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Humidifiers Egan 35
| Question | Answer |
|---|---|
| Humidity Therapy | adding water to vapor and (sometimes) heat to the inspired gas |
| Heat and moisture exchange is a primary function of...... | the respiratory tract, mainly the nose |
| Condensation occurs on the mucosal surfaces during what? | exhalation |
| In cold weather, the formation of condensates exceed the ability of mucus to reabsorb water results in what? | a runny nose |
| Is the mouth less effective than the nose for heat and moisture exchange? | Yes |
| What is the pharyngeal temperatures when a person inhales through the mouth? | 3 degrees less than when breathing through the nose, with 20% less relative humidity |
| During exhalation, the relative humidity of expired gas varies little between what? | mouth and nose breathing |
| The mouth is less efficient in reclaiming what? | heat and water |
| At what point does inspired gas achieve BTPS? | point approximately 5 cm below the carina |
| What is the name of the point where inspired gas achieves BTPS? | isothermic saturation boundary (ISB) |
| Above the ISB, temperature & humidity during inspiration & exhalation do what? | decrease during inspiration. increase during exhalation |
| Below the ISB, temperature and relative humidity what? | remain constant (BTPS) |
| Name factors that can shift the ISB deeper into the lungs. | 1) When a person breathes through the mouth rather than nose, the ISB shifts distally. 2) Breathing cold, dry air. 3) Upper airway is bypassed. (breathing through artificial tracheal airway) 4) Minute ventilation is higher than normal. |
| Shifts is the ISB affect the body's normal heat and moisture exchange mechanism resulting in the need for what? | Humidity Therapy |
| The primary goal of humidification is to maintain normal physiologic conditions in what? | the lower airways |
| Name the 2 primary indications for humidification therapy. | 1) Humidifying dry medical gases 2) Overcoming the humidity deficit created when the upper airway is bypassed |
| Name the secondary indications for humidification therapy. | 1) Managing hypothermia 2) Treating bronchospasm caused by cold air |
| Administration of dry medical gases to the upper airway should never have flows great than what? | 4 L/min |
| What effect do dry medical gases administered to the upper airway at more than 4 L/min cause? | immediate heat and water loss. structural damage to the epithelium if prolonged |
| What does "inspissated" mean? | Thickened due to dehydration |
| Breathing dry gas through an endotracheal tube can cause what? | damage to tracheal epithelium within minutes |
| What should the inspired humidity be when given though a tracheal airway? | at least 60% of BTPS conditions |
| Prolonged breathing of improperly conditioned gases through a tracheal airway can result in conditions? | 1) hypothermia 2) inspissation of airway secretions 3) mucociliary dysfunction 4) destruction of airway epithelium 5) atelectasis |
| The amount of heat and humidity the patient needs depends on what? | the site of gas delivery |
| Name conditions that warm, humidified gases are used to treat or prevent. | 1) treatment of hypothermic patient. (raises core temperatures back to normal) 2) prevent intraoperative hypothermia 3) alleviate bronchospasm in patients who develop airway narrowing after exercise or breathing cold air |
| How may a patient reduce cold-air induced bronchospasm? | wearing a scarf over nose and mouth when outside in cold weather |
| What is the delivery of cool humidified gas used to treat? | upper airway inflammation resulting from: 1) croup 2) epiglottitis 3) postextubation edema |
| Delivery of cool humidified gases are mostly used with what? | bland aerosol delivery |
| What is a humidifier? | a device that adds molecular water to gas |
| How does a humidifier add molecular water to gas? | by evaporation of water from a surface |
| Name 3 variables that affect the quality of a humidifier's performance. | 1) temperature 2) surface area 3) time of contact |
| Why is temperature important in a humidifier? | the greater the temperature of a gas, the more water vapor it can hold (increased capacity) |
| How do passover humidifiers work? | pass gas over a large surface area of water |
| The greater the area of contact between water and gas gives opportunity for what? | evaporation to occur |
| Name more space-efficient ways to increase the water/gas surface-area ratio. | 1) bubble diffusion 2) aerosol 3) wick technologies |
| Explain the bubble-diffusion technique. | directs a stream of gas underwater, where it is broken up into small bubbles. As the gas bubbles rise to the surface, evaporation increases the water vapor content within the bubble. The smaller the bubble, the greater is the water/air surface-area. |
| What is an alternative to dispersing gas bubbles in water? | spraying water particles into the gas by generating an aerosol in the gas stream. |
| What is an aerosol? | suspension of water droplets |
| What do wick technologies use to increase surface are? | porous water-absorbent materials |
| How do wick technologies work? | wick draws water into its fine honeycombed structure by means of capillary action. |
| Why is contact time important? | the longer a gas remains in contact with, the greater the opportunity for evaporation to occur. |
| For bubble humidifiers, what does the contact time depend on? | the depth of the water column: the deeper the column, the greater the time of contact as the bubbles rise to the surface. |
| Name the 3 primary types of humidifiers. | 1) bubble humidifiers 2) passover humidifiers 3) HME (heat and moisture exchangers) |
| What does "active" mean? | |
| What does "passive" mean? | recycles exhaled heat and humidity from the patient |
| Specifications covering the design and performance requirements for medical humidifiers are established by who? | American Society for Testing and Materials (ASTM) |
| What are unheated bubble humidifiers commonly used with? | oronasal oxygen delivery systems |
| At room temperature, unheated bubble humidifiers can provide absolute humidity levels of what? | 15 - 20 mg/L |
| Unheated bubble humidifiers have limited effectiveness at flow rates higher than what? | 10 L/min |
| Why shouldn't the reservoirs of bubble humidifiers be heated? | the resulting condensate tends to obstruct the small bore delivery tubing to which they connect |
| Humidifier pop-offs should provide what? | both an audible and visible alarm and should automatically resume normal position when pressures return to normal |
| Failure of a pop-off to sound, may be an indication of what? | a leak of faulty pop-off valve |
| At high flow rates, what can bubble humidifiers produce? | aerosols |
| Any device that generates an aerosol, poses what? | a high risk of spreading infection |
| How do aerosols spread infections? | not visible to the naked eye, the water-droplet suspensions can transmit pathogenic bacteria from the humidifier reservoir to the patient |
| Name the 3 common types of passover humidifiers. | 1) the simple reservoir type 2) the wick type 3) the membrane type |
| What are simple reservoir type used with and for? | heated fluids for use with mechanical ventilation. |
| may be used with room temperature fluids with noninvasive ventilatory support (nasal continuous positive airway pressure or bilevel ventilation) | |
| How does the nose affect normal airway humidification? | filters, warms, and humidifies inspired air |
| What happens to air as it reaches the carina? | It has been warmed to body temperature of 37 degrees C and is 100% saturated |
| When inspired air is fully saturated (100%) at 37 degrees C it holds what? | 44 mm H2O per liter of gas and exerts a water vapor pressure of 47 mmHg |
| What is the actual content or weight of water present in a given volume of gas and is expressed in mg/L? | Absolute Humidity |
| What is the formula for calculating Absolute Humidity? | AH = RH x mg H2O/L = |
| What is Relative Humidity? | the ratio between the amount of water in a given volume of gas and the maximum amount its capable of holding at that temperature. Humidity expressed as a percentage of a gas's capacity (water content when fully saturated) |
| How is Relative Humidity measured? | hygrometer |
| What is the formula for calculating Relative Humidity? | RH = Absolute (content) humidity ----------------------------------- x 100 Capacity |
| What is Relative Humidity at body temperature and is expressed as a %? | Body Humidity |
| What is the capacity of water at body temperature? | 44 mm/L |
| What is the formula for calculating Body Humidity? | BH = absolute humidity ----------------------- x 100 44 mg/L |
| What is the physiologic term that refers to the difference between inspired gas's water content and the water content of a gas at body temperature? | Humidity Deficit |
| At body temperature and pressure saturated, inspired gas is what? | 37 degrees C, contains 44 mg/L of water and exerts a partial pressure of 47 mmHg and is fully saturated |
| What is the formula for calculating Humidity Deficit? | HD = Body Humidity - actual humidity (mg/L) or as a % deficit --------- x 100 44 mg/L |
| Room humidifiers work off of what principle? | Centrifugal Force (spinning). Electrically powered. |
| Why is it important to keep room humidifiers clean and change the water in the reservoir frequently? | source of nosocomial infections. large reservoir is source for bacterial growth |
| What is the simplest of all humidifiers? | Pass-Over humidifier (non-heated) |
| Why is the Pass-Over Humidifier low humidification? | decreased contact time. |
| What is the most common of the disposable humidifiers used in Respiratory Care? | Bubble Humidifier (non-heated) |
| The efficiency of the bubble humidifier depends on what? | (contact) water level in reservoir. |
| What should be done if water is low in a bubble humidifier? | replace set-up if disposable. refill with sterile water if permanent |
| Would a clogged inlet prevent the pop off alarm from sounding? | Yes |
| How is proper function checked? | pinching the connected tubing and listening for the alarm |
| If the alarm sounds without intentional occlusion, what may be the problem? | gas flow is too high. kink in the tubing. obstruction at the outlet. |
| What happens if the down tube becomes obstructed? | no bubbling or alarm will occur. Compensated flow meter will read ZERO |
| If oxygen fails to flow from the humidifier, what should you check? | 1) is flowmeter turned on 2) if pre-filled, make sure the reservoir has been pierced and that gas can flow through it 3) check the outlet for obstruction 4) check the oxygen tubing for obstruction or kinks 5) replace the humidifier |
| Does bubbling occur with wick humidifiers? | No |
| No bubbling means what is not produced? | aerosol |
| A membrane-type humidifier separates the water from the gas stream by means of a what? | hydrophobic membrane |
| How does the "hydrophobic" membrane work? | water vapor molecules can easily pass through this membrane, but liquid water (and pathogens) cannot. |
| Does bubbling occur in the membrane-type humidifier? | No |
| If a membrane-type humidifier were inspected while in use, would liquid water be seen in the humidifier chamber? | No |
| What are some advantages of passover humidifiers over bubble humidifiers? | 1) maintain saturation at high flow rates - unlike bubble 2) add little or no flow resistance to spontaneous breathing circuits 3) do not generate any aerosols 4)thus, minimal risk for infection |
| A HME has been describes as what? | "artificial nose" |
| The typical HME is a _________ humidifier. | passive |
| How much heat and moisture does an HME return to the patient during their next inspiration? | up to 70% |
| Name the 3 types of HMEs. | 1) simple condenser 2) hygroscopic condenser 3) hydrophobic condenser |
| Simple condenser humidifiers contain a condenser element with what? | high thermal conductivity, usually with metallic gauze, corrugated metal, or parallel metal tubes |
| How much of a patient's exhaled moisture can a simple condenser humidifier recapture? | 50% |
| Hygroscopic condenser humidifiers provide higher efficiency by using what? | 1) condensing element of low conductivity (paper, wool, foam) 2) impregnating material with a hygroscopic salt (calcium or lithium chloride) |
| What is the benefit of using a condensing element of low thermal conductivity? retain more heat unlike simple condenser humidifiers | retain more heat than simple condenser systems |
| What does the hygroscopic salt do? | helps capture extra moisture from the exhaled gas |
| What do hydrophobic condenser humidifiers use? | a water-repellent element with a large surface area and low thermal conductivity |
| What is the efficiency of the hygroscopic and hydrophobic condenser humidifiers? | 70% |
| What are some values for an ideal HME? | 1) should operate at 70% efficiency or better (providing at least 30 mg/L water vapor) 2) use standard connections 3) have a low compliance 4) add minimal weight, dead space, and flow resistance to a breathing circuit |
| What is a servo-controlled heating system? | monitors temperature at or near the patient's airway using a thermistor probe |
| Who are heated humidifiers mainly used for? | patients with bypassed upper airway and those receiving mechanical ventilatory support |
| What elements are used for heating bubble and passover humidifiers? | 1) "hot-plate) 2) "Wraparound" type that surrounds chamber 3) yolk, or collar that sits between water reservoir & gas outlet 4) immersion-type heater, element placed in water 5) heated wire in the inspiratory limb warming a wick or hollow fiber |
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