I have never had respiratory distress in a garter become serious yet. I have seen early warning signs and caught them in time to turn it around. The raising head posture is an early warning sign. if i see that i pick up the snake and put the middle of it next to my ear in a quiet place and listen to the breathing. If I hear early signs of distress (popping, wheezing, gurgly noises) I isolate the snake, up the heat (the heat helps their body run at its fullest to fight infection) and keep it scrupulously clean and dry on paper toweling. I don't feed until the snake appears to be okay.