Dogs usually first get sedation injected under the neck skin (like a vaccination).
Dogs react very individually to sedatives. Most fall asleep calmly. Others are insensitive to sedatives and may need more to come to rest. Nausea is not common in dogs unless they have an underlying illness that make them sensitive. Therefore, I also mix in anti emetic supplements to the sedation but there is no guaranteed effect of this.
I try to divert the attention by letting the owner stimulate the nose with the favorite food/treat. Best is if the owner holds and give a comforting scratch around the ears while I inject sedation under the neck skin (takes just a few seconds). When the dog sleeps after 5-10 minutes, I insert a catheter into a vein. After the cannula is secured with surgical tape and flushed with saline the overdose of sleep agents is given. This causes the dog to fall into the eternal asleep quickly.
Dogs that have a very poor general condition can’t always get a catheter in a vein. The overdose of sleep agents is in that case given via a cannula directly in the well vascularized liver in the abdomen. It is very individual how fast dogs fall asleep. It depends on the condition of the dog, the dogs’ blood circulation and exactly where the injection is administered in the abdomen. During 5-20 minutes, sleep becomes deeper and breathing irregular until breathing ceases and the heart stops beating. Just as with sedatives, some dogs may have to get a second dose to fall asleep for good. The veterinarian listens to the heart to ensure the cardiac arrest.
Worth knowing about the last few moments is that all animals fall asleep with their eyes more or less open. Sometimes reflective breaths (also called ”the last sighs”) are heard. Vibrations or contractions in the muscles can be seen. The coat may rise after the heart has stopped beating and death has occurred. This does not mean that the dog is alive or suffers in any way. It is only the body’s last muscle energies that run out.