In the authors' experience, dogs can develop unexpectedly high MAP values after induction of anesthesia and before the start of ophthalmic surgery. Such an increase in MAP is occasionally severe enough to warrant treatment. We have also found that this type of hypertension occurs specifically in dogs undergoing phacoemulsification for cataract removal.
In our practice, dogs undergoing phacoemulsification receive a specific set of adjunct medications applied topically to the eye or eyes in preparation for surgery. A 1% atropine ointment is applied the evening before surgery. Then, every 30 minutes during the 2-hour period immediately prior to anesthesia, ophthalmologic solutions containing antimicrobials and dexamethasone, 0.03% flurbiprofen, and 10% phenylephrine plus 0.3% scopolamine are administered at a dose of 1 drop of each/eye. These drugs are administered to induce maximal mydriasis before phacoemulsification and to maintain pupillary dilation during surgery, improving conditions for removal of the lens. Among the medications given shortly before anesthesia, phenylephrine and scopolamine are likely to have adverse cardiovascular effects should sufficient plasma concentrations be attained. Phenylephrine is an α1-adrenoceptor agonist that causes vasoconstriction, and scopolamine is an anticholinergic agent capable of enhancing the chronotropic actions of the heart.1–3
The purpose of the study reported here was to determine whether dogs that received eyedrops containing phenylephrine and scopolamine would have a higher MAP when anesthetized than would dogs that did not receive the eyedrops. We specifically hypothesized that in our institution, anesthetized dogs about to undergo phacoemulsification would have a higher MAP than would a control group of dogs. We further hypothesized that this hypertension would be attributable to eyedrops administered prior to anesthesia.
Mean arterial blood pressure
Atropine sulfate ophthalmic ointment 1%, Fougera & Co, Melville, NY.
Murocoll 2 phenylephrine HCl 10%, Bausch & Lomb Inc, Tampa, Fla.
Scopolamine HBr 0.3%, Bausch & Lomb Inc, Tampa, Fla.
Neomycin and polymyxin B sulfates and dexamethasone ophthalmic suspension, Falcon Pharmaceuticals Ltd, Fort Worth, Tex.
Escort II, MDE Inc, Arleta, Calif.
Cardell Veterinary Monitor 9401 B P, Sharn Veterinary Inc, Tampa, Fla.
Atracurium besylate, Bedford Laboratories, Bedford, Ohio.
Statistix, version 9.0, Analytical Software, Tallahassee, Fla.
McMurphy RM, Stoll MR & McCubrey R. Accuracy of an oscillometric blood pressure monitor during phenylephrine-induced hypertension in dogs. Am J Vet Res 2006; 67:1541–1545.
Herring I P, Jacobson JD, Pickett J P. Cardiovascular effects of topical ophthalmic 10% phenylephrine in dogs. Vet Ophthalmol 2004; 7:41–46.
Kantelip J P, Alatienne M, Gueorguiev G, et al. Chronotropic and dromotropic effects of atropine and hyoscine methobromide in unanaesthetized dogs. Br J Anaesth 1985; 57:214–219.
Kenefick S, Parker N, Slater L, et al. Evidence of cardiac autonomic neuropathy in dogs with diabetes mellitus. Vet Rec 2007; 161:83–88.
Brown S, Atkins C, Bagley R, et al. Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. J Vet Intern Med 2007; 21:542–558.
Basta SJ, Ali HH, Savarese JJ, et al. Clinical pharmacology of atracurium besylate (BW 33A): a new non-depolarizing muscle relaxant. Anesth Analg 1982; 61:723–729.
Sawyer DC, Guikema AH, Siegel EM. Evaluation of a new oscillometric blood pressure monitor in isoflurane-anesthetized dogs. Vet Anaesth Analg 2004; 31:27–39.
Pascoe PJ, Ilkiw JE, Stiles J, et al. Arterial hypertension associated with topical ocular use of phenylephrine in dogs. J Am Vet Med Assoc 1994; 205:1562–1564.
Meyer RE. Anesthesia of pediatric small animal patients. In: Recent advances in veterinary anesthesia and analgesia: companion animals. Available at: www.ivis.org/advances/Anesthesia_Gleed/meyer2/chapter.asp?LA=1. Accessed Oct 5, 2009.
Hackett GH, Jantzen J P & Earnshaw G. Cardiovascular effects of vecuronium, atracurium, pancuronium, metocurine and RGH-4201 in dogs. Acta Anaesthesiol Scand 1989; 33:298–303.
Amaranath L, Zanettin GG, Bravo EL, et al. Atracurium and pheochromocytoma: a report of three cases. Anesth Analg 1988; 67:1127–1130.