Heat and Moisture Exchanger (HME)

Heat and Moisture Exchanger (HME)

Einführung

During a total laryngectomy, the entire voicebox (larynx) is removed, which leads to a permanent disconnection of the upper and lower airways and a permanent tracheostoma, a breathing hole in the neck. Prior to the operation, breathing primarily occurs through the nasal airways. In the upper airways, the inhaled air is warmed up or cooled down, to prepare the optimal temperature before the air reaches the lungs. After a total laryngectomy, the upper airways are bypassed and breathing in and out occurs through the tracheostoma in the neck which means that the inhaled air flows directly into the lungs. These anatomical changes lead, among others, to changes in voice production, breathing, and olfaction. The nasal functions of regulating the temperature, humidifying, and filtering of the inhaled air are lost. The lack of these functions impairs the lower airways and the activity of the cilia, which leads to pulmonary problems such as tracheobronchial mucus, excessive sputum production, crusting, which can also cause fatigue and shortness of breath. To at least partially reduce these restrictions and compensate the nasal functions, an HME (Heat-and Moisture Exchange) cassette can be attached over the tracheostoma to provide a mean for conditioning, humidifying and to a certain extent even filtering the inhaled air. HMEs have been in clinical use for over 30 years and are currently the only effective, non-pharmaceutical treatment option for pulmonary symptoms experienced by laryngectomized patients. Hence an HME cassette plays a central part of lung rehabilitation after a total laryngectomy.

Function of Heat and Moisture Exchange devices

An HME has three physical properties: 1) heat and moisture exchanging capacity; 2) resistance; and 3) filtering particles.

Heat and moisture exchanging capacity

In the lungs a temperature of 37°C and 100% RH is the ideal condition for the ciliary activity. If the conditions differ i.e. too warm (fever) or too cold the cilia beat slower and at some point not at all. During normal nasal inspiration, air of 22°C and 40% Relative Humidity (RH) is conditioned into air of 32°C and 99% RH at the level of the trachea. In a clinical study these numbers for laryngectomized persons were examined without and with the use of an HME cassette. Without an HME cassette the numbers for the inhaled air were much lower for laryngectomized patients - air of 22°C and 40% RH was only conditioned to 27-28°C and 50% RH at the level of the upper trachea. The lower temperature and minor humidity have an impact on the ciliary activity in the trachea, which is significantly restricted if the RH drops. But the tracheal climate rapidly changed after application and removal of an HME by increase of the temperature and improvement of the RH.

Resistance

The effect of the increased resistance (compared to stoma breathing without HME) in laryngectomees is still poorly understood, but it is clear that HMEs add a variable resistance to the airflow resistance, depending on the flow rate, though the outcomes of studies are not consistent, . Although the breathing resistance of the HME contributes to a more ‘normal’ breathing situation, it should not be too high. Patients would not tolerate a breathing resistance like the normal upper airways because they do not have the possibility to breathe in through their mouth like non-laryngectomized people do when the breathing resistance of the nose is too high (for example when running).

Filtering particles

There are special HME cassettes with an electrostatic filter to enhance the protection against airborne microbes to help to reduce the transfer of viruses and bacteria. This is especially important since laryngectomees often have a compromised immune system. Wearing an HME cassette does not compensate for the loss of upper airway filtration of smaller particles such as bacteria and viruses; the pores of the HME filter are larger than the diameter of the infectious particles. Only larger particles are filtered by the HME. In a clinical study it is concluded that the use of HMEs does not endanger the exposure to infectious microorganisms.

Pulmonary function rehabilitation

With the regular use of an HME cassette over a couple of weeks, the pulmonary functions can be significantly improved in the majority of patients regarding reduced sputum production, reduced forced expectoration in order to clear the airways, and thereby reduced stoma cleaning. This is due to improved ventilation and blood oxygenation values, which leads to a better ciliary activity and thus more efficient coughing for mucus clearance from the trachea. Diverse studies, e.g. from Spain and the US show that with regular and enduring use of an HME cassette, pulmonary complaints decrease, regardless of country and climate. These improvements can even have an impact on voice quality regarding pitch, loudness and intelligibility. Apart from that it can have a positive impact on sleeping disorders and fatigue, which is often related to pulmonary problems.

Properties of HMEs

Material

The basic component of a heat and moisture exchanger is foam, paper, or another substance, which acts as a condensation and absorption surface. The material is often impregnated with hygroscopic salts such as Calcium Chloride, in order to enhance the water-retaining capacity. The HMEs used for laryngectomees are mostly hygroscopic, that refers to the ability to attract and hold water and might have been impregnated with a bactericide solution in order to control bacterial colonization.

Sizes

HMEs can vary in size but they are designed to fit all adhesives or other attachment devices within a certain product line. There exist even HME cassettes for tracheostomy patients, those can vary in size and are usually a bit larger.

Design

Air openings are at the side or at the front of the HME. It is important that it cannot be accidentally covered by clothes or sheets. Some designs use crossbars to prevent clothing from blocking. Usually a rim on the lid helps to find the correct finger position for occlusion.

Hands-free HME

A hands-free HME enables laryngectomees to speak without requiring finger occlusion. The device consists of a combination of HME and an automatic speaking valve, which closes automatically, when exhaling air for speaking, enabling the pulmonary air to be diverted through the voice prosthesis into the esophagus. It reopens automatically, when exhalation decreases. Beside that the hands-free HME enables easy removal in case of coughing, or even an adjustable cough relief valve, to release the air that is build up during coughing. In some devices, speech membranes in different strengths can accommodate different speaking pressures. Even though the hands-free device offers a convenient method for speaking without using ones hands, the overall speech quality was reported to be slightly impaired compared to a regular HME, due to the fact that more air pressure is required to close the valve. Another problem can occur with the seal of the base plate that is used to attach the HME.

Special HME devices

HME devices used for physical exercise

There are special HME devices which have a lower airflow resistance, this makes them suitable for example during physical exercise or when adapting to the breathing resistance for patients that have not used any stoma protection before and start using an HME or have not used an HME for a longer time.

HME devices with antimicrobial filter

During normal nasal breathing, the inhaled air is also filtered to a certain extend. This filtration is important because the spread of viral and bacterial disease by way of the atmosphere requires, among other things, that infectious particles be inhaled by susceptible individuals and deposited at effective sites within the respiratory system for the initiation of disease. An HME is not considered to be an efficient barrier for microorganisms due to a relatively poor bacterial filtration capacity of simple hygroscopic HMEs. There are special HMEs provided with an electrostatic filter, to provide some protection from small particles and airborne microorganisms. These HMEs can be compared to when individuals who breathe through their mouth are wearing an inhalation protection with an electrostatic filter.

Attachment of the HME

HME devices can be attached to the tracheostoma in two different ways: peristomally, by use of a base plate, to which the HME can be attached, and intraluminally, by putting the HME into a laryngectomy tube or a stoma button. Adhesive baseplates come in different shapes and properties to meet the users’ differences in anatomy and skin types.

Peristomally through an adhesive on the neck surrounding the stoma

There is a variety of adhesive baseplates, that can be used to attach the HME and products that are recommended for proper application and removal of the adhesive complement the portfolio.

Intraluminally through a device that is inserted into the tracheostoma

Some laryngectomized patients require a laryngectomy tube to maintain stoma patency, especially in the early postsurgical days and during postoperative radiotherapy. Laryngectomy tubes are available in different models, e.g. the Provox LaryTube is designed in a way that it can even hold a Provox HME. A stoma button however is primarily used in stomas that are shrinking. This is the preferred solution for many users, but there has to be a tight ‘lip’ or ‘rim’ that holds the button in place.

Device lifetime

The majority of patients use one adhesive per day and 1-2 HME cassettes per day.

Voice prosthesis and HME

An individual combination of voice prosthesis, HME (Heat and Moisture Exchanger) and attachment is important for good speech and pulmonary rehabilitation.