Medical Devices Sanity: Life Scope VS (BSM-3500 and BSM-3700 series) bedside monitors from NIHON KOHDEN

Category: Product Review of NIHON KOHDEN Life Scope VS (Venus) series bedside monitors and related. The Life Scope VS series consists of BSM-3521, BSM-3552, BSM-3562, BSM-3572, BSM-3733, BSM-3753, BSM-3763 and BSM-3773.

Launched in early 2011, the configured LIFE SCOPE VS (BSM-3500 and BSM-3700) series patient monitors targets mid-acuity sites with the configured BSM-3500 series using a 12.1 inch touchscreen display while the configured BSM-3700 series uses a 15-inch touchscreen display. (The BSM-3500 series was belatedly launched in the USA market in 2016).

Configured Life Scope VS (BSM-3000) series models

There are four models for the 12.1-inch configured BSM-3500 series, namely

a. Life Scope BSM-3532 bedside monitor

b. Life Scope BSM-3552 bedside monitor

c. Life Scope BSM-3562 bedside monitor

d. Life Scope BSM-3572 bedside monitor

The difference among the monitors is the SpO2 algorithm; the latest international version is refrained from use in the USA market for undisclosed reasons.

Another four models are for the 15-inch configured BSM-3700 series, namely

a. Life Scope BSM-3753 bedside monitor

b. Life Scope BSM-3755 bedside monitor

c. Life Scope BSM-3763 bedside monitor

d. Life Scope BSM-3773 bedside monitor

# The failed attempt to deliver customer value using flexible sockets

The prominent feature of Life Scope VS bedside monitors is the utilization of two flexible MULTI (short for multi-parameter) sockets for the 12.1-inch models and three flexible MULTI sockets for the 15-inch models. The flexible MULTI sockets are colored yellow and meant for frugal sharing by a group of internal hardware, and can also be diverted to be serial ports.

For the Life Scope VS bedside monitors, the yellow MULTI sockets can be utilized for IBP, Temperature and Cardiac Output, plus a variety of digital serial kit sets. There is no free lunch, so what cost are incurred to achieve the flexibility of these yellow MULTI sockets? Ordinary measurement cables cannot be used on such flexible sockets, and the manufacturer is trying to hide the additional expenses needed to pay for mandatory use of custom measurement cables embedded with digital parameter codes in their yellow plugs. This is a necessary basic step because a flexible MULTI socket must by definition, accept more than one type of measurement cable; the parameter code embedded in the plug is the mean to differentiate the cables, and inform the monitor what internal hardware/ software are needed for support when a measurement cable is being plugged in.

The manufacturer made the mistake of thinking a flexible MULTI socket exhibits characteristics similar to what a modular monitor offers, what they did not expect to learn painfully is the reality a flexible MULTI socket is indeed, only a poor man's socket. The consequence of using flexible sockets for general use actually translates to insufficient physical sockets for users, and the deprived users are not hesitating to demand them back. There is no customer value in socket flexibility when its use creates a shortage of physical sockets for users, and the manufacturer had failed to make socket flexibility relevant.

# This peculiar MULTI-PARAMETER UNIT (MPU) design from the 1990s should never be utilized when out of context

Veiled in secrecy, NIHON KOHDEN does not explain to the market how they could make sockets that are flexible enough for a total five types of internal hardware, as well as being diverted for use as serial ports for self-contained kit sets. Almost the entire sales and marketing people employed in Japan Head Office have no engineering background, so there are plenty of "company secrets" that should not be discussed with the distributors or customers.

Here are the relevant facts, and it was just a quest to find the solution for a small module with a front panel that did not have enough panel space to mount all the numerous connection sockets needed.

The special need that was searching for a solution

The problem was not unique to NIHON KOHDEN, with the most common solution in the market being to integrate more than one signal onto a socket and using an external splitter to obtain back the original individual signals. The interesting solution from NIHON KOHDEN was, however, to frugally share a small number of common sockets.

That was in the 1990s, and NIHON KHODEN development team managed to identify five types of analog hardware (Temperature, IBP, Cardiac Output, Thermistor-method Respiration, FiO2) that could form a hardware group frugally sharing just two flexible sockets for common use. The two flexible sockets are known as MULTI (short for multi-parameter) sockets and are specially colored yellow for easy identification.

The hardware group and sockets together made up the MULTI-PARAMETER UNIT (MPU), and was only a peculiar design to minimize the number of physical sockets needed on a front panel that had a limited space area; thus, the MPU has the unusual characteristics of having more hardware than physical sockets. It is a design to optimize a fraction of total needed physical sockets for sharing, and is therefore operating under constraint of limited sockets.

We need to view the MPU from the right perspective, to understand that that it is illogical to use it when there is no lack of panel space, because we should typically be optimizing the use of expensive hardware instead of the cheap connection sockets.

It was a design to optimize a fraction of total needed physical sockets for sharing, and is operating under constraint of limited sockets

To access each type of hardware, an external measurement cable with a digital parameter code stored in its plug needs to be inserted into one of the two MULTI sockets. These measurement cables that come with yellow coded plugs are collectively cited as Smart Cables by the manufacturer and each embedded digital parameter code pinpoints the exact type of internal hardware and software needed by a particular measurement cable. Thus, the mission of the Smart Cables is to make use of digital codes to share the yellow flexible MULTI sockets.

Each yellow MULTI socket can only link to one channel of the internal hardware, except for Temperature which can accommodate up to two.

As an exception, a MULTI socket can link up to two channels of internal analog Temperature amplifiers

# Note the hardware mentioned here (Temperature, IBP, Cardiac Output, Thermistor-method Respiration and FiO2) are linked to the flexible MULTI socket internally, and not from the outside

An external measurement cable with a valid digital code embedded in its plug selects the intended internal hardware (only if available)

Below image shows the MULTI-PARAMETER UNIT (MPU), complete with two yellow MULTI sockets for group sharing. An external Smart Cable with a valid parameter code selects the needed hardware in the MPU using one of the two MULTI sockets.

Based on the fact both MULTI sockets must be capable of doing IBP monitoring, and the logic that IBP hardware should not be more than the number of MULTI sockets, the IBP hardware are therefore not placed in the common pool for sharing; instead, each MULTI socket comes with its own dedicated IBP hardware.

A MULTI socket can only access its own dedicated IBP hardware, and makes use of its when an IBP measurement cable is plugged into it. For non-IBP monitoring, both MULTI sockets can access the common sharing pool comprising Temperature, Cardiac Output, Thermistor-method Respiration and FiO2 hardware in the MPU.

Given the large amount of hardware idling in the MPU, more physical sockets are needed to make good use of these valuable hardware; yet, only physical sockets in the form of MULTI sockets can access the MPU. The arrangement to add more physical sockets is thus achieved using external expansion boxes filled with two or more MULTI sockets (each with its own dedicated IBP amplifier hardware). It is important at this point to be clear the purpose is to add more physical sockets linking to the existing MPU, and not to add more monitoring parameters.
This is a process of adding more physical sockets, not more monitoring parameters

The additional MULTI sockets are integrated using analog interface, and must be limited to a maximum of four sockets to avoid signal deterioration caused by voltage drop and noise.

The MULTI sockets are additionally diverted to be serial ports to save on one more physical socket
A MULTI socket can be diverted to be a serial port by bypassing the internal analog hardware

The design concept of MPU was to solve the problem of limited panel space area, and by using MULTI sockets as serial port does help in furthering the reduction of a physical socket on the front panel. The serial port in the original design was only for use by the mainstream CO2 serial kit sets.

Shown above is the original label for the two yellow MULTI sockets. It shows each socket can be utilized for monitoring of IBP, Temperature, Cardiac Output, FiO2 and Thermistor-method Respiration, as well as diverted to be a serial port for mainstream CO2 kit sets.

The small module mentioned earlier was named Saturn multi-parameter module and the outcome of the MPU solution is as shown below. The Saturn module is housed in a 8-slot module rack, with two expansion boxes next to it; altogether there were six MULTI sockets (with six channels of IBP hardware) available for use in this arrangement. It is possible to use the Saturn module alone, but the two MULTI sockets would not be enough and at least four MULTI sockets were needed to be practical.
The MPU block without the module rack housing is meaningless

Unfortunately, the measurement LAN network for data communication between module rack housing and monitor main unit was unstable with plenty of performance issues, and had to be finally given up for good. This means the first two modular monitors developed by the manufacturer were failures, and they were withdrawn before registration in the biggest US market.

Note the failed LAN network is not referring to the real-time clinical LAN network for data exchanges between bedside monitors and central nurse stations.

After the decision to stop development work on the measurement LAN network, a younger team of risk-averse engineers took over key positions and decided to keep the MPU, and using the expansion sockets to simulate scalability. This is desperate and unprofessional behavior, because they did it to avoid working on a new measurement LAN; at the same time, they also knew they could get away with it in Japan given the low bargaining power of users in the domestic market.

The MPU was only a compromise to accommodate limited space area and should never be mistaken as an innovation; without the module rack, the MPU is meaningless and most importantly, there is no demand for socket flexibility outside of Japan.

Professionally, many are puzzled by the behaviors of the MPU but refrained from asking or faced with a wall of silence. The situation was so acute that at one point we had regular telephone calls and letters from undergraduates around the world (excluding Japan) hoping to understand the principle behind the MULTI sockets; we of course could not help them in any way then. When we have ample panel space area, there is no need for such a compromise and the use of an MPU (with its Smart Cables and MULTI sockets) actually becomes a burden, a waste of money and time for the users. Its continued use regardless of need is the very reason for its eventual failure.

Besides, there are other cheaper and practical ways to solve the problem of insufficient space on the input panel, such as commonly integrating more than one signal onto a socket and using an external splitter to resolve back the original signals.

Example of resolving an integrated signal back into original P1 and P2

So far, time-sharing of connector sockets is only done by Nihon Kohden and avoided by all other manufacturers of patient monitors.

Variations to the basic theme

There are variations to the basic theme, such as
a. doing without use of external expansion box,
b. increasing the number of multi-parameter sockets in the MPU,
c. reducing the hardware configured in the MPU.

In the Life Scope 3500 series bedside monitors which has two MULTI-parameter sockets each, the configured hardware in the MPU includes two channels of IBP amplifiers, two channels of Temperature and one channel of Cardiac Output.

In the Life Scope 3700 series bedside monitors which has three MULTI-parameter sockets each, the configured hardware in the MPU includes three channels of IBP amplifiers, two channels of Temperature and one channel of Cardiac Output.

Users should first find out how many channels of internal IBP hardware are supplied, it is most likely more than your need. Knowing a true yellow MULTI socket always come with its own dedicated one-channel IBP hardware, a user can accurately tell how many IBP monitoring hardware channels are supplied with any monitor, just by tallying the total number of available MULTI sockets. For example, if your monitors were each delivered with five functional MULTI sockets, you had unknowingly paid for five channels of built-in IBP hardware when you may indeed only need one or two.

The key word here is "true" because a fake MULTI socket does not need to care about the capability to do IBP monitoring, such a socket can be found on the CardioLife TEC-5600 series defibrillators. The fake yellow MULTI socket on said TEC-5600 series defibrillators is just a serial port dressed as a shared-use socket that cannot be used for any other parameter except mainstream CO2 kit sets.

It is important to know the Life Scope VS series was not designed for using expansion units, this was an after-thought and adaptation following massive complaints from users.

The digital hexadecimal parameter code is programmed into a non-volatile EEPROM chip (Electrically Erasable Programmable Read-only Memory) mounted on a small flexible PC board wired to plug of a Smart Cable at the factory, and users cannot change the code after production using settings on the monitors. It is not costly to make the Smart Cables but they are being priced highly by the manufacturer; only the common IBP cable can be sourced from China suppliers at a reasonable price.

A non-volatile digital parameter code is embedded in the plug of the measurement cable

# It is wishful thinking to believe the use of Smart Cables and MULTI sockets upgrades a configured monitor to be modular

A yellow multi-parameter socket by itself does not automatically mean all the five types of mentioned parameters are available for measurements; it still depends on whether what hardware are actually being placed inside the MPU for selection by Smart Cables.

Additional parameter capability can only be added using serial kit sets or via interfaces to external equipment.

When a model is not equipped with FiO2 hardware internally, no amount of yellow multi-parameter sockets is going to provide this measurement capability. The amount of configured hardware linked to each multi-parameter socket varies, so is the system support for serial kits and external interfaces.
Examples of configured hardware and serial kits using Smart Cables

# It is the built-in hardware that determine the parameter capability; and in the case of serial kit sets, the system software. This of course, is the same description as a configured patient monitor
Actual internal hardware and system support for serial kits varies for each MPU

Monitors using Smart Cables and MULTI sockets are therefore still configured monitors. It is precisely to forestall the market from making this conclusion that we began to see wild claims of "proprietary Smart Cables technology miniaturizes circuitry found in traditional modules and embed that capability into the cable". The manufacturer is saying the hardware are in the cable and therefore the design is modular in nature; we have explained the cable is just the code to use the hardware and software which are already embedded inside the monitor, and can reference the official block diagram details as proof. We show beyond any doubt, there is absolutely no need for any active electronics in the Smart Cables.

The only advantage of using Smart Cables is to allow sharing of connector sockets, which are of negligible hardware cost; on the other hand, the costs needed to make use of Smart Cables are way far higher! The customers are paying for the unnecessary higher costs, only to be led into having an unrealistic expectation of what the Smart Cables and MULTI sockets can actually deliver.

Messages such as "New Modular Technology" and "The Module is in the cable!" are just the wild imaginations of people without the necessary electronics knowledge. These are unsubstantiated marketing messages and the manufacturer should not have condoned it.

What do the manufacturer mean by this statement?

It started with the Life Scope TR (BSM-6000) series monitors in the USA market and gradually adopted officially for International markets. These are precise statements.

Remember, the constant iteration of the same assertion while avoiding to provide any proof does not make it the truth!

This is just assertion without offering any proof

Which chip manufacturer is willing to take a big loss to supply NIHON KOHDEN the variety of analog chips given the extremely low volume in demand? When we opened up the plug of a Smart Cable, we found a small PC board being soldered to some pins of the yellow plug (as shown below).

A small PC Board is soldered to some pins of the yellow connection plug

Upon inspection, the board confirms a cheap non-volatile digital EEPROM chip is being made used of to custom code each Smart Cable.

A cheap digital EEPROM chip was what we found inside the yellow Smart Cable plug

The same thing can be found in a compatible IBP cable from China suppliers, they just copied the digital code defined by NIHON KOHDEN. Do you really think they managed to put an active IBP amplifier inside?

Under US FDA rule,

Below service screen shows the MPU knows what cable is being inserted by reading the parameter codes in the plugs.

# Here is irrefutable proof the IBP amplifier hardware is located internally, an important fact no longer shown on later monitor manuals

The Life Scope BSM-2301 bedside monitor was launched in 2001, and the Service Manual is clear on the design; manuals for later models stop providing such information. The major move to curb details in manuals started from Life Scope J (BSM-9101) Bedside Monitor, which was launched in June 2007. The Life Scope TR bedside monitors also do not provide details, as it was launched in April 2008 (after Life Scope J monitor).

In BSM-2301 service manual, you can see the IBP and thermistor respiration are internal hardware inside the Life Scope BSM-2301 monitor. These hardware are clearly shown being linked internally to the MULTI socket, and to make use of either hardware, a Smart Cable with the correct code must be plugged into the MULTI socket.

The block diagram also tells us the MULTI socket of Life Scope BSM-2301 monitor cannot measure Temperature because there is no Temperature hardware internally linked to it, and the sole Temperature amplifier hardware is dedicated to an external jack. The observation is confirmed by the label for the yellow MULTI socket indicating PRESS/ CO2/ RESP, i.e. no TEMP.

This manual confirms the IBP amplifier and thermistor respiration hardware are internal components of the Life Scope BSM-2301 monitor

# The above block diagram means there is no need for any amplifier hardware to be embedded in a NIHON KOHDEN Smart Cable

The MULTI socket when used as a serial port bypasses the internal analog hardware, going straight to the digital APU (Analog-block Processing Unit) and onward to the DPU. For a parameter using the internal analog hardware, the analog signal needs to converted to digital before it can go to the APU for processing.

What was the reason the manufacturer had to return back a physical socket to users of a yellow flexible MULTI socket?

Preceding Life Scope VS bedside monitors was the Life Scope BSM-2300K series monitors, let's see how the sole yellow MULTI socket was actually being used in this series.

The portable 8.4-inch Life Scope i (BSM-2301K)

*# It does not make sense that one flexible socket can do the jobs of three fixed-purpose sockets*

To insist on the use of Smart Cables, the Life Scope BSM-2301K monitor has one yellow MULTI socket flexible enough for three types of measurements, namely:

a. Invasive Blood Pressure

b. Thermistor-method Respiration

c. Mainstream CO2 (using self-contained serial kit sets)

Without any use of Smart Cables, all IBP, Thermistor-method Respiration and mainstream CO2 are freely available for carefree use via their respective dedicated sockets. The use of Smart Cables makes things unnecessarily complicated and requires deliberate operator attention and choice to choose one among three (IBP, Thermistor-method Respiration and mainstream CO2), but why introduced a need to choose?

This is obviously unwarranted stress and inconvenience, what is wrong with the conventional way of using three dedicated sockets for the job? If MULTI socket is such a superior proposal, why is the Temperature socket a dedicated one?

There are not enough physical sockets for users

The patient monitoring hardware in the Life Scope BSM-2301 bedside monitor are divided into a conventional block and an MPU block. The conventional block uses dedicated sockets and ordinary measurement cables while the MPU block makes use of Smart Cables with different parameter code for different hardware.

CONVENTIONAL BLOCK

- 1-ch TEMP

- ECG

- SpO2

- NIBP

MPU BLOCK with one MULTI socket

- 1-ch IBP

- Thermistor-method Respiration

- <MULTI socket as serial port> Mainstream CO2 Kit Sets

The reality is the absence of two physical sockets for users. However, one of the parameter for the yellow MULTI socket is thermistor-method respiration, which is for use in the operating room to overcome electrical noise interference; this parameter is therefore not for use in the ward. The real shortage felt by users is one missing physical socket, and they are not hesitating to demand it back. Imagine the initial wonder of a flexible socket turned into an outrage for being shortchanged!

Users do not want to be shortchanged with a poor man's socket

The manufacturer was pressured to respond with an updated model, Life Scope BSM-2303K. The solution from the new model was to add a new yellow socket only for IBP.

The MPU of the Life Scope BSM-2301K was not designed to take on expansion, and any additional MULTI socket will load the operation of existing MPU, causing it to malfunction. An additional MULTI socket not linked to the MPU is just an independent socket with its own dedicated IBP amplifier hardware. Such was the additional yellow socket offered for Life Scope BSM-2303K, noting there was a need to recognize the IBP Smart Cable.

With a new socket for IBP, the existing MULTI socket can move away from doing IBP monitoring, and just focus on being a serial port for mainstream CO2 or being an amplifier for respiration monitoring using thermistor transducer.

It was ironical, a solution relying on an extra dedicated socket for IBP; there are now two IBP amplifier hardware in the monitor, which was not the original intention. It was clear the complaints was the market rejection of sharing a flexible socket, and the solution offered by Life Scope BSM-2303K was to return back one missing physical socket demanded by users.

Market rejection forced the manufacturer to return back one missing socket demanded by users

# Only to be pressured to return back even more physical sockets in the case of Life Scope VS bedside monitors

Undeterred, NIHON KOHDEN again launched the Life Scope VS bedside monitors with the BSM-3500 series monitors having two MULTI sockets while the BSM-3700 series monitors have three. The value captured by users for both models are again negative.

The patient monitoring hardware inside the Life Scope BSM-3500 series (12-inch) bedside monitors are divided into a conventional block and an MPU block. The conventional block uses dedicated sockets and ordinary measurement cables while the MPU block makes use of Smart Cables with different parameter code for different hardware.

CONVENTIONAL BLOCK

- ECG

- SpO2

- NIBP

MPU BLOCK with two MULTI sockets

- 2 channels of IBP

- 2 channels of TEMP (1 MULTI socket = 2-ch TEMP)

- Cardiac Output

- <MULTI sockets as serial ports> BIS, APCO, mainstream CO2 and NMT

Note:

Other third party parameter options are connected using the external device interface, not by using the MULTI sockets.

Hardware in the MPU of BSM-3500 series bedside monitors

The patient monitoring hardware inside the Life Scope BSM-3700 series (15-inch) bedside monitors are similarly arranged.

CONVENTIONAL BLOCK

- ECG

- SpO2

- NIBP

MPU BLOCK with three MULTI sockets

- 3 channels of IBP

- 2 channels of TEMP (1 MULTI socket = 2-ch TEMP)

- Cardiac Output

- <MULTI sockets as serial ports> BIS, APCO, mainstream CO2 and NMT

Hardware in the MPU of BSM-3700 series bedside monitors

As seen, the difference between the BSM-3500 series and the BSM-3700 series is the addition of one yellow MULTI socket, and of course it also means an additional IBP amplifier hardware.

In below picture, users of the left monitor (BSM-3500 series with 2 channels of IBP) requires five physical connection sockets but only two yellow shared-use sockets are provided for a 2/5 availability ratio. The manufacturer cannot provide more than two MULTI sockets because the IBP hardware channels intended for this model is only two, and therefore fixed at two flexible MULTI sockets.

Without any use of Smart Cables, all five parameters are freely available for carefree use via their respective dedicated sockets. The use of Smart Cables just makes things unnecessarily complicated and requires deliberate operator attention and a conscious efforts to choose two among the five; this is unwarranted attention, stress and inconvenience. What is wrong with using five dedicated sockets, which is a far superior norm since all parameters are available for connections at any time without hesitation. What user benefit is the manufacturer trying to provide?

Similarly, users of the right monitor (BSM-3700 series with 3 channels of IBP) requires six physical connection sockets for carefree use but the manufacturer insists three shared-use sockets are enough. This means the manufacturer only wants to place 3 channels of IBP hardware in the MPU of the BSM-3700 series monitors and ignore the user's pain; this kind of forceful approach can only happen in a protected Japanese market where bargaining power of users is low. It is another matter for the export markets, the manufacturer had to respond to the complaints as long there is still interest to export their monitors.

How does such dire shortage of connector sockets benefit a user?
These monitors are in dire shortage of physical sockets, and the values captured by users are negative
Manufacturers make their profits by providing product benefits to users but the yellow MULTI sockets is a burden to the users.
What benefit can it offer users when necessary physical sockets are missing?

As expected, users soon found out the small number of MULTI sockets on Life Scope VS bedside monitors are not enough for use. The situation for Life Scope VS series bedside monitors is the same as Life Scope BSM-2301K bedside monitor, customers want their physical sockets back because they need it! This time, the manufacturer offers option of AA-372 Smart Expansion Unit to return back two missing physical sockets and AA-374 Smart Expansion Unit to return back four missing physical sockets.

Life Scope VS series bedside monitors were not designed for expansion, although we were not surprised to find expansion units from Life Scope TR belatedly being offered as solution to the demand from users for more physical sockets. There are modifications done to the original items since the model names (AA-372P, AA-374P) are different; the makeshift solution makes the bedside monitor look awkward, resembling a product prototypes still undergoing tests.

The manufacturer found a way to return back the missing physical sockets

These are futile efforts, it is now as good as going back to dedicated sockets, but at a high cost! The underlying problem is the the use of an MTU block when there is no problem of panel space area, there is no need for frugality when you have plenty of space resource.

This picture tells us some users want back all their missing physical sockets!

The Life Scope VS monitors were originally not designed for socket expansion, there should be limitations and users may have to pay additional attention to correct socket selections as a result.

Sharing must make economic sense

Elaborate time-sharing are applied to things that are expensive (high in demand, an asset), and not worth the efforts for things that are cheap (high in supply, a commodity) like a connector socket or switch.

Time-sharing of a car (an asset) creates value for the customers but time-sharing of a cheap connector socket does not

The next picture shows Philips time-sharing one channel bio-amplifier hardware between IBP and Temperature measurements, and there was no sharing of connector socket; this is exactly the opposite of what NIHON KOHDEN is doing. The said manufacturer merely ensures physically it is not possible to make use of both the PRESS and the TEMP socket at the same time.

This design optimizes the use of expensive hardware, not the cheap sockets

Watch out the careless and dangerous use of estimated CO2 values as true values

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 weakness, Nihon Kohden monitors have never been able to offer benefits of integrated sidestream CO2 measurement.

The inability to integrate the sidestream CO2 unit into the patient monitor main unit

The adoption of semi-quantitative mainstream CO2 measurement 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 (P907) has very small sensors because semi-quantitative measurement is adopted, the method is not commonly seen and many are not aware of the risks of obtained CO2 readings from the semi-quantitative CO2 kit sets, and to make matter worse, the semi-quantitative measurements are also being made used of to display a flawed continuous CO2 waveform.

Nihon Kohden cap-ONE P907 (TG-920P) mainstream CO2 sensor kit

How do users remove a relatively big 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. This means the transducers are unlikely to last.

Users just doing the inevitable

Shown below is another TG-900P etCO2 kit set (order code P903) that makes semi-quantitative CO2 measurements on a traditional mainstream CO2 sensor. The TG-901T3 kit set (order code P906) is the same thing but using a non-coded connection plug. The medical devices from same manufacturer that make use of semi-quantitative CO2 kit sets for patient CO2 measurements and waveform include:

- Life Scope patient monitors

- Vismo patient monitors

- Cap-STAT OLG-2800

- CardioLife defibrillators

- Neurofax EEG machines etc.

Nihon Kohden semi-quantitative CO2 kit sets with traditional mainstream transducer

Semi-quantitative means there is a duty cycle, and measurements are 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 delivers 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.

In other words,

1. The measured CO2 value is not the true CO2 level,

2. The true CO2 level = (measured CO2 value + x);

where x is the unknown CO2 value carried forward from the inspiration phase. Only when x = zero will the measured CO2 value reflect the true CO2 level.

# It is thus impossible that any manufacturer using a semi-quantitative design can specify a measurement tolerance when there is an unknown in the equation

Struggling to specify an impossible measurement tolerance!

As seen from the duty cycle, there is no measurement being made during the inspiration phase, how does the manufacturer know the measured CO2 value is the true CO2 level? The specified measurement tolerance is conditional on this assurance and the CO2 value shown to users is therefore misleading!

Each semi-quantitative CO2 measurement is in fact only an estimation, because the manufacturer has no way to tell if the value of x is indeed zero. It is only assumed to be zero.

In addition, since the users are not alerted on screen that there is no CO2 measurement being made during the inspiration phase, they are unknowingly made to take on an unnecessary risk.

For example, semi-quantitative methodology can be used as an 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

# The manufacturer ended up ignorantly displaying a flawed continuous CO2 waveform using semi-quantitative measurement kits that do not have 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!

Note the end tidal CO2 (etCO2) value shown is also not alerted as "estimated etCO2" only.

A flawed CO2 waveform with non-measurement intervals reflected as zero measured CO2 value

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 to display a true CO2 waveform on the screen.

Use only quantitative method for waveform display; the quantitative TG-950P (P905) shown here was already discontinued.

What you should know about fully-quantitative type miniaturized mainstream CO2 sensors

The TG-907P CO2 Sensor kit (order code P909) shown in above table is declared as using quantitative method. This sensor was designed for non-intubated adult CO2 monitoring, as well as neonatal CO2 monitoring. Nihon Kohden is thus offering an alternative to sidestream CO2 sampling methodology.

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!

Common defects of a TG-970P CO2 sensor kit (P909), reflecting an impractical design.

*# The fragile miniaturized CO2 sensors are clearly of poor design, and easily broken*

The key point is, it does not last

Beware the mandatory need for network isolation units for patient safety when connecting to a Central Nurse Station

For hardwired Ethernet networking, a Life Scope VS bedside monitor (equipped with a non-isolated Ethernet LAN interface) connecting to a real-time LAN network is a danger to the patient. It is mandatory to observe patient electrical safety by using a network isolation unit to protect the vulnerable patients.

NIHON KOHDEN network isolation transformer

When an isolated monitor with an non-isolated Ethernet port is connected to a hardwired network, it is no longer a medical device unless the above-shown network isolation transformer is introduced between the monitor and network. If the network isolation transformer is not installed, dangerous electric shocks can be delivered to a monitored patient through the wired Ethernet network. Such dangerous electric shocks are potentially lethal and no hospital should ignore this mandatory requirement.

For telemetry networking, the ZS-900P Telemetry Transmitter is optionally required. This is required specification for the Japanese domestic market due to government subsidy but unpopular outside of Japan because of cost.

Telemetry networking is not popular outside of Japan due to absence of government subsidy