Does the Addition of Oral Sampling Improve Waveform Capnography When Compared to Traditional Nasal Sampling in Open-Airway Patients?

Abstract

BackgroundEnd-tidal carbon dioxide (EtCO2) is an invaluable anesthesia measure due to minimal delay in monitoring ventilation. Oral and Maxillofacial Surgery (OMS) presents special challenges because oral exhalations are not sampled effectively via nasal cannula normally used to avoid interfering with procedures. PurposeThe purpose of the study was to compare EtCO2 waveforms obtained in subjects using nasal monitoring and combined nasal and oral monitoring under simulated ventilatory conditions. Study design, setting, sampleA single-blinded, randomized crossover controlled study was conducted at the University of Illinois Chicago with healthy volunteers, who were blinded to the monitoring system used. Inclusion criteria required subjects be >18 years of age, be consentable and English-speaking. Exclusion criteria required no airway abnormalities, no edentulism, no conditions that preclude undergoing an OMS procedure under sedation. Predictor variableThe primary predictor variable was the EtCO2 monitoring system: nasal with a standard nasal cannula, and combined with a nasal cannula and oral device. The secondary predictor variable evaluated three ventilatory states (nasal breathing, oral breathing, apnea) in each arm, standardizing by maintaining consistent breath counts across observation periods. Main outcome variableThe main outcome variable was the number of waveforms recorded over 30 seconds for nasal and combined monitoring. Each recording was standardized by dividing it by the baseline waveforms and multiplying by 20. Higher values, closer to baseline, were considered more accurate depictions of ventilation. CovariatesCovariates were body mass index (BMI), age, sex, Mallampati score, and breathing method. AnalysesANOVA, ANCOVA, and MANOVA were performed. P-value<0.05 was considered statistically significant. ResultsThe sample included 25 subjects (18 male, 7 female) with mean age 29.9+7.98 years and BMI 23.9+3.51 kg/m2. Combined sampling detected more waveforms during nasal and oral breathing (p<0.001). Higher BMI correlated with reduced waveform capture during nasal sampling in oral breathing (p=0.013). Combined sampling detected more waveforms during nasal breathing (p=0.005) in subjects with BMI < 23.5 kg/m2. Mallampati score correlated with increased waveforms during nasal breathing. Conclusions and RelevanceOral EtCO2 sampling may improve accuracy of capnography waveform capture. Further clinical studies in sedated subjects undergoing OMS procedures are needed.