Carbon dioxide absorption

Published on 07/02/2015 by admin

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Last modified 07/02/2015

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Carbon dioxide absorption

John M. VanErdewyk, MD

Scientists first began experimenting with substances capable of absorbing carbon dioxide (CO₂)in the early 1900s. Progress was made during World War I, when chemical warfare stimulated research to eliminate CO₂ from the closed breathing system of the gas mask. Today, CO₂ absorption is used daily to remove CO₂ from semiclosed or closed anesthetic circuits.

CO₂ absorbers

An ideal CO₂ absorber would have the following characteristics: efficiency, ease of handling, low resistance to airflow, low cost, lack of toxicity, and lack of reactivity when used with common anesthetics.

The amount of CO₂ that can be absorbed varies depending upon the absorbent. In practical use, the maximum amount is rarely achieved because of factors such as channeling of gas flow around the granules of absorbent. Channeling refers to the preferential passage of exhaled gases through the canister via the pathways of least resistance. Excessive channeling will bypass much of the granule bulk and decrease efficiency. Proper canister design—with screens and baffles plus proper packing—helps decrease channeling (Figure 8-1).

Figure 8-1 The dual-chamber absorber is now the most commonly used type of absorber for containing CO₂ absorbent. This device is permanently mounted, with a vertical gas-flow axis. This positioning eliminates dusting, channeling, and packing problems. Because condensation may collect at the bottom of the chamber, forming a caustic lye solution with the dust, it is important that the unit contains a drain valve. Each absorber design has unique opening, closing, and sealing components; however, most have a single-action clamp mechanism.

A dual-chamber canister is more efficient than a single-chambered canister, and an ideal water content of the absorbent is needed for optimal CO₂ absorption. For the greatest efficiency of absorption, the patient’s entire tidal volume should be accommodated within the void space of the container. Therefore, a properly packed canister should contain approximately one half of its volume in granules and one half as intergranular space.

The greater the surface area available for CO₂ absorption, the greater the absorptive ability. However, as granule size decreases (surface area increases), the resistance to airflow through the canister increases. A compromise has been reached in a granule size of 4 to 8 mesh, which allows good CO₂

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