The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

WHAT IS THE THRESHOLD OF PCO2 NEEDED TO ACTIVATE THE MEASUREMENT OF QUANTIFIED VERSUS QUALIFIED CO2 DETECTOR

Carter K. Tong1, Michael H. Terry1, Yomna Ibrahim1, Elba Fayard1, Ricardo Peverini1, Goldstein Mitchell1



Background: Use of ETCO2 detectors in verification of correct endotracheal tube placement is recommended as an adjunct to other clinical methods. However, during neonatal resuscitation these devices are occasionally associated with both false positive or false negative results.

Objective:
To determine the minimum threshold CO2 needed to activate 2 types of ETCO2 detectors; the colorimetric Pedi-Cap and the quantitative BCI Capnocheck.

Methods:
A Bird VIP Sterling (Viasys Healthcare) ventilator was attached to an Anesthesia Bag with a BCI Capnocheck (Smith-Medical) and Pedi-Cap (Nellcor) connected in series. The Bird VIP Sterling was preset with the following settings: IMV 20, Inspiratory time 0.5 seconds, peak inspiratory pressure 25, Peep of 4 and a bias flow of 6 LPM. Carbogen (95:5 O2:CO2) was infused through a low flow flowmeter into the flow input port of an Anesthesia Bag. Carbogen flow was set at 4 lpm and titrated to 2 lpm with O2 flow set to equal a combined total flow of 4 lpm. When 1 lpm of Carbogen was attained, we further titrated the Carbogen gas by 0.1 lpm increments until 0.2 lpm of Carbogen gas was achieved. This insured phasic inflation of the anesthesia bag to provide a physiologic end tidal CO2 signal. Equilibration periods of one minute were used between measurements. Three clinicians independently scored each measurement. CO2 gas measurements were performed at Carbogen flowrates of 4, 1, 0, 1, 0.4 and 0.3 lpm via a 3-way stopcock attached to a port in the bridge between the devices and the Anesthesia Bag. The syringe was filled and emptied x 3 and on the 4th filling was sealed, then analyzed by a Radiometer/Copenhagen ABL 725 blood gas analyzer (Copenhagen, Denmark).

Results:
Both devices were in agreement at Carbogen flowrates of 8.8 mmHg CO2. Below 7.5 mmHg CO2 the Capnocheck continued to provide an end tidal CO2 reading, however without a respiratory rate. The Pedi-Cap continued to show color change in response to CO2 as low as 3.8 mmHg.

Conclusion:
Although the Pedicap was able to measure levels of CO2 as low as 3.1 mmHg, without the respiratory rate trace, there is a possibility that in vivo these levels may mimic ambient levels of CO2 in the stomach or hypopharynx and be indicative of a "false positive" intubation.