Capnography monitors respirations and ventilation -- important information when you give a patient a possible respiratory depressant.
I had an 80 year old woman with a broken hip in extreme pain. She had taken one tramadol, which obviously hadn't touched her. I like to premedicate the patient before I even try to move them so, in increments, I gave her 7mg of Morphine over ten minutes. I waited about five minutes more, and then we packaged her on a scoop stretcher. Out in the ambulance she was still in a fair amount of pain and the roads we were on were pretty bumpy so I called to get permission to give her 3 more mg, and I was pleased the doctor actually told me to go ahead and give her 5 more mg. (We can give up to 0.1 mg/kg on standing order, and have to call for more.)
The extra morphine worked wonders. I had her on capnography to monitor her respirations/ventilation. By the time we got to triage, while she was still awake, she was feeling no pain and her respirations, which had been in the high twenties were down to 8. Her ETCO2 remained constant.
Here's the wave form strip:
Here's the trend summary for ETCO2 and RR.