Easily-broken Cap-ONE miniaturized mainstream CO2 sensors

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 article, we review NIHON KOHDEN Cap-ONE as an input signal to display a continuous waveform, the unprofessional practice could change the outcome of a patient under CO2 monitoring and is not acceptable. Compact mainstream CO2 transducers are easily damaged by the users during routine use.

 
 
The dubious faith to rely on small mainstream CO2 sensors for CO2 monitoring
 
 
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 decided to apply mainstream semi-quantitative CO2 measurement as solution to sidestream CO2 monitoring. The adoption of technology was to reduce cost and its simplicity also help in miniaturization of the transducers.

The first solution offered by NIHON KOHDEN was the 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.

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
 

Do users know semi-quantitative measurements are only estimations?
    
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.

It is impossible for users to know if measurements are valid when they cannot tell if CO2 is present during inspiration!
  
Measurements are invalid when CO2 is present during inspiration, but CO2 is not measured during this period

 
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 possible 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!
 
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!
 
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