The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

EVALUATION OF BREATH RATE MEASUREMENT BY CAPNOGRAPHY IN SEDATED VOLUNTEERS

Joseph Orr, Lara M. Brewer, Dwayne Westenskow, Ken B. Johnson; Anesthesiology, University of Utah, Salt Lake City, UT

BACKGROUND: Capnometry is used to monitor respiration in non-intubated, spontaneously breathing patients undergoing procedural sedation, patient controlled analgesia and other procedures where respiration may be compromised. Capnometers detect a breath when a change CO2 expired CO2 concentration is observed without regard for the volume of gas responsible for creating this change. Accurate respiratory rate (RR) measurement using capnometry in non-intubated patients is prone to false breath detection and missed breaths due to sample site location changes, irregular breathing, patient movement, etc. We evaluated the accuracy of capnometry breath detection algorithms in volunteers administered several combinations of a sedative hypnotic and a short acting opioid. METHODS: 24 volunteers were fitted with a tightfitting, sealed mask connected to a combination flow and CO2 sensor. Each volunteer received 15 effect site concentration combinations of propofol and remifentanil delivered as target controlled infusions. We separately compared the accuracy of two breath detection algorithms (1) a simple threshold and (2) an advanced breath identification algorithm (ReNE) algorithm, as implemented in the test capnometer (Capno5/LoFlo, Respironics, Wallingford CT), against RR detected by a reference pneumotach system. The simple threshold algorithm detects a breath each time the CO2 exceeds 10 mm Hg and then goes below 5 mm Hg. The ReNE algorithm incorporates a complex set of heuristics for detecting breaths and rejecting spurious changes in PetCO2. Breaths smaller than 200 mL, which did not clear the airway dead space, were not counted as breaths. RESULTS: Using the simple algorithm, the average detected RR was 3.0 breaths per minute (bpm) higher than the rate detected by the reference. The standard deviation of the difference (SD) was 4.7 bpm. Using the ReNE algorithm, the detected breath rate was 0.97 bpm higher than the reference with SD of 2.92 bpm. CONCLUSIONS: While both algorithms detected more breaths than the pneumotach reference did, the ReNE algorithm was substantially more accurate than the typically used threshold method. False breath detects were often attributed to cardiogenic oscillations detected during periods of apnea and small breath attempts that occurred during periods of airway obstruction. Both of these conditions may cause the capnometer to fail to identify periods of respiratory failure during sedation. Sponsored Research - Philips/Respironics

You are here: RCJournal.com » Past OPEN FORUM Abstracts » 2009 Abstracts » EVALUATION OF BREATH RATE MEASUREMENT BY CAPNOGRAPHY IN SEDATED VOLUNTEERS