However, the concentration of anesthetic present is so low that this is considered a negligible effect. Halogenated anesthetic agents, such as isoflurane, can absorb infrared light, also resulting in a false elevation. Condensation can result in false elevations of CO2 readings of 1.5-2%. Possible mixing of gas in the sampling lineĬapnographs are included in many multiparameter monitors available, and overall the measurements are demonstrated to be accurate. Removal of gas from the breathing circuit (which particularly can be an issue in small patients with small minute ventilations and may need to be accounted for by an increased flow rate)Ī need to scavenge gas as the samples being removed will usually contain inhalant anesthesia Less dead space added to the breathing systemįewer issues with condensation affecting results Potential for the weight of the device to result in kinking of the endotracheal tubeĬondensation of respiratory secretions in the measurement chamber resulting in inaccurate results Increased dead space in the breathing circuit No loss of gas volume due to a closed breathing system There are advantages and disadvantages to both nondiverting and diverting devices (see Table I).
Gas that is exhaled by the patient is continuously removed by a suction pump located in the main unit, which is also where the CO2 measurement occurs. With a sidestream system, there is a sampling port and tubing attached to the breathing circuit. In a mainstream capnograph, CO2 is measured directly in the breathing system, with an optical chamber inserted between the endotracheal tube and the breathing circuit. The measuring device can be located in a nondiverting (mainstream) or diverting (sidestream) position. A photo detector opposite the LED measures the light intensity reaching it, which is inversely proportional to the concentration of CO2. CO2 molecules in the chamber absorb light proportionally to the CO2 concentration. In this method, an LED generates a light beam, which passes through a measuring chamber. There are different techniques by which capnographs measure CO2, but infrared absorption is by far the most common. The most common type of capnogram plots CO2 concentration on the y axis versus time on the x axis. A more useful device is a capnograph, which creates a continual CO2 waveform: a capnogram. Capnometers are available which measure the maximum inspired and expired CO2 concentration, without a graphical display. It is now recommended as part of the ACVAA Monitoring Guidelines aimed at anesthetized veterinary patients for assessment of appropriate ventilation. It became part of the standard of care for basic anesthesia monitoring in humans in the 1980s, and has been used in veterinary medicine since the 1990s. Veterinary Clinic for Low Income Pet OwnersĬapnography, the measurement and graphical display of carbon dioxide (CO2) concentration in exhaled respiratory gas, was developed in the 1940s.Vet Services Report Cruelty Animal Advocacy Adopt
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