Oridion took a completely new approach to capnography in developing
its Microstream® technology and FilterLine® components. In order to
understand how these products conquer past problems with
capnography, it helps to understand how conventional capnography
works.
Capnography is based on the principle that CO2 molecules absorb
infrared radiation at specific wavelengths. The capnograph contains
special photodetectors tuned to these wavelengths that enable the
calculation of CO2 levels in the breath sample.
Conventional capnographs typically use a heated element called a
blackbody emitter for the infrared radiation source. Unfortunately, this
type of emitter is both imprecise and inefficient because it produces a
broad infrared spectrum. As a result, the capnograph requires a large
sample cell and high flow rate, which causes occlusion and accuracy
problems. Blackbody emitters also generate large amounts of heat,
creating hardware challenges that restrict monitor portability and
ruggedness.
Microstream® - A Unique CO2 Emission Source
Microstream® employs a unique, laser-based technology called
molecular correlation spectroscopy (MCS™) as the infrared emission
source. Operating at room temperature, the Microstream® emitter is
electronically activated and self-modulating, which eliminates the need
for moving parts.
Unlike the broad infrared spectrum produced by a blackbody emitter,
MCS™ creates an infrared emission precisely matching the absorption
spectrum of CO2. The Microstream® emitter radiates a focused beam of
infrared energy characterized by the narrow region (0.15 ?m wide) of
the spectrum where CO2 molecules absorb infrared radiation. A
blackbody emission is typically 135 times broader. Because MCS™ is
highly accurate with all gas samples, there is no need to create
special algorithms within the monitor to correct for high concentrations
of oxygen or anesthetic gases.
Small Sample Cell
The highly efficient and CO2-specific emission source used in
Microstream® technology results in an extremely short light path. This
sets the stage for a number of technological advantages and clinical
benefits. Because of the short light path, the breath sample cell can
be greatly reduced in size (down to 15 ?l) compared to sample cells
used in conventional capnography.
Accuracy in Monitoring Neonates
The advantage of a small sample cell is most apparent with neonatal
patients who have high respiratory rates and small tidal volumes. A
large sample cell can cause the inspired and expired breath to blend
within the cell, resulting in slow response time, falsely low EtCO2
measurements and a distorted waveform shape. With Microstream®, a
small sample cell designed for laminar flow, accurate monitoring can
be attained with a much lower flow rate.
Minimal Flow Rate
A low flow rate is important because it prevents moisture and humidity
from entering the sample line and obstructing the pathway, a problem
common in sidestream technology. Microstream® operates at a flow
rate of only 50 ml/min. Other capnography systems typically require
flow rates two or three times as high. As with the small sample cell,
the low flow rate ensures accurate and responsive monitoring for
neonates and infants, despite their small tidal volumes.
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