A Simple, Disposable End Tidal Carbon Dioxide Detector

Anesth Prog 38:24-26 1991
CLINICAL TECHNIQUES
A Simple, Disposable End Tidal Carbon Dioxide Detector
Detection of expired carbon dioxide is one of the
most reliable methods of avoiding accidental
esophageal intubation. Although capnography has
become a standard monitoring technique in the
hospital operating room, it is rarely available in
the office setting or other arenas where
emergency endotracheal intubation may be
required. A new and inexpensive device,
however, has been developed for assessing endtidal
carbon dioxide. This semi-quantitative
detector fits between the endotracheal tube and
the breathing circuit and uses a pH-sensitive
indicator that changes color in response to
different concentrations of carbon dioxide. Clinical
studies indicate that this device provides similar
results to standard capnography, and its inclusion
in the emergency kit is strongly recommended.
nrecognized esophageal intubation is a major cause
of anesthesia mortality and morbidity.1 Positive
confirmation of endotracheal tube position has become a
standard of care, with direct observation of the passage
of the endotracheal tube into the trachea and detection
of expired carbon dioxide (CO2) considered the most
reliable methods of assuring correct tube placement.2,3 In
the hospital setting, the use of an expensive, electrically
powered infrared detection capnograph or mass spectroscopy
has become an essential monitoring technique to
confirm proper placement of an endotracheal tube.
The majority of oral and maxillofacial surgeons and
other dentists administering general anesthesia for office
outpatient procedures use non-endotracheal techniques,
reserving endotracheal intubation for long, difficult cases
or for emergency situations. Capnography is generally
not available in the dental office. Alternative methods,
however, such as auscultation or pulse oximetry, are not
Received July 1, 1990; accepted for publication February 27, 1991.
Address correspondence to Morton Rosenberg, DMD, Department
of Anesthesiology, 750 Washington St., New England Medical Center
Hospitals, Boston, MA 02111.
© 1991 by the American Dental Society of Anesthesiology
Morton Rosenberg, DMD, and Christopher S. Block, MD
Department of Anesthesiology, New England Medical Center Hospitals, Boston, MA 02111
24
sufficiently accurate or responsive for the quick, reliable
identification of tube placement, especially during a medical
emergency.4 This need for proper tube placement
confirmation may occur in the unanticipated intubation in
the dental office or other prehospital settings, as well as in
emergency intubations at the hospital that are performed
outside of the operating room. It is our belief that auscultation
and questionable visualization are simply not definitive,
particularly in the office setting.
Described in this article is a disposable, inexpensive,
colorimetric, end-tidal CO2 (ETCO2) detector (FEF End-
Tidal CO2 Detector, FENEM, Inc., New York, NY) that
permits the immediate confirmation of proper endotracheal
tube position.
The FEF End-Tidal CO2 Detector is a disposable plastic
device designed to fit between the endotracheal tube and
the breathing circuit. The device has a nontoxic, chemically
treated, pH-sensitive indicator strip that colorimetrically
reflects CO2 concentrations in expired gas.5 The
detector (Figure 1) consists of a transparent dome containing
the chemical indicator, metacresol purple,
mounted on a mesh. Inlet and outlet ports are the standard
15 mm diameter. The indicator strip's response is almost
instantaneous; fast enough to reflect a color change from
inspiration to expiration within a single breath.
There is a semiquantitative comparison color chart
printed directly on the dome in three color ranges (Figure
2). If CO2 is present, the initial purple color, the "A" range
(representing 0.03% to 0.3% CO2) fades to a beige color
(the "B" range representing 0.5% to 1.0% CO2) and then
to pale yellow (the "C" range representing 2.0% to 5.0%
CO2). Fresh gas containing no CO2 restores the original
purple color. The devices are packed individually in airtight
foil bags and have a shelflife of 15 months if unopened.
The detector has been evaluated clinically to confirm
tube placement in the operating room,6-8 in emergency
room and prehospital settings,4 during cardiopulmonary
resuscitation (CPR),9 and as an adjunct to blind nasal
intubation. 10 In those patients where inadvertent esophageal
intubation occurred, diagnosis was easily accomplished.
After emergency intubation for respiratory distress
or cardiopulmonary arrest, an ETCO2 range- 15.2
torr recorded by this device indicated correct endotracheal
tube placement.9 In a study of 62 intubations comparing
the efficacy of colorimetric ETCO2 assessment versus
ISSN 0003-3006/91/$3.50

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Anesth Prog 38:24-26 1991 Rosenberg and Block 25
Figure 1. Side view of the FEF End-Tidal CO2 Detector.
chest auscultation and capnography, colorimetric CO2 detection
of esophageal intubation was more rapid than
auscultation and equivalent to the use of capnography.
There were no false-positive or false-negative results with
,. ,.,~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~......
..:..i:i the ETCO2 detector.8 The manufacturer recommends that
Figure 2. Top view of the FEF End-Tidal CO2 Detector.
".
six breaths be assessed before interpreting a color change.
This will avoid errors due to the forcing of CO2 into the
stomach during mask ventilation or the generation of CO2
in the stomach by prophylactic antacids or carbonated
beverage ingestion.11l
Effective CPR has been shown to produce ETCO2 values
of 0.5% to 2.5%, well within the range of this device
to demonstrate detectable color changes. 12 If the detector
does not change color in the cardiac arrest setting, there
still is a possibility that the endotracheal tube may be in
the trachea. This limitation, also experienced with capnography,
occurs when the cardiac output is extremely low,
resulting in decreased pulmonary blood flow and reduced
delivery of CO2 to the alveoli. As both devices may occasionally
fail to confirm a successful endotracheal intubation
in extremely low flow states, clinicians should immediately
verify endotracheal tube position by other means
and attempt to increase perfusion.
Changes in ETCO2 may serve as a prognostic indicator
of the effectiveness of therapy in cardiac arrest.4,13,14 If the
ETCO2 range detected by this device during CPR remains
low (< 15.2 torr despite correct endotracheal intubation
and optimization of perfusion), successful resuscitation is
unlikely. 14 An increase in ETCO2 provides an immediate
bedside validation of the efficacy of the resuscitative effort.
The FEF Detector is extremely sensitive to the presence
of CO2; the mean CO2 concentration required for detection
of a color change has been shown to be 0.54% (4.1
torr). 11
In summary, a disposable, compact ETCO2 detector
has been developed that can be extremely valuable in
the office setting to verify endotracheal tube placement.
Among its attributes are that it fits all standard airway
connections and requires no warm-up time, calibration,
or servicing. In locations where intubation is performed
routinely, capnography is an essential monitor. It will not
only confirm endotracheal tube placement, but give valuable
information in the diagnosis of other conditions, such
as malignant hyperthermia and rebreathing. For practices
where intubation is the exception rather than the rule,
we strongly recommend the inclusion of a colorimetric
ETCO2 detector as a safe, reliable, and rapidly acting
device in the emergency kit to verify tube placement.
REFERENCES
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intubation. Anaesthesia 1989;44:64-65.
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Scand 1983;27:199-202.
3. Birmingham PK, Cheney FW, Ward RJ: Esophageal
intubation: A review of detection techniques. Anesth Analg
1986;64:886-891.

26 Disposable End-Tidal CO2 Detector Anesth Prog 38:24-26 1991
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