- In severe asthma, expiratory time may be inadequate to reach a
stable ETCO 2 reflecting mixing of all lung units and may be
significantly lower than arterial PCO 2. - In low cardiac output states, decreased delivery of CO 2 to the lung
will result in diminished ETCO 2.
The graphical representation of expired CO 2 , capnography, is also
valuable in the interpretation in the interpretation of respiratory derangements. A
normal waveform begins from a baseline value of zero (inspired gas washout),
increasing towards an upper baseline, slowly rising towards the end-expiration
value (gradual increase expiration of lung units), a rapid down-sloping line
(initiation of inspiration), and rapid return to zero during the remainder of
inspiration. Several important scenarios should be recognized: - Extubation, disconnection, or complete airway obstruction will result in
the immediate disappearance of the waveform and reporting of a
value of “zero”. - Cardiac arrest will also cause disappearance of the waveform and
ETCO 2 will read as “zero”. - Asthma and other expiratory restrictive changes will manifest a slower
upslope and either truncated or, more commonly, absent upper
baseline. The waveform returns to the lower baseline.
marcin
(Marcin)
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