution (0.3 mL; black bars; n = 6) or BSS (0.3 mL; white bars; 6) that required supplemental analgesia at various times after extubation (E) following intraocular surgery.

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Evaluation of the analgesic effect of intracameral lidocaine hydrochloride injection on intraoperative and postoperative pain in healthy dogs undergoing phacoemulsification

Shin Ae Park DVM, PhD1, Young Woo Park DVM2, Won Gyun Son DVM3, Tae Hyun Kim DVM4, Jae Sang Ahn DVM5, Jeong Taek Ahn DVM6, Se Eun Kim DVM7, Inhyung Lee DVM, PhD8, and Kangmoon Seo DVM, PhD9
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  • 1 Department of Veterinary Surgery and Ophthalmology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 2 Department of Veterinary Surgery and Ophthalmology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 3 Department of Anesthesiology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 4 Department of Veterinary Surgery and Ophthalmology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 5 Department of Veterinary Surgery and Ophthalmology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 6 Department of Veterinary Surgery and Ophthalmology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 7 Department of Veterinary Surgery and Ophthalmology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 8 Department of Anesthesiology, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.
  • | 9 College of Veterinary Medicine and BK21 Program for Veterinary Science, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-742, Republic of Korea.

Abstract

Objective—To evaluate the intraoperative and postoperative analgesic effects of intracameral lidocaine hydrochloride injection in dogs undergoing phacoemulsification.

Animals—12 healthy Beagles with healthy eyes.

Procedures—Dogs were randomly assigned to receive 1 of 2 intracameral injections: 2% lidocaine hydrochloride solution (0.3 mL) or an equivalent amount of balanced salt solution (BSS). All dogs were treated with acepromazine (0.05 mg/kg, IV) and cefazolin (30 mg/kg, IV), and tropicamide drops were topically applied to the eyes. Anesthesia was induced with propofol and maintained with isoflurane. The initial end-tidal isoflurane concentration was maintained at 1.2%. Heart rate, respiratory rate, arterial blood pressure, esophageal temperature, inspired and end-tidal isoflurane concentrations, and oxygen saturation were recorded every 5 minutes. The allocated agent was injected intracamerally after aspiration of the same volume of aqueous humor. Ten minutes after injection, phacoemulsification was performed. After surgery began, the isoflurane concentration was adjusted according to heart rate and mean arterial blood pressure. Pain scores were recorded before surgery and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, 8, 16, and 24 hours after extubation.

Results—Isoflurane requirements were significantly higher in the BSS group than in the lidocaine group. Mean ± SD time to administration of supplementary analgesia was significantly shorter in the BSS group (1.4 ± 1.2 hours) than in the lidocaine group (4.9 ± 1.2 hours).

Conclusions and Clinical Relevance—Intracameral lidocaine injection had significant analgesic effects in dogs undergoing cataract surgery. Results of this study suggest the value of intracameral lidocaine injection as an analgesic for intraocular surgery in dogs.

Abstract

Objective—To evaluate the intraoperative and postoperative analgesic effects of intracameral lidocaine hydrochloride injection in dogs undergoing phacoemulsification.

Animals—12 healthy Beagles with healthy eyes.

Procedures—Dogs were randomly assigned to receive 1 of 2 intracameral injections: 2% lidocaine hydrochloride solution (0.3 mL) or an equivalent amount of balanced salt solution (BSS). All dogs were treated with acepromazine (0.05 mg/kg, IV) and cefazolin (30 mg/kg, IV), and tropicamide drops were topically applied to the eyes. Anesthesia was induced with propofol and maintained with isoflurane. The initial end-tidal isoflurane concentration was maintained at 1.2%. Heart rate, respiratory rate, arterial blood pressure, esophageal temperature, inspired and end-tidal isoflurane concentrations, and oxygen saturation were recorded every 5 minutes. The allocated agent was injected intracamerally after aspiration of the same volume of aqueous humor. Ten minutes after injection, phacoemulsification was performed. After surgery began, the isoflurane concentration was adjusted according to heart rate and mean arterial blood pressure. Pain scores were recorded before surgery and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, 8, 16, and 24 hours after extubation.

Results—Isoflurane requirements were significantly higher in the BSS group than in the lidocaine group. Mean ± SD time to administration of supplementary analgesia was significantly shorter in the BSS group (1.4 ± 1.2 hours) than in the lidocaine group (4.9 ± 1.2 hours).

Conclusions and Clinical Relevance—Intracameral lidocaine injection had significant analgesic effects in dogs undergoing cataract surgery. Results of this study suggest the value of intracameral lidocaine injection as an analgesic for intraocular surgery in dogs.

Cataracts are one of the most common treatable causes of blindness in dogs.1 Consequently, cataract surgery is also common, with phacoemulsification as the preferred technique.2 Intraoperative and postoperative pain can be caused by intraocular manipulations that irritate the iris, ciliary body, and zonular tissue and by pressure changes in the anterior chamber of the eye.3 Eyes are quite sensitive to surgical pain because they are densely innervated with AD and C fiber nociceptors, which are necessary for perception of acute pain and are particularly sensitive to mechanical stimulation.3,4 Alleviation of surgical pain in animals that have undergone ocular surgery is important for humane reasons and for preventing postoperative complications, delayed wound healing, and self-mutilation at the surgical site.3

For pain management in dogs undergoing intraocular surgery, systemic opioid administration and systemic and topical NSAID administration are usually performed before and after surgery. These medications, however, have several limitations in dogs and other animals. Preoperative systemic opioid administration can cause miosis, which can impede intraocular surgery.5 However, the pupillary constriction cannot be reversed by application of mydriatics before or after opioid injection.5 Systemic administration of NSAIDs can cause gastrointestinal distress, hemorrhage due to platelet activity impairment, renal failure, and hepatotoxic effects.6–8 Therefore, their use may not be appropriate in dogs with preexisting gastrointestinal, hematologic, renal, or hepatic diseases. Several topically administered NSAIDs reportedly delay corneal wound healing and cause corneal perforation and melting in humans.8,9 In dogs, an association of topical NSAID treatment with delayed corneal epithelial healing has also been suggested.10 Preoperative topical treatment with NSAIDs can cause ocular irritation, increase the risk of intraocular hemorrhage during surgery, and lead to postoperative ocular hypertension.11,12

Lidocaine, a local anesthetic that blocks conduction of nerve impulses by binding at voltage-gated sodium channels, interrupts neural transmission in sensory nerves and tracts.13 In dogs undergoing intraocular surgery, systemic lidocaine infusion has a preemptive analgesic effect but no effect on pupil size and no important adverse effects on cardiorespiratory or visceral organ systems.3 The analgesic effects of systemic lidocaine administration are believed to be attributable to the fact that lidocaine blocks sodium channel subtypes that are upregulated from injured peripheral nerves.3,14 Systemic use of lidocaine is still limited in animals with liver and heart problems.15

Intracameral lidocaine injection is reportedly a safe means of providing additional analgesic effects in humans undergoing cataract surgery.16–20 Clinical trials in humans have revealed that intracameral lidocaine injection increases patient cooperation, compared with the effects of topical anesthetic administration alone.16,18–20 Intracamerally administered lidocaine is believed to diffuse into the iris and ciliary body and to be directly absorbed by the unmyelinated small nerve fibers located therein.21

A potential analgesic effect of intracameral lidocaine administration in dogs has been suggested.22 The safety of intracamerally injected, preservative-free 1% or 2% lidocaine hydrochloride solution was established in another study.22 It is likely that lidocaine administered via this route has a remarkable analgesic effect in dogs undergoing intraocular surgery, but to the authors' knowledge, clinical studies on intracameral anesthesia in companion animals have not been reported. The purpose of the study reported here was to evaluate the intraoperative and postoperative analgesic effects of intracameral lidocaine injection in dogs undergoing phacoemulsification.

Materials and Methods

Animals—Twelve healthy sexually intact female Beagles were included in the study. Ages ranged from 2 to 4 years, and body weights ranged from 7 to 10 kg. Prior to the start of the experiment, each dog underwent a physical examination, CBC, and serum biochemical analysis. A complete ophthalmic examination was performed with a slit-lamp biomicroscope,a an indirect ophthalmoscope,b and an applanation tonometerc to verify that dogs had healthy eyes. Dogs were housed individually in cages in a quiet room prior to the study. Food was withheld for 12 hours prior to anesthetic induction. Before premedication of dogs for the experiment, ophthalmic and physical examinations were performed to confirm the health of the dogs. Initial variables measured included heart rate, respiratory rate, and systolic arterial blood pressure (as measured noninvasively by use of a Doppler monitoring system,d with the probe applied in the region of the metacarpus) before start of experiment. All procedures adhered to the guide for the care and use of laboratory animals of Seoul National University and were approved by the Institutional Animal Care and Use Committee of Seoul National University (SNU-081007-1).

Experimental design—Dogs were randomly assigned to 1 of 2 treatment groups: preservative-free 2% lidocaine hydrochloride solutione (0.3 mL; lidocaine group; n = 6) and BSSf (0.3 mL; control group; 6). The dose and concentration of lidocaine were chosen on the basis of a study23 of the mydriatic effect of intracameral lidocaine in dogs. The right eye in each dog served as the treated eye; the left eye was not treated.

Anesthetic and surgical procedure—A catheter was placed in a cephalic vein in each dog, and lactated Ringer's solution was administered (10 mL/kg/h, IV). Dogs were treated with acepromazineg (0.05 mg/kg, IV) and cefazolinh (30 mg/kg, IV). Tropicamide dropsi were instilled in the right eye every 5 minutes during the last 20 minutes before anesthetic induction.

Anesthesia was induced with propofolj (6 mg/kg, IV) and maintained with isofluranek in 100% oxygen. After each dog was endotracheally intubated, it was monitored by means of electrocardiography,l pulse oxymetry,l esophageal temperature,l and respiratory gas analysis.l The initial end-tidal isoflurane concentration was maintained at 1.2% until surgery began. Mechanical ventilation was performed with a ventilator,m and a nerve stimulatorn was placed on the ulnar nerve to monitor the action and recovery of the neuromuscular blockade. A catheter was placed in the anterior tibial artery to directly measure arterial blood pressure during surgery with an automated monitoring device.l Every 5 minutes during the anesthetic period, the following variables were recorded: heart rate; respiratory rate; systolic, mean, and diastolic arterial blood pressure; esophageal temperature; inspired and arterial end-tidal isoflurane concentration; and oxygen saturation as measured by pulse oximetry.

For surgery, each dog was positioned in dorsal recumbency, with the head stabilized with a vacuum pillow, as is routine for intraocular surgery. The right eye was cleansed with 0.2% povidone iodine solution. The eye speculum was placed, and anterior chamber paracentesis was performed slightly to the right side of the 12 o'clock position of the limbus in the right eye under an operating microscope.o Aqueous humor (0.3 mL) was aspirated into a 1-mL syringe by use of a 30-gauge needle. Immediately after aspiration, a second paracentesis was performed slightly to the right of the first paracentesis, with the same size needle and syringe used; then, 0.3 mL of the assigned treatment was injected into the anterior chamber.

Five minutes after intracameral injection of the agent, atracuriump (0.3 mg/kg) was administered IV. Ten minutes after intracameral injection, a 3-mm corneal incision was made on the right eye. After surgery was started, the isoflurane concentration was adjusted according to heart rate and mean arterial blood pressure. The inhaled isoflurane concentration was increased every 5 minutes in increments of 0.25%, in response to an increase of > 10% in mean arterial blood pressure or heart rate, compared with values obtained immediately prior to corneal incision. The isoflurane concentration was reduced in a similar manner when a decrease in either variable exceeded 10% of the values measured before corneal incision. Viscoelastic materialq was injected into the anterior chamber of the right eye, and continuous-tear curvilinear capsulorhexis was performed. Subsequently, 1-handed phacoemulsification and irrigation-aspiration were performed. Heparinr (2 U/mL of BSS) and epinephrines (0.0008 mg/mL of BSS) were added to the intraocular irrigating fluid (BSS). The times of performance of corneal incision, continuous-tear curvilinear capsulorhexis, phacoemulsification, irrigation-aspiration, and corneal suture were recorded, as was the end-tidal isoflurane concentration after the start of each surgical stimulus. All surgeries were performed by the same surgeon (SAP).

After surgery was completed, the end-tidal isoflurane concentration was maintained at 1.2%. When response to the train of 4 twitches (one of the patterns of stimulation provided by nerve stimulator) was recovered, mechanical ventilation and anesthesia were discontinued and the dogs were extubated. The dogs were housed individually in a quiet room and observed continuously for the first 4 hours after extubation and at 6, 8, 16, and 24 hours after extubation.

Evaluation of pain—A modified scoring system3 was used to subjectively assess pain in each dog immediately before premedication (baseline), every 30 minutes until 4 hours after extubation, and at 6, 8, 16, and 24 hours after extubation (Appendix). Scores were assigned by a trained observer who was unaware of treatment received. Any dog with a total pain score ≥ 9 or with a score ≥ 3 in any category received supplementary analgesia (tramadolt; 4 mg/kg, IV) and was excluded from further pain score assessment. The interval between extubation and receipt of supplementary analgesia was defined as interval to treatment failure.

Statistical analysis—Results are expressed as mean ± SD. Statistical analysis was performed by use of a commercially available statistical software program.u Surgery duration (from the time corneal incision began to the time corneal suturing ended), total anesthetic duration (from the time of endotracheal intubation to extubation), and intraoperative data (end-tidal isoflurane concentration, heart rate, and mean arterial blood pressure) were compared between treatment groups with the Student t test and Mann-Whitney U test. Preoperative and postoperative subjective pain scores at each measurement point and interval to treatment failure for each treatment group were compared with the Mann-Whitney U test. Values of P < 0.05 were considered significant.

Results

Mean ± SD durations of intraocular surgery and anesthesia in dogs that received intracameral injection of 2% lidocaine hydrochloride solution were 20.0 ± 4.5 minutes and 110.5 ± 15.8 minutes, respectively. Those of dogs that received intracameral injection of BSS were 19.1 ± 4.9 minutes and 107.7 ± 22.5 minutes, respectively. There was no significant (P > 0.70) difference in surgery and anesthetic durations between the 2 groups.

Mean end-tidal isoflurane concentration recorded every 5 minutes during surgery was significantly (P < 0.05) higher in the BSS group (1.5 ± 0.1%) than in the lidocaine group (1.2 ± 0.1%). Isoflurane requirements were significantly (P < 0.05) higher in the BSS group than in the lidocaine group 5 minutes after continuous-tear curvilinear capsulorhexis, irrigation-aspiration, and corneal suturing were performed (P < 0.05; Figure 1). There was no significant (P > 0.10) difference in heart rate and mean arterial blood pressure between the 2 groups at any point during surgery.

Figure 1—
Figure 1—

Mean end-tidal isoflurane concentration recorded 5 minutes after the start of various intraocular surgical stimuli in dogs that received an intracameral injection of 2% lidocaine hydrochloride solution (0.3 mL; white squares; n = 6) or BSS (0.3 mL; black squares; 6). Stimuli included corneal incision (incision), continuous-tear curvilinear capsulorhexis (CCC), phacoemulsification (phaco), irrigation-aspiration (I/A), and corneal suture (suture). *Values differ significantly (P < 0.05) between treatment groups for the indicated stimuls.

Citation: American Journal of Veterinary Research 71, 2; 10.2460/ajvr.71.2.216

Baseline overall subjective pain scores were not significantly (P = 0.86) different between the lidocaine and BSS groups (Table 1). There was also no significant (P ≥ 0.05) difference in subjective pain scores between the groups at any point after extubation. Five dogs in the BSS group required additional analgesia (ie, had treatment failure) during the first 180 minutes after extubation, whereas no dogs required additional analgesia in the lidocaine group during the same period (Figure 2). In the lidocaine group, 1 dog received supplementary analgesia 210 minutes after extubation, and the incidence of treatment failure in that group increased afterward. In total, 5 dogs in the BSS group and 4 dogs in the lidocaine group received additional analgesia. The mean interval to treatment failure was significantly (P = 0.014) shorter in the BSS group (1.4 ± 1.2 hours) than in the lidocaine group (4.9 ± 1.2 hours).

Table 1—

Mean ± SD subjective pain scores before (baseline) and at various points after phacoemulsification in healthy Beagles treated with intracameral injection of 2% lidocaine hydrochloride solution (0.3 mL) or BSS (0.3 mL).

Measurement timeLidocaineBSS
No. of dogs*ScoreNo. of dogs*Score
Baseline63.3 ± 0.563.2 ± 0.4
30 min64.2 ± 1.856.5 ± 1.4
60 min64.3 ± 2.245.5 ± 1.0
90 min64.8 ± 1.545.3 ± 1.0
120 min64.8 ± 0.835.7 ± 1.2
150 min65.0 ± 2.125.0 ± 4.0
180 min64.8 ± 1.226.5 ± 2.1
210 min65.7 ± 3.716
240 min55.2 ± 3.316
6 h45.0 ± 1.817
8 h24.5 ± 0.718
16 h24.0 ± 0.015
24 h23.5 ± 0.715

Includes only dogs that had not received supplementary analgesia at the indicated measurement point.

Scores did not differ significantly between groups at any point.

Figure 2—
Figure 2—

Cumulative number of dogs treated with intracameral injection of 2% lidocaine hydrochloride solution (0.3 mL; black bars; n = 6) or BSS (0.3 mL; white bars; 6) that required supplemental analgesia at various times after extubation (E) following intraocular surgery.

Citation: American Journal of Veterinary Research 71, 2; 10.2460/ajvr.71.2.216

Discussion

The present study revealed that intracameral injection of 2% lidocaine hydrochloride solution versus BSS in dogs undergoing phacoemulsification resulted in a significant reduction in the intraoperative isoflurane requirement and the proportion of dogs with postoperative pain for up to 180 minutes after surgery. These findings suggested that intracameral lidocaine injection may be useful for analgesia in intraocular surgery.

Intracameral lidocaine injection is reportedly an effective intraoperative analgesic in combination with topical anesthesia in humans undergoing cataract surgery.16,18–20 A randomized clinical trial24 in humans revealed that adjunct intracameral lidocaine injection decreased pain scores at various points during surgery, decreased the need for additional IV sedation, and increased surgeon satisfaction, compared with intracameral placebo injection.24 The present study also revealed that intracameral lidocaine injection resulted in a lower end-tidal isoflurane concentration required for maintenance of stable anesthesia during cataract surgery, compared with intracameral placebo (BSS) injection in dogs.

To compare isoflurane requirements between 2 groups, anesthetic administration should be controlled. In the study reported here, therefore, dogs received the same preanesthetic medications and the initial end-tidal isoflurane concentration was maintained at the same value (1.2%). No perioperative analgesic medications such as systemically or topically administered opioids or NSAIDs were administered because such medications can obscure the analgesic effect of intracamerally injected lidocaine. In anesthetized dogs, definition of the anesthetic depth is usually attempted through monitoring of changes in palpebral, corneal, and pedal reflexes; eyeball position; muscle tone; and physiologic variables such as respiratory rate, heart rate, and blood pressure.25 However, when dogs receive neuromuscular blocking agents, assessment of changes in voluntary movements is impossible. Therefore, defining anesthetic depth can depend on changes in variables affected by the sympathetic nervous system, including heart rate and blood pressure. Investigators in another study26 involving dogs undergoing cervical or thoracolumbar laminectomy considered > 20% increases in heart rate and systolic arterial blood pressure as reflective of inadequate analgesia and the need for additional analgesic treatment. In the present study, the isoflurane concentration was adjusted to prevent an increase or decrease in heart rate and to prevent the mean arterial blood pressure from increasing > 10%, compared with the baseline value measured immediately before surgery began.

A clinical trial24 involving humans revealed that supplementary intracameral injection of lidocaine results in a lower mean pain score at the conclusion of cataract surgery than does intracameral injection of a placebo. However, clinical trials in which the analgesic effect of intracameral lidocaine injection was evaluated after intraocular surgery are limited. It has been suggested that systemic lidocaine infusion prior to cataract surgery may provide preemptive analgesic effects in dogs, leading to an increase in postoperative comfort.3 In the present study, the mean interval to treatment failure in lidocaine-treated dogs was 4.9 hours, which was significantly longer than in the BSS group (1.4 hours). Treatment failure occurred during the first 3 hours in all dogs in the BSS group, requiring administration of rescue analgesia. In the lidocaine group, additional analgesic was not needed until > 3.5 hours after extubation. This finding indicated that the analgesic effect of the intracameral lidocaine injection may persist for at least 3 hours after intraocular surgery. The theoretical duration of the analgesic effect of lidocaine is 60 to 120 minutes,13 which is considerably shorter than was evident in the present study. In addition, intracamerally injected lidocaine may be rapidly taken up by the iris, ciliary body, and cornea, but it is quickly removed from these tissues after BSS irrigation.21 Therefore, the fact that no lidocaine-treated dogs required additional analgesic for the first 3 hours after surgery suggested that intracameral lidocaine injection might have had a preemptive analgesic effect in the setting of intraocular surgery.

The assessment of pain in animals is highly subjective, and various pain-scoring systems have been established to make the assessment as objective as possible.27 The subjective numerical pain scoring system used in the present study was a modification of a published system,3 and similar numerical rating systems have been widely used for pain assessment in dogs.3,27,28 We included typical clinical signs of ocular pain such as third eyelid protrusion and blepharospasm in our pain-assessment criteria to adapt the system for ocular pain assessment. In this study, the pain score was evaluated by a sole trained observer to avoid interobserver discrepancies in pain-score assignment.

The safety of intracameral injection of unpreserved lidocaine was established in several studies that revealed no toxic changes to the corneal endothelium in humans,29 pigs,30 rabbits,31 or dogs.22 Toxic retinal effects are another potential concern, particularly in the situation of posterior capsular rupture and vitreous humor loss.32,33 These toxic effects are reportedly transient34,35; nevertheless, careful monitoring should be performed when a patient has a clinical condition that allows for diffusion of lidocaine into the posterior segment of the eye.

Adverse effects associated with systemic lidocaine administration include cardiovascular signs such as bradycardia, vasodilation, and negative inotropy. These occur when plasma concentrations of lidocaine exceed 15 μg/mL in humans.36 A study in dogs revealed that plasma concentrations of 2.7 to 5.27 μg of lidocaine/mL have no influence on arterial blood pressure, cardiac index, systemic vascular resistance, or cardiac electrical rhythm.37 A human clinical study38 revealed that injection of 0.5 mL of 1% lidocaine solution was not systemically therapeutic (ie, plasma concentration < 100 ng/mL), nor did it yield detectable changes in heart rate or ECG findings. Therefore, we suggest there was no considerable influence of systemically absorbed lidocaine on the heart rate or arterial blood pressure in the present study.

The mydriatic effects of intracameral lidocaine injection in humans undergoing cataract surgery have been investigated.39,40 In the present study in dogs, we could not evaluate the mydriatic effect of intracameral lidocaine injection because we used a preoperative mydriatic to prevent those performing the surgery and assigning pain scores from being able to detect whether lidocaine had been used. However, it is likely that intracamerally injected lidocaine is effective at yielding both analgesia and mydriasis for intraocular surgery in dogs.

Perioperative pain may be influenced by various factors such as preoperative ocular condition, cataract maturity, surgery duration, surgical techniques used, degree of conjunctival manipulation, dose and type of preanesthetic administered, use of eyedrops, and experience and expertise of the surgeon. In our study, the variables dog age and breed were controlled. One surgeon performed all operations on healthy eyes so that potential confounding of the analgesic effect by a disease process or surgeon's surgical skill could be prevented. Intracameral lidocaine injection will need to be evaluated in dogs with cataracts to determine its effectiveness in clinical settings. Studies are also needed to evaluate the effectiveness of intracamerally administered lidocaine as an adjunctive analgesic.

Given our findings that intracameral lidocaine injection was effective in reducing the intraoperative isoflurane concentration and additional postoperative analgesic requirement in dogs undergoing phacoemulsification, we believe this form of treatment may improve analgesia during and following intraocular surgery and may be particularly beneficial in dogs that are not candidates for analgesia with opioids or NSAIDs. Intracameral lidocaine injection may be useful in conjunction with other analgesics to enhance dog comfort during intraocular surgery.

ABBREVIATION

BSS

Balanced salt solution

a.

SL-202, Shin-Nippon, Tokyo, Japan.

b.

Keeler Vantage, Keeler, Windsor, Berkshire, England.

c.

Tonopen, Mentor, Norwell, Mass.

d.

Vet-Dop Doppler, Vmed Technology Inc, Mill Creek, Wash.

e.

Daehan Lidocaine HCl 2%, Dai Han Pharm Co Ltd, Seoul, Republic of Korea.

f.

Balanced salt solution plastic bag type, Baxter Co, Alliston, ON, Canada.

g.

Sedaject, Samwoo Medical, Yesan, Republic of Korea.

h.

Chong Kun Dang Pharm, Seoul, Republic of Korea.

i.

Ocutropic, Sammil Pharm Co, Seoul, Republic of Korea.

j.

Provive 1%, Claris Lifesciences, Vasana, India.

k.

Forane solution, Choongwae Pharm Co, Seoul, Republic of Korea.

l.

Datex-Ohmeda S/5, GE Healthcare, Madison, Wis.

m.

Ventilator Ace-3000, Acoma Co Ltd, Tokyo, Japan.

n.

Peripheral nerve locator-stimulator, Life-Tech Inc, Stafford, Tex.

o.

Leica M-651, Leica Microsystems, Heerbrugg, Switzerland.

p.

Acrium, Myung Moon Pharm, Seoul, Republic of Korea.

q.

Acri Bio Visc, Acri-Tec Inc, Salt Lake City, Utah.

r.

Heparin Sodium, Choongwae Pharm Co, Seoul, Republic of Korea.

s.

Epinephrine inj, Dai Han Pharm Co Ltd, Seoul, Republic of Korea.

t.

Toranzin, Samsung Pharm Ind, Seoul, Republic of Korea.

u.

SPSS, version 12.0, SPSS Inc, Chicago, Ill.

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Appendix

Subjective pain scoring system (modified from Smith et al3) used to assess the analgesic effects of intracameral lidocaine injection in dogs undergoing phacoemulsification.

CharacteristicScoreCriteria
Comfort0Asleep or calm
1Awake and interested in surroundings
2Mild agitation or depressed and uninterested in surroundings
3Moderate agitation, restless, and uncomfortable
4Extremely agitated or thrashing
Movement0Quiet
11 to 2 position changes/min
23 to 6 position changes/min
3Continuous position changes
Appearance of treated eye0Normal
1Mild changes (affected eye partially closed)
2Moderate changes (blinking or third-eyelid protrusion of affected eye)
3Severe changes (affected eye continuously closed or pawing at eye)
Behavior (unprovoked)0Too sedate to evaluate
1Normal
2Minor changes
3Moderately abnormal (less mobile or alert than normal, unaware of surroundings, or restless)
4Markedly abnormal (very restless, vocalizing, self-mutilating, grunting, or facing back of cage)
Interactive behaviors0Too sedate to evaluate
1Normal
2Pulls away or blepharospasm when surgical site touched; mobile
3Vocalizes when wound touched and reluctant to move but will when coaxed
4Violent reaction to touching of surgical site, snapping, growling when approached, or failing to move when coaxed
Vocalization0Quiet
1Crying but responds to quiet voice and stroking
2Intermittent crying, with no response to quiet voice and stroking
3Constant crying (unusual for this particular dog), with no response to stroking or voice

Contributor Notes

Supported by the BK21 Program for Veterinary Science and the Research Institute for Veterinary Science, College of Veterinary Medicine, Seoul National University.

Address correpondence to Dr. Seo (kmseo@snu.ac.kr).