The heat and moisture exchange filter (HME)

By Alex Yartsev - Jul 13, 2015

The HME is covered in greater detail elsewhere in a small chapter dedicated to its rugged beauty. Here, one will find only a brief point form summary, designed with the intention of answering Question 27.1 from the first paper of 2012. The question shows a picture of the HME, and asks the candidate to "list the features of the device depicted". Only 38% of the candidates passed that question. Earlier, in Question 15 from the first paper of 2005, the college also wanted their candidates to compare the HME with a wet circuit. In Question 30 from the first paper of 2018, they wanted too know when this sort of humidifier is inappropriate.

In brief, the HME is a device for the passive humidification of inspired gas in short-term invasively ventilated patients. It is not as effective as a water-bath humidifier, insofar as it achieves less gas humidification; however in the short term (in the first 24-28 hours) it is equivalent to a "wet" circuit, and much cheaper

Indications for the use of a HME:

Humidification of inspired gas in short-term invasively ventilated patients, where equipment cost is a factor.

Contraindications:

Conditions which demand minimsation of apparatus dead space
Large volume of secretions or froth

Large minute volume ( over 10L/min)

Large air leak, eg. bronchopleural fistula

Long term ventilation

Frequent nebulised medications

Safety features

Transparent outer casing, to better inspect the filter material
Standardised connectors to ventilation equipment
Antibacterial filter material in some models
Small volume, to minimise apparatus dead space
Single use item

Complications

The inspissation of secretions
Difficulty aspirating thickened secretions
The incrustation of endotracheal tubes with thick secretions, with increasing peak airway pressures
Possibility of undetected circuit disconnection, or airway obstruction
Increased airway resistance with an aging filter
Colonisation of filter with respiratory pathogens (but this is an unproven allegation)

References

Drager have a nice brochure, spruiking the virtues of their HME systems.

However, the depicted item is the Pall Ultipor 25 Breathing System Filter.

Its all I had. Thank you to the theatre staff for kindly letting me break this piece of equipment.

The international standard for adequate humidifcation can be found here, at the ISO:

Respiratory tract humidifiers for medical use -- Particular requirements for respiratory humidification systems

Wilkes, A. R. "Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 1–history, principles and efficiency."Anaesthesia 66.1 (2011): 31-39.

Wilkes, A. R. "Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 2–practical use, including problems, and their use with paediatric patients." Anaesthesia 66.1 (2011): 40-51.

Cole, P. H. I. L. I. P. "Some aspects of temperature, moisture and heat relationships in the upper respiratory tract." J Laryngol Otol 67.8 (1953): 449-456.

Williams, Robin, et al. "Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa." Critical care medicine24.11 (1996): 1920-1929.

COHEN, IAN L., et al. "Endotracheal tube occlusion associated with the use of heat and moisture exchangers in the intensive care unit." Critical care medicine16.3 (1988): 277-279.

Chiaranda, M., et al. "Use of heat and moisture exchanging (HME) filters in mechanically ventilated ICU patients: influence on airway flow-resistance."Intensive care medicine 19.8 (1993): 462-466.

[Submit a comment or correction]