People receiving anesthesia must be carefully watched, because the medicines used for anesthesia affect the central nervous system, cardiovascular system, and respiratory system (airway and lungs). Anesthesia suppresses many of the body's normal automatic functions. So it may significantly affect your breathing, heartbeat, blood pressure, and other body functions.
Instruments commonly used for monitoring during anesthesia include:
A pulse oximeter, a small instrument that is attached to your finger, toe, or earlobe to measure the level of oxygen in your blood.
An electrocardiogram (EKG, ECG) to monitor your heart activity. Small wires (leads) are placed on the skin of your chest and held in place by small adhesive patches.
A temperature probe. A monitor connected to your skin by a lead held in place by a small round adhesive patch may be used to measure skin temperature. A thermometer that is attached to a small tube inserted through the mouth into the esophagus after you are unconscious may be used to measure internal body temperature.
An oxygen analyzer and carbon dioxide analyzer on the anesthesia machine. These instruments measure the amount of oxygen and carbon dioxide gases inhaled and exhaled in your breath.
Other monitoring instruments may also be used, depending on your condition, the type of surgical procedure you are having, and the type of anesthesia used. These may be invasive monitors that need to be placed inside the body, including:
Catheters that are inserted into certain arteries or veins. These can accurately measure blood pressure or measure heart or lung function. These larger catheters also are sometimes needed to deliver medicines or blood transfusions.