Oxygen enters your body's bloodstream through the lungs and travels throughout your body to aid metabolism. Your body's metabolism breaks down the food you eat to produce energy, and as a byproduct of this process, your body excretes a gaseous waste product called carbon dioxide into your bloodstream. It then returns to your lungs and exits your body through exhaled air. Capnography refers to the use of a capnograph to measure the level of carbon dioxide or carbon dioxide excreted in the blood. Capnography machines are most commonly used to anesthetize patients to ensure that patients receive adequate oxygen throughout the procedure. However, they are also often used in emergency medicine when a patient is intubated with an endotracheal tube (also called a breathing tube) to ensure proper placement of the tube.
Oxygenation and capnography, although related, are still distinct elements in respiratory physiology. Ventilation refers to the mechanical process of the lungs expanding and exchanging gas volumes, but breathing further describes the gases (mainly carbon dioxide and oxygen) at the alveolar level. The breathing process can be divided into two main functions: eliminating carbon dioxide waste with fresh oxygen and replenishing tissue oxygenation (usually measured by a pulse oximeter) measured in the second half of the system. Capnography describes the elimination of carbon dioxide which may show more clinical use than oxygenation status.
During anesthesia, there is an interaction between two parts: the patient and the anesthesia delivery device (usually the breathing circuit and the ventilator). The critical connection between the two components is either an endotracheal tube or a mask, and carbon dioxide is usually monitored at this junction. Capnography machines directly reflect the elimination of carbon dioxide from the lungs to the anesthesia device. Indirectly, it reflects the production of carbon dioxide through tissues and the circulation of carbon dioxide transport to the lungs. According to a closed claims study by the ASA (American Society of Anesthesiologists), a capnograph and pulse oximeter together can help prevent 93% of avoidable anesthesia accidents.
Hospitals and other healthcare facilities have also come to rely on capnography machines to help patients with asthma and chronic obstructive pulmonary disease. To determine the severity of a patient's disease, doctors use a capnography machine to measure how well his or her lungs are functioning. As the science of breathing advances, capnographs have more and more uses and are being discovered every day.