Anesthetic mishaps due to airway problems, leaks and disconnections in the anesthesia system often develop and may become apparent only when a crisis occurs. Circuit leaks which decrease the minute volume may not be indicated by airway pressure monitoring but may be detected by C02 monitoring because the PETCO2 gradually increases. Airway pressure monitors used to detect breathing system leaks occasionally fail to detect some disconnections. Under these circumstances a C02 monitor would detect disconnection instantaneously in paralyzed patients.5 Carbon dioxide monitoring gives an early warning of C02 retention by the patient due to a faulty Bain anesthetic system, an exhausted C02 absorbent in a semi-closed anesthetic system, leaks in the anesthetic system, disconnections within the anesthetic machine or malfunction of valves in circle anesthetic systems.5-12

Further, a total occlusion or accidental extubation of the endotracheal tube results in an abrupt decrease in PETCO2, whereas a partially kinked or obstructed tube can result in either increased or decreased PETCO2, or in no change in PETCO2 depending on the severity of the obstruction.6,13 Capnography is considered more valuable than capnometry in detecting partially kinked endotracheal tubes, as distortions in C02 waveforms (prolonged phase II, steeper phase III, irregular height of the CO2 waveforms) occur earlier than changes in PETCO2.11,13,14 However, it should be noted that endotracheal tube obstruction must be severe (at least 50% occlusion) to produce changes in PETCO2 or in the C02 waveforms.11,13