Invasive Ventilation

Invasive ventilation

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What is invasive ventilation?
Why is humidity important for invasive ventilation?
How can humidity be added to inspired gas?
Why choose heated humidification over HMEs?

What is invasive ventilation?

Invasive ventilation, including conventional mechanical ventilation and high-frequency oscillatory ventilation, refers to respiratory support delivered directly to a patient’s lower airways via an endotracheal (ET) or tracheostomy tube. These modes of delivery:

bypass the natural mechanisms of filtration, humidification and warming, which are typically provided by the upper airways
inhibit primary mechanisms of airway defense such as coughing, sneezing, gagging and particle filtration.

A ventilator is required for invasive respiratory support to enable – or support – lung function and gas exchange.

View these resources for more information on:

Negative and positive pressure ventilation (article by John Landry, BS, RRT)
Volume and pressure controlled ventilation (YouTube video by Respiratory Therapy Zone)

This diagram shows an invasive ventilation system incorporating a heated humidifier that warms and moistens the air.

Why is humidity important for invasive ventilation?

The heating and humidifying of respiratory gases is crucial and mandated in clinical guidelines for invasively ventilated patients.

When the primary mechanisms of the upper airway are bypassed with the presence of a tracheostomy or ET tube in invasively ventilated patients, the mucociliary transport system becomes the last line of airway defense against debris and other pathogens. This system relies strongly on the heat and humidity of inspired air to function optimally.

Delivering gases at or as close as possible to 37 °C and fully saturated (44 mg/L H₂O) helps restore and support natural mucociliary clearance that aids the transportation of debris up and out of the airway.¹ In addition, it allows the patient to conserve energy as the airway doesn’t need to provide additional heat or moisture to the inspired gases.

Learn about principles of heat and humidity in the airway

Intubated patient receives optimal humidity

How can humidity be added to inspired gas?

There are two types of humidification devices that can add heat and humidity to inspired gas – active and passive.

Active humidification devices utilize an external water source to add humidity to the inspired air. While these devices can be unheated, such as in-line vaporizers or bubble humidifiers, heated humidifiers (HH), including passover and counterflow humidifiers, are commonly used. Unlike unheated humidifiers, HHs use an additional heat source to condition the inspired gas. The suggested levels of humidity for active humidifiers are between 33 and 44 mg/L H₂O and temperatures range from 34 to 41 °C.²

Passive humidification devices, including heat and moisture exchangers (HMEs), utilize the heat and moisture in patient-expired air to condition the next breath. HMEs can be hygroscopic, hydrophobic or hydrophobic-hygroscopic and are placed between the Y-piece of the ventilator circuit and the patient interface. The efficiency of passive devices varies with design and can have implications for ventilation³ such as increased dead space and expiratory resistance.

Why choose heated humidification over HMEs?

Improved humidity

Because heated humidifiers are independent of a patient’s respiratory function, they minimize heat and water loss compared with passive methods that rely on patient-expired heat and humidity for inspired gas conditioning. ⁴

A large body of clinical evidence demonstrates the effect of heated humidification on mucociliary function and clearance, including a reduction in ET-tube-obstruction rates, compared with passive humidification.^5-11

Learn about heated respiratory humidification

Improved ventilation

Lung-protective ventilation (LPV) refers to mechanical ventilation strategies that use tidal volumes and pressures closer to physiological values than conventional mechanical ventilation settings. These strategies aim to prevent ventilator-associated lung injury and are largely considered standard practice for invasive ventilation.^12,13

Instrumental dead space is particularly crucial when considering effective application of LPV techniques. It refers to the volume of ventilated air that does not participate in gas exchange, caused by any additional equipment after the Y-piece of the ventilator circuit. Increases in instrumental dead space can have a negative effect on a patient’s ability to clear CO₂ from their airways.

Unlike HMEs, HHs don’t contribute to additional instrumental dead space. The body of literature has shown that using heated humidification rather than passive devices allows for the effective implementation of LPV, facilitating reductions in tidal volumes and PaCO₂^14,15 without affecting cerebral perfusion.¹⁶ The use of active humidification has also been shown to reduce inspiratory effort and the work of breathing.^14,17

View key clinical references:

Heated Humidification – Clinical Evidence Summary

Issue 1, Evidence-based Humidification - Patient Indications

Issue 2, Evidence-based Humidification - Al Dorzi et al. (2022)

Issue 3, Evidence-based Humidification - Minimizing Instrumental Dead Space

Humidification and respiratory support devices

Working alongside the continuum of care.

Fisher & Paykel Healthcare's world-leading respiratory devices work alongside the continuum of care to support patients of all ages throughout the hospital.

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Williams R., Rankin N., Smith T., Galler D., Seakins P. Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa. Crit Care Med. 1996 Nov;24(11):1920–9. View abstract
Restrepo R.D., Walsh B.K. Humidification During Invasive and Noninvasive Mechanical Ventilation: 2012. Respir Care. 2012 May 1;57(5):782–8. View abstract
Lellouche F., Taillé S., Lefrançois F., Deye N., Maggiore SM., Jouvet P., et al. Humidification performance of 48 passive airway humidifiers: comparison with manufacturer data. Chest. 2009 Feb;135(2):276–86. View abstract
Thomachot L., Boisson C., Arnaud S., Michelet P., Cambon S., Martin C. Changing heat and moisture exchangers after 96 hours rather than after 24 hours: a clinical and microbiological evaluation. Crit Care Med. 2000 Mar;28(3):714–20. View abstract
Villafane M.C., Cinnella G., Lofaso F., Isabey D., Harf A., Lemaire F., et al. Gradual reduction of endotracheal tube diameter during mechanical ventilation via different humidification devices. Anesthesiology. 1996 Dec;85(6):1341–9. View abstract
Al Dorzi H.M., Ghanem A.G., Hegazy M.M., AlMatrood A., Alchin J., Mutairi M., et al. Humidification during mechanical ventilation to prevent endotracheal tube occlusion in critically ill patients: A case control study. Ann Thorac Med. 2022 Mar;17(1):37–43. View abstract
Jaber S., Pigeot J., Fodil R., Maggiore S., Harf A., Isabey D., et al. Long-term effects of different humidification systems on endotracheal tube patency: evaluation by the acoustic reflection method. Anesthesiology. 2004 Apr;100(4):782–8. View abstract
Roustan J.P., Kienlen J., Aubas P., Aubas S., du Cailar J. Comparison of hydrophobic heat and moisture exchangers with heated humidifier during prolonged mechanical ventilation. Intensive Care Med. 1992;18(2):97–100. View abstract
Martin C., Perrin G., Gevaudan M.J., Saux P., Gouin F. Heat and moisture exchangers and vaporizing humidifiers in the intensive care unit. Chest. 1990 Jan;97(1):144–9. View abstract
Doyle A., Joshi M., Frank P., Craven T., Moondi P., Young P. A change in humidification system can eliminate endotracheal tube occlusion. J Crit Care. 2011 Dec;26(6):637.e1-4. View abstract
Luchetti M., Stuani A., Castelli G., Marraro G. Comparison of three different humidification systems during prolonged mechanical ventilation. Minerva Anestesiol. 1998 Mar;64(3):75–81. View abstract
Griffiths M.J.D., McAuley D.F., Perkins G.D., Barrett N., Blackwood B., Boyle A., et al. Guidelines on the management of acute respiratory distress syndrome. BMJ Open Respir Res. 2019;6(1):e000420. View abstract
Papazian L., Aubron C., Brochard L., Chiche J.D., Combes A., Dreyfuss D., et al. Formal guidelines: management of acute respiratory distress syndrome. Ann Intensive Care. 2019 Jun 13;9(1):69. View abstract
Girault C., Breton L., Richard J.C., Tamion F., Vandelet P., Aboab J., et al. Mechanical effects of airway humidification devices in difficult to wean patients. Crit Care Med. 2003 May;31(5):1306–11. View abstract
Morán I., Bellapart J., Vari A., Mancebo J. Heat and moisture exchangers and heated humidifiers in acute lung injury/acute respiratory distress syndrome patients. Effects on respiratory mechanics and gas exchange. Intensive Care Med. 2006 Apr;32(4):524–31. View abstract
Pitoni S., D’Arrigo S., Grieco D.L., Idone F.A., Santantonio M.T., Di Giannatale P., et al. Tidal Volume Lowering by Instrumental Dead Space Reduction in Brain-Injured ARDS Patients: Effects on Respiratory Mechanics, Gas Exchange, and Cerebral Hemodynamics. Neurocrit Care. 2021;34(1):21–30. View abstract
French C.J., Bellomo R., Buckmaster J. Effect of ventilation equipment on imposed work of breathing. Crit Care Resusc J Australas Acad Crit Care Med. 2001 Sep;3(3):148–52. View abstract

View references

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