We all know capnography can detect such critical events as hypoventilation earlier than pulse oximetry when used in conjunction with standard vital signs monitors, but are you aware that capnography can tell us so much more?

1. Anesthesia delivery apparatus. Abnormal capnography readings may indicate inadequate anesthetic delivery or faulty equipment. Capnography monitors can help you adjust fresh gas flows and detect circuit disconnections or leaks, one-way valve malfunctions and other device problems.

2. Airway. Capno-graphy was originally developed to aid intubation by confirming the proper positioning of the tracheal tube — since the presence of CO2 in the endotracheal tube confirms tracheal intubation — and this remains one of its most vital applications for anesthesia. Even when used with laryngeal mask airways, it can help detect dislodgement or inappropriate positioning. If the tube is inadvertently positioned in the esophagus or at any time gets displaced, the monitor will detect no CO2.

3. Breathing. End tidal CO2 is a useful indicator of how well the patient is breathing. Abnormal readings may help detect distal airway obstructions (such as bronchospasm) and other breathing complications while patients are under sedation or general anesthesia.

4. Circulation. Another basic use of capnography is estimating cardiac output. It also detects certain circulatory abnormalities. A sudden drop in the end tidal CO2 concentration may alert you to a possible pulmonary embolism.

5. Homeostasis. You can use capnography to detect a variety of complications associated with general anesthesia and sedation, including awareness, sepsis and acid-base balance disorders.

6. Non-perioperative. Many practitioners outside the OR use capnography during ER and ICU tracheal intubation as a non-invasive measure of ventilation during transport of critically ill patients and in sleep lab studies, just to name a few.

7. Neuromuscular function. When using muscle relaxants in anesthesia, the capnograph will change as the patient's neuromuscular function is altered. If the muscle relaxant wears off during anesthesia, we see the eponymous "curare cleft" in the capnograph. Toward the end of the anesthetic, as the patient's neuromuscular function returns to normal, the capnograph demonstrates the adequacy of spontaneous respiration. In conjunction with other parameters, we often extubate the patient only when the capnograph returns to normal.

8. Malignant hyperthermia. A rapidly increasing end tidal CO2 value, along with other signs, is considered one of the first and most important warning signs of malignant hyperthermia.

A versatile tool
Capnography has come a long way since it was introduced in anesthesiology more than 3 decades ago. As this technology has advanced, practitioners across different specialties have found more interpretations for it to learn more about their patients' well-being.