CO2 MEASUREMENTS WITH THE CAPNOVUE M1 ARE SIGNIFICANTLY MORE
CONSISTENT THAN WITH A “JERRY-RIGGED” DEVICE
Monitoring exhaled CO2 (capnography) of
spontaneously breathing sedated patients is the
standard of care for anesthesiologists in the US1, UK2,
and Canada3. Accurate and consistent CO2
measurements provide the optimal information to
guide clinician decision making. Each component of the
capnography system, from gas analyzer to oxygen face
mask, contributes to the accuracy of measured results.
The assembly of “jerry-rigged” devices is not
standardized in any way by anesthesia groups,
professional societies, or the FDA. In many cases the IV
catheter attached to the gas sample line will have a
smaller cross sectional lumen than the sample line
itself, thus increasing resistance to gas flow within the
monitoring system.
Capnography utilizes continuous sampling of gas near
the patient’s nose and mouth to measure CO2 levels
over time. During exhalation, CO2 levels rise and during
inhalation, CO2 levels fall. Rising and falling levels of
CO2 create a waveform on the capnograph that can
guide clinical intervention in real time. Changes to the
size and shape of CO2 waves correspond to respiratory
alterations and demand immediate assessment.
The CapnoVue M1 (manufactured by Monitor Mask
Inc., Seattle, Washington) is a face mask designed
specifically for use in the operating room and is cleared
by the FDA for face mask capnography. The CapnoVue
M1 features two integrated CO2 sampling ports
encircled by gas exhalation vents on the lateral surfaces
of the mask that enable direct connection of the CO2
sample line (Figure 2). The CapnoVue M1 requires no
assembly and has a standardized manufactured design.
Face Mask Comparison
Figure 2: The CapnoVue M1
In this study, measured exhaled CO2 (etCO2) levels of
spontaneously breathing subjects were assessed using
two devices; a "jerry-rigged" oxygen face mask and the
CapnoVue M1.
"Jerry-rigged" devices are used by anesthesiologists in
the vast majority of face mask capnography cases and
are not cleared or regulated by the FDA. Most often,
these devices are assembled by the off-label process of
sticking an IV catheter through a gas vent or wall of an
oxygen mask to attach a gas sample line (Figure 1).
Figure 1: A “jerry-rigged” face mask
CO2 monitor sample line attached
CO2 Measurement Results
In the current study, etCO2 measurements with a
"jerry-rigged" mask and a CapnoVue M1 device were
assessed. The data was collected on five subjects for
both nose and mouth breathing with an oxygen inflow
rate of six liters per minute.
The "jerry-rigged" mask testing results include three
etCO2 sample locations due to non-standardized
assembly and numerous sample location
possibilities. For example, when an IV catheter is used
to attach the sample line to the mask (Figure 1), the tip
of that catheter may be located in a number of
positions. It is additionally possible that the catheter
may begin in one position and then move to another
during the patient’s clinical course due to the instability
of assembly. In this study we assessed etCO2 levels
during nose and mouth breathing (Figure 3) at three
potential catheter tip locations within the “jerry-rigged”
mask:
1.
2.
3.
strong correlation for nose and mouth breathing etCO2
levels.
Figure 4: Nose and mouth breathing mean etCO2 levels in mmHg
with the CapnoVue M1
Less than 1 cm from the nose
Less than 1 cm from the mouth
Less than 1 cm from the oxygen inflow
The “jerry-rigged” mean testing results demonstrate
significant inconsistency. Physiology dictates that an
individual patient will have one arterial CO2 level at any
moment in time but “jerry-rigged” masks show marked
variability of etCO2 measurements.
Figure 3: Nose and mouth breathing mean etCO2 levels in mmHg
with a “jerry-rigged” face mask at three sample locations
Summary
CO2 Measurements with the CapnoVue M1 are
significantly more consistent than with a “jerry-rigged”
device. etCO2 levels obtained with “jerry-rigged”
devices vary significantly by sample location and
whether nose or mouth breathing is occurring. etCO2
measurements obtained by the CapnoVue M1 are
highly consistent with minimal difference observed
between nose and mouth breathing.
The CapnoVue M1 provides fixed, standardized
locations for etCO2 measurement with two integrated
CO2 sampling ports. The ports are in mirror image
locations on opposite sides of the mask midline and
provide equivalent gas sampling results as confirmed
with bench testing during the FDA clearance process.
During clinical use, the anesthesia provider will choose
to use one of the two ports for etCO2 monitoring based
upon the specific clinical scenario. As in clinical care,
this study measured etCO2 levels during nose and
mouth breathing (Figure 4) by connecting a capnograph
to one of the two integrated CO2 monitoring ports.
Monitoring etCO2 with the CapnoVue M1 yields highly
consistent, nearly singular, etCO2 levels analogous to
the patient’s unique arterial CO2 level. Furthermore,
the CapnoVue M1 mean testing results demonstrate a
Fluctuating etCO2 levels with the “jerry-rigged” mask
that do not correspond to changes in a patient’s clinical
condition may lead clinicians to place less value on
etCO2 monitoring and slow response times to actual
changes in respiratory status. Consistent etCO2 results,
such as those from the CapnoVue M1, more clearly
identify changes in clinical status, increase the value of
etCO2 monitoring for the clinician, and optimize
response times to respiratory alterations.
When compared to a common “jerry-rigged” face
mask, the CapnoVue M1provides significantly more
consistent etCO2 measurements with closely correlated
nose and mouth breathing etCO2 levels.
References
1. American Society of Anesthesiologists, "Standards for Basic
Anesthetic Monitoring," 2011.
2. Association of Anaesthetists of Great Britain and Ireland, "The use of
capnography outside of the operating theatre," 2011.
3. Canadian Anesthesiologists' Society, "Guidelines To The Practice of
Anesthesia," 2012.
COPYRIGHT © 2016 MONITOR MASK INC. ALL RIGHTS RESERVED.
www.MonitorMask.com
[email protected]
Monitor Mask Inc., Bellevue, WA
600010 Rev 1
.