Cardiopulmonary effects of fentanyl-droperidol, nitrous oxide, and atropine sulfate in dogs.

The cardiopulmonary effects of droperidol-fentanyl, nitrous oxide, and atropine were evaluated in 12 adult male Beagle dogs. All dogs were surgically instrumented with a cardiac output thermistor and arterial and venous catheters and were prepared with a chronic tracheostomy. Each dog was used as its own control, and data obtained when dogs were nonanesthetized and nonmedicated were compared with data recorded after the test drugs were administered. The dogs were randomly allotted to 3 groups of 4 dogs each. Group I dogs were given droperidol-fentanyl alone intravenously (IV); group II dogs were given droperidol-fentanyl IV with 67% nitrous oxide; and group III dogs were given atropine sulfate intramuscularly followed by droperidol-fentanyl IV with 67% nitrous oxide. Minute volume was decreased in the 3 groups of dogs for 3 to 5 minutes after droperidol-fentanyl was injected. This resulted in respiratory and metabolic acidosis in all dogs, as indicated by increased arterial carbon dioxide tension, decreased pH, and increased base deficit. In addition, droperidol-fentanyl given alone caused a decrease in systolic pressure and a slight decrease in heart rate. Group 1 dogs were sensitive to auditory stimulation. Cardiovascular changes were not seen when nitrous oxide was added; however, analgesia and muscle relaxation were improved. Premedication with atropine sulfate resulted in increased cardiac output, heart rate, and diastolic pressure, and subsequent administration of droperidol-fentanyl with nitrous oxide caused a transient increase in mean arterial and systolic pressure. This last anesthetic regimen, along with assisted or controlled respiration, seems to provide an excellent anesthetic state with minimal cardiopulmonary depression.