Get Connected: Troubleshooting end-tidal CO2 readings



John Jui, MD, MPH | From the May 2008 Issue | Friday, July 25, 2008

I was at a meeting recently and a few of my colleagues mentioned that some of their crews reported having absent or inaccurate end-tidal CO2 (EtCO2) readings on their monitors. We use LIFEPAK 12 (LP12) defibrillator/monitors, so I asked if the crews involved were fully tightening the EtCO2 cable to the monitor.

They looked surprised when I told them our agency in the Portland/Multnomah County (Ore.)EMS system had a similar experience in 2006, prompting us to develop an operational policy to address the way crews connected the EtCO2 cable to the monitor.

If the CO2 cable isn_t twisted on completely, the reading could be inaccurate, through no fault of the LP12 monitor. The CO2 indicator is activated when the gold ring of the FilterLine connection contacts the device.

Similar to a firefighter connecting a hose to a pumper that drafts water using suction, the capnography cable works on a vacuum principle; it cannot be accurate if there_s a loose connection that doesn_t allow the cable to be fully seated according to manufacturer guidelines.

Here are a few tips from our operating policy that might help your personnel troubleshoot their EtCO2 cable connection and readings:

Turn the CO2 FilterLine tubing three times in a clockwise manner until the CO2 FilterLine connector is firmly seated to the monitor_s CO2 port (you will feel resistance) and the wings of the connector are in a ˙flat-wingÓ position, parallel to the base of the monitor (see Photo 1).

If the CO2 FilterLine tubing is not properly seated or rotated counter-clockwise even half of a turn (see Photo 2), you may experience a degraded (solid) signal, with changes in the waveform and CO2 value (see Photo 3).

Once FilterLine connection and initialization has occurred, loss of connection to the device results in dashed lines, with no waveform present, but will also be accompanied by a ˙FILTERLINE OFFÓ message (see Photo 4).

A normal waveform will be accompanied by a solid line (see Photo 5).

Table 1 presents the causes and corrective actions to take based upon various CO2 waveform readings.

Critical points

The CO2 value must be > 3 mmHg for a waveform to be displayed. The CO2 must be > 7 mmHg for a respiratory rate to be displayed.

Capnography waveforms on the monitor are condensed to provide adequate information in the four-second view. Printouts of the waveforms are in real time; therefore, they may differ in duration from those on the monitor.

The monitor shows the maximum CO2 value over the last 20 seconds. If the EtCO2 values are increasing, the change can be seen with every breath. However, if the values are continually decreasing, it will take up to 20 seconds for a lower numerical value to be displayed in the CO2 area. Therefore, the EtCO2 waveform may not always match the CO2 value.

The Oridion capnography module performs self-maintenance within the first half-hour of monitoring and once every hour during continuous monitoring. This self-maintenance includes ˙auto-zeroingÓ and is initiated if the ambient temperature changes by 8_ C or more, or the ambient pressure changes to > 20 mmHg.

The Oridion capnography module also resets after a shock is delivered to ensure system stability. Note: This reset can take up to 15 seconds.

Jon Jui, MD, MPH, is EMS medical director forPortland andMultnomah County,Ore., and the Oregon State Police, and the deputy team commander for Oregon DMAT. He_s also a professor in the department of emergency medicine at the Oregon Health andScienceUniversity,Portland.

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Related Topics: Patient Care, Cardiac and Circulation, Jems Medical Director Forum


John Jui, MD, MPHJon Jui, MD, MPH, is EMS medical director for Portland and Multnomah County, Ore., and the Oregon State Police, and the deputy team commander for Oregon DMAT. He's also a professor in the department of emergency medicine at the Oregon Health and Science University, Portland.


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