Accurate determination of end-tidal carbon dioxide during administration of oxygen by nasal cannulae

Abstract

Measurement of end-tidal carbon dioxide tension (PETCO2) by mass spectrometry or infrared capnometry provides a clinically useful approximation of arterial carbon dioxide tension (PaCO2) in intubated patients. Although several devices have been proposed to sample PETCO2 during spontaneous breathing (i.e., unintubated patients receiving supplemental oxygen), thus far no reports have documented their efficacy. This article reports the use of an easily constructed modification of simple nasal cannulae that permits accurate sampling of PETCO2 during oxygen administration to unintubated patients. After amputation of the closed tip, a cap from a syringe was inserted via a slit made at the base into one prong of a pair of nasal cannulae. A capnometer was connected to the syringe cap, and PETCO2 and PaCO2 were determined simultaneously during the administration of 3 L/min oxygen via nasal cannulae to 21 normocapnic patients. The PaCO2 - PETCO2 gradients were calculated and compared with values obtained in the same patients after intubation and mechanical ventilation. No significant difference was found between the calculated gradients with nasal cannulae (2.09 +/- 2.18 mm Hg) versus intubation (2.87 +/- 2.82 mm Hg). Simultaneous oxygen administration and accurate sampling of PETCO2 may be achieved in unintubated patients by using this easily constructed modification of nasal cannulae.

Correlations between capnographic waveforms and peak flow meter measurement in emergency department management of asthma

“…They were then directed to breathe normally. One end of this specially designed nasal cannula provided oxygen from a humidified wall source (all patients in this study were given oxygen at a rate of 3 l/min via this nasal cannula) whereas the other end was connected to an aspiration pump and the sampling port [12, 13]. The capnogram was then recorded and stored within a PC card.…”

Capnographic monitoring of ventilatory status during moderate (conscious) sedation

“…Artificially low expired end-tidal CO 2 readings may be obtained from individuals with a perforated nasal septum because crossover oxygen from the other nares will add to the dilution of the CO 2 reading [4]. High oxygen flow via either the nasal sampling technique or the rebreather face mask may reduce the quality of the capnographic waveform and grossly underestimate the expired end-tidal CO 2 [6].…”

The Use of End-Tidal Capnography to Monitor Non-Intubated Patients Presenting with Acute Exacerbation of Asthma in the Emergency Department

“…They were then directed to breathe normally. One end of this specially designed nasal cannula provided oxygen from a humidified wall source (all patients in this study were given oxygen at a rate of 3 L/min via this nasal cannula) and the other end was connected to an aspiration pump and the sampling port (8,9).…”