User Manual

3 Monitoring

Monitoring

LIFEPAK 20e Defibrillator/Monitor Operating Instructions 3-17

How Capnography Works

An EtCO2 sensor continuously monitors carbon dioxide (CO2) that is inspired and exhaled by

the patient. The sensor employs Microstream non-dispersive infrared (IR) spectroscopy to

measure the concentration of CO2 molecules that absorb infrared light.

The CO2 FilterLine system delivers a sample of the exhaled gases directly from the patient into

the CodeManagement Module for CO2 measurement. The low sampling flow rate (50 ml/min)

reduces liquid and secretion accumulation and prevents obstruction, which maintains the shape

of the CO2 waveform.

The CO2 sensor captures a micro sample (15 microliters). This extremely small volume allows

for fast rise time and accurate CO2 readings, even at high respiration rates.

The Microbeam IR source illuminates the sample cell and the reference cell. This proprietary IR

light source generates only the specific wavelengths characteristic of the CO2 absorption

spectrum. Therefore, no compensations are required when concentrations of O2, anesthetic

agent, or water vapor are present in the exhaled breath.

The LIFEPAK 20e defibrillator/monitor is set at the factory 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 x the measured EtCO2 value. The BTPS conversion can be turned off in the

Setup Options. Refer to "CO2 Setup Menu," page 8-10 for more information.

EtCO2 Monitoring Waveform Analysis

Valuable information concerning the patient’s expired CO2 can be acquired by examination and

interpretation of the waveform.

The Phases of the Waveform

Figure 3-5 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 CO2-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

(EtCO2) value that is recorded and displayed by the monitor. Phase IV–V (Inspiratory

Downstroke), a sharp fall, reflects the inhalation of gases that are CO2-free. Alterations of the

normal capnograph or EtCO2 values are the result of changes in metabolism, circulation,

ventilation, or equipment function.

Figure 3-5 Phases of the Respiratory Waveform

Infection hazard

Do not reuse, sterilize, or clean Microstream

CO2 accessories as they are designed for single-

patient one-time use.

WARNINGS! (CONTINUED)

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