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diphenhydramine solution has been shown to have an anesthetic effect when administered topically to rabbits (Suffridge et al. 2009).
Advantages and Disadvantages
Certain topical anesthetics will decrease tear production and improve drug bioavailability from the conjunctival
sac (Patton & Robinson 1975). Decreased lacrimation
will affect results of Schirmer tear test values for at least 45 minutes and possibly longer after the application of
1 drop of 0.5% proparacaine. Schirmer tear tests aimed at evaluating both basal and stimulated tear production should therefore be performed prior to the application of topical anesthetic (Hamor et al. 2000). Repeat application of topical anesthetics is toxic to the corneal epithelium and should not be used therapeutically (Herse&Siu
1992; Judge et al. 1997; Nam et al. 2006; McGee &Fraunfelder 2007). Sample acquisition for culture from the corneoconjunctival area is recommended prior to instillation of local anesthetic due to their antimicrobial activity. Finally, storage of proparacaine at room temperature for more than 2 weeks results in a decrease in drug effect; therefore, refrigeration of opened bottles is recommended (Stiles et al. 2001).
Specific aspects of loco-regional anesthesia of the eye in cats
Intravenous administration of lidocaine is commonly considered to be particularly toxic in cats due to the potential of myocardial and CNS depression (Chadwick 1985; Lemke & Dawson 2000). However, numerous studies evaluating the toxic effects of lidocaine do not support the cat as being particularly sensitive to this drug (Pypendop&Ilkiw 2005). Cats are generally of lower body weight than most dogs, thus care must be taken to calculate the correct volume of local anesthetic drug that can be safely administered to the feline patient (O’Brien et al. 2010). In addition to careful dose calculation,
as with dogs, aseptic technique should be used and syringes should be aspirated before local anesthetic injection to avoid inadvertent intravascular administration.
Acknowledgements: Special thanks to Drs. Karen Walsh and Ellison Bentley for their contributions to these lecture notes
Suggested References
Accola PJ, Bentley E, Smith LJ et al. (2006) Development of a retrobulbar injection technique for ocular surgery and analgesia in dogs. J Am Vet Med Assoc 229, 220-225.
Bartfield JM, Holmes TJ, Raccio-Robak N (1994) A comparison of proparacaine and tetracaine eye anesthetics.AcadEmerg Med 1, 364-367.
Chadwick HS (1985) Toxicity and resuscitation in lidocaine- or bupivacaine- infused cats.Anesthesiology 63, 385-390.
Clark JS, Bentley E, Smith LJ (2011) Evaluation of topical nalbuphine or oral tramadol as analgesics for corneal pain in dogs: a pilot study. Vet Ophthalmol 14, 1-7.
Giuliano EA (2008) Regional anesthesia as an adjunct for eyelid surgery in dogs. Top Companion Anim Med 23, 51-56.
Herring IP, Bobofchak MA, Landry MP et al. (2005) Duration of effect and effect of multiple doses of topical ophthalmic 0.5% proparacaine hydrochloride in clinically normal dogs. Am J Vet Res 66, 77-80.
Lemke KA, Dawson SD (2000) Local and regional anesthesia. Vet Clin North Am Small AnimPract 30, 839-857.
Myrna KE, Bentley E, Smith LJ (2010) Effectiveness of injection of local anesthetic into the retrobulbar space for postoperative analgesia following eye enucleation in dogs. J Am Vet Med Assoc 237, 174-177.
Stiles J, Honda CN, Krohne SG et al. (2003) Effect of topical administration of 1% morphine sulfate solution on signs of pain and corneal wound healing in dogs. Am J Vet Res 64, 813-818.
Stiles J, Krohne S, Rankin A et al. (2001) The efficacy of 0.5% proparacaine stored at room temperature. Vet Ophthalmol 4, 205-207
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