Humidity and Aerosol Therapy Flashcards
Complications associated with dry medical gases
Administration at flows greater than 4 L/min to the upper airway causes immediate heat and water loss, and if prolonged can cause structural damage. Ciliary motility is reduced, airways become irritable, mucus production increases, and pulmonary secretions because inspissated (thickened due to dehydration). As long as humidity is 60% of BTPS conditions, no injury occurs.
Clinical signs and symptoms
-Atelectasis, dry nonproductive cough, increased airway resistance, increased incident of infection, increased WOB, substernal pain and airway dryness, thick dehydrated secretions.
Indications for Humidity Therapy
Humidifying dry medical gases, overcoming humidity deficit created when airway is bypassed, managing hypothermia, treating bronchospasm caused by cold air.
Recommended gas heat and humidity delivered to the…
Nose, Hypopharynx, and trachea
Nose- 20-22 degrees C, 50% rel. humidity, 10 mg/L abs. h.
Hypopharynx- 29-32 degrees C, 95% rel. humidity, 28-34 mg/L abs. h.
Trachea- 32-55 degrees, 100% rel. hum., 36-40 mg/L abs. h.
Principles governing humidifier function (4)
- Temperature (increase temp=increase capacity)
- Surface area (increase S.A.=more evaporation)
- time of contact (“ “)
- thermal mass (increased T.M. = increased capacity to hold and transfer heat.
Bubble Humidifier
Absolute humidity ~15-20mg/L
increase in gas flow is a decrease in efficiency
Pressure release valve (2psi)
Passover humidifiers
Simple- gas directed over surface of water, typically used with heated fluids for MV, but can be used with room temp. solution for nasal CPP or bilevel ventilation
Wick- increases surface area of air to water interface. No aerosol produced because there is no bubbling.
Membrane-type-hydrophobic membrane only allows water vapor molecules to pass through but not water.
Types of HME’s
HME’s passively humidify by absorbing exhaled humidity of patient and returning it to them on the next inhalation. Returns up to 70% humidity
Simple condenser HME- condenser element with high thermal conductivity consisting of metallic gauze, corrugated metal, or parallel metal tubes, recapture ~50% efficient
Hygroscopic HME- low thermal conductivity, paper, wool, foam, impregnated with hygroscopic salt, ~70% efficient
Hydrophobic HME- water repellent element, low thermal conductivity, temp. increases on exhalation, ~70% efficiency, may increase artificial airway occlusion.
Contraindications to HME use
-Patients with thick, copious or blood secretions, expired Vt less that 70% of the delivered Vt (patients with large bronchopleural fistulas or incompetent or absent endotracheal tube cuffs), body temp. lower than 32 C, patients with Ve greater than 10 L/m, for patients receiving in-line aerosol drugs.
Types of heating elements used (5 types)
- Hot-plate element at base of humidifier
- fischer-paykal, vapor humidifiers - a wrap-around type that surrounds the humidifier chamber
- pneumotac - a yolk, or collar, element that sits between the reservoir and the gas
- bubble humidifier - an immersion-type heater with the element placed in the water reservoir
- passover humidifier - a heated-wire in the insp. limb warming a saturated wick
- incubators and radiant warmers, MV
Indications, contraindication, and hazards of humidity therapy during MV.
Indications- humidity therapy is mandatory during MV
Contraindications- Same as HME contraindications.
Hazards/Complications- high flows may aerosolize contaminated condensate, underhydration and mucous impaction, increased WOB, hyppovent. caused by Vd, elevated airway pressures caused by condensation, ineffective low pressure alarm during disconnection, improper ventilator function caused by condensation, gas trapping or hypovent. caused by mucous plugging, hypothermia, potential burns, potential electric shock, airway burns, inadvertent over filling, tracheal lavage from pooled condensate.
Monitoring patients on MV
HH should be set to 33C plus or minus 2, and should provide at least 30mg/L of wv. Monitor inspired gas temp, airway temp. should never exceed 37C, probe placed outside of incubator or away from radiant warmer, water level monitored, secretion characteristics noted, remove HME and substitute HH if secretions become copious.
Factors that influence condensation
- temp. difference across the system
- the ambient temperature
- the gas flow
- set airway temperature
- the length, diameter, and thermal mass of the breathing circuit
Indications, contraindications of bland aerosol therapy
Indications- presence of upper airway edema (cool bland aerosol), laryngotracheobronchitis, subglottic edema, postextubation edema, postoperative management of the upper airway, presence of a bypassed upper airway, need for sputum specimens or mobilizations of secretions.
Contraindications- bronchoconstriction, history of airway hyperresponsiveness
Assessment of need/outcomes of aerosol therapy
Need- stridor, croup like cough (brassy), hoarseness after extubation, history of upper airway irritation, and increased WOB, patient discomfort associated with airway instrumentation, bypassed upper airway
Outcome- decreased WOB, improved vitals, decreased stridor, decreased dyspnea, improved ABG, improved sats,
Sputum induction
Gather supplies, check chart, wash hands, introduction, position the patient upright, have patient rinse mouth and clear excess saliva, perform pretreatment (vitals, muscle tone, ability to cough and auscultation), assemble neb, fill med chamber with 3% sterile saline, adjust output of unit, place mask on pt, assess patients condition, end treatment after 15-30 minutes, encourage patient to cough, observe volume, color, consistency, odor, and presence or absence of blood.
Factors affecting aerosol deposition
Impactation- collision or deposition on a surface, primary deposition mechanism for particles larger than 5um
Sedementation- primary mechanism of deposition of particles 1 to 5 um. Occurs mostly in central airways, a 10 seconds hold increases the deposition by 10% and increase ration by 4 fold.
Diffusion- primary mechanism of deposition of particles less than 3um. mainly in the respiratory region of the alveoli. Most particles of 1 to 0.5 um are so stable they remain suspended and are exhaled whereas particles smaller than 0.5 have a greater retention in the lungs.
Site of deposition based on particle size
Upper airways- 5 to >50um
Lower airways- 2 to 5um
Parenchyma (alveoli)- 1 to 3um
Parenchyma- <0.1um
Aerosol drug delivery devices
-pMDI’s, DPI’s, SVN’s, LVJN, hand-bulb atomizers, USN’s, and vibrating mesh nebulizers
MDI’s
preferred method of delivery of maintenance bronchodilators and steroids to spontaneously breathing pt’s, highly technique dependant
DPI’s
Do not require hand breath coordination, requires high inspiratory flows (40-60, not for children under 5)
SVN’s
Even less technique dependent than MDI’s and DPI’s and more commonly used in acute care. Affected by baffles, fill volume, residual drug volume, neb position, continuous vs intermittent nebulization, reservoirs an extensions, vents, valves, gas entrainement. 30-60% of medicine trapped as residual volume, more than 60% wasted to atmosphere.
LVJN
Can be used to provide continuous aerosol delivery when traditional dosing strategies are ineffective in controlling severe bronchospasm. Lower out put compared to USN and VMN.
Small volume USN’s
used to administer bronchodilators, antiinflammatory agents, and antibiotic. Output determined by amplitude setting, the greater the amplitude the greater the nebulizer output. Particle size is inversely proportional to the frequency of vibrations. Higher output than LVJN but lower than VMN
Vibrating mesh
Highest output rate. contain more than 1000 funnel shaped apertures attached to a piezceramic element . Vibrates at a frequency of 130kHz. Particle size ranges from 2 to 3 um, less residual drug volume than other devices.
Assessing response to bronchodilator therapy
Patient interview, expiratory airflow test, vital signs, auscultation, ABG analysis, and oximetry.
Factors affecting aerosol drug delivery during MV
Proper selection of aerosol generation type, position of the circuit, dose and accessory equipment is needed to optimize deposition and achieve the desired clinical outcome.
Protecting patients and caregivers from exposure to aerosolized drugs
Negative pressure rooms, use of high-efficiency particulate air filters (HEPA), booths or stations during sputum induction and aerosolized medication treatments in an area where more than one patient is present. Use of personal protective equipment including N95 masks.
