Ketamine/Xylazine dose for rats?

Wise Young wisey at
Thu May 18 23:24:52 EST 1995

In article <3pdsro$388 at>, Michael Vagell writes: 
>What doses of Ketamine & Xylaxine (Rompum) should be administered for 
>30-45min deep anesthesia during stereotaxic surgery in adult male Long 
>Evans rats (300-400g)?  I have been using 100mg/Kg Ketamine ip and 
>15mg/Kg Xylaxine im with good results up until now.  It is the 
>strangest thing.  We seem to lose  a lot of animals after 5pm (the 
>animals are kept on a 12:12 reverse light/dark schedule).  Does anyone 
>else find this temporal hypersensitivity in rodent anesthesia?  Any 
>suggestions for different doses or using another anesthetic agent?  
We use pentobarbital for spinal cord injury studies in Long-Evans hooded
rats.  The doses of ketamine and xylazine that you used seem adequate and
appropriate for male hoods.  In general, we find that male hooded rats
require significantly higher (nearly twice) the dose of pentobarbital than
females (on a per kg basis).  Light and dark cycles are unlikely to be
responsible for the increased mortality.  A major cause of post-anesthesia
mortality is hypothermia.  I would measure rectal temperatures and make
sure that the rats are adequately warmed postoperatively and in the cages
(we use incubators).  Adequate water intake also improves survival.  Rats
need at least 20 ml of fluid per 24 hours and we often give 10 ml
supplemental saline injections subcutaneously.  Make sure that the rats are
pathogen-free by doing an screen.  Rat colonies sometimes develop
infections that do not manifest preoperatively (particularly mycoplasma)
but such infections increase post-operative mortality.  Finally, check the
blood sugar of the rats; they sometimes become hypoglycemic after surgery. 
You should provide them with sweetened water, juice, apple slices, and the
like.  It helps.  Rats have a high metabolic rate and can lose as much as
8-10% of their body weight 24 hours after anesthesia if they are not eating
and drinking. 
Wise Young, Ph.D., M.D. 
Department of Neurosurgery 
NYU Medical Center 
550 First Avenue 
New York, NY 10016

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