Ok, so his respiratory rate is normal... that is what I was most concerned about because with any difficulty breathing, you need to get into the ER right away no matter what the cause...
If the snoring is coming from the nose/throat area, then yes he could be congested. Although dogs do not typically get nasal congestion like you or I do with the common cold. Kennel cough in adult dogs results in coughing, rarely nasal congestion alone. He could also have swelling or inflammation in is nose or throat.
More concerning is actually if the congestion is in his chest. It can be very difficult to distinguish the two. Even with a stethoscope, noises from the throat/nose can mask what is coming from the chest. Reasons for chest congestion in a 12 year old minature poodle... congestive heart failure would be at the top of my list, pneumonia, cancer - but with a resp rate of 18, it is unlikely.
The 1/2 benedryl should not have any adverse effects.
If this is the first time your dog has ever had this type of sign, I would definitely see your veterinarian to determine what the cause is. If you notice any difficulty breathing, I would rush him right into the ER.
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