But the main thing I look at when classifying the severity of respiratory distress is the amount of effort it is taking the animal to breathe. This dog that has been hit by a car and has severe pulmonary contusions. This is the worst that respiratory effort gets. His rate has actually slowed a bit due to the effort required to expand his blood filled lungs. This degree of effort means that respiratory arrest is imminent and this dog went into cardiopulmonary arrest only minutes after this video was taken.