Humidification

1. HUMIDIFICATION MANISH MASIH Critical Care Therapist Intensive Care Unit Duncan Hopsital Raxaul

2. Objective Describe how airway heat and moisture exchange normally occurs. State the effect dry gases have on the respiratory tract. State when to humidify and warm inspired gas. Describe how various types of humidifiers work. Identify the indications, contraindications, and hazards that pertain to humidification during mechanical ventilation. Describe how to monitor patients receiving humidity therapy. Describe how to identify and resolve common problems with humidification systems.

3. Humidity Therapy Humidity is the quantity of moisture in air or gas that is caused by the addition of water in a gaseous state, or vapor. Also called molecular water or invisible moisture . Clinical Uses of Humidity To provide 100% body humidity of the inspired gas for patients with ET tubes or tracheostomy tubes To humidify dry therapeutic gases

4. Normal Airway Humidification The nose warms, humidifies, and filters inspired air. The pharynx, trachea, and bronchial tree also warm, humidify, and filter inspired air. By the time the inspired air reaches the oropharynx, it has been warmed to approximately 34°C and is 80% to 90% saturated with H 2 O. By the time the inspired air reaches the carina, it has been warmed to body temperature (37°C) and is 100% saturated. when the inspired air is fully saturated (100%) at 37°C, it holds 44 mg H 2 O per liter of gas and exerts a water vapor pressure of 47 mmHg. As inspired gas moves into the lungs, it achieves BTPS conditions (body temperature, 37°C; barometric pressure; saturated with water vapor[100% relative humidity at 37°C]).

5. Absolute and Relative Humidity Absolute humidity is the amount of water in a given volume of gas; its measurement is expressed in milligrams per liter. Relative humidity is a ratio between the amount of water in a given volume of gas and the maximum amount it is capable of holding at that temperature (capacity). Its measurement is expressed as a percentage and is obtained with a hygrometer. Relative humidity = absolute humidity capacityx100

6. Isothermic saturation boundary(ISB) As inspired gas moves into the lungs, it achieves BTPS conditions (body temperature, 37°C; barometric pressure; saturated with water vapor[100% relative humidity at 37°C]). This point, normally approximately 5cm below the carina, is called the isothermic saturation boundary(ISB). Above the ISB, temperature and humidity decrease during inspiration and increase during exhalation. Below the ISB, temperature and relative humidity remain constant (BTPS). Numerous factors can shift the ISB deeper into the lungs.

7. The ISB shifts distally when a person breathes through the mouth rather than the nose; when the person breaths cold, dry air; when the upper airway is bypassed (breathing through an artificial tracheal airway); or when the minute ventilation is higher than normal. When this shift of ISB occurs, additional surfaces of the airway are recruited to meet the heat and humidity requirements of the lung. This recruitment of airways that do not typically provide this level of heat and humidity can have a negative impact on epithelial integrity. These shifts of the ISB can compromise the body’s normal heat and moisture exchange mechanisms, and humidity therapy is indicated.

8. Types of humidifiers Humidifiers are either active (actively adding heat or water or both to the device-patient interface) or passive (recycling exhaled heat and humidity from the patient). Active humidifiers typically include Bubble humidifiers Passover humidifers Nebulizers of bland aerosols, and Vapourizers Passive humidifiers refer to typical heat and moisture exchangers (HMEs).

9. Indication Primary Humidifying dry medical gases Overcoming humidity deficit created when upper airway is bypassed Secondary Managing hypothermia Treating bronchospasm caused by cold air

10. Clinical signs and symptoms of inadequate airway humidification Atelectasis Dry, nonproductive cough Increased airway resistance Increased incidence of infection Increased work of breathing Patient complaint of substernal pain and airway dryness Thick, dehydrated secretions

11. Humidifiers Humidifiers add molecular water to gas Factors that affect performance: Temperature Surface area Time of contact Thermal mass

12. Humidifier Performance Temperature: as temperature increases, capacity (potential humidity) will increase Surface area: the greater the surface area, the more potential for evaporation Contact time: the longer the time of contact, the more time for evaporation to occur Thermal mass: the more water in the humidifier, the more potential for transfer of heat

13. Types of Humidifiers

14. Bubble Humidifier Gas passes through tube to bottom of water reservoir Gas bubbles through reservoir Unheated bubbles through humidifier Provides humidity for oxygen therapy

15. Bubble Humidifier (Cont.)

16. Passover Humidifiers Direct gas over liquid or over surface saturated by liquid Types: Simple reservoir model Wick units Membrane devices

17. Passover Humidifiers (Cont.) Simple reservoir Gas flows over surface of volume of water Usually used as heated system to provide humidity to mechanically ventilated patients

18. Heated Humidifier Adding heat increases absolute humidity of gas Heating of gas increases risk of condensation in tubing, causing obstruction Risk is decreased by using large-bore tubing Heated wire circuits are used to decrease amount of condensation in circuit

19. Heat Moisture Exchanger Considered to be passive humidifier Traps heat and humidity in expired gas Has been used to provide humidity for spontaneously and mechanically ventilated patients Types of heat moisture exchangers (HMEs): Simple condenser Hygroscopic condenser Hydrophobic condenser

20. Simple condenser humidifier Contains condenser element to trap heat and humidity of expired gas Retains about 50% of expired heat and humidity Maximum absolute humidity is 18 to 28 mg/L Hygroscopic heat exchanger Uses condenser element made of paper, wool, or foam Material includes a salt Maximum absolute humidity is 22 to 34 mg/L

21. Active Heat Moisture Exchangers Add heat or humidity (or both) to inspired gas External heat and moisture is introduced into inspired gas Capable of providing 100% relative humidity at BTPS

22. contraindications There are no contraindication to providing physiologic conditioning of inspired gas during mechanical ventilation. However, an HME is contraindicated in the following circumstances For patients with thick, copious, or bloody secretions For patients with an expired tidal volume less than 70% of the delivered tidal volume ( eg ., patients with large bronchopleural fistulas or incompetent or absent endotracheal tube cuffs) For patients whose body temperature is less than 32°C For patients with high spontaneous minute volumes (>10 L/min) For patients receiving in-line aerosol drug treatments (an HME must be removed from the patient circuit during treatments)

23. Hazards and complications Hazards and complication associated with the use of heated humidifier (HH) and HME devices during mechanical ventilation include the following: High flow rates during disconnect may aerosolize contaminated condensate in heated humidifer circuit Increased work of breathing (HME or HH) Elevated airway pressures caused by condensation (HH) Inadvertent overfilling resulting in unintended tracheal lavage (HH) Inadvertent tracheal lavage from pooled condensate in circuit (HH)

24. Monitoring The humidifier should be inspected during the patient-ventilator system check, and condensate should be inspected and replaced if secretions have contaminated the insert or filter. The following should be recorded during equipment inspection: During routine use on an intubated patient, an HH should be set to deliver inspired gas at 33°C ± 2°C and should provide a minimum of 30 mg/L of water vapor. Inspired gas temperature should be monitored at or near the patient’s airway opening (HH) Specific temperature may vary with the patient’s condition; airway temperature should never exceed 37°C. For heated wire circuits used with infants, the probe must be placed outside the incubator or away from the radiant warmer. The high temperature alarm should be set no higher than 37°C, and the low setting should not be less than 30°C. Water level and function of automatic feed system (if applicable) should be monitored. Quantity, consistency, and other characteristics of secretions should be noted and recorded. When using an HME, if secretions become copious or appear increasingly tenacious, an HH should replace the HME.

25. Problem Solving and Troubleshooting Common problems with humidification systems include dealing with condensation, avoiding cross contamination, and ensuring proper conditioning of the inspired gas. Condensation As the gas cools, its water vapor capacity decreases, resulting in condensation. Factors influencing the amount of condensation include The temperature difference across the system (humidifier to airway) The ambient temperature The gas flow The set airway temperature; and The length, diameter, and thermal mass of the breathing circuit

26. Condensation can disrupt or occlude gas flow through the circuit, potentially altering fractional inspired oxygen or ventilator function or both. Condensate can work its way toward the patient and be aspirated. For these reasons, circuits must be positioned to drain condensate away from the patient and must be checked often, and excess condensate must be drained from heated humidifier breathing circuits on a regular basis. Several techniques are used to minimize problems with breathing circuit condensate. One common method is to place water traps at low points in the circuit(both the inspiratory and the expiratory limbs of ventilator circuits).

27. Cross contamination Aerosols and condensate from ventilator circuits are known sources of bacterial colonization. However, advances in both circuit and humidifier technology have reduced the risk of nosocomial infection when these systems are used. Heated wire circuits reduce production and pooling of condensate within the circuit. In addition, the high reservoir temperature in humidifiers are bactericidal.

28. Important points concerning Humidifiers Most nonheated humidifiers have a pressure pop-off valve set at 2 psi, after the device is set up, the tubing of the oxygen delivery device (e.g., cannula, mask ) should be kinked to obstruct flow. If the pop-off sounds, there are no leaks. If no sound is heard, all connections, as well as the humidifier top, should be tightened. Water levels of all humidifiers should be maintained at the levels marked on the humidifier jar to ensure maximum humidity output. Condensation occurs in the tubing of heated humidifiers. This water should be discarded in a trash container or basin and should never be put back into the humidifier. Warm moist areas, such as heated humidifiers, are a breeding ground for microorganisms (especially pseudomonas species). The humidifier should be replaced every 24 hours(2). Without a heated wire circuit, the humidifier may need to be heated to as much as 50°C for the gas temperature to approximate body temperature (37°C) by the time it reaches the patient’s upper airway. As the highly saturated and warm gas passes through the ventilator circuit, ambient air surrounding the circuit tubing cools(3).

29. References EGANS, Fundamentals of Respiratory Care. Respiratory care exam review, Gary Persing Clinical Application of Mechanical ventilation Susan Pilbeam’s.