Compare and contrast the advantages and disadvantages of humidification of a ventilator circuit using a wet circuit versus a Heat and Moisture Exchanger.
Wet ventilator circuits require power for heating, a chamber for water to be heated, and temperature sensors to feedback appropriate temperature within chamber and ideally to within circuit. Benefits include potential for optimal efficiency (under all circumstances), reliability, ability to warm patient, and proven track record of safety. Disadvantages include potential for condensation (rain-out) with excessive (potentially hot) fluid delivery to airways, microbiological colonisation, lack of transportability, and increased cost.
Heat and moisture exchangers come in a variety of types (with more emphasis on humidification and/or microbiological filter). Benefits include ease of use (including during transport), lower staff workload, lower costs and potential for decreased ventilator associated pneumonia [Kola, Intensive Care Med (2005) 31:5-11]. Disadvantages include inability to use with all patients (eg. those haemoptysis, tenacious secretions, increased airway resistance, ARDS), problems with increased dead space and resistive load, and potential for airway occlusion.
The various features of the HME are discussed in greater and more general detail elsewhere. A good article which is both recent and detailed is this 2014 piece from BioMed Research International.
This question would benefit from a tabulated answer.
| HME | Humidified circuit | |
| Device description | A hygroscopic in-line air filter | A circuit which incororates an inline heated water chamber, with an integrated thermostat-controlled heating element |
| Cost | Cheap | Expensive - both the device and the attached consumables |
| Reusability | Single-use | Reusable humidified, disposable circuit |
| Workload | Minimal | Requires attention to water replacement and occasional troubleshooting |
| Humidification efficiency | Low efficiency; approximately 50% of the required humidity is achieved. The devices are expected to produce a consistent level of humidity around 30mg/L; whereas 20mg/L is the more typical performance |
Highly efficient. Humidity acieved ranged from 33mg/L to 44mg/L, which is near to the humidity achieved by the human respiratory tract. |
| Lifespan | Should not be used for longer than 72-96 hrs | Provided the circuit is well maintained and regularly changed, humidified ventilation can continue indefinitely |
| Risks with use | Increases dead space; Becomes progressively more waterlogged, increasing resistance to gas flow; Potentially, can become a source of infection |
"Rain-out": evaporated water collects in the circuit, pooling and attracting bacteria.The water bath itself is a nice warm environment which acts as a good incubator for bacteria |
| Contraindications to use | Need to minimise dead space; Large volumes of secretions Decreased expiratory airflow Large minute volume (>10L/min) Bronchopleural fistula Long term ventilation Frequent nebulised medications |
There are no contraindications to circuit humidification. |
| Evidence |
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Martin, Claude, et al. "Comparing two heat and moisture exchangers with one vaporizing humidifier in patients with minute ventilation greater than 10 L/min."CHEST Journal 107.5 (1995): 1411-1415.
Kirton, Orlando C., et al. "A Prospective, Randomized Comparison of an In-Line Heat Moisture Exchange Filter and Heated Wire Humidifiers Rates of Ventilator-Associated Early-Onset (Community-Acquired) or Late-Onset (Hospital-Acquired) Pneumonia and Incidence of Endotracheal Tube Occlusion." CHEST Journal 112.4 (1997): 1055-1059.
Kollef, Marin H., et al. "A randomized clinical trial comparing an extended-use hygroscopic condenser humidifier with heated-water humidification in mechanically ventilated patients." CHEST Journal 113.3 (1998): 759-767.
Siempos, Ilias I., et al. "Impact of passive humidification on clinical outcomes of mechanically ventilated patients: A meta-analysis of randomized controlled trials*." Critical care medicine 35.12 (2007): 2843-2851.
Al Ashry, Haitham S., and Ariel M. Modrykamien. "Humidification during Mechanical Ventilation in the Adult Patient." BioMed research international2014 (2014).