Physio-Control LIFEPAK 15 - Manual (Page 91)

MONITORING
4
©2007-2013 Physio-Control, Inc. LIFEPAK 15 Monitor/Defibrillator Operating Instructions
4-47
You can set up the LIFEPAK 15 monitor/defibrillator to use the capnography Body Temperature
Pressure Saturated (BTPS) conversion method. This option corrects for the difference in
temperature and moisture between the sampling site and alveoli. The correction formula is 0.97 ×
the measured EtCO
2
value. See the LIFEPAK 15 Monitor/Defibrillator Setup Options provided with
your device.
EtCO2 Monitoring Waveform Analysis
Valuable information concerning the patient’s expired CO
2
can be acquired by examination and
interpretation of the waveform.
The Phases of the Waveform
Figure 4-13 is a graphic representation of a normal capnograph waveform. Four phases of the
waveform require analysis. The flat I–II baseline segment (Respiratory Baseline) represents
continued inhalation of CO
2
-free gas. This value normally is zero. The II–III segment (Expiratory
Upstroke), a sharp rise, represents exhalation of a mixture of dead space gases and alveolar
gases from acini with the shortest transit times. Phase III–IV (Expiratory Plateau) represents the
alveolar plateau, characterized by exhalation of mostly alveolar gas. Point IV is the end-tidal
(EtCO
2
) value that is recorded and displayed by the monitor. Phase IV–V (Inspiratory
Downstroke), a sharp fall, reflects the inhalation of gases that are CO
2
-free. Alterations of the
normal capnograph or EtCO
2
values are the result of changes in metabolism, circulation,
ventilation, or equipment function.
Figure 4-13 Phases of the Respiratory Waveform
Respiratory Baseline Elevation of the waveform baseline (I–II segment) usually represents
rebreathing CO
2
. This elevation usually is accompanied by gradual increases in the EtCO
2
value.
Rebreathing CO
2
is common in circumstances of artificially produced increased dead space and
hypoventilation. Precipitous rises in both baseline and EtCO
2
values usually indicate
contamination of the sensor.
Expiratory Upstroke In the normal waveform, the rising phase (II–III segment) is usually steep.
When this segment becomes less steep, CO
2
delivery is delayed from the lungs to the sampling
site. The causes of this delay can be physiologic or mechanical and include bronchospasm,
obstruction of the upper airway, or obstruction (or kinking) of an endotracheal tube (ETT).
Expiratory Plateau The plateau of the waveform, which represents the remainder of expiration
(III-IV segment), should be nearly horizontal. The end of the plateau represents the EtCO
2
value.
Upward slanting of the expiratory plateau occurs when there is uneven emptying of the alveoli.
IV
V
II
III
I