Integration of Capnography and Continuous Positive Airway Pressure (CPAP) in the Prehospital Setting

Abstract

AbstractBACKGROUNDCapnography is one of the most important respiratory monitoring tools used in EMS because changes to end-tidal CO2(ETCO2) generally precede blood oxygen desaturation, and waveform morphology can be used to assess bronchial patency. Many of capnography’s indications overlap with those of continuous positive airway pressure (CPAP) therapy. However, there are currently no convenient methods to administer CPAP while using capnography, and no peer-reviewed studies have examined combining the two technologies in the prehospital setting.METHODS & FINDINGSTwo types of capnography sampler were used to investigate how ETCO2, capnogram shape, and respiration rate (RR) are affected by applying a CPAP mask both with and without oxygen flowing. A traditional nasal-oral cannula (NC) sampler, as well as a novel sampler that does not break the seal between the CPAP mask and the patient’s face (called the CPAP-Capnography Adapter, or CCA), were evaluated on a Human Patient Simulator (HPS). No significant differences between the NC and CCA were found for ETCO2and RR percent error. Placement of a CPAP mask without turning on O2increased ETCO2. During CPAP therapy, the two samplers maintained their RR measurement accuracy, but ETCO2values were significantly reduced and the capnogram depicted an increased β-angle with severe blunting of the inspiratory downstroke.CONCLUSIONSThe HPS had set-point ETCO2and PaCO2values, indicating that the local CO2concentration at the nares was diluted during CPAP and no longer accurately reflected the simulated subject’s breathing. The compromise in waveform morphology could be overcome by further research into interpreting capnogram differences during CPAP between healthy patients and those with respiratory pathologies. However, at this time, our results show that ETCO2values and capnogram shape should be interpreted with caution during CPAP.