Capnography

Capnography is the best monitor for detecting airway obstruction.

During partial obstruction the capnograph trace is narrowed with an upward slope and has a smaller area, as less carbon dioxide is exhaled into the airway. See Fig 1.

During complete airway obstruction there is no exhalation of carbon dioxide.

Airway pressures

Greater sub-atmospheric (negative) pressures occur during spontaneous ventilation as the respiratory muscles work harder against the obstructed airway.

High peak airway pressures occur if ventilation is attempted.