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Project

Optimizing CO2 absorbent usage during low flow anesthesia with automated low flow anesthesia workstations

Inhalational anesthetics are often used to maintain general anesthesia. However, it is known that volatile anesthetics are greenhouse gases and some can damage the earth’s ozone layer. To lower the use of these anesthetic agents, a low flow anesthesia technique can be applied. This technique is based on re-inhaling expired anesthetic agent by reducing fresh gas flow (mixture of administered oxygen, air and anesthetic agent) below the set minute ventilation. Lowering fresh gas flow increases rebreathing and consequently reduces use of volatile anesthetics. But lowering the fresh gas flow also affects oxygen and CO2 concentrations in the anesthesia machine. To avoid hypoxic gas mixture formation, the delivered oxygen concentration needs to be increased, and more so as fresh gas flows are lowered. Finally, to safely recycle a part of the exhaled gas, CO2 needs to be removed. High concentrations of inspired CO2 leads to high arterial CO2 partial pressures with dangerous consequences if excessive. CO2 absorbers, part of the anesthesia work station, contain Ca(OH)2 based granules which absorb the exhaled CO2, thus making rebreathing possible. Although a low flow anesthesia technique is used to minimize anesthetic agent waste for environmental reasons, the use of these granules has an impact on environment too. First, manufacturing Ca(OH)2 granules out of lime stone causes high CO2 emissions. In addition, CO2 absorbers need to be frequently refreshed, often before granules are fully saturated because, as more granules become saturated, more CO2 molecules will find a way to bypass unsaturated granules, leading to rising inspired CO2 concentrations. Finally, increasing rebreathing fraction will minimize anesthetic agent waste but cause the time to saturation of the granules to shorten. To allow us to understand the impact of a low flow anesthesia on cost and environment, we need to be able to quantify the impact of a low flow anesthesia technique on both CO2 absorber life and anesthetic agent waste. This Ph.D. thesis will focus on CO2 absorbers. We want to investigate which factors influence absorber life by creating different in vitro scenarios, based on known respiratory physiology and a proper understanding of the anesthesia workstation, and this over the entire clinically used fresh gas flow range. Effects of techniques that might prolong absorber life will be studied. With this research we will gain more insight in factors determining absorber life and what effects it has on respiratory physiology. And last but not least, absorber life and its determinants will be linked to its costs.

Date:23 Jun 2021 →  Today
Keywords:CO2 absorbers, low flow anesthesia
Disciplines:Anaesthesiology not elsewhere classified
Project type:PhD project