Humidifiers - Vocabulary Flashcards (Lecture Notes)

Factors Affecting Humidifier Performance

• Higher Temperature = Higher capacity for water vapor
  • in liquid + gas containing the humidity
• Higher Surface Area = Higher Evaporation
• Higher Contact Time = Higher Evaporation
• Higher Flow = Lower time for evaporation to occur

Humidifiers: Devices Overview

• Devices that transform liquid into vapor, gaseous water, or molecular water
• Types: Passover, Bubble, HME (Heat Moisture Exchanger)

Passover Humidifiers

• Types: Simple reservoir; Directs gas over the surface of a volume of water; Wick; Membrane
• Advantages:
  • Maintain saturation at high flow rates
  • Add little or no flow resistance to spontaneous breathing circuits
  • Do not generate any aerosols; pose minimal risk for spreading infection

Wick Humidifier

• Cylinder of absorbent material (increases surface area)
• Placed in water reservoir with heating element
• Capillary action draws water up from reservoir to keep wick saturated
• Dry gas flows around wick picking up heat and moisture
• No bubbling occurs; no aerosol produced

Membrane Type

• Separates water from gas stream by means of hydrophobic membrane
• Water vapor molecules can easily pass through membrane but liquid water cannot

Bubble Humidifiers

• Gas flows down into a reservoir of water through a hollow tube with a diffusing element at the bottom
• Diffuser breaks the gas flow into tiny bubbles
• As the bubbles float to the surface, they pick up humidity by way of evaporation
• Most commonly used humidifier for O2 therapy
• Best for use with nasal cannula (cannot be heated)
• Factors affecting efficiency and output:
  • Liter flow
  • Ambient temperature
  • Time of operation
• Relief valve: indicates obstruction to flow; protects device from pressure damage (bursting bottle)

Bubble Humidifiers: Hardware Features (from Page 9)

• Large, easy to grip quad-wing nut. Resists cross-threading, simplifies secure connection to oxygen supply source
• Audible safety pressure pop-off alarm. Automatically resets
• Pressure relief port
• Easy-flow dome lid design combined with unique 360b0 diffuser helps to reduce rain-out
• MAXIMUM Easy jar to lid assembly with half turn positive seal
• No gasket required
• Stem and diffuser resists clogging due to mineral build-up on and inside diffuser
• Permanent, maximum-minimum water level indicators. Will not wash, wear or rub off

Heat Moisture Exchanger (HME)

• Most often a passive humidifier described as an “artificial nose”
• Types: simple, hygroscopic, hydroscopic (as listed in transcript; terminology may vary: hygroscopic and hygroscopic)
• Does not add heat or water to the system
• Captures exhaled heat and moisture, which is then applied to the subsequent inhalation
• For short term use only (up to 96 hours)

Hygroscopic Condenser

• Uses a condenser element with low thermal conductivity (paper, wool, foam) impregnated with a hygroscopic salt
• Hygroscopic = readily taking up and retaining moisture
• Efficiency: rac{70}{100}
• Example: exhaled moisture ~40 \,\mathrm{mg/L}; returned moisture ~27 \,\mathrm{mg/L}
• Efficiency: 70\%

Hydrophobic Condenser

• Uses a water-repellant element with a large surface area and low thermal conductivity
• Efficiency: 70\%

Heated Systems

• Heat improves humidifier output
• Primarily for bypassed airways
• Risk of airway burns

Five Types of Heating Elements

• Hot plate element at base of humidifier
• Wraparound type that surrounds the humidification chamber
• Yolk or collar element
• Immersion type heater
• Heated wire on the inspiratory limb

Hot Plate

• Markings: MAX; Control; HumidAire
• Important safety note: ENSURE WATER CHAMBER IS EMPTY BEFORE TRANSPORTATION

Collar Element

• (Page 16 heading in transcript; related to a collar-type heating element)

Servo-Controlled Heating Element

• Monitors temperature at or near the patient7s airway using a thermistor probe
• Controller adjusts heater power to achieve desired airway temperature
• Rule of thumb: Place thermistor probe in inspiratory limb far enough away from patient wye to ensure that warm, exhaled gas does not fool the controller system
• Egan7s guideline (intubated patient): set temp at T = 33 \pm 2^{\circ}\mathrm{C} with minimum of 30 \mathrm{\,mg/L} water vapor; depends on patient condition
• Never exceed 37^{\circ}\mathrm{C}

Heated Humidifier (General)

• Heated humidifier (illustrated as 3.70 in transcript)

Reservoir and Feed Systems

• Heated humidifiers can evaporate more than 1\ \mathrm{L/day}
• To avoid constant refilling, devices use:
  • Large water reservoir, manually refilled with sterile water; at risk for cross-contamination
  • Gravity fed IV bag and line

Gravity Feed Systems

• Figure caption: Sterile Water Bag Connected to a Humidification Unit
• Example models referenced: LIV Enterolite Infinity, Fyber

Problem Solving / Troubleshooting: Condensation (Rain-out)

• Condensation occurs as gas cools; water vapor capacity decreases
• Factors that affect condensation:
  • Temperature difference between humidifier and airway
  • Ambient temperature
  • Gas flow
  • Set airway temperature
  • Length, diameter and thermal mass of breathing circuit

Problems with Condensation Conte9d (Cont’d)

• Occlusion of gas flow through circuit that will alter FiO2 and/or vent function (FiO2 increases)
• Aspiration to the patient 6 water in tubing can be shifted into patient airway
• Infection 6 condensation is breeding ground for infectious bacteria in circuits
• Minimizing condensation:
  • Keep water traps at low points in circuit
  • Maintain appropriate temperature in circuit

Cross-Contamination and Infection Control

• Condensation as infectious waste; do not drain water from circuit back into humidifier
• Position circuit to drain condensate away from patient to avoid aspiration
• Keep changing of circuits to a minimum; frequent changing can increase risk of infection
• Rule of thumb: treat breathing circuit condensation as infectious waste 211 drain away from patientn airway, wear goggles and gloves, dispose of according to hospital policy

Reading List (from Transcript)

• Egans 35/36
• Equip Theory 3
• Lab Competencies 14/15