Sub-ambient pressure alarm
Physics, Monitoring, & Devices
The sub-ambient pressure alarm is intended to identify a breathing system pressure of <-10 cmH2O. Common causes of negative pressure include spontaneous respiration by the patient with an obstruction in the circuit, scavenging system problems, or application of a suction device into the circuit (suction catheter in the endotracheal tube) . This alarm would function if an OG or NG tube was mistakenly placed in the trachea and put to suction.
In terms of scavenging systems, in active disposal systems a vacuum is applied to move waste gas from the circuit to the scavenger. Both excessive scavenger flow (via the vacuum) and a valve stuck in the “open” position (resulting in the vacuum from entering the breathing circuit) may result in sub-ambient pressure in the breathing circuit.