What are Passive HME Filters?

 

This is a hygroscopic sieve that substitutes the normal warming, humidifying, and sieving functions of the upper airways when these structures are sidestepped during anesthesia and intensive care.

Structure of the HME

 Surely, there are vast droves of them, and they come in all forms and sizes. The rudimentary types though remain the same. The HME Filter bought from HME Filter Dealers at a rudimentary level is a box with some crumpled-up cardboard inside it. The covering is naturally made of transparent plastic and is practically impermeable. Surely, it does not seem to donate to the circuit escapes.

Device dead space

The capacity of the HME differs but inclines to be as low as can be attained because the HME snips gas from your tidal volume. This is no matter for the huge seven-foot-tall Maori football player intubated for their elective arthroscopy because their tidal capacity is about 1000mle and they don't care about a little extra "device dead space". However, if your tidal capacity is considerably less, like if you're a minute little grandma with ARDS, well - you need every milliliter of capacity, you cant have 100ml of your 250ml VT ventilating dead plastic.

Normal airway and airing circuit connectors

The HME filter supplied by HME Filter Dealers has connectors that are unmistakably one-sided. There is no means to peg it up to the ventilator the wrong way around. Only one end pegs up to ETT and ETT extensions; the other end pegs into T-pieces and ventilator circuit tubing.

The aim of this sort of preparation is the fact that the creased cardboard filling has a polarity. That is to say, it grants a layer of physical to the humid expired patient breath, which favors the deposition of water, and therefore heat. A porous plastic layer is sometimes existing on the ventilator side, in instruction to act as a physical size barrier to the route of microorganisms and viruses.

CO2 specimen port

This is just your normal Luer-lock port for linking an EtCO2 sampling tube. One can positively overlook this attachment for the majority of one's HME experience. It only becomes a basis of excitement when the little yellow elastic port cap falls out of the hole unintentionally, and the ventilator records a rather large leak. Fears will ring, the patient will desaturate, and all means of comedy will describe until somebody checks the little yellow rubbery port cap. Capnometry with one of these sieves is stimulating. If the sieve is too huge, the capnometry trace will be changed, or it may vanish altogether. Not only that but there is typically some alteration between the pre-filter and post-filter CO2 levels, which is unclear (which one is accurate?). A damp old sieve may become so thick and swampy that all the CO2 is trapped in it, and the EtCO2 trace becomes flat.

Sieve material

As there are hundreds and hundreds of HME plans, so there are hundreds and hundreds of filter resources, each proprietary, original, their chemical properties masked in mystery. In the days gone by, these were refillable and completed from temperature-resistant resources such as silver-coated copper wire gauze and glass wool. Of course, it remains to be established whether these preposterously over-engineered filter boxes are in any way an enhancement on the glass cylinder of dampened blotting paper pellets.

Anyhow. HME filters found with HME Filter Dealers can be branded into two rudimentary subtypes.

Electrostatic sieves tend to gather water vapor using electrostatic attraction; because of this, the sieve tends to be thinner and therefore offers less resistance to flow.

Pleated filters tend to gather water vapor by revealing the gas to a large surface area. These incline to be denser, fluffier, and more foam-like, and they offer greater resistance to gas flow. They are occasionally called "hydrophobic" sieves because the surface of the sieve repels water. This might seem counterintuitive, but the dislike of water does not mean resistance to the accretion of moisture - rather, it means the tiny droplets which form on this exterior do not absorb into the sieve material, but instead remain on the surface, where they can be unprotected to gas flow.