Correlation of end tidal carbon dioxide to arterial partial pressure carbon dioxide measured by Sentri nasal cannula: A study in spontaneously breathing non-intubated patients / Lee Jia Wen

Lee, Jia Wen (2018) Correlation of end tidal carbon dioxide to arterial partial pressure carbon dioxide measured by Sentri nasal cannula: A study in spontaneously breathing non-intubated patients / Lee Jia Wen. Masters thesis, University of Malaya.

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Abstract

Background: Continuous end tidal carbon dioxide (ETCO2) monitoring by capnography is essential during procedural sedation to detect adverse respiratory event. The aim of the study was to determine accuracy of ETCO2 as a measure of arterial carbon dioxide( PaCO2) by using Sentri nasal cannula in non-intubated patients and to assess correlation between ETCO2 and PaCO2 across different flow rates of oxygen among sedated and non-sedated patients. Methods: A prospective, interventional study. 36 patients who underwent elective surgery in which arterial line monitoring was indicated were recruited. ETCO2 was sampled via Sentri nasal cannula at various oxygen flow rates (baseline, 2,4,6L/min) with and without sedation. Arterial blood gas and ETCO2 measurement were performed and recorded. The difference between PaCO2 and ETCO2 was tested by paired t test and correlated with Pearson correlation. Bland Altman analysis was used to assess the ETCO2 bias (defined as PaCO2 minus ETCO2). Results: A significant correlation was found between PaCO2 and ETCO2 irrespective of oxygen flow among sedated and non-sedated patients(r=0.75,p<0.005).ETCO2 bias at baseline was 0.9±3.2mmHg(p=0.084) , showing good limit of agreement with PaCO2. There is increase in ETCO2 bias with increase oxygen flow rate in non-sedated patient (1.6±3.5mmHg vs 2.2±4.4mmHg vs 3.1±5.2mmHg) , but they were still within normal range. There is significant increase in ETCO2 bias in sedated patient (7.2±6.1mmHg at 2L/min vs 9.3±6.4mmHg at 4L/min, p<0.001) iv Conclusion: ETCO2 measured via Sentri nasal cannula correlate well with PaCO2 among sedated and non-sedated patients irrespective of oxygen flow rate. It is useful in tracing the trend and monitoring of ventilation status in spontaneously breathing patients with or without sedation.

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