Ebook Equipment anaesthesia in and critical care: Part 2
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Ebook Equipment anaesthesia in and critical care: Part 2
Chapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................ Ebook Equipment anaesthesia in and critical care: Part 2....................................2347.3Filters.................................................................238231Passive humidifiersFig. 7.1.1: A heat and moisture exchange filter (HMEF).OverviewHumidifiers add heat and moisture to cool dry inspired gases. Passive humidifiers do not require e Ebook Equipment anaesthesia in and critical care: Part 2xternal energy to function. The heat and moisture exchanger (HME) is the commonest passive humidification device used in anaesthesia. It is used in paEbook Equipment anaesthesia in and critical care: Part 2
tients whose nasal passages (the body’s own HME) are bypassed by an airway device such as an endotracheal tube (ETT) or laryngeal mask. Mechanical venChapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................ Ebook Equipment anaesthesia in and critical care: Part 2ng intra-operative heat loss. HMEs are simple, efficient devices that provide a solution to these problems.UsesHMEs are incorporated into breathing systems in most ventilated patients. They are also attached to tracheostomy tubes in patients who no longer require a breathing system. These are known Ebook Equipment anaesthesia in and critical care: Part 2by several different terms, including: Swedish nose. Thermal Humidifying Filter, Artificial nose, Thermovent T and the Edith Trach.HMEs can also be coEbook Equipment anaesthesia in and critical care: Part 2
mbined with electrostatic microbial filters (HME filters, HMEF) so that they also protect the ventilated patient and equipment from particulate matterChapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................ Ebook Equipment anaesthesia in and critical care: Part 2cool, dry gas that passes in the opposite direction on inspiration. An HME comprises a core of material within a plastic casing. The ability of an HME to recover and transfer heat and moisture depends largely on the characteristics of the material within its core. HMEs can be classified into three g Ebook Equipment anaesthesia in and critical care: Part 2roups, each with their own particular performance characteristics, based on the nature and configuration of their core material:•hydrophobic (water reEbook Equipment anaesthesia in and critical care: Part 2
pelling) HMEs•hygroscopic (water retaining) HMEs•combined hygroscopic-hydrophobic HMEs.232Section?] Passive humidifiersThe simplest and earliest HMEs Chapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................ Ebook Equipment anaesthesia in and critical care: Part 2 vapour to condense and collect between the aluminium inserts. During inspiration cool, dry inspired gas passes through this insert in the opposite direction and absorbs heat and moisture from it. This returns the aluminium to its cooled state and the cycle repeats itself during the next expiration. Ebook Equipment anaesthesia in and critical care: Part 2 Hydrophobic devices are the simplest and cheapest, but least efficient, HME devices, producing a modest moisture output of 10-14 mg HjO.r* at tidal vEbook Equipment anaesthesia in and critical care: Part 2
olumes of 500-1000 ml. In addition, they can suffer from problems caused by the pooling of condensed water.The efficiency of HMEs was increased by theChapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................ Ebook Equipment anaesthesia in and critical care: Part 2cium or lithium chloride. Instead of moisture being stored as condensed water droplets, the moisture is preserved by a chemical reaction with the salts. These HMEs are more efficient and can produce higher absolute humidities of 22-34 mg HjO.r1 at tidal volumes of 500-1000 ml.Newer devices combine h Ebook Equipment anaesthesia in and critical care: Part 2ygroscopic, hydrophobic and electrostatic filters in varying configurations to produce even more efficient devices.o Advantages•Cheap and simple.•Do nEbook Equipment anaesthesia in and critical care: Part 2
ot require a power source.•Produce 60-80% humidification of inspired gases.•Reduce heat and moisture loss from the conducting airways and therefore imChapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................ Ebook Equipment anaesthesia in and critical care: Part 2w a reduction in rates of ventilator-associated pneumonia in critical care.o Disadvantages•Increase the dead-space of the breathing system. Smaller HMEs are therefore used for children.•Increase the resistance of the breathing system.•A progressive increase in resistance through the HME is seen afte Ebook Equipment anaesthesia in and critical care: Part 2r several hours of use due to an increase in the material density of the HME.•Add bulk to the patient end of the breathing system.•HMEs can become occEbook Equipment anaesthesia in and critical care: Part 2
luded with secretions, blood or water.•The efficiency falls as tidal volumes and inspiratory flow rates increase.Chapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................Chapter 7Filters and humidifiers7.1Passive humidifiers.....................................................2327.2Active humidification................Gọi ngay
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