Humidity Therapy and Humidifiers RET 2274 Respiratory Care Theory 1 Module 5.0

Humidity Therapy and Humidifiers Water that exists as individual molecules in the vaporous or gaseous state and is present in the air we breathe – often described as water vapor

Humidity Therapy and Humidifiers Involves adding water vapor and (sometimes) heat to an inspired gas Primary goal of humidification is to maintain normal physiological conditions in the lower airways or treat abnormal conditions

Humidity Therapy and Humidifiers Administration of dry medical gases at flows greater than 4 L/min to the upper airway causes immediate heat and water loss, and if prolonged, causes structural damage

Humidity Therapy and Humidifiers Absolute Humidity Is the actual content or weight of water present in a given volume of gas Expressed as: Grams per cubic meter (g/m3) Milligrams per liter (mg/L) Also know as water content

Humidity Therapy and Humidifiers Relative Humidity (RH) Is the ratio of actual content or weight or the water present in a gas relative to the sample’s capacity to hold water at that temperature Expressed as a percentage RH = measured humidity (content) X 100 water capacity When the amount of water that a gas contains at a given temperature is equal to the gas’s capacity, the RH is 100% - described as saturated

Humidity Therapy and Humidifiers Relative Humidity (RH) Increasing the temperature of a gas, increases its capacity to hold water If absolute humidity is held constant, increasing the temperature of the gas will decrease the RH If absolute humidity is held constant, decreasing the temperature of the gas will increase the RH or it will remain at 100%

Humidity Therapy and Humidifiers Relative Humidity (RH) Temp RH Temp RH

Humidity Therapy and Humidifiers Condensation Cooling a gas that has an RH of 100% decreases its capacity to hold water, which results in water being squeezed out of the gas Temp RH

Condensation

Humidity Therapy and Humidifiers Evaporation The process of water moving from a liquid to a gaseous state at temperatures lower than its boiling point The warmer the air contacting the water surface, the faster the rate of evaporation Heating water will increase the rate of evaporation

Humidity Therapy and Humidifiers Partial Pressure The random motion of water molecules exerts a pressure (water vapor pressure) in a way similar to gas exerting pressure As the temperature of a gas increases, kinetic activity increases, so the pressure also increases

Humidity Therapy and Humidifiers Partial Pressure Its magnitude is solely dependent upon temperature and relative humidity – not upon barometric pressure The partial pressure of water vapor must always be accounted for (subtracted) when calculating the partial pressure of other gases in a mixture

Humidity Therapy and Humidifiers Partial Pressure Alveolar Air Equation [FiO2 (PB – Water Vapor Pressure)] – PaCO2 0.8 [.40 (760mm Hg – 47 mm Hg)] – 40 mm Hg

Humidity Therapy and Humidifiers Physiological Control of Heat and Moisture Exchange Primary function of the upper respiratory tract Nose (primary) Heats and humidifies gas on inspiration and cools and reclaims water from the gas that is exhaled Sinuses, Trachea, and Bronchi Also aid in heating and humidifying the inspired gases

Humidity Therapy and Humidifiers Physiological Control of Heat & Moisture Exchange As inspired gas moves into the lungs, it achieves BTPS (body temperature, 37 C; barometric pressure; saturated with water vapor [100% relative humidity at 37 C]) Isothermic Saturation Boundary (ISB) The point in the respiratory tract at which incoming gas reaches BTPS Below the ISB, temperature and relative humidity remain the same

Humidity Therapy and Humidifiers Indications for Humidification Primary goal of humidification is to maintain normal physiological conditions in the lower airways or treat abnormal conditions

Humidity Therapy and Humidifiers Indications for Humidification Administration of dry medical gases at flows greater than 4 L/min to the upper airway causes immediate heat and water loss, and if prolonged, causes structural damage Ciliary motility is reduced Airways become irritable Mucous production increases Pulmonary secretions become thick and inspissated

Humidity Therapy and Humidifiers Indications for Humidification Prolonged breathing of improperly conditioned gases through a tracheal airway can result in the following: Hypothermia Inspissation of airway secretions Mucociliary dysfunction Destruction of airway epithelium Atelectasis As long as inspired humidity is at least 60% of BTPS conditions, no injury occurs in normal lungs

Humidity Therapy and Humidifiers Indications for Humidification Humidified gas delivered to an artificial airway (endotracheal or tracheostomy tube) must be between 31 and 35 C with a minimum of 30 mg/L of absolute humidity To maintain the appropriate temperature and humidity levels, monitoring at the interface of the patient and humidifying device is necessary

Humidity Therapy and Humidifiers Equipment Humidifier is a device that adds molecular water to gas

Humidity Therapy and Humidifiers Physical Principles Governing Humidifiers Temperature The greater the temperature of a gas, the more water it can hold The cooler the water in a humidifier the less efficient they are

Humidity Therapy and Humidifiers Physical Principles Governing Humidifiers Surface Area The greater the area of contact between water and gas, the more opportunity for evaporation to occur Passover humidifiers pass gas over a large surface area of water

Humidity Therapy and Humidifiers Physical Principles Governing Humidifiers Surface Area Bubble-diffuser type humidifiers

Humidity Therapy and Humidifiers Physical Principles Governing Humidifiers Surface Area Wick technologies use porous water-absorbent materials to increase surface area

Humidity Therapy and Humidifiers Physical Principles Governing Humidifiers Contact Time The longer gas remains in contact with water, the greater the opportunity for evaporation to occur Depth of water column (bubble type)  depth of water  evaporation  depth of water  evaporation Flow rate of gas (passover and wick)  flow rate  evaporation  flow rate  evaporation

Humidity Therapy and Humidifiers Types of Humidifiers Active Actively adds heat and/or water to the device/patient interface Bubble Passover Membrane Passive Recycling exhaled heat and humidity from the patient HME

Humidity Therapy and Humidifiers Types of Humidifiers Bubble Humidifier (Active) Breaks an underwater gas stream into small bubbles Unheated – commonly used oronasal O2 delivery systems (e.g., cannula) Goal; to raise the water vapor content of the gas to ambient levels Can generate aerosols at high flows Equipped with pressure-relief valve “pop-off”

Humidity Therapy and Humidifiers Types of Humidifiers Passover Humidifier (Active) Directs gas over a water surface Two types Wick Membrane

Humidity Therapy and Humidifiers Types of Humidifiers Passover Humidifier Wick type A cylinder of absorbent material (wick) is placed upright in a reservoir of water and surrounded by a heating element Dry gas enters the chamber, flows around the wick, picks up moisture, and leaves the chamber saturated with water vapor

Humidity Therapy and Humidifiers Types of Humidifiers Passover Humidifier Membrane type Separates the water from the gas stream by means of a hydrophobic membrane Water vapor molecules pass through the membrane (liquid cannot) Dry gas enters the chamber, flows across the membrane, picks up moisture, and leaves the chamber saturated with water vapor

Humidity Therapy and Humidifiers Types of Humidifiers Heat and Moisture Exchangers (HME) Passive humidifier Functions similar to the upper airway Captures exhaled heat and moisture during a patient’s exhalation and returns it to the patient during the next inspiration

Humidity Therapy and Humidifiers Types of Humidifiers HME (Passive) Best Suited for: Short-term mechanical ventilation (≤ 96 hours) Minute ventilation < 10 L/min Limited secretions Normal body temperature

Humidity Therapy and Humidifiers Types of Humidifiers HME (Passive) Rule of Thumb You can estimate if an HME is performing well at the bedside by visually confirming condensation in the flex tube. Lack of condensate may be a clue that humidification is less than adequate and that alternative systems may be appropriate for use with that particular patient.

Humidity Therapy and Humidifiers Heaters, Reservoirs, and Feed Systems Heat improves the water output of bubble and passover humidifiers Heated humidifiers are used mainly for patients with bypassed upper airways and/or for those receiving mechanical ventilatory support

Humidity Therapy and Humidifiers Heaters, Reservoir, and Feed Systems

Humidity Therapy and Humidifiers Heaters, Reservoir, and Feed Systems

Humidity Therapy and Humidifiers Heaters, Reservoir, and Feed Systems