Do dogs have something different about their physiology that allows them to pant without hyperventilating?
This article quotes a professor of respiratory physiology that says "dogs are built to pant just right. The mechanics of their lungs and chest set a precise rate for panting that minimizes the amount of work while maximizing cooling power." They also don't breathe fully when panting, so they can still cool themselves without increasing gas exchange. This is different than humans, who will hyperventilate to get rid of carbon dioxide (or you can intentionally hyperventilate and cause respiratory alkalosis).