CO2+Analyzers

=CO2 Analyzers= toc

Different Types of CO2 Analyzers
> >>>> This relationship may be expressed as: **A = εdc** >>>> A = absorbance >>>> ε = molar extinction coefficient >>>> d = pathlength in cm >>>> c = molar concentration >
 * ===**Mass Specrometry**===
 * Measures concentration of CO2 largely on basis of molecular weight. CO2 passes through an ionizer creating ion fragments. These fragments are accelerated in a vacuum through a high magnetic field. The magnetic field separates the fragments by their mass and charge. The fragments are deflected onto a detector plate, where CO2 has a specific landing site. The processor section calculates the concentration of CO2.
 * ===**Raman Scattering**===
 * Photons generated by a high-intensity argon laser collide with CO2. After impact, CO2 is momentarily excited to unstable vibrational and rotatory state. When CO2 returns to the normal state, photons of a characteristic frequency are emitted. The scattered photons are measured as peaks in a spectrum that determines the concentration.
 * ===**Infrared Absorption Spectrophotometry (IRAS)**===
 * Most commonly used method
 * IRAS devices have 5 components:
 * **An infrared light source** - produces infrared energy. CO2 absorbs light with a characteristic peak at a wavelength close to 4300nm.
 * **A gas sampler**
 * **An optical path**
 * **A detection system** - calibrated to determine the concentration of CO2 by creating electric currents.
 * **A signal processor** - Analyze electric currents created by detectors. Transforms current change to a measurement. The capnogram is an oscilloscopic representation of the electrical current changes over time. The signal-processing section has a memory section that correlates the absorbed energy with a concentration as predicted by the //__Lambert-Beer law__.//
 * Lambert Beer's law is a mathematical means of expressing how light is absorbed by matter. The law states that the amount of light emerging from a sample is diminished by three physical phenomena:
 * 1) The amount of absorbing material in its pathlength (concentration)
 * 2) The distance the light must travel through the sample (optical pathlength OPL)
 * 3) The probability that the photon of that particular wavelength will be absorbed by the material (absorptivity or extinction coefficient)
 * Where:
 * ===**Colorimetric** -===

Infrared CO2 Monitors Categories

 * ===**Sidestream Capnographs -**===
 * a fixed volume of gas is continuously sampled from the circuit via a sample tubing
 * The sampled gas is aspirated through nylon or Teflon tubing into the measuring cell and then released into the atmosphere or returned to the circuit through a second tube
 * Sampling should take place as close to the patient as possible to minimize the effects of circuit dead space
 * The rate is usually adjusted to between 50 and 500 mL/min
 * There are several sources of potential error :
 * Water vapor, liquids and particulate matter can enter the measuring cell and produce erroneous readings ( filters and water traps help to minimize these factors )
 * Response time delay (can be minimized by using short tubing with a small lumen and high sample flow rates)
 * CO2 can diffuse out of sample tubing and cause falsely low readings
 * ===**Mainstream Capnographs**===
 * incorporate the infrared sensor into the circuit very close to the endotracheal tube (thus many problems with sidestream capnometry have been eliminated)


 * No complicated sampling system because CO2 is measured directly in the circuit and no gas is subtracted
 * Minimized effects of breathing circuit and sample tubing dead space and faster response time
 * Require frequent calibration, usually daily, and are prone to soiling with saliva or mucus because of their close proximity to the patient.

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