Category:
日本光電 Cap-ONE mainstream etCO2 semi-quantitative measurement, its
inappropriate use for continuous waveform display and the vulnerability
of the compact CO2 sensors.
In
this review, we remind the fact continuous
waveform display on screen is a quantitative real time display and cannot be taken lightly
using a semi-quantitative measurement as input.
Displaying a continuous CO2 waveform on screen using mainstream semi-quantitative estimation method is inappropriate professional conduct
Nihon
Kohden lacks
sidestream CO2 sampling expertise and buys OEM units to offer them as
expensive standalone. The AG-400 CO2 unit as shown, for example, is technology from Oridion Medical. For monitoring such as post-surgery recovery,
integration of
the sidestream CO2 into the monitor is a mandatory requirement because
an external unit requires additional power socket besides necessitating
the use of a trolley.
For some unknown reason, Nihon Kohden monitors could not offer integrated sidestream CO2 unit.
 |
| The inability to integrate the sidestream CO2 unit into the patient monitor main unit |
Nihon
Kohden solution was to offer miniaturized mainstream cap-ONE TG-920P CO2 sensor kit (order code P907) that can be used on non-intubated patients.
The
cap-ONE TG-920P CO2 sensor kit (order code P907) has very small sensors because semi-quantitative measurement is adopted, the method is not
commonly seen and many are not alerted to the risk of using data from semi-quantitative etCO2 kit sets
for critical measurements and true CO2 waveform display.
 |
| Nihon
Kohden cap-ONE P907 (TG-920P) mainstream CO2 sensor kit |
| Beware it is difficult to remove the disposable adapter from
the two tiny transducers after use! |
When
the sensors become smaller, it also means the disposable adapter
becomes relatively much bigger as seen in this below picture. When
trying to remove the disposable adapter from the transducers, it is
difficult to separate the two because of the latching mechanism. A small
size transducer means anything that latches onto it must be even
smaller.
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| It is not easy to separate the disposable adapter from the Cap-ONE transducers after use |
|
When
removing disposable adapter from the mini sensors,
users tend to just pull from the cables and this action quickly weakens
the joint holding the sensors and cables. The action will
cause stress to the two joints and quickly degenerate the performance of
the transducers.
 |
| Users just doing the inevitable |
Shown
below is another TG-900P etCO2
kit set (order code P903) that makes semi-quantitative CO2 measurements; the TG-901T3 kit
set (order code P906) is the same thing using a different connection plug. The medical
devices from same manufacturer that uses semi-quantitative etCO2 kit
sets for patient CO2 waveform monitoring
have Life Scope patient monitors, Vismo patient
monitors, Cap-STAT OLG-2800, CardioLife defibrillators and Neurofax EEG
machines etc.
 |
| Nihon Kohden semi-quantitative etCO2 kit sets |
| A very important question: Can users accept estimated measurements for critical care? |
To
save costs, the semi-quantitative kit sets do not make measurement
during the inspiration phase, the measurement duty cycle is as shown. This means semi-quantitative CO2 measurements are not made continuously.
 |
Semi-quantitative means there is a duty cycle, and measurement is not continuous
|
Semi-quantitative measurement is also of low-accuracy type, performed using one IR detector instead of the usual two to save cost. This is reflected in the measurement tolerance.
Contrasting, quantitative measurement demands high accuracy for critical care. To ensure the necessary high accuracy, quantitative measurement employed two IR detectors for simultaneous CO2 measurements at different wavelength for results comparison. CO2 measurements are also being made continuously.
 |
Quantitative measurement employs two detectors to make
continuous measurement at different wave-lengths to compare readings for high accuracy
|
NIHON KOHDEN specification
for TG-901T CO2 sensor kit
shows even the specified low accuracy of CO2 measurement using semi-quantitative
method no longer holds true once CO2 is present during the inspiration
phase.
| As
seen from the duty cycle, there is no measurement being made during the
inspiration phase; how can one be sure the specified measurement accuracy
is valid? |
 |
| Measurements are invalid when CO2 is present during inspiration, but CO2 is not measured during this period; so, how do you achieve certainty in measurements? |
It
should be clear each semi-quantitative CO2 measurement is an
estimation since its accuracy is rendered uncertain by the inability to confirm if CO2 is present during the inspiration phase. The specified measurement tolerance therefore has no meaning for the users!
The users are also not alerted on screen there is no CO2 measurement being made during the inspiration phase, and unknowingly made to take an unnecessary risk.
| Semi-quantitative methodology means cost-effective estimations and the design cannot be used in a general way, only on a selective basis with known risks |
For example, semi-quantitative methodology can be used as a simple estimation tool for obtaining the numerical value of End-tidal Carbon Dioxide level (etCO2).
Below
picture shows the semi-quantitative method in the way it was intended
for, estimating only the etCO2 numerical value for purpose of airway tube placement confirmation. It is not for
continuous waveform display.
 |
| A hand-held semi-quantitative etCO2 estimation tool (with SpO2) for airway tube placement confirmation |
| How is it feasible to display a true continuous CO2 waveform when the
semi-quantitative measurement kits do not have the ability to make continuous
measurements? |
NIHON KOHDEN also allows data from semi-quantitative measurements to be
displayed on screen with the non-measurement period reset to zero level. The insistence to display a continuous waveform using discontinuous measurement data from
semi-quantitative mainstream CO2 estimation kits is unacceptable; the
manufacturer is just subjecting the monitored patients and users to dangerous
misinterpretation risks.
A zero CO2 reading on the
waveform means zero measured value. No measurement can only mean a defective sensor, not by design!
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| A flawed CO2 waveform with non-measurement intervals reflected as zero measured CO2 value |
| As seen from the two true CO2 traces below, expiratory upstrokes do not always start from zero CO2 level! |
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Quantitative measurements confirming expiratory upstrokes do not
always start from zero CO2 level
|
Check
the latest updated table to make sure you only use quantitative method for
critical measurements and true CO2 waveform display
on screen.
 |
| Use only quantitative method for waveform display; the quantitative TG-950P (P905) shown here was already discontinued. |
| How about fully-quantitative type miniaturized mainstream CO2 sensor? |
The TG-907P CO2 Sensor kit (order code P909) shown in above table
is using quantitative method as declared. This sensor was designed for
non-intubated adult CO2 monitoring, as well as neonatal CO2 monitoring.
In short, Nihon Kohden is trying not to rely on others for sidestream
CO2 sampling expertise.
 |
| The miniaturized CO2 sensor is easily broken by the bigger and stronger adapter |
In addition to the dead space problem,
they had not foreseen miniaturized mainstream CO2 sensors could be easily broken by the
disposable adapters. This happened because the disposable adapters are now relatively bigger and stronger!
 |
| These are common defects of a TG-970P CO2 sensor kit (P909). The design is impractical. |
| The fragile miniaturized CO2 sensor is easily broken but the blame was on users instead of poor design |
 |
| Key point is, it does not last |
