Vital signs such as heart rate, respiratory rate, and blood pressure can be monitored using specialized devices. Rapid-acting, anesthetic drugs are easier to control if they are continuously administered. The animal's depth of anesthesia is determined by evaluating reflexes, muscle tone, and response of vital signs to surgical stimulation. If an animal is judged to be too light for the surgical procedure being performed, an increased amount of anesthetic is administered. Conversely, if the patient is judged to be in an excessively deep plane of anesthesia, the amount of anesthetic administered is decreased.
All anesthetic drugs are potent and can cause serious problems although new drugs are much safer.
Inhalant agents are those that are breathed in and out rather than being injected into a blood vessel or muscle. Newer anesthetics such as Isoflurane are less likely to aggravate a pre-existing abnormal heart rhythm. Additionally, inhalation agents such as Isoflurane enter and exit the brain rapidly, allowing for a rapid onset of and recovery from anesthesia. Some think of general anesthesia as a relaxing sleep. It is probably much more accurate to compare general anesthesia to a period of very strenuous exercise.