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T.J. Bunch, B. Tian, B.T. Gabelt, P.L. Kaufman; Intraocular Pressure Response to Repeated Ketamine Administration . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3434.
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Purpose: Ketamine (KET) is commonly used to sedate non-human primates when non-invasively measuring intraocular pressure (IOP). After being sedated with i.m. KET for several hours per day on a number of consecutive days, it was observed that the IOPs of an experimental group of monkeys were drastically reduced. We further investigated possible causal relationships between repeated KET anesthesia and decreased IOP.Methods: The IOPs of 3 cynomolgus monkeys (3.1-5.6 kg, group 1) sedated with i.m. KET (10mg/kg initial, 5-10mg/kg maintenance) were measured hourly for 6 hours using Goldmann tonometry on three consecutive days by investigator 1. A different group of 6 monkeys (2.8-4.6 kg, group 2) was studied similarly on 5 consecutive days by investigator 2. In group 2, blood pressure (BP) was measured by brachial or femoral cuff every hour. On day 5 each animal also received i.v. lactated Ringers fluids with 5% dextrose at a rate of 10 ml/kg/hr throughout the experiment.Results: The initial IOP (mean±sem mmHg) for group 1 was 12.8 ± 0.6 on day 1. By the end of each 6 hour experimental day, IOP had significantly decreased compared to the starting IOP on that day as follows: day 1, - 2.5 ± 0.3 (p< 0.02); day 2, - 4.0 ± 0.6 (p< 0.025); day 3, -7.4 ± 0.9mmHg (p< 0.02). There was a similar but less dramatic trend in IOP reduction in group 2 which had an initial IOP on day 1 of 13.7±0.5mmHg. After 6 hours of KET on each experimental day, IOPs had decreased from the starting IOP on that day by the following amounts: day 1, -0.1 ± 0.3; day 2, -1.5±0.4 (p<0.02); day 3, -1.6 ± 0. 4 (p< 0.02); day 4, -2.3 ± 0.2 (p< 0.001); day 5, -0.6±0.6. IOP on day 5 appeared to be maintained by fluid supplementation. BP was not affected by consecutive days of KET anesthesia.Conclusions: Animals that are anesthetized with i.m. KET for long periods of time on consecutive days can show a reduction in IOP. This is most likely due to physical stresses including dehydration and decreased caloric intake. Caution should be exercised since these effects could adversely affect other ocular physiological measurements.
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