Combination Auriculopalpebral Nerve Block and Local Anesthesia for Placement of a Nictitating Membrane-to-Superotemporal Bulbar Conjunctiva Flap in Dogs

Introduction

Nictitating membrane (NM) flap is a simple and rapid procedure that is frequently performed in dogs with corneal ulcers. The NM-to-superotemporal bulbar conjunctiva flap is one of several NM flaps available, and it can be pursued in the interest of avoiding the complications associated with other NM flaps. One complication associated with NM-to-superior- lid technique is necrosis of the upper lid; complications of NM-to-episclera technique include inadvertent penetration of the globe and premature flap failure.¹ This procedure is usually performed under general anesthesia, even though some dogs with corneal ulcers may have clinical conditions that increase their general anesthetic risk.

Many reports on topical, sub-Tenon’s capsule, intracameral, retrobulbar, and regional anesthesia for ocular surgery in humans and animals have been published.^2–6 Nictitating membrane flaps can likely be performed in conscious dogs under local anesthesia with adequate analgesia, but to our knowledge, the clinical evaluation of NM flaps without general anesthesia has not been reported. We constructed the NM-to-superotemporal bulbar conjunctiva flap in conjunction with auriculopalpebral nerve block, topical anesthesia of the eye, and infiltration anesthesia of the superotemporal bulbar conjunctiva and palpebral surface of the NM. The purpose of this study was to evaluate the efficacy of combined local anesthesia in dogs undergoing NM-to-superotemporal bulbar conjunctiva flap construction.

Materials and Methods

We reviewed medical records of 47 consecutive dogs that had received local anesthesia for NM-to-superotemporal bulbar conjunctiva flap between January 2006 and December 2007. Signalment, reason for combined local anesthesia administration for NM flap, temperament of the dog, and compliance with the anesthetic procedure and surgery were investigated.

Auriculopalpebral nerve block and topical and infiltration anesthesia were performed to achieve combined local anesthesia of the eye. Auriculopalpebral nerve block was induced by inserting a 1.2-cm, 26-gauge needle through the skin dorsal to the zygomatic process at its caudal one-third and injecting 0.4 mL of 2% lidocaine^a subcutaneously [Figure 1A].⁷ The palpebral reflex was tested at the initial ophthalmic examination and 5 minutes after the auriculopalpebral nerve block was carried out.

Immediately following the auriculopalpebral nerve block, one drop of topical anesthetic (0.5% proparacaine^b) was applied to the eye. After 1 minute, 0.1 mL of 2% lidocaine was injected subconjunctivally at the projected suture sites in the superotemporal bulbar conjunctiva and palpebral surface of the NM, approximately 3 to 5 mm ventral to the margin of the nictitans [Figure 1B]. Five minutes after the injection, the NM injection site was lightly pinched with mosquito hemostat forceps in order to evaluate analgesia. When the dog no longer reacted to the stimulus, we proceeded with NM-to-superotemporal bulbar conjunctiva flap construction using 4-0 polygalactin 910.^c The dog was placed in a sitting position, underminimal head restraint, with the eyelids manually held open by an experienced handler.

Corneal ulcers were treated by debridement, punctate keratotomy, and grid keratotomy when needed. The entire surgical procedure lasted <5 minutes from beginning to the completion of suture placement. Treatment success was defined as compliance of the dog during the anesthetic procedures and surgery, without the need for sedation or general anesthesia. Postoperative palpebral reflex was assessed 1 hour after the operation to evaluate for any residual akinesia.

Results

Combined local anesthesia for NM-to-superotemporal bulbar conjunctiva flap was performed in 47 dogs with corneal ulcer. Mean age at the time of the procedure was 8.3±3.9 years (range 2 months to 17 years). The most common dog breed was the shih tzu (n=23) [see Table]. The main reasons for choosing combined local anesthesia included owner reluctance for general anesthesia to be used (n=15), senility (n=10), hepatic problems (n=6), cardiovascular problems (n=4), and renal problems (n=4).

All dogs that received combined local anesthesia had a negative or significantly reduced palpebral reflex 5 minutes after the auriculopalpebral nerve block was achieved. Complete recovery of the reflex was observed 1 hour after the operation in all dogs. The overall success rate of combined local anesthesia for NM flap was 89.3% (n=42). During the procedure, no anesthesia- or surgery-related complications were noted. The causes of treatment failure included resistance to injection of lidocaine for the auriculopalpebral nerve block (n=1), resistance to infiltration anesthesia of the superotemporal bulbar conjunctiva (n=2), and lack of compliance with the surgery after the local anesthesia was achieved (n=2). These dogs required general anesthesia (n=2) or sedation (n=3) in order to complete the surgery. The NM-to-superotemporal bulbar conjunctiva flaps remained in place for the intended period (10 to 19 days) in 43 dogs. Premature flap failure occurred in four dogs; the NM flap held for 5 to 7 days in these cases. Causes of premature flap loosening were buphthalmia in two cases and inexperience of the operator in two cases.

Discussion

The combined local anesthetic technique reported here provides adequate analgesia for the surgical site and induces akinesis of the eyelid to facilitate NM-to-superotemporal bulbar conjunctiva flap placement under minimal physical restraint in dogs. Ocular surgery in a conscious patient under local anesthesia offers many advantages. First, the surgery can be performed in cases that would be at high risk under general anesthesia. Second, local anesthesia saves the extra time, money, and effort necessitated by general anesthesia. Local anesthesia can also serve as an alternative in veterinary practices that have limited access to the resources necessary for general anesthesia.

Ocular surgery is commonly performed without general anesthesia in humans and large animals.^8–11 Auriculopalpebral nerve block is used forminor corneal procedures; supraorbital, lacrimal, and infratrochlear nerve blocks are used for upper eyelid repair; and infratrochlear nerve block is used for nictitans surgery in horses.⁸ Retrobulbar block, Peterson block, and/or auriculopalpebral nerve block are used for enucleation and radiation therapy in cattle with squamous cell carcinoma.¹¹ In humans, various local anesthesia techniques (e.g., sub-Tenon’s capsule, intracameral, peribulbar, retrobulbar, and topical anesthesia) have been reported, especially in the setting of cataract surgery.^4,9,10,12 Regional nerve block of the upper eyelid has also been reported in the setting of oculoplastic surgery in humans.⁶

Conversely, general anesthesia is usually required for ocular surgery in dogs and cats to achieve immobilization and relaxation. However, NM flap construction does not require complete immobilization, because it is a less delicate procedure than most other ocular surgeries, and it is short in duration—typically <5 minutes. Therefore, we believed NM flap construction could be performed successfully under combined local anesthesia.

We did not note any complications related to NM-to-superotemporal bulbar conjunctiva flap construction in conscious dogs in this study. Inadvertent globe penetration is the major complication that can occur when this surgery is performed in conscious dogs. However, with the NM-to-superotemporal bulbar conjunctiva flap technique, the bulbar conjunctiva is picked up with forceps, and the needle is passed through the conjunctiva so that the needle point is unlikely to penetrate the globe.

The three anesthetic steps described in the present study were auriculopalpebral nerve block, topical anesthesia of the conjunctiva and cornea, and infiltration anesthesia of the superotemporal bulbar conjunctiva and the NM. Auriculopalpebral nerve block is a widely used method for paralyzing the orbicularis muscle in horses and cattle to facilitate ophthalmic examination and ocular surgery.^8,11 In this study, the palpebral reflex was suppressed significantly or completely in all dogs, and adequate akinesia was achieved concurrently. Persistent paralysis of the orbicularis muscle may cause corneal problems in other procedures, but the cornea was protected by the NM in the procedure discussed in this study. However, orbicularis paralysis must be considered carefully during other ophthalmic procedures in order to avoid corneal damage; generous application of eye lubricant is recommended.⁷ Topical instillation of 0.5% proparacaine facilitated the subconjunctival injections of 2% lidocaine and the operations on the cornea. A combination of topical and infiltration anesthesia is considered to provide adequate analgesia for the flap.

When auriculopalpebral nerve block and infiltration anesthesia of the conjunctiva are performed, the administrator should remember that toxic doses of lidocaine can cause systemic and local side effects in the central nervous system, cardiovascular system, and skeletal muscles.¹³ The maximum dose of lidocaine allowed in healthy dogs is 12 mg/kg.¹⁴ The total dose of lidocaine used in auriculopalpebral nerve block and infiltration anesthesia for NM flap construction in this study was 12 mg. Therefore, when this anesthetic procedure is performed in dogs weighing ≤1 kg, the lidocaine dose should be reduced according to body weight of the dog. In order to have an adequate volume for local infiltration, the calculated dose of lidocaine can be diluted in an equal or greater volume of sterile saline.

Injecting anesthetic around the eyes of two aggressive dogs and one hyperactive young dog was impossible. Two other dogs became agitated after completion of combined local anesthesia, and they failed to tolerate surgery. These dogs were either sedated or generally anesthetized in order to have surgery completed. Temperaments of animals must be carefully considered before the procedure. When combined with sedation, the NM flap procedure is better tolerated than when the combined local anesthetic technique is used alone, especially in dogs with poor temperament.

Conclusion

This study showed that combined local anesthesia is a time- and cost-effective procedure in NM-to-superotemporal bulbar conjunctiva flap construction, and it provides both analgesia of the surgical site and akinesia of the eyelid. This anesthetic technique would be particularly useful in dogs that are compliant and may be at high risk for general anesthesia. Furthermore, the technique may be beneficial in providing prolonged postoperative analgesia of the surgical site in dogs undergoing general anesthesia. For this supplementary postoperative analgesia, the local anesthetic can be chosen based on the specific needs of duration and onset of anesthetic effect.