HUMIDIFICATION& FILTRATION – Flashcards

is a general term used to describe the amount of water vapor in a gas

The mass of water vapor present in a volume of gas Changes when temperature changes Reported as milligrams of water per liter of gas (mg/H2O/L)

The maximum amount of water vapor that can be carried in a volume of gas -varies with temperature

The amount of water vapor at a particular temperature expressed as a percentage of the amount that would be held if the gases were saturated Equation= absolute humidity/humidity at saturation

The amount of water that can be held as a vapor depends on the ambient temperature. The warmer the temperature, the more water vapor a gas can hold. As temperature decreases, amount of water the air holds goes down. Water begins to condense out of the air at cooler temperatures.

a measure of the temperature of the gas when liquid water will appear

Notice that as temperature goes down, relative humidity decreases Actual water content is the same Just the temperature has changed Same thing happens in the breathing circuit

Water is intentionally removed from medical gases to prevent corrosion and condensation in regulators and valves Gases emerging from the anesthesia machine are dry and room temperature Tracheal intubation or the use of an LMA bypasses the upper airway, modifying the pattern of heat and moisture exchange leaving the tracheobronchial mucosa to assume the burden of heating and humidifying gases

Gases specific heat value LOW Gases thermal conductivity value LOW Gases assume temp of the environment (in vaporizer, or circuit for example) Cold, dry air from anesthesia machine to patient Warm moist 100% relative humidity alveolar air from patient at 37 C (normal in patient) Travels into breathing circuit at room temp 20 C At 20 C, gases cannot hold as much water (dec. temp, dec. H2O held). Water 'rains out' inside breathing circuit Expiratory limb and expiratory check valve (have condensation) Would be ideal to retain this heat & moisture

-Damage to the respiratory tract Reduced mucous flow Interference with mucociliary transport Decreased ciliary activity, twisting, tangling Occurs as early as 30 minutes after induction Complete cessation of ciliary activity after exposure to gases with an absolute humidity of 22mg/H2O/L Also affected by GA, narcotics, nicotine (decreased) Morphologic damage to epithelium (change in structure) Increased viscosity of mucous (thicker) Inspissation, encrustation (hard, booger like) Atelectasis, Inflammation Increased bacterial colonization Pneumonia Ventilation/perfusion mismatching Decreased FRC, compliance, oxygenation -Loss of body heat Body temperature is lowered as the airways bring the inspired gas into thermal equilibrium and saturate it with water Use of a humidification device can decrease the heat loss that occurs during anesthesia and may provide heat input Insensible loss of heat from patient

Increases with duration of exposure Few clinically important changes If anesthesia exposure is short 1-3 hours in non smokers If patients lungs are healthy, severe underlying lung pathology, eg, cystic fibrosis Important in longer cases, patients with active pulmonary disease, and for infants (body temp falls 3 times faster than adults when breathing dry unhumidified air) Bottom line...warmed, humidified air is better than cold, dry gases, even in short cases

Cases ranged 2-3 hours increased pulmonary complications Early cytology changes in epithelial cells Before declines in PFTs significant Flowrates not published Smokers may deserve protection even if case is 'short-term'

Occurs as early as 30 minutes after induction Complete cessation of ciliary activity after exposure to gases with absolute humidity of 22 mg/H2O/L This represents 100% humidity @ 24-25 C Breathing circuit temp 20 C Breathing circuit humidity with air 8% Breathing circuit humidity with O2 0% Breathing circuit humidity with N2O 0% Anesthetist should actively preserve humidity in all cases more than 30 minutes ? YES

22 mg/H2O/L

An inspired absolute humidity of 28-32mgH2O/L is associated with minimum heat loss and minimal damage to tracheal epithelium when anesthesia lasts longer than 1 hour For shorter cases, a humidity level of 12mgH2O/L is required to prevent cellular damage

The ISO set the following humidification characteristics for HMEF: Should at least provide a moisture output of 25.4 mgH2O/L ANSI and the American Association for Respiratory Care standards are 30 mg/H2O/L for patients ventilated in intensive care units

Condensed water in the circuit is a perfect home for bacterial growth Heat and water gain which is hazardous in infants and small children (lead to ARDS) Degeneration of the cilia Increased secretions Atalectasis Decreased FRC Diminished surfactant activity hyperthermia

Strive for what is physiologically normal If not bypassing moist airways, strive for what is ideal for the human airway If intubating, strive for higher values Strive for higher numbers, especially if.. Long case Patient has active pulmonary disease or smokes

Pass the anesthetic gases through a carbon dioxide absorber (they contain 15% water) Decrease the fresh gas flowrate, the lower the FGF the higher the inspired humidity Add a heat and moisture exchanger to the breathing circuit Use of a heated humidifier - rare/ICUs Look at some of the breathing circuits...

The surface area is high to achieve high gas flow with low resistance Provides moderate moisture output Are efficient viral and bacterial filters Consistently prevents passage of Hep C Stop particles because of the small size of their pores but allow passage of water vapor not liquid

Contain a wool, foam , or paper like material coated with a moisture retaining chemical, may be impregnated with a bactericide Consists of a hygroscopic layer plus a thin membrane that has been subjected to an electric field to increase polarity which improves filtration efficiency and hydrophobicity (charged to improve filter efficiency) 'Electret' fiber loses efficiency in environments of high humidity Usually used in dry environments

Heat and moisture exchange: Hygro - good, Hydro - fair Increased TV on heat/mositure Hygro - slight decrease, Hydro - significant decrease Filtration efficiency when dry: Hygro - good (86-99%), Hydro - >99% Filtration efficiency when wet: Hygro - poor, Hydro - >99% Resistance when dry: Hygro - low, Hydro - low Resistance when wet: Hygro - increased, Hydro - low Effect of nebulized meds: Hygro - increased resistance, Hydro - little affect

HMEs are most useful during short-term ventilation in patients who are adequately hydrated May be used in a patient with a tracheostomy Should be used in a patient with a known infectious disease

Patients with thick, copious, or bloody secretions Patients with an expired tidal volume less than 70% of delivered tidal volume (e.g.,leaking or absent tracheal tube cuff) Patients with body temperatures less than 32C (purposeful hypothermia) Patients with a bronchopleurocutaneous fistula

The type of heat and moisture exchanger used, remember that hygroscopic HMEs have better heat and moisture exchanging properties than hydrophobic Inspiratory/expiratory flows - the faster the gas passes through the HME, the less time there is to absorb or deposit moisture so an increased tidal volume will cause humidity of the inspired gas to fall (increased TV = decreased humidity) Continuity of the system - a leak around the tracheal tube or between the tube and the HME will decrease inspired humidity

Selection should be appropriate for the size of the patients tidal volume, if a small HME is used in large patients, there will not be enough surface area for absorption of moisture so the HME will be insufficient The greatest inspired relative humidity occurs with the HME positioned next to the tracheal tube or LMA, RH declines as the space between the tracheal tube and HME increases (Best right by elbow) Can be used with any breathing system May be used as the sole source of humidity or may be combined with another source such as an unheated humidifier (should not be used with heated humidifiers) Some HMEs can be moistened before use to increase efficiency...do not moisten a hygroscopic unit because it will reduce its efficiency

Inexpensive Easy to use, reliable Small and light weight, silent in operation Low compliance and resistance when dry Disposables require no cleaning/sterilization and do not require water No danger of overhydration, hyperthermia, burns of the skin or respiratory tract or electric shock Eliminates the condensation of water in expiratory limb Acts as a barrier to large particles, some are efficient bacterial and viral filters...decrease nosocomial pneumonia and contamination of the breathing system Decreased heat loss from patient due to decreased rate of evaporation of water from tracheal mucosa May increase correlation between esophageal and core temperature

Excessive resistance Increases resistance to respiration Use of nebulized medication increases the resistance of hygroscopic (but not hydrophobic) HMEs Observe frequently for plugging, observe spontaneously breathing patients for increased work of breathing If peak airway pressures increase, measure with and without HME in place

Airway obstruction Any time you place a device on a breathing circuit in addition to providing a benefit you may be causing a problem. Although they are simple devices, they may have faults. The most common fault is a plastic defect that causes a partial or complete obstruction If exhalation is obstructed what happens? The lungs get over expanded possibly causing a tension pneumothorax If the obstruction is on the inspiratory side what happens? High peak airway pressures and obstruction to flow Always place the device on the circuit prior to machine check-out. The most common fault is a plastic defect that causes a partial or complete obstruction An HME can become obstructed because of fluids, blood, secretions, a manufacturing defect, or nebulized drugs The weight of an HME may cause the endotracheal tube to kink

Inefficient Filtration Liquid will break through composite hygroscopic HMEs which may contaminate the breathing system Aspiration of Particles Some HMEs contain materials that may be released in the form of particles then inhaled by the patient Rebreathing The deadspace of the HME may cause excessive rebreathing, especially with small tidal volumes

Interference with Monitoring If the gas sampling line is connected on the machine side of the HME, end tidal carbon dioxide values may be significantly lower, especially in spontaneously breathing patients Leaks and Disconnections Adding an additional component to a breathing system increases the potential for disconnection. The HME can come apart and cause a leak

Flowover, heated water bath Requires a minimum fresh gas flow Rely on temp sensor near Y piece Heated wire circuit Do not require minimum fresh gas flow Rely on tem sensor near Y piece

Over/under hydration Hypo/Hyperthermia -problematic in infants Melting of disposable circuits Aspiration Infection Costly May not produce as much humidity as assumed Increased chance of malfunction

Provides 100% humidity Maintains temperature

Increased airway resistance Hyperthermia Airway thermal burns Positive water balance Infection, growth of organisms Altered ciliary epithelium Altered surfactant function Atalectasis

Increased viscosity of sputum Loss of ciliary function Inspissation, encrustation, retention of secretions Mucous plugs in airway Atalectasis Decreased pulmonary compliance Increased airway resistance Decreased FRC Increased shunting Loss of surfactant function Hypothermia

Varies widely depending on hospital Causes 15% of infections Leading cause of nosocomial deaths Increases ICU stay by 6 days Increases hospitalization by 10.5 days Primary cause of mechanical ventilation Gram negative bacteria are the most frequently isolated pathogen

There is no sterile anesthesia machine...expensive & impractical Pathogenic organisms contaminate most clean systems...surface of machine strep and staph from oropharynx In a patients with transmissible pulmonary disease, contamination of the anesthesia machine does occur with potential for cross contamination unless a filter is used Facemask, elbow, breathing circuit are the most frequently contaminated Long term ventilation increases incidence of contamination of the ventilator Any equipment that is wet has a higher incidence of contamination...vent tubing and filters Contamination of hands with blood and oral secretions...increases the incidence of anesthesia machine contamination as well as the breathing circuit - change gloves >>> Use blue towel for dirty stuff

Removes unwanted bacteria, virus & particulates from air going to and coming from patient Keeps machine protected from the patient Keeps patient protected from the machine (ex. dust, contaminated pipeline)

Determines hydrophobicity Solid material repels water the best, but won't let gas through Large pores allow water to pass through, also lets gas molecules through Small pores will repel water, and will let gas molecules pass through 0.3 microns well suited for anesthesia (typical filter) Eventually pores fill up and resistance increases as filter gets clogged or water breeches filter

The more microorganisms filtered and removed, the more efficient the filter Testing uses particles similar in size to those of bacteria and viruses Non-pathogenic organisms utilized Analysis shows diverse testing by manufacturers and poor accuracy in reporting

Level of filtration depends on what you want to remove, most manufacturers state airborne pathogens are the concern while some contend that virus contamination of surfaces may lead to breathing circuit contamination Critical applications 0.2 microns=micrometer (0.3 for HEPA) Mycobacterium Tuberculosis 0.4um HIV 0.1um Hepatitis C 0.06um Filtration below 1 micron insignificant No bacteria or virus can propel via dry gas Smaller droplets act like a gas and are exhaled

Efficiency is variable dependent on the media used for construction Cost is in direct proportion to their efficiency

A better filter costs more, Pall is typically the most expensive since they do their own testing and they institute a more stringent test method. So look at the length of cases and the amount of pulmonary disease at your particular institution to decide what is needed. If you are doing 2 hour cases on healthy patients you may not need to spend a lot on filters Major routes for viral transmission do not involve droplet transmission Rhinovirus transmitted from contaminated surfaces Hepatitis survives 6 months at room temp Smaller organisms should be used for testing Hepatitis and HIV could infect breathing circuit if they are in patient secretions 1993: 3 cases in Australian confirmed this