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Contents:
Volume 2, Number 1; July, 2003 |
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Role
of Capnography on Laryngeal Mask Airway Positioning: Preliminary
Experience |
Yuh-Jeng Yang,
MD; Kuo-Chih Chen, MD; Chien-Chih Chen, MD; I-Yin Lin, MD; Chun-Chieh
Choa, MD; Tzong-Luen Wang, MD, PhD |
From the Department of Emergency Medicine (Yang
YJ, Chen KC, Lin IY, Choa CC, Wang TL), Shin-Kong Wu Ho-Su Memorial
Hospital.
Correspondence to Dr. Tzong-Luen Wang, Department
of Emergency Medicine, Shin-Kong Wu Ho-Su Memorial Hospital, 95
Wen Chang Road, Taipei, Taiwan. E-mail M002183@ms.skh.org.tw
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Abstract
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Laryngeal mask airway (LMA) has
been shown to be an alterative method of definite airway in first
aid. However, the adequate methods to confirm LMA positioning remain
to be elucidated. We reported our preliminary experiences of 5 cases
with trauma who underwent awake application of LMA. Of them, three
cases couldn¡¦t be confirmed the positioning of LMA by physical
examination. Capnogaphy demonstrated two of the patients have initial
improper positioning of the LMA. Under the guidance of end-tidal
CO2 readings, these two cases could be finally well
positioned the LMA. In summary, our preliminary experience demonstrated
that capnography should be routinely used as the confirmatory method
of LMA positioning.
Key words---Laryngeal Mask Airway; Capnography; First
Aid; Emergency Medicine |
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Introduction
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Since the first infra-red
CO2 measuring and recording apparatus was introduced
in 1943 by Luft, capnography has evolved into an essential component
of standard anesthesia monitoring armamentarium. The primary goal
of anesthesiologists is to prevent hypoxia, and capnography helps
to identify situations that can lead to hypoxia if uncorrected.
Moreover, it also helps in the swift differential diagnosis of hypoxia
before hypoxia can lead to irreversible brain damage. Because of
these advantages, the utility of capnography has been extended outside
of the operating room arena, in recent times, to emergency rooms,
endoscopic suites, X-ray rooms and even on-site at emergency and
trauma fields. Secondary confirmation of endotracheal tubing has
been developed as one of the most important applications of capnogaphy. 1-3
The laryngeal mask airway (LMA) has been well developed and has
gained widespread popularity in clinical use in recent 10 years. 4,5
It allows either spontaneous or positive-pressure ventilation. With
advances in the design, it has also received more attention as a
tool for management of the difficult airway. 6-8
Because the placement of this device is less technique-dependent,
the learning curve will be adequate. 9-13
In other words, the LMA has theoretical basis for the rescue team
to learn and use under difficult situations. 13-17
However, there was still lacking in guidelines concerning confirming
the adequacy of LMA positioning. We therein report our preliminary
experiences of five cases that underwent LMA with secondary confirmation
by capnography.
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Methods |
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Study population and protocol |
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Five patients who consulting our
institute due to multiple trauma and airway compromise were enrolled
in this study. The protocol has been reviewed by our institute review
board and informed consent was obtained. After detailed evaluation,
emergency physicians decided to use LMA as the initial conduit for
securing airway in the above five cases for whom awake intubation
were determined.
After maintaining cervical immobilization, the patients were well
pre-oxygenated. Under Sellick¡¦s maneuver, the physicians
applied carefully the LMA and then confirm tube placement immediately,
assessing the first breath delivered by the bag-mask unit. As the
bag is squeezed, listen over the epigastrium and observe the chest
wall for movement. The moisture condensation on the inside of the
connecting tube with exhalation was also observed. Secondary confirmation
was determined by a pulse oximetry, a continuous capnography and
chest radiographs.
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Capnography |
The capnography we used was a commercialized
product, Capnogard, from NovaMatrix Medical System Inc. (USA). It
possessed a solid state mainstream sensor using single beam, non-dispersive
infrared absorption, ratiometric measurement. Capnogram could be
obtained within 15 sec., and full specifications within 60 sec.
It could be applied to any adult and pediatric airway size, including
LMA tubing. The accuracy was ¡Ó2 mmHg for 0-40 mmHg, ¡Ó5%
of reading for 41-70 mmHg, ¡Ó8% of reading for 71 - 100 mmHg.
When used with the standard technique of listening to breath sounds,
CO2 monitoring is probably the best way to detect esophageal
intubation. Although CO2 may be present in the stomach
it is rapidly flushed out during ventilation of the stomach and
the end tidal CO2 reading would decrease, resulting in a flat capnogram.
Recently, the end tidal CO2 detectors, which change color on exposure
to 4% CO2, have been used successfully to confirm tracheal
intubation. These detectors can be used where CO2 monitors
are not available. It should be noted that in the presence of carbonated
beverages in the stomach a PETCO2 as high as 38 mmHg
can be observed with esophageal ventilation and it may take at least
six breaths for the end tidal CO2 to decrease to zero.
However, the CO2 waveforms produced as a result are abnormal
in shape and, therefore, could be detected earlier by capnography
than capnometry.
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Table 1. Clinical characteristics |
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Results |
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Table 1
depicts the clinical characteristics of five patients enrolled in
this survey. Of them, three cases (case 2, case 3, and case 5) couldn¡¦t
be confirmed the positioning of LMA by primary method (or physical
examination). The uncertainty was due to audible breathing sound
and epigastric bubbling. Continuous end-tidal CO 2 readings
provided by near infra-red capnography revealed that two of the
three cases (case 2 and case 3) did not have proper positioning
of the LMA. Under guidance of the end-tidal CO 2 readings,
the LMA was adjusted to a most adequate position. Chest radiographs
demonstrated proper positioning of the LMA in all of these five
cases.
Of the two cases with initial improper LMA positioning, the initial
end-tidal CO 2 reading was 12 mmHg and 8 mmHg, respectively.
Pulse oximetry demonstrated 93% and 92%. After repositioning, the
end-tidal CO 2 readings increased to 30 mmHg and 29 mmHg,
whereas oxygen saturation was 95% and 92%. Concomitant hemodynamic
measurements were also depicted in Table 1 .
There were no definite hemodynamic changes for these five cases
during the procedure.
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Discussion |
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It has been well
established the LMA and the Combitube dual-lumen tube are both time-saving
procedure for maintaining patent airways in emergency situations. 12,13,18-20
However, in one study comparing the LMA and the Combitube for inexperienced
operators, the rate of successful LMA placements in anesthesized
and paralyzed patients was 100%, but the success rate only 92% with
a Combitube.13 More complicated procedures may contribute to the
failure of the Combitube. In addition, the Combitube cannot be used
in patients with a protective reflex or in pediatric victims, whereas
the LMA has no such limitations. 21
In our previous study, 22 the rescue
team and DMAT learned application of LMA easily and successfully.
Evidence from some preliminary studies revealed that the application
of the LMA is not affected by the patient position, 23
past experience, 10-12consciousness
level, 4-7 or cervical immobilization. 24-26
These characteristics make the LMA more attractive in rescue of
victims in first aid.
The most important issue in intubating the patients is to confirm
proper positioning of the tubing in the airway. A variety of electronic
and mechanical devices are available for use both in-hospital ad
outside the hospital. These devices range from simple and inexpensive
to complex and costly and include several models of end-tidal CO 2
detectors and several types of esophageal detector devices. The
American Heart Association International Guidelines 2000 Conference
addressed this topic in detail to determine whether evidence now
supports secondary confirmation devices as a required adjunct. Although
no device or adjunct can substitute for proper visualization of
the tracheal tube passing through the vocal cords, the devices for
secondary confirmation still played an important role in difficult
situations such as trauma. 27
The quantitative end-tidal CO 2 detectors are widely accepted
as the best, albeit most expensive, secondary confirmation device.
A capnometer provides a single quantitative readout of the concentration
of CO 2 at a single point in time, whereas the capnograph
provides a continuous display of the level of CO 2 as
it varies throughout the ventilation cycle. These monitors can confirm
successful tracheal tube placement within seconds of an intubation
attempt. Patient deterioration associated with declining clinical
status or subsequent tracheal tube dislodgement can also be detected
with these devices. Dislodgement is an adverse event that is alarmingly
common during out-of-hospital transportation of a patient. 28-32
In our report, five patients underwent awake application of LMA.
Of them, three couldn¡¦t be confirmed the proper positioning
by physical examination. It may have double meanings; the first
is that there is a difficulty of primary confirmation of LMA positioning
by physical examination because the device always covers both the
airway (or glottic opening) and partially the esophagus. This hypothesis
should be examined by radiographs or fluoroscopy. Capnogaphy is
therefore to be recommended as routine or primary confirmation of
LMA positioning. The second is that awake intubation itself may
be a risk factor for dislodgement of LMA because of the patients
still have intact gag reflex and may move anyway although cervical
immobilization has been applied. The observation is especially important
when the patients were applied LMA during transportation.
In summary, our preliminary experience demonstrated that capnography
should be routinely used as the confirmatory method of LMA positioning.
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