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 photo detectors tuned to these wavelengths that enable the calculation of CO2 levels in the breath sample.
Conventional capnographs typically use a heated element called a black body 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. Black body 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 black body 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 µm wide) of the spectrum where CO2 molecules absorb infrared radiation. A black body 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 µl) 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.