The actual content of weight of H2O in a given volume of air (mg/L)
Comparison of H2O content in a volume of gas (absolute humidity) vs the amount of gas it is capable of holding (at a given temp)
RH= content/capacity x 100%
Water vapour pressure
The atmospheric pressure which is exerted by water vapour (water in its gaseous state).
It is one way of measuring the humidity of the air.
At a given temperature, an increase of water vapour in the air corresponds to an increase in the humidity of the air (i.e. it is dependent on RH and Temp).
Comparsion of absolute humidity between inspired air and air in the lungs.
The deficit is the amount of humidity not present in the inspired gas and needs to be supplied by the body
humidity therapy is used to prevent the humidity deficit that can result from breathing a dry gas. *The output of any therapeutic gas delivery system should match the conditions occuring at its point of entry.
The atmospheric temperature at which the air becomes saturated with H2O and water droplets begin to "rain out." (reaching dew point will require cooling of the gas)
Ex. if ambient air is 37 'C with an RH of 37%, its pressure would be 17.5 mmHg (46.9 x .37). Looking at the Temp/Humidity/PH2O chart we can see that a pressure of 17.5 mmHg is related to a temp of 20 'C.
Thus, the air would have to be cooled to 20 'C before it becomes saturated with water (RH = 100%)
This happens as a person exhales gas and it cools to room temp
Conditions at certain points of entry in the respiratory tract:
a) Mouth and nose
c) Lower tract (via tracheostomy or ETT)
a) 22 'C, RH =50% (room conditions)
b) 29-32 'C, RH = 95%
c) 32-34 'C, RH = 100%
These should be matched by the therapy system (depending on enterance) to avoid humidity deficit (or fluid overload)
Name 3 consequences of supplying inadequate humidity
- impaired ciliary action
- impaird mucus movement and plugging
What 3 environmental factors influence humidity?
1. Temperature** increased temp = increased molecular movement which results in evaporation of H2O into the air
2. Pressure: the greater the pressure, the less vaporization (pressure/force keeps molecules together). i.e. H2O will boil faster at high altitudes.
3. Surface Area: The greater the air-to-H2O interface, the greater the evaporation
What are the capacity and vapour pressure values at the following temps:
a) 37 'C
b) 32 'C
c) 20 'C
a) 43.9 mg/L, 46.9 mmHg
b) 33.8 mg/L, 35.5 mmHg
c) 17.3 mg/L, 17.5 mmHg
Capacity is absolute humidity at 100% RH, i.e. it's only the actual content if the RH is 100%. Capacity is used in the RH equation.
Calculate the humidity deficit of a patient with normal body temperature while breathing a gas that is 57% humidified at body temperature.
a) Determine the capactiy of the gas at the given temp (37 'C):
- at 100% RH, capacity= 43.9 mg/L
b) to find the actual H2O content at the given RH, rearrange the RH equation:
content = RH x capacitycontent = .57 x 43.9 mg/L
content = 25.023 mg/L
c) subtract the content (aka the actual humidity) from the humidity of the body (100% RH at 37 'C) to find the deficit
43.9- 25.023= 18.9
The calculated humidity deficit while breathing room air at 20 'C with an RH of 25% is:
At 20 'C, capactiy is 17.3 mg/L.
25% of that capacity is 4.33 mg/L
A patient's temp is 37 'C at 100% RH = a capacity of 43.9 mg/L
The deficit is then 39.5 mg/L
There is a popping noise or whistle coming from the room of a patient who is receiving humidified O2 via a nasal cannula. What is the noise and why is it happening?
It means that there is an obstruction of the tubing such as a kink.
The noise is from the pressure release which has just been activated.
Simple (Low-flow) Humidifiers (reference)
- Best for Flows <10 L/min
- Capable of providing up to 100% RH at room temp conditions only (20 'C and 17.3 mg/L).
- This results in only 1/3 (30-40%) of the body's humidity requirements. (need to use something stronger if the upper A/W is bypassed)
- Used with nasal cannulas, catheters, simple masks etc.
High Flow (heated) Humidifiers
Supply 100% RH at near body temperature.
Types of Low-flow/simple humidifiers
Bubble diffuser humidifier
Types of high flow humidifiers
Vapour Phase humidifier
Factors affecting performance of low-flow humidifiers:
B) More efficient at low flow rates:
- more time at gas-water interface
b) More efficient with more water in the reservoir
- not true for Jet H's
c) Efficiency is inversley related to bubble size or particle size:
- depends on device
Match the statement with the proper humidifier:
a) usually provides 50-90% RH at body temp
b) will provide 100% RH at any temp and most flow rates
c) the least efficient of all humidifiers
d) produces aerosol particles
e) will generally supply approx 40% of total requirements at body temp
a) Heat-moisture exchangers (HME: an artificial nose)
b) Wick (most efficient, least resistance; work well with venturi or ventilator circuit)
What is the major advantage of heated humidifiers?
100% RH is easily attained at body temp.
A heated humidifier is being used to delivery humidity to a patient intubated with an ETT. The tubing between the pt and the device is filling with water:
b) If the pt is on 50% O2 via blender and flowmeter, will the water collecting affect FiO2?
a) This is normal, it is a result of heated gas being cooled in the tube (due to ambient air temp) to its dew point and condensation forming.
- condensation is an indication that the gas is at 100% RH
b) No, this is not an entrainment device so flow rate and FiO2 are constant
What happens to a nebulizers operation as water accumulates in the wide-bore tubing creating backpressure?
Nebulizers work using air-entrainment so backpressure (i.e. due to obstruction) results in decreased flows to the patient.
As flows decrease, the patient may inspire more room air= unknown O2 concentrations being delivered.
Why do many nebulizers set at or > 50-60% O2 need to be paired with a second nebulizer to deliver appropriate gas flow?
At higher FiO2 settings, total flow is decreased as less air is entrained (max flow is approx 12-15 L/min).
This may result in the patient inhaling increased ambient air (which decreases FiO2)
Attatching 2 nebulizers in tandem doubles the total flow allowed at higher FiO2 settings.
What factors affect the concentration of oxygen delivered by an entrainment device (Jet nebulizer)?
The size of the entrainment ports
Jet orifice size
The nozzle and entrainment ports dictate the ratio of mixing (= independent of source flow)
Which device(s) utilize piezoelectric transducers?
Match the statement with the proper nebulizer:
a) the worst device for spreading microbes
b) may cause bronchospasm
c) utilized primarily for medication administration
d) usually have built in adjustable FiO2's
a) Centrifugal nebs
b) ultrasonic nebs
c) small volume nebs (aka reservoir)
d) large volume nebs (aka reservoir)
Match the statement with the appropriate particle sizes:
a) too large to penetrate the nose, enter the aw only via mouth breathing
b) deposit in the lung periphery
c) for airway deposition
d) most stable (can be exhaled vs deposited)
e) ideal for medication delivery
f) ideal for humidification delivery
g) for lung parenchyma
a) 5-10 um
b) 1-5 um
c) 2-4 um (i.e. bronchdilators)
d) < 1 um
e) 3-5 um
f) 5-20 um
g) 1-2 um (i.e. antibiotics)
What is the difference between an atomizer and a nebulzer?
Nebulizers are the same with the addition of a "baffle ball" which results in reduced particle size (more uniform sizes as well)
Atomizers are primarily used for medication delivery during larygo/bronchoscopy procedures.
Large Volume Nebulizers
Pneumatic Jet Nebulizer
+ heated and high-flow delivery systems
Ultrasonic nebulizers (lg volume)
Spinning disc nebulizers
Small Volume Nebulizers
Metered dose inhaler (MDI)
Dry powder inhaler
Small particle aerosol generator (SPAG)
Ultrasonic nebs (small volume)
Pneumatic Jet nebulizers (reference)
- For bland aerosol therapy (i.e. water, O2 or saline) and humidity
- Long-term/continuous use (30 min- days)
- Run between 7-15 L/min at 50 psig
- Deliver 28-100% FiO2
- Use air-entrainment (use magic box and dilution eq for values)
- Particle sizes = 2-20 um (Ave =2-4 um)
- Output of 30-50 mg/L
Normal Peak inspiratory flow
Important to know for ventilatory demands, need high-flow systems to deliver this and high FiO2's along with air entrainment
@ 40% O2 and 10 L/min = > 40 L/min
Ultrasonic Nebulizers (reference)
Particle sizes of 1-10 um (MMAD= 3 um)
Output of 60-100 mg/L
Use a piezoelectric transducer to produce waves
Vibrational freq and partical size are inversley relarted
MMAD= mass median aerodynamic diameter: 50% of particles are larger, 50% are smaller
Artificial Noses/Passive humidifiers
Uses the patients expired gas to heat and humidify
Used to humidify during mechanical ventilation and tracheostomy situations
- moisture output of 22-34 mg H2O/L (at normal VT of 500-1000mL)
3 hazards of high flow/heated humidifiers
1- Nosocominal (hospital acquired) infection
2- Accidental levage of the airway
3- Retrograde drainage
Penetration and Deposition of particles in the lower respiratory tract
a) Inertial Impartion: Tends to cause deposition of particles at bifurcations (where airstream changes). Determined by particle momentum (mass x velocity)
b) Sedimentation: Deposition in the lungs due to gravity. Determined by particle size and density.
c) Diffusion: Deposition of really small particles with surrounding gas molecules.
Physical nature of aerosol particles:
a) Take on water and increase in size
b) Loose water and decrease in size
c) Take on water and increase in size:
a + b in the respiratory tract will take on water if they pass through humid gas streams.
Important to know if using hypotonic solutions (bc the sol'n will increase paricle size and it may not work as intended)
Typical drug deposition of a small-volume nebulizer
Output of a MDI
1 unit dose:
> 30 m/s (high velocity)
> 30 um particle size= high oropharyngeal deposition
actuation volumes of approx 15-20 mL
Advantage of a dry powder inhaler over an MDI?
They are "breath-actuated" (inhalation causes actuation to occur)
Small particle aerosol generators (SPAG's)
Used specifically for Ribavirin (virazole)- used to treat RSV
Aerosol is delivered to a mask, oxyhood, tent or ventilatior
MMAD = 1.3 um
Flow = 6-10 L/min
Proper sizing for an oropharyngeal airway is determined by:
measure from the lips (corner of mouth) to the ear lobe
Match the statement with the appropriate airway device:
a) measured from the tip of the nose to the earlobe
b) often utilized as a bite block
c) usually considered as long-term airway choice
d) most frequently made of PVC
e) frequently utilized soley for weaning
a) Nasopharyngeal A/W
b) Oropharyngeal A/W
c) Tracheostomy tube
d) Endotracheal tube
e) Tracheal button
Device best suited to help prevent short-term upper airway obstruction in a conscious patient who does not require mechanical ventilation?
Which is the worst reflex we may have to deal with when inserting a nasotracheal tube?
Match the statement with the appropriate ETT
b) acute angle in tube
d) steel reinforcing wire
e) bronchial insertion
a) Carlens and White tubes- provide independent lung ventilation
b) Rae tube
c) High-low jet tube: irrigation lumen and insufflation lumen
d) Anode tube
e) Endobronchial tubes (carlens and white)
When using a straight blade laryngoscope, where is the blade tip to be placed?
Against the epiglottis, lifting it directly
Wisconsin and Miller blades
When using a curved blade laryngoscope, where is the blade tip to be placed?
Into the vallecula, lifting the epiglottis indirectly
Macintosh blade (*most common)
What is the primary advantage of a fenestrated tracheostomy tube?
Match the statements with the proper airway cuff:
A) Fome cuff:
- max 20mmHg, syringe deflates the cuff (opposite to normal)
b) Troller cuff:
- max 20mmHg, 2 compartments
c) McGinnis pressure regulatoing balloon: max 25mmHg
d) High-volume and Low-pressure**.
What is the advantage of artificial airways that have large residual cuff volumes over the "high pressure" cuffs
A lower cuff-tracheal wall pressure
Overinflation of the cuff of an ETT would most likley result in:
Decreased local capillary blood flow= ischemic injury
if cuff pressure exceeds local venous pressure
ideally < 25mmHg
What is an ideal suction pressure for pleural vacuum (thoracic drainage)?
anything < 25 cmH2O
What is the diameter rule for tracheal suction catheters?
OD should be < 1/2 the ID of the ETT
A diameter that is too large will result in the total pressure of the lungs falling close to that of the vacuum.
Length from teeth to the carina and nasal vestibule to the carina
27 cm and 29 cm respectivley
cuff placed @ 2cm below vocal cords (1-2 in infant/child)
tip placed @ 3-5 cm above the carina
Resistance (too flow) is inversley proportioanl to radius
-important with airway tubes, too small= increased resistance.
Advantages of tracheostomy tubes over ETT's and its consideration
fixation is easier
pt can sometimes eat and speak
changing is easier
*Considered 10-14 days post-intubation
4 parts of a tracheostomy tube
1) Inner cannula: can be changed
2) Outer cannula
3) Obturator: prevents blood/mucus enterance
Normal Tracheal Pressures
arterial: 30 mmHg
venous: 18 mmHg
avoid ETT cuff pressures that exceed these= ischemic injury
Appropriate bottle placement during suciton of:
a) above the patient
b) above the patient (avoid syphon effect)
c) the floor or 50 cm below the patient (prevent syphoning back into the cavity)
d) floor (to increase total suction)
Match the statement with the type of suction tubing:
a) gastric decompression
b) for continuous suction of stomach
c) for poison suction (goes through mouth at times)
d) for intestinal decompression
a) short tubes (aka NG tubes): Levine is the most used
b) Sump tube (an NG tube)
c) Ewald tube (an NG tube)
d) Long tubes
Placement of thoracic suction/drainage tubes
Placed in the pleural space or the medistatinum
Inserted into the pleural cavity after an incision is made:
a) for pneumothorax: 2nd or 3rd intercostal space (at mid clavicular line)
b) for pleural effusions: 5th intercostal space (at mid axillary line)
c) mediastinal drainage: mediastinal pleura
a CXR should be used to verify placement
Chest tube removal
the patient must perform a valsalva maneuver (take a deep breath and force exhalation)
= creates a positive pressure in the pleural cavity and prevents air from entering.
The tube is quickly withdrawn
What is the volume that will realistically be delivered by the average sized adult bagging a patient with one hand, using a, 1800 mL resuscitator bag?
What is the reason and action for a slow recoil time (the resuscitator bag refills very slowly).
the inlet valve is most likely partially or completely stuck.
Again, stabilize the patient before fixing
What is the reccomended minimum Vt to be delivered?
adults: 800-1200 mL
children: 70-300 mL
infants: 20-70 mL
The FiO2 delivered by a bag-valve mask is dependent on:
O2 flow rate
bag refill time
manual ventilation rate
With flow-inflating resuscitator bags, the end expiratory pressure in the bag is controlled by:
FIB's are continuous flow, semi-open systems
The O2 flow into the bag
The bleed off rate
Thus, they can provide CPAP or PEEP
Why does gastric insufflation occur during resuscitation and what are 2 steps to help minimize it?
- occurs because there is no tube to direct flow and esophageal openeing pressure is less than pharyngeal (= easy route for air to travel)
- use slower inspiratory flow rates
- cricoid press
Approximate delivered O2 content when using expired gas ventilation (i.e. mouth-mouth/ mask resuscitation)
What alalyzer uses photoelectric plethysmography?
A capnogram tracing rises quickley and levels off at 60mmHg. What is the mostly likley reason for this?
Elevated PETCO2 can mean that PaCO2 is elevated.
May be due to an increase in CO2 production or decreased alveolar ventilation; commonly seen in the COPD patient
A real-time waveform record of the concentration
of CO2 in the respiratory gases:
a) CO2-free gas is cleared from the anatomic dead space (phase I)
b) rapid sharp rise = mixed dead space and alveolar gas (phase II)
c) alveolar plateau; represents the exhalation of mostly alveolar gas (phase III)
- note that the slope of phase III or from c to d (alpha angle) is determined by the V/Q rlsp [normally 100-110']
d) end-tidal CO2 tension (PETCO2)
-note that the 90' angle after phase III or (d) = the beta angle, is used to assess rebreathing exhaled gas
A capnogram tracing has a downward spike right in the middle of the exhalation plateau. Explain why?
The patient has attempted inhalation in the middle of exhalation
A capnogram tracing has a series of expiratory plateaus occuring rapidly at 20 mmHg. Explain why?
Rapid respiratory rate, hyperventilation (= less CO2 production) or possible VD/VT (deadspace to tidal vol ratio)
Which would not affect the reliability of a capnograph in reporting an appropriate end tidal CO2 reading?
D) a change in FiO2 will not affect the tracing
a) end tidal CO2 value, used to estimate PaCO2
- depends on V/Q rlsp and thus, is not accurate of PaCO2 in patients with deadspace-producing disease.
- The principle determinants of ETCO2 are:
(1) alveolar ventilation,
(2) pulmonary perfusion (cardiac output) and
(3) CO2 production.
b) visual assessment of patient's airway integrety
- increased alpha angles or phase III slopes are indicative of obstructive lung diseases.
c) verification of proper ET tube placement**
- with accidental esophageal intubation, readings will = zero
d) assessment of ventilator/breathing circuit integrity
What type of analyzer is most affected by hypotension?
Transcutaneous PO2 (PtcO2) monitor
PtcO2 monitors and neonates:
room air can be used to calibrate a high point
probe temp may be 6-7 'C higher than normal body temp (37'C)
transcutaneous values should be correlated with arterial values periodically
What priciple is utilized for transcutaneous CO2 monitors?
CO2 will diffuse through a membrane and react with a bicarbonate solution resulting in a pH decrease
What is the primary purpose of calorimetry?
To facilitate/assess weaning from mechanical ventilation
They measure energy expenditure patients, i.e. those on ventilators, to assess nutritional states as this can have an impact on weaning off of the ventilator.
What oxygen concentration is used for calibration of O2 monitors (i.e. polarographic andgalvanic)
21% and100%, room air and pure oxygen
What do pulse oximeters measure and how accurate are they?
SpO2: hemoglobin O2 saturation
- note: it is not a good indicator of PaO2
Accuracy is +/- 4% (if saturation reading is >80%)
Describe pricliples of pulse oximetry
Combines the principles of spectrophotometric oximetry (light absorption) and plethysmography (volume change= pulse) to determine the saturation of Hb with oxygen.
Hb and oxy-Hb exibit different absorption characteristics so 2 beams of light are used on the area. The probe detects the absorbtions during arterial pulsation to produce plethysmograghic waveforms of the 2 wavelengths (pulse so that other tissue constituents don't interfere). The ratio of the amplitude of the 2 waveforms can be converted into saturation.
Realtionship between arterial blood gases and transcutaneous values. (reference)
Tc measures the gas values from the skin and thus, depends on diffusion of the gas from circulation to the electrode on the skin. = values are not the same as arterial because:
a) some oxygen will be consumed by the skin between the vascular bed and the electrode
= dec O2 and inc CO2
b) heat from the electrode can increase O2 as well as CO2
= sometimes the O2 effects cancel out and readings are similar to arterial levels, but CO2 effects are additive
Open vs Closed circuit methods in indirect calorimetry
Indirect Calorimetry: provides accurate estimates of energy expenditure from measures of carbon dioxide production and oxygen consumption
The primary distinction between an open and closed method is in the measurement of VO2 (oxygen consumption)
3 categories of flow and volume measuring devices
1) Spirometers (volume)
2) Pneumotachometers (flow rate)
3) Plethysmographs (pressure)
If an instrument measures the same value as the reference (known value) it is said to be:
when a measurement is accurate over the entire range of measurement, it is said to be:
When an instrument generates reproductable results, it is said to be:
What is the most commonly used low pressure manometer in respiratory therapy?
What is the most common type of electromechanical device ultilized in hospitals for pressure measurements?
Strain gauge transducers
also common for hemodynamic pressure measurements
A low pressure or disconnect alarm should generally be set at:
5 cmH2O or 10% below the desired pressure
Name some reasons for accidental breathing circuit disconnections:
Inadequate connection force
High pressure within circuit
Tension on tubing
Do incentive spirometers use volume, flow or pressure-type devices?
Volume or Flow
Most cases of nosocomial pneumonia are caused by what type of microbe? Community acquired?
gram negative bacteria
Because its the most common flora in the body.
Staphylococcus aureus is the most common gram + cause of nosocomial pneumonia.
Streptococcus pneumoniae is accountable for 50% of community acquired pneumonias
How does Charles' Law apply to volume measuring devices?
Volume displacement spirometers linearly expand (expir'n) and contract (inspir'n), but the readings and the actual volumes are not identical because of the Temp differences between the lungs and the room, which affects volume.
Recorded volumes are converted from ambient to body temperature and saturated conditions (BTPS) either manually or by computer
Factors that affect flow and thus, accuracy and precision of pneumotachometers. How are they delt with?
- Devices should be calibrated with a viscosity and temp similar to the gas being measured (Temp~viscosity)
- Many units are heated to prevent condensation (resistance)
Dry Rolling seal
Flow measuring devices (spirometers)
- Fleisch and modified
Pressure measurement devices:
Gravity-dependent fluid manometers
Mechanical Aneroid manometers
- variable capacitance
- variable inductance
What type of flow measuring devices requires laminar flow for best accuracy?
Distinguish between decontamination, disinfection and steralization
Decontamination is a broad term for the reduction of microbial contamination. Disinfection refers to the destruction of organisms on the surface of objects while sterilization is an absolute term for the complete destruction of all micbrobes (inc spores)