The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts


Paul F. Nuccio1, Kathleen H. Niebel2, Jonathan B. Waugh3

Background: Capnography provides quantitative end tidal CO2 (etCO2) and respiratory frequency (f)values and qualitative CO2 waveform measurement of ventilation. Spontaneously breathing healthy volunteers were measured to investigate the effects of oxygen dilution on etCO2 measurements while receiving supplemental O2 via a variety of masks during either mouth-closed (MC) or mouth-open (MO) breathing.

Baseline spirometry, pulmonary and smoking history were obtained on 14 participants (9 female) ages 20-47 years (28.6±8.0, mean±SD) to determine lung status. Volunteers wore Smart Capnoline Plus H O2 FilterLines (Oridion Capnography Inc.) providing simultaneous oral and nasal CO2 sampling throughout the trial. Baseline etCO2 on room air (RA) with MC was established for a minimum of 3 minutes. Five different O2 delivery configurations using FDA-cleared masks were worn over the CO2 sampling FilterLine for 5 minutes each during testing (masks: 40% air-entrainment, 60% aerosol, 12 L/min non-rebreather, 12 L/min partial rebreather, 8 L/min simple). During each phase (mask) of the trial, subjects were evaluated with 3 minutes of MO followed by 2 minutes of MC. Ventilation (etCO2, RR), oxygenation (SpO2) and heart rate during resting breathing were recorded each minute manually and electronically using the Capnostream 20™.

Mean value of EtCO2 for each mask type over 5 minutes was not different (p=0.973). The mean etCO2 (all masks combined) at minutes 1-3 (MO) were different (p<0.001) from minutes 4-5 (MC).

Differences found between MC to MO may be explained by increased anatomical deadspace with residual posterior nasal-pharyngeal mixing just prior to exhalation. A previous study (J Appl Physiol 1998;85(2):642-652) indicated that the nasal cavity contaminates the oral exhalation gas profile and recommends a negative pressure (20 cm H2O) to the nasal cavity after a swallow to elevate the soft palate and seal the nasal cavity. Since isolation of the nasal cavity did not occur in this study, oral breathing is better described as mouth-open breathing and nasal breathing as mouth-closed breathing as commonly occurs in patients receiving supplemental O2 under any mask configuration. Simultaneous supplemental O2 delivery via various delivery masks and obtaining an undiluted sample of etCO2 in the non-intubated patient may be achieved when the CO2 sampling ports are under the mask and close to the orifices. [Partial support by Oridion]