1. RT Physics Week 4 QUIZ Review of Pressure Conversions
Humidity and Aerosol
Review
PAO2
P(A-a)
CaO2
DO2

2. Pressure Conversions
Respiratory therapists use several different pressure measurement scales. We have already discussed conversion from gauge to absolute pressure. It is also important to be able to convert from one scale to another, ie: cmH2O to torr or psig to cmH2O.

3. Pressure Conversions
One approach to converting from one pressure scale to another would be to memorize a conversion factor for each pressure scale. An easier approach is to remember the value for 1 atmosphere in each of the commonly used pressure scales.
Remember: 1 ATM = 15 psi = 760 torr = 1034 cmH2O

4. Pressure Conversion Then use the following equation to convert:
New Pressure= 1 ATM in new scale
x Given pressure Value
1 ATM given scale

5. Pressure Conversion Example: Convert 590 torr to cmH2O
New Pressure value= 1034 cmH2O x 590 torr
760 torr
Torr units cancel
New pressure value= 1.36 x 590 = 802 cmH2O
Remember: 1 ATM = 15 psi = 760 torr = 1034 cmH2O

6. Humidity and Aerosol
The body’s systems require a certain amount of hydration in order to maintain homeostasis. The best way is through drinking plenty of fluids and administration of IV fluids. Signs of dehydration are chapped lips, flaky skin, dry cracked elbows and heels. The respiratory signs include crusty nasal cavities, nosebleeds, dry mouth, scratchy throat and a dry hacking cough.

7. Humidity and Aerosol
Many of our patients have bypassed normal airway and an important part of our job is to provide for their special needs.
Under normal conditions, body water loss through respiration is approximately 200 – 500 mL / day. Respiratory therapists deliver oxygen that needs to humidified and often heated to adequately meet the needs of their patients.

8. Humidity and Aerosol
Vapor pressure – Pressure water as a vapor or gas exerts and is part of the total atmospheric pressure. Water vapor pressure in the lungs exert 47 mmHg
Absolute Humidity – the actual amount (in mg./l) of water vapor in the atmosphere
Relative Humidity – the percent of water vapor in the air as compared to the amount necessary to cause saturation at the same temperature.
% Body Humidity – the relative humidity at 37 degrees Celsius
Humidity Deficit – the amount of water vapor needed to achieve full saturation at body temperature (44 mg/l - A.H)

9. Vapor pressure
Vaporization: the change of matter from a liquid to a gaseous form
Water vapor pressure – the direct measure of the kinetic activity of water vapor molecules
Reducing the pressure above a liquid lowers its boiling point. Ex. water boiling in mountains

10. Water Vapor Pressure
When a gas is in contact with a liquid, and is in equilibrium (saturated) with the liquid, the partial pressure of the gas is a function of temperature. The one gas to which this applies in a normal respiration is water. The lungs and airways are always moist, and inspired gas is rapidly saturated with water vapor in the upper segments of the respiratory system. The temperature in the airways and lungs is almost identical with deep body temperature (approximately 37°C); at this temperature water vapor has a partial pressure of 47 mmHg. (Note that the gaseous form of a liquid frequently is termed a "vapor").
Using the value of 47 mmHg, we can calculate partial pressure of oxygen and nitrogen in inspired air, after the gas mixture becomes saturated with water vapor in the upper airway (so-called tracheal air):
Ptotal = 760 mmHg PH20   = 47 mmHg mmHg for remaining inspired gases (21% O2 and 79% N2)
PO2 = 0.21 · 713 = 150 mmHg PN2 = 0.79 · 713 = 563 mmHg

11. Water Vapor Pressure
That is, since water vapor partial pressure must be 47 mmHg in a saturated gas mixture at 37°C, the total pressure remaining for the inspired gases is only or 713 mmHg. The composition of this remaining gas is 21% O2 and 79% N2, giving the partial pressures indicated above which is then substrated by the partial pressure of PaCO2 (PACO2, is a product of the amount of CO2 diffused into the lung)
PAO2 = FIO2 (Pb-PH2O) – (PaCO2/0.8)

13. Humidification Both are essential in effective ventilation.
Absolute humidity: the actual content or water vapor present in a given volume of air
Relative humidity: the actual water vapor present in a gas compared with the capacity of that gas to hold the vapor at a given temperature
If the water vapor content of a volume of gas equals its capacity, the relative humidity of the gas equals 100%
Both are essential in effective ventilation.
Prevents drying of airway mucosa and irritation.
Various respiratory care devices are used to ensure adequate humidification of inspired gases.
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14. Humidity
The NOSE is the bodies natural humidifier and filter, when bypassed we must use a artificial humidifier

15. Humidity Terms
Vapor pressure – Pressure water as a vapor or gas exerts and is part of the total atmospheric pressure. Water vapor pressure in the lungs exert 47 mmHg
Absolute Humidity – the actual amount (in mg./l) of water vapor in the atmosphere
Relative Humidity – the percent of water vapor in the air as compared to the amount necessary to cause saturation at the same temperature.
% Body Humidity – the relative humidity at 37 degrees Celsius
Humidity Deficit – the amount of water vapor needed to achieve full saturation at body temperature (44 mg/l - A.H)
Isothermic Saturation Boundary – At or just below carina (end of trachea) The point at which inspired gases are fully 100% saturated and warmed to body temperature (44 mg/L at 37oC)

16. Humidity Uses of Humidity therapy Humidification of inspired gases
Thinning of bronchial secretions
Sputum induction
Solutions Used
Sterile water used in humidifiers and continuous nebulizers (Hypotonic)
(Normal) Isotonic saline (.9% Na) with (Aerosol / Medicine) Treatments
Hypertonic saline (10%) (for sputum induction)

17. Example
A gas is flowing thru a ventilator circuit at 50 C with a relative humidity of 100%. As it flows thru the tubing it is cooled to 37 C by the surrounding ambient temperature of the room.
What effects will occur within the tubing? What will occur to the ambient temperature of the air surrounding the tubing?
Condensation will occur on the inside surface of the tubing as the water vapor reaches its dew point
There will be visible droplet formation when dew point is reached
There will be warming of the adjacent air due to convection

18. Humidity and Aerosol Solutions Used
Sterile water used in humidifiers and continuous nebulizers (Hypotonic)
(Normal) Isotonic saline (.9% Na) with (Aerosol / Medicine) Treatments
Hypertonic saline (10%) (for sputum induction)

19. Consequences of Inadequate Humidification
Inspissated secretions
Damage to tracheal epithelium
Decrease in ciliary activity
Retention of secretions

20. Consequences of Inadequate Humidification
Hypothermia
Infection
Blockage of airway
Atelectasis

21. Indications For Humidification
Provide humidity for dry gases
Correct humidity deficit in intubated or tracheostomized patients
Treatment of hypothermia
Correct bronchospasm induced by inspiration of cold air

22. Factors Affecting Efficiency of Humidifiers
Temperature
Surface area of fluid exposed to water
Time of contact with water

23. Basic Concepts As gas travels through the lungs it achieves BTPS:
Body temp ~ 37C
Barometric pressure
Saturation with water vapor (100% relative 37C)

24. Basic Concepts
The point at which this occurs is called the isothermic saturation boundary (ISB)
Usually occurs ~ 5 cm below the carina
If the upper airway is bypassed or VE is significantly higher than norm,
The ISB will be deeper into the lungs and HUMIDITY therapy may be indicated

25. Basic Physical Principles of Humidity
Humidity is essentially the water vapor in a gas.
This water vapor can be described in several ways, as:
1. Absolute humidity - The actual content of water vapor in a gas measured in milligrams per liter.
2. Potential humidity - The maximum amount of water vapor that a gas can hold at a given temperature.
3. Relative humidity - The amount of water vapor in a gas as compared to the maximum amount possible, expressed as a percentage
4. Body humidity - The absolute humidity in a volume of gas saturated at body temperature of 37 C; equivalent to 43.8 mg/L

26. Formulas Used When Calculating Humidity
%RH=(absolute humidity/saturated capacity) x 100
%BH = (absolute humidity/43.8mg/L) x 100

27. Primary Humidity Deficit
If the atmosphere's relative humidity is less than 100%, the air of the atmosphere has what is referred to as a humidity deficit.
If outside air at 20°C has 14 mg/l of water vapor, and needs to have mg/l to be fully saturated, it is said to have a primary humidity deficit of 3.3 mg/l.
17.3 mg/L (potential) – 14 mg/L (absolute) = 3.3 mg/L (primary deficit)
Remember that the potential is based temp
The primary humidity deficit occurs in the atmosphere and represents the difference between what humidity there is and what there could be.
Primary Humidity Deficit = Potential Water Vapor Content - Actual Water Vapor Content

28. Secondary Humidity Deficit
This is the moisture deficit in the inspired air that the nose and upper airway need to compensate for.
The amount of water vapor the body needs to add to inspired air to achieve saturation at body temperature.
When air is breathed into the nasal cavity and heated to body temperature, its potential water vapor rises to 44 mg/l, which is the potential water vapor content of air at 37°C.
Therefore, unless the air of the atmosphere is at least 37°C and fully saturated, there exists a moisture deficit.
Secondary Humidity Deficit = 44 mg/l - Absolute Humidity.

29. Water Losses Insensible: skin and lungs
Sensible: urine, GI tract, sweat
Additive: vomiting, diarrhea, suction from intestines, severe burns, and fever
For each degree of temperature above 99F for over 24 hours, 1000m of fluid is required for replacement

30. Water Vapor Correction
Water vapor acts in most ways like any other gas, it creates a partial pressure when it’s in a mixture of gases.
That partial pressure depends
The amount of water vapor present
Which in turn depends on the temperature.
Unlike other gases in the air, changes in the barometric pressure of the atmosphere under normal conditions do not have much impact on the partial pressure of water.

31. Water Vapor Correction
As a result, it is best to calculate the partial pressures of the other gases in the air after the partial pressure of water vapor has been determined--especially when measuring the air within the lungs.
Inside the lungs, the partial pressure of water vapor is approximately 47 mm Hg.
This value is relatively constant because the air entering the lungs is normally saturated and at 37°C.
By subtracting the partial pressure of the water vapor from the total atmospheric pressure, you will find what is referred to as the dry gas pressure

32. Importance of Humidity
It is needed to maintain normal bronchial hygiene
It promotes functions of the normal mucociliary escalator
It maintains the body's vital homeostasis
Without humidity:
the nearly 100 ml of mucus secreted daily would become quite thick and tenacious.
actual lung parenchyma would dry up, causing a loss of normal compliance which would restrict lung movement and reduce ventilation.

33. Importance of Humidity
If the upper airway were bypassed or dry gases were inhaled, a series of adverse reactions could occur, including:
Slowing of mucus movement
Inflammatory changes and possible necrosis of pulmonary epithelium
Retention of thick secretions and encrustation
Bacterial infiltration of mucosa (bronchitis)
Atelectasis
Pneumonia
Impairment of ciliary activity

34. Importance of Humidity

35. Clinical Evaluation of the Need for Humidity and/or Aerosol Use
Patient's age and ability to move normal secretions
Neuromuscular status
Recent or planned surgeries
Trauma
Disease conditions
The presence of any of these may impair the patient's ability to cough and move secretions.
Another problem may occur when patients develop very thick and abundant amounts of secretions which cannot be moved with normal muscle activity-- making humidity or aerosol therapy necessary.

36. Indications for delivery of humidified gases and aerosols
Primary indications for humidifying inspired gases include:
Administration of medical gases
Delivery of gas to the bypassed upper airway
Thick secretions in nonintubated patients

37. Indications for delivery of humidified gases and aerosols
Additional indications for warming inspired gases:
Hypothermia
Reactive airway response to cold inspired gas

38. Sign/Symptoms of Inadequate Airway Humidification
Atelectasis
Dry, nonproductive cough
Increased airway resistance
Increased in incidence of infection
Increased work of breathing
Substernal pain
Thick, dehydrated secretions

39. Humidification Devices
The purpose of humidifiers is to deliver a gas with a maximum amount of water vapor content.
May be heated or unheated, and the factors affecting the efficiency of humidification devices include:
temperature
time of exposure between gas and water
surface area involved in the gas/water contact

40. Humidification Devices
As temperature rises, the force exerted by the water molecules increases, enabling their escape into the gas, adding to the humidity.
So the higher the tempthe more humidity
Longer exposure of a gas to the water increases the opportunity for the water molecules to evaporate during the humidifier's operation.
The greater the area of contact between water and gas, the more opportunity for evaporation to occur.

41. Aerosol Therapy
Basic Concepts

42. Aerosol Therapy
It is important to remember that an aerosol is not the same as humidity.
Humidity is water in a gas in molecular form, while an aerosol is liquid or solid particles suspended in a gas.
Examples of aerosol particles can be seen everywhere: as pollen, spores, dust, smoke, smog, fog, mists, and viruses.

43. Aerosol Therapy
Aerosol therapy is designed to increase the water content delivered while delivering drugs to the pulmonary tree
Deposition location is of vital concern
Some factors that affect aerosol deposition are aerosol particle size and particle number.

44. Aerosol Output
The actual weight or mass of aerosol that is produced by nebulization.
Usually measured as mg/L/min also called aerosol density
Aerosol output does not predict aerosol delivery to desired site of action.

45. Particle Size

46. Particle Size Heterodisperse:
aerosol with a wide range of particle sizes (medical aerosols)
Monodisperse:
aerosol consisting of particles similar in size (laboratory, industry)

47. Deposition
The aerosol particles are retained in the mucosa of the respiratory tract. They get stuck!
The site of deposition depends on size, shape, motion and physical characteristics of the AIRWAYS

48. Mechanism resulting in Deposition: Inertial Impaction
Moving particles collide with airway surface.
Large particles (>5micros), upper and large airways
Physics: the larger the particle, the more likely it will remain moving in a straight line even when the direction of flow changes.
Physics: greater velocity and turbulence results in greater tendency for deposition

49. Mechanism resulting in Deposition

50. Mechanism resulting in Deposition: Sedimentation
Particles settle out of aerosol suspension due to gravity.
The bigger it is the faster it settles!
Medium particles: 1-5 microns, central airways
Directly proportional to time.
The longer you hold your breath the greater the sedimentation

51. Mechanism resulting in Deposition: Diffusion
Actual diffusion particles via the alveolar-capillary membrane and to a lesser extent tissue-capillary membranes of respiratory tract
Lower airways: 2-5 microns
Alveoli: 1-3 microns
These values are from your book

52. Deposition of Particles is also affected by:
Gravity –
Gravity affects large particles more than small particles, causing them to rain-out.
Viscosity - The viscosity of the carrier gas plays an important role in deposition.
For example, if a gas like helium, which has a low viscosity and molecular weight, is used as a carrier gas, gravity will have more of an effect upon the aerosol.
Helium is very light and hence can't carry these particles well, leading to rain-out and early deposition.

53. Deposition of Particles is also affected by:
Kinetic activity - As aerosolized particles become smaller, they begin to exhibit the properties of a gas, including the phenomenon of "Brownian movement."
This random movement of these small (below lmm) particles causes them to collide with each other and the surfaces of the surrounding structures, causing their deposition.
As particle size drops below 0.1m, they become more stable with less deposition and are exhaled.

54. Deposition of Particles is also affected by:
Particle inertia (repeated) - Affects larger particles which are less likely to follow a course or pattern of flow that is not in a straight line.
As the tracheobronchial tree bifurcates, the course of gas flow is constantly changing, causing deposition of these large particles at the bifurcation.

55. Deposition of Particles is also affected by:
Composition or nature of the aerosol particles - Some particles absorb water, become large and rain- out, while others evaporate, become smaller and are conducted further into the respiratory tree.
Hypertonic solutions absorb water from the respiratory tract, become larger and rain-out sooner.
Hypotonic solutions tends to lose water through evaporation and are carried deeper into the respiratory tract for deposition.
Isotonic solutions (0.9% NaCl) will remain fairly stable in size until they are deposited.

56. Deposition of Particles is also affected by:
Heating and humidifying - As aerosols enter a warm humidified gas stream, the particle size of these aerosols will increase due to the cooling of the gas in transit to the patient.
This occurs because of the warm humidified gas cooling and depositing liquid (humidity) upon the aerosol particles through condensation.

57. Deposition of Particles is also affected by:
Ventilatory pattern - RCPs easily control this by simple observation and instruction.
For maximum deposition, the patient must be instructed to:
Take a slow, deep breath.
Inhale through an open mouth (not through the nose).
At the end of inspiration, use an inspiratory pause, if possible, to provide maximum deposition.
Follow with a slow, complete exhalation through the mouth.

58. Aerosol vs. Systemic
In many cases, aerosols are superior in terms of efficacy and safety to the same systemically administered drugs used to treat pulmonary disorders.
Aerosols deliver a high concentration of the drugs with a minimum of systemic side effects.
As a result, aerosol drug delivery has a high therapeutic index; especially since they can be delivered using small, large volume, and metered dose nebulizers.

59. Aerosol delivery is accomplished in a variety of ways:

60. Formula Review PAO2 (page 55) FIO2(PB-PH2O) – PaCO2/0.8
This formula represents the amount of partial pressure of Oxygen that is in a patients lung
Normal value is approximately 100 given normal conditions
FIO2 is the inspired fractional oxygen concentration. When breathing room air this is 21%

62. Formula Review PAO2 (page 55) FIO2(PB-PH2O) – PaCO2/0.8
PB is the atmospheric pressure, at sea level this is 760 mmhg
PH2O is the water vapor pressure in the lung. Under normal conditions this is 47 mmHg
PaCO2 is the partial pressure of CO2 in a patients arterial blood. Obtained through a blood draw from the artery
0.8 is a factor which represents the amount of O2 vs Co2 is produced by the body

63. Formula Review Normal values will vary as a patient is:
PAO2 (page 55)
FIO2(PB-PH2O) – PaCO2/0.8
Normal values will vary as a patient is:
On supplemental FIO2 greater than 21%
In environment where the atmospheric pressure is higher or lower
In a state where they are inhaling dry air
Have an increase in their PaCo2

64. Formula Review http://www.youtube.com/watch?v=zZX9jJqSlQs

65. Formula Review CaO2 (Total Oxygen Content)
This formula is used to determine the amount of oxygen that is available to the tissues
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x 0.003)
Hb= Hemoglobin (carries O2)
1.34 (sometimes 1.36 is used) carrying capacity of Hb for O2 is 1.34ml O2 / Gram Hb
SaO2= Saturation of Hb with Oxygen, obtained from a ABG. HBO2/Total Hb

66. Formula Review CaO2 (Total Oxygen Content)
(Hb x 1.34 x SaO2) = the amount of O2 binded with Hb
(PaO2 x 0.003)= amount of O2 dissolved in plasma
PaO2 = partial pressure of Oxygen found in arterial blood, obtained with a ABG
Normal values: (14 x 1.34 x .97) + (90 x 0.003)

67. O2 Content

68. Formula Review
DO2
The delivery of oxygen to the tissues per minute is calculated from: DO2 = [1.39 x Hb x SaO2 + (0.003 x PaO2)] x Q
Q = Cardiac Output

69. Formula Review
The amount of oxygen in the blood: the oxygen binding capacity of hemoglobin x the concentration of hemoglobin x the saturation of hemoglobin + the amount of dissolved oxygen all Multiplied by the Cardiac Output (Q).
The cardiac output is determined by preload, afterload and contractility.
The hemoglobin concentration  is determined by production, destruction and loss.

70. Formula Review
CvO2
The amount of O2 in the venous blood (left over after cellular metabolism)
CvO2 used to estimate Oxygen consumption when compared to CaO2
CvO2 = (Hb x 1.34 x SVO2) + (PvO2 x 0.003)
Oxygen Consumption (VO2)= C(a-v)QT
*QT= Cardiac Output