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Effects of chemical restraint on electroretinograms recorded sequentially in awake, sedated, and anesthetized dogs

Kate S. Freeman MEM, DVM1, Kathryn L. Good DVM2, Philip H. Kass DVM, PhD3, Shin Ae Park DVM, PhD4, Natalia Nestorowicz DVM5, and Ron Ofri DVM, PhD6
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  • 1 Veterinary Medical Teaching Hospital.
  • | 2 Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.
  • | 3 Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.
  • | 4 Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.
  • | 5 Przychodnia Weterynaryjna Viva, Strachocieska 58, 51-511 Wrocław, Poland.
  • | 6 Koret School of Veterinary Medicine, Hebrew University of Jerusalem, Rehovot, Israel.

Abstract

Objective—To quantitatively and qualitatively compare electroretinography (ERG) recordings in awake, sedated, and anesthetized dogs.

Animals—Six 6-month-old Beagles.

Procedures—A brief ERG protocol for dogs was used. Following 1-minute and subsequent 5-minute dark adaptation, mixed rod-cone responses were recorded bilaterally with a handheld multispecies ERG device with dogs in each of 3 states of consciousness: awake, sedated (dexmedetomidine and butorphanol), and anesthetized (atropine and hydromorphone, followed by propofol and midazolam and anesthetic maintenance with isoflurane). Low- and high-frequency noise levels were quantified via Fourier analysis, and the effect of consciousness state on signal amplitude, implicit time, and noise was analyzed via repeated-measures ANOVA. In addition, 13 veterinary ophthalmologists who were unaware of the dogs’ consciousness states subjectively graded the ERG recording quality, and scores for each tracing were compared.

Results—ERG amplitudes were highest in awake dogs and lowest in anesthetized dogs. Implicit times were shortest in awake dogs and longest in anesthetized dogs. Differences in b-wave amplitudes and a-wave implicit times were significant. Neither low- nor high-frequency noise levels differed significantly among consciousness states. Furthermore, no significant differences were identified among observers’ scores assigned to ERG tracings.

Conclusions and Clinical Relevance—Anesthesia and sedation resulted in significant attenuation and delay of ERG responses in dogs. Chemical restraint of dogs had no consistently significant effect on low- or high-frequency noise levels or on observer perception of signal quality.

Contributor Notes

Dr. Freeman's present address is Ophthalmology for Animals, 2585 Soquel Dr, Santa Cruz, CA 95065.

Supported in part by the National Eye Institute grant No. P30EY12576; Ocular Services On Demand, LLC; and the UC Davis Toots Fund.

Presented in abstract form at the 42nd Annual Meeting of the American College of Veterinary Ophthalmologists, Hilton Head, SC, October 2011.

The authors thank Dr. Christopher Murphy, Monica Motta, and Dr. Carolyn Craig for technical assistance.

Address correspondence to Dr. Freeman (kate.s.freeman@gmail.com).