What is a capnometer?

A capnometer or capnograph is a medical instrument that measures the amount of carbon dioxide (CO2) in the expired breath of patients. These devices are used in a variety of settings, ranging from the field to operating rooms, and are stocked by many medical equipment and supply companies. Models designed for specific applications, such as anesthesia, may have special features designed to make them easier to use and more efficient.

When healthy people exhale, the air expelled from the lungs carries CO2 as a result of gas exchange that occurs in the lungs, and carbon dioxide is a waste product of internal metabolism. There are situations that can interfere with gas exchange in the lungs, alter the composition of gases in the lungs, or make it difficult for people to remove CO2 from their bodies, and a capnometer can be used to identify changes in CO2 expiration that could indicate that a medical problem is occurring.

In anesthesia, a capnometer is one of many devices used to monitor a patient during surgery. Changes in exhaled carbon dioxide levels during surgery may indicate that there is a problem with the anesthesia or that a surgical complication is developing. By tracking the amount of CO2 a patient exhales over time or with the volume of each breath, an anesthesiologist can stay alert for emerging signs of a troubling complication.

Capnometry is also used in the intensive care unit, when patients are stable but still critical. The device can indicate when CO2 levels are changing, alerting doctors to a change in the patient's condition and to the possibility of a problem with the lungs. Like other devices used in critical care, a capnometer can be programmed to transmit to a remote monitoring location so that it can be observed by nurses at a nursing station. It can also be connected to a remote alarm that signals when levels reach a dangerous point.

The capnometer can also be used in respiration studies. Patients with breathing problems such as asthma, chronic obstructive pulmonary disorder, emphysema, etc. may be asked to undergo a breathing study so that a doctor can collect important information about the patient's lung function. This information can be used to monitor a patient's condition, collect data on the success of a treatment plan, or to establish a baseline that can be referenced during future treatment and evaluations.

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