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The dose of ephedrine is 0.02 to 0.1 mg/kg IV. Personally, I would repeat 0.02 mg/kg IV until blood pressure comes up.
The indication of ephedrine is hypotension with bradycardia. It is especially effective for animals that do not respond to atropine. Ephedrine works well in hypothermic small dogs and cats although atropine may be ineffective in those.
Although dilution is not particularly necessary, you can dilute when the volume is low. There is also no particular rate of administration, but ephedrine should be given slowly. The duration of action would be around 20 minutes.
Adverse effects include tachycardia, hypertension, tachyarrhythmia, and ventricular premature complex.
As the duration of action is short, undesirable effects disappear quickly. Thus, you let it go unless they turn into fatal arrhythmias with hypotension.
In addition, you should pay attention to the depth of anesthesia, because ephedrine increase MAC of inhalants.