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December
1997
Comparison
of end-tidal and arterial carbon dioxide in infants using laryngeal mask
airway and endotracheal intubation.
Chhibber AK; Fickling K; Kolano JW; Roberts WA
Anesth Analg1997; 84:51-3.
[ see
abstract below ]
This is an interesting
study because it systematically compared the end-expired carbon dioxide
values obtained at the 15 mm connector in infants anesthetized with a
non-rebreathing system with controlled ventilation, with both a laryngeal
mask airway and an endotracheal tube. As expected, the carbon dioxide
values obtained at the y-piece were consistently lower than actual measurement
of arterial carbon dioxide values; more importantly this difference was
as great as 12 mmHg but no different between the LMA and the endotracheal
tube.
Although very useful
as a trend monitor, end-expired carbon dioxide sampling , particularly
in infants ventilated with a non-rebreathing system, is always associated
with a wide range of differences between end-expired and arterial values.
If control of carbon dioxide is essential to the anesthetic technique,
then direct measurement is always the gold standard. This study once again
demonstrates this caveat. The authors are to be congratulated for clarifying
this issue.
On a different note
I am concerned with the idea that it is acceptable to use controlled mechanical
ventilation with a laryngeal mask airway. The LMA should never be viewed
as a substitute for endotracheal intubation. If an LMA is placed, then
I feel it is essential that assisted manual ventilation, along with a
precordial stethoscope, be used so as to immediately identify leaks or
the sound of regurgitated gastric contents.
Return to the Current
Literature Review Front Page, or read the abstract:
ABSTRACT
The laryngeal mask airway
(LMA) has become a popular tool for airway management in selected adult
and pediatric patients undergoing routine surgical procedures. The relationship
between end-tidal and arterial carbon dioxide during controlled ventilation
via the LMA in infants under 10 kg has not been reported.
After induction of
general anesthesia, the LMA was placed in 12 healthy infants and mechanical
ventilation initiated. After maintaining steady-state level of end-tidal
carbon dioxide (minimum 5 min), an arterial blood sample was obtained
and end-tidal carbon dioxide level noted. The laryngeal mask was then
removed, the trachea intubated, and mechanical ventilation resumed with
initial ventilatory variables. After reaching a steady-state level of
end-tidal carbon dioxide, a second arterial sample was obtained and end-tidal
carbon dioxide level noted.
The mean end-tidal
carbon dioxide and arterial partial pressure of carbon dioxide obtained
during ventilation were 42.2 +/- 7.9 and 47.1 +/- 11.0 (LMA) and 37.4
+/- 4.6 and 42.6 +/- 6.7 (endotracheal tube), respectively. Analysis of
differences between partial pressure of carbon dioxide and end-tidal carbon
dioxide using the Bland and Altman method revealed bias+/-precision of
4.9 +/- 3.9 and 5.3 +/- 3.2 with ventilation via the laryngeal mask and
endotracheal tube. Our data indicate that, while ventilating infants under
10 kg with LMA, end-tidal carbon dioxide is an accurate indicator of arterial
partial pressure of carbon dioxide.
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