Why may my animal benefit from sedation for an ultrasound exam or echocardiogram?

The typical thorough abdominal ultrasound exam or echocardiogram takes 30-45 minutes. This is a long time for many dogs and cats to hold still and lie on a table. Lying on a table on their side or back in a strange place is quite stressful for most cats and dogs. Some cannot tolerate it at all and start to struggle or even try to scratch and bite. Even if they tolerate it, dogs often pant very heavily. Cats and dogs often have tense abdominal walls with muscle tremors. Panting, heavy breathing, frequent movement, and tense or tremoring muscles lead to motion artifacts which often makes the ultrasound study suboptimal and some more subtle abnormalities become impossible to diagnose.
Therefore, sedation is a safe and easy way to decrease stress for the animal and makes it easier and safer for the person to hold them and significantly improves the diagnostic yield. Often a mild sedative given by mouth at home 2-3 hours before the scheduled ultrasound exam is enough, but sometimes an injectable sedative is given right before the ultrasound study.
General anesthesia is very rarely needed.
Sedation is very safe, and we often use reversible medications, so in the rare event of negative side effects, a reversal agent can be administered immediately.
Owners often ask if they can come into the ultrasound room to calm their animal down. I will say, this occasionally works, but most of the time, the already stressed dog or cat gets more worked up when their owner enters the room. They want them to take them home and do not understand why they must stay on the table in a strange place and position. Once they are very worked up and have a high-level of stress hormones in their body, the sedatives do not work as well anymore. Therefore, when we recognize that an animal is stressed, I always recommend administering the sedative as soon as possible.