RCP Exam 3 (Part 1)

Humidity

Water that is in the gaseous state.

Humidity behavior

Exerts pressure and is in constant random motion like gas molecules.

Dalton's Law of Partial Pressures

When calculating the partial pressure of a gas containing humidity, the partial pressure of water vapor must be accounted for

Aerosols

Particulate matter suspended in a gas.

Measurements of humidity

Water content or absolute humidity, Relative humidity, Evaporation, Humidity deficit

Water Content / Absolute Humidity

Physical measurement of how much water a gas is currently holding, measured in g or mg.

Partial Pressure of Water

Constant regardless of barometric pressure; depends on temperature and relative humidity.

Effect of Cooling on Gas Capacity

As a gas is cooled and temperature decreases, its carrying capacity decreases.

Fully Saturated Gas

Reaches maximum absolute humidity or capacity; adding more water results in condensation.

Relative Humidity Formula

Expressed as % of water capacity which is (how much water can the gas actually hold); calculated as Actual Humidity / Capacity.

Evaporation Process

Water moving from liquid to a gaseous state where overall energy level and temperature decline.

-Higher temp = more energy = more escape

Humidity Deficit

Difference b/t inspired gas content & content of gas @ BTPS (Body Temperature Pressure Standard)

-370C, 44 mg/L, 47 mmHg (carrying capacity of a gas at 37 C is 44 mg/L and at 37 C were at full saturation so the water vapor partial pressure is 47 mmhg)

How does the carrying capacity change with increased temperature

As temperature increases so does the carrying capacity

Clinical Significance Humidity Deficit

Clinically significant if it is LARGE & SUSTAINED and it causes retained secretions, airway plugging, obstruction, and infection.

Humidifier

Adds water vapor to a gas.

Factors Influencing Humidifier Efficiency

Temperature, surface area, time for contact, and gas flow.

Temperature & Humidifier Efficiency

Temperature: Warmer liquid = more molecules entering gaseous state + can hold more water.

Surface Area & Bubble Humidifier Efficiency

More surface area (bubbles coming in contact w/ water) = more humidity (e.g., a wider bubble humidifier = more bubbles= more humidity).

Time for Contact & Humidifier Efficiency

More time in contact w/ water = more humidity.

Gas Flow & Humidifier Efficiency

Cannot slow gas flow if patient requires it; slowing gas flow decreases the saturation.

AARC Guideline for Mechanical Ventilation Humidification

The humidifier should provide a minimum of 30 mg H2O/L of delivered gas at 30°C (the largest deficit we can make with mechanical ventilation).

Heated Humidifier Monitoring

Appropriate monitoring should include temperature probe(s) at the humidifier and the airway to monitor heat output.

Risk of Condensation on Temperature Probes

Can cause inaccurate readings which can lead to overheating.

3 types of humidifiers

Room Humidifier, Bubble Humidifier, Pass-Over Humidifier

Room Humidifier

-An aerosol generator that provides humidity indirectly

-carries a large potential for infection due to moving large amounts of air and large water reservoirs and it has to be kept clean

Bubble Humidifier Output

Delivers 33-40% relative humidity at 37°C, affected by liter flow, ambient room temperature, and long operation time.

Bubble Humidifier Safety and usage

Features a built-in pop-off valve at 2 psi (may have a whistle alarm)

-diffuser that breaks gas into small bubbles = more surface area;

-always used with sterile water.

3 types of pass-over humidifiers

-Simple Reservoir

-Wick

-Membrane

Pass-Over Humidifier Mechanism

Gas flow passes over a water reservoir or water-saturated material, evaporating water due to higher temperatures allowing it to hold more water.

Simple Reservoir Pass-Over Humidifier

Gas flows over the surface of a volume of water; usually used as a heated system to provide humidity to mechanically ventilated patients.

Wick Pass-Over Humidifier

Gas passes over or through water-saturated material where a wick absorbs the water (Usually a heated system used with mechanical ventilation)

-it is the most common humidifier used

Membrane Humidifier

Water is allowed to pass through a membrane, which leaves behind contaminants (e.g., Vapotherm).

Condensation / Rain-Out Cause

Gas cools as it leaves the humidifier, leading to more rain out because lower temperature equals lower carrying capacity.

Factors Affecting Condensate Amount

Temperature difference across system, ambient temperature, gas flow, and set airway temperature.

Minimizing Condensate

Placing water traps (drainage bags to drain rain-out) at the lowest point in the circuit and using a heated-wire circuit.

Heated Circuit with Humidifier

Aims to maintain temperature to minimize condensation/rainout.

Servo Heater

Digitally controlled via feedback from sensors.

Heated Wires in a Heated Circuit with Humidifier do what

What maintains the temperature.

Heat & Moisture Exchange (HME) / Artificial Nose

Absorbs heat & moisture from exhaled gas, then returns it to inhaled gas (Gives the patient back whatever the patient gives out).

HME Humidity and Temperature Output

Gives 70-90% relative humidity @ 30-31°C.

HME Airway Requirement

MUST be used with an artificial airway.

HME Resistance

Resistance increases dramatically with mucous.

HME Usage Duration

Short-term usage (<96 hrs.).

Long-term HME Complication

Bronchial cast formation secondary to secretion retention from long-term use.

Proper HME Placement

The HME comes first then the wye in a circuit, HME proximal to the patient.

HME Gas Communication

Must communicate with both inhaled and exhaled gas.

HME Breathing Path

Patient inhales and it passes through HME and then the patient exhales and it goes back through the HME

Indications for Bland Aerosols

-Upper airway edema

-bypassed upper airway,

-sputum specimen/secretion mobilization (make my patient cough)

(e.g., cool mist therapy).

Indications for Upper Airway Aerosols

-Upper airway inflammation

-anesthesia

-rhinitis

-systemic disease

(e.g., inhaled insulin).

Indications for Lung Parenchyma Aerosols

Delivering topical medication to the parenchyma or for systemic absorption (e.g., Albuterol).

Bland Aerosol vs. Aerosol

A bland aerosol is cool mist, whereas a regular aerosol contains medicine.

Humidity Requirement with Flow

Not required unless < 4 lpm; > 7 lpm requires heated humidity.

Particle Size and Mass Relationship

Radius, volume, and mass all increase or decrease directly.

Mass and Gravity Effect on Particles

As mass decreases, gravity has less effect and particles remain suspended longer.

-The finer the particle the easier gravity acts upon it

Hygroscopic Definition

Absorbs water, falls out of suspension

-Leave it with water; it will eventually merge

Tonicity Definition

Concentration of salt, coming in hypertonic, isotonic, and hypotonic.

Hypertonic Solution Concentration

Greater than 0.9% salt; draws water out of cells and causes a cough reflex.

Isotonic Solution Concentration

0.9% normal saline solution used for nebulizing.

Hypotonic Solution Concentration

Lower than 0.9% (sterile water); pushes water into cells.

Electrical Charge of Aerosols

No physiologic effects, but may affect other equipment like EKGs.

Factors Influencing Aerosol Deposition in the Airways

-Particle size and gravity (1 to 5 microns ideal)

-Inertia: Object in motion will stay in motion until something stops it

(Larger particles impact in oropharynx so the larger the particle more inertia: size and speed matters)

Temperature and Humidity Effect on Aerosols

Particles may evaporate or coalesce.

Optimal Respiratory Pattern for Aerosol Deposition

Slow, deep inspiration followed by a brief inspiratory pause.

Choked Flow Pressure in Aerosol Generators

Choked flow is applied in many aerosol generators to produce an aerosol (Nebulized at 26 PSI to produce an aerosol.

Capillary Action in Aerosol Generation

Draws liquid into the gas stream.

Baffle Function in Aerosol Generators

Causes larger particles to fall out of suspension while smaller particles follow gas flow.

Atomizer Baffle Presence

Atomizers have no baffles to stabilize particle size.

Nebulizers

Produces particulate matter delivered into a gas stream (Pneumatic so gas source pushes aerosol to the patient)

Side Stream Nebulizers

Large particles hit the baffle and only small droplets reach the patient.

Main Stream Nebulizers

Deliver large particles because they do not hit a baffle, resulting in unstable particle size.

Small-Volume Nebulizers (SVNs) Specifications

Volume of <30 mL and particle size of 1.5 to 7 microns.

Bulb-Type Handheld Nebulizers

Coordination is key; no longer common in the U.S.

Disposable Gas-Powered Small-Volume Nebulizers

Known as Updraft; uses choked flow, shear forces, and vorticity.

Minimum Volume Requirement in SVNs

3 mL minimum required in most SVNs to nebulize properly.

Sputtering in SVNs

Tap the side to collect residual volume (dead volume) collecting on sides.

Gas-Powered SVN Flow Sources

Connects to wall or compressor, uses 6-8 lpm, runs on O2 or medical air.

Flow Effect on Aerosol Devices

Higher flow equals more aerosol, smaller particles, and faster treatment.

Respigard II Small-Volume Nebulizer

-Utilizes an expiratory filter 

-Capable of particles < 2 microns 

-Often used to administer Pentamidine (antibiotic) (for PCP)- Pneumosistic pneumonia

Salter Labs NebuTech HDN

Enhances delivery during inspiration via one-way valves but no reservoir so most of medication is deposited; 80% of delivery is <5 microns.

Monaghan Medical Corporation AeroEclipse Breath-Actuated Nebulizer

Nebulizes only on inspiration so patient only gets medication when they inhale; less medication wasted, smaller doses may be effective, and can give continuous and intermittent flow.

Brigg's Adapter / Aerosol T

Use with large bore 6" aerosol tubing as a reservoir

Aerosol Mask

Similar to simple mask, but inlet is for large bore (blue) tubing (22mm) with holes on side for releasing CO2

Trach Mask

Fits over a tracheostomy tube; secured w/ elastic strap;

Face Tent

Straps under chin, enclosing only lower part of face; used in recovery & for facial burns for aerosol administration