Wet Circuit / Humidifier
OVERVIEW
A “wet circuit” is a breathing circuit with active humidification, as opposed to a “dry circuit” that uses a Heat and Moisture Exchanger (HME)
USES
- humidification of respiratory gases
DESCRIPTION
- requires power for heating
- disposable or reusable humidification chamber that holds water +/- a reservoir that adds water as needed
- heating element to warm water
- inspiratory tube that transmits heated, humidified gas. Ideally this will be heated (e.g. by a heated wire along the tube) and insulated. If this tube is not heated, condensation will occur and a water trap will be required.
- temperature monitor (at the patient end of the circuit) adjusts the amount of heating required
METHOD OF INSERTION AND/OR USE
- inserted into the inspiratory limb of the ventilator circuit
- provides a minimum of 30mgH2O/L delivered at an appropriate temperature
Pitfalls
- should not be used with a HME
- must not be placed in the expiratory limb
- if a filter is used with active humidification it should be upstream to prevent clogging with water
- ensure the heated humidifier is turned off of there is no flow through the circuit. If not, the absence of flow will cause temperature to fall at the patient end, leading to increased heat output which may case the inspiratory tube to melt
COMPLICATIONS
- condensation (“rain-out”):
- risks water aspiration
- potential delivery of excessively hot fluid to the airways
- may interfere with monitoring (e.g. flows and volumes)
- may damage equipment (e.g. ventilator)
- microbiological colonisation and growth (e.g. in reservoir or condensate)
- overhydration
- thermal injury
- increased work of breathing due increased resistance (some cannot be used with spontaneously breathing patients)
- potential electrical hazard
PROS AND CONS
Advantages
- optimal efficiency (more efficient than HME)
- reliability
- ability to warm patient
- proven track record of safety
- some can be used for spontaneously breathing and tracheotomized patients
Disadvantages
- lack of transportability
- increased cost and maintenance
- not all humidifiers are compatible with all circuits
- increased work for staff (temperature control, refilling the reservoir, draining condensate, cleaning, and sterilization)
- risk of complications (see above)
References and Links
CCC Ventilation Series
Modes: Adaptive Support Ventilation (ASV), Airway Pressure Release Ventilation (APRV), High Frequency Oscillation Ventilation (HFOV), High Frequency Ventilation (HFV), Modes of ventilation, Non-Invasive Ventilation (NIV), Spontaneous breathing and mechanical ventilation
Conditions: Acute Respiratory Distress Syndrome (ARDS), ARDS Definitions, ARDS Literature Summaries, Asthma, Bronchopleural Fistula, Burns, Oxygenation and Ventilation, COPD, Haemoptysis, Improving Oxygenation in ARDS, NIV and Asthma, NIV and the Critically Ill, Ventilator Induced Lung Injury (VILI), Volutrauma
Strategies: ARDSnet Ventilation, Open lung approach, Oxygen Saturation Targets, Protective Lung Ventilation, Recruitment manoeuvres in ARDS, Sedation pauses, Selective Lung Ventilation
Adjuncts: Adjunctive Respiratory Therapies, ECMO Overview, Heliox, Neuromuscular blockade in ARDS, Prone positioning and Mechanical Ventilation
Situations: Cuff leak, Difficulty weaning, High Airway Pressures, Post-Intubation Care, Post-intubation hypoxia
Troubleshooting: Autotriggering of the ventilator, High airway and alveolar pressures / pressure alarm, Ventilator Dyssynchrony
Investigation / Indices: A-a gradient, Capnography and waveforms, Electrical Impedance Tomography, Indices that predict difficult weaning, PaO2/FiO2 Ratio (PF), Transpulmonary pressure (TPP)
Extubation: Cuff Leak Test, Extubation Assessment in ED, Extubation Assessment in ICU, NIV for weaning, Post-Extubation Stridor, Spontaneous breathing trial, Unplanned extubation, Weaning from mechanical ventilation
Core Knowledge: Basics of Mechanical Ventilation, Driving Pressure, Dynamic pressure-volume loops, flow versus time graph, flow volume loops, Indications and complications, Intrinsic PEEP (autoPEEP), Oxygen Haemoglobin Dissociation Curve, Positive End Expiratory Pressure (PEEP), Pulmonary Mechanics, Pressure Vs Time Graph, Pressure vs Volume Loop, Setting up a ventilator, Ventilator waveform analysis, Volume vs time graph
Equipment: Capnography and CO2 Detector, Heat and Moisture Exchanger (HME), Ideal helicopter ventilator, Wet Circuit
MISC: Sedation in ICU, Ventilation literature summaries
Journal articles
- Al Ashry HS, Modrykamien AM. Humidification during mechanical ventilation in the adult patient. Biomed Res Int. 2014;2014:715434. [pubmed]
- Esquinas Rodriguez AM, Scala R, Soroksky A, et al. Clinical review: humidifiers during non-invasive ventilation–key topics and practical implications. Crit Care. 2012;16:(1)203. [pubmed]
- Kelly M, Gillies D, Todd DA, Lockwood C. Heated humidification versus heat and moisture exchangers for ventilated adults and children. Cochrane Database Syst Rev. 2010 Apr 14;(4):CD004711. doi: 10.1002/14651858.CD004711.pub2. Review. PubMed PMID: 20393939. [Free Fulltext]
- Wilkes AR. Humidification: its importance and delivery. BJA CEPD Reviews (2001) 1 (2): 40-43. doi: 10.1093/bjacepd/1.2.40 [Free Fulltext]
FOAM and web resources
- Respiratory2011 — Wet Circuit Ventilator 1 and Wet Circuit Ventilator 2 (Youtube videos demonstrating set-up)
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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