RSPT 1060

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RSPT 1060

• MODULE C
• Lesson 5
• GAS MOVEMENT

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Objectives

• At the end of this module, the student will
• Define terms associated with gas movement.
• Differentiate between flow, speed and velocity.
• Describe how flow is measured.
• Describe how velocity is measured.
• Differentiate between the types of flow.
• State how Poiseuilles law is used to define the
  amount of pressure needed to move a fluid through
  a tube.

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Objectives

• At the end of this module, the student will
• State the Reynolds number where a transition
  from laminar to turbulent flow occurs.
• Describe the effects of gas velocity, gas
  density, tube radius, and viscosity on Reynolds
  number.
• Differentiate between a low-flow oxygen delivery
  system and a high-flow oxygen delivery system.
• Differentiate between
• Jet mixing
• Bernoulli principle.
• Venturi principle

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Objectives

• At the end of this module, the student will
• State the effect on an increase in minute volume
  on oxygen delivery percentage with a high-flow
  oxygen delivery system.
• Given an FIO2, determine the air oxygen ratio.
• Given an FIO2 and an oxygen flow rate, determine
  the total flow.
• Given an FIO2, an oxygen flow rate, and a
  patients minute volume, determines if the total
  flow is adequate.

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Terms Associated with A Fluid In Motion

• FLUID A substance that is capable of flowing
  and that changes its shape at a steady rate when
  acted upon by a force tending to change its shape
  and to assume the shape of its container.
  Includes both liquids and gases.
• FLOW The bulk movement of a substance through
  space.
• Expressed as volume of fluid moved per unit of
  time.
• Liters per minute (L/min)
• Liters per second (L/sec)

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Terms Associated with A Fluid In Motion

• SPEED The distance traveled per unit of time.
• A scalar measurement.
• Miles per hour or centimeters per second.
• VELOCITY The rate at which an object changes
  position.
• A vector quantity.
• Involves not only magnitude but also direction.
• Miles per hour or centimeters per second in a
  specified direction.

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Flow
minute

• Volume/Time
• Force Occurs as a result of a pressure gradient
  from high energy to low energy.
• The pressure difference (gradient) that exists is
  also known as the driving pressure.
• Measurement tool
• Flow meter

5L
5L
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Velocity
distance

• Distance per unit time with a direction.
  (vector quantity)
• Force Occurs as a result of a pressure gradient
  from high energy to low energy.
• Measurement tool
• Ruler watch and some mechanism to quantify
  direction.

start
finish
minute
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Velocity and Flow

• Since gas flow in and out of the lungs is
  directional, velocity can be assessed.
• Gas flow (volume/time) can also be expressed as
  the velocity of the gas as it relates to the
  cross-sectional area it is moving through.
• Flow Cross-sectional area x velocity

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Law of Continuity

• The velocity of a fluid moving through a tube
  varies inversely with the cross-sectional area.
• As the cross-sectional area decreases, the
  velocity increases to maintain a constant flow.
• Example A hose that is pinched results in an
  increased velocity to maintain a constant flow.
• This follows the conservation of mass in that the
  amount of a fluid entering a tube must be the
  same as the amount leaving the tube.
• This principle is used in jet and nozzles and
  clinically in nebulizers and gas entrainment
  devices.

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• If you have a tube with a cross-sectional area of
  5.08 cm2, and a gas moving at a velocity of 16.4
  cm/sec, the measured flow will be 5 L/min.

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Additional Terms Associated With A Fluid In Motion

• VISCOSITY The property of a fluid that resists
  the force tending to cause the fluid to flow.
• This can be due to thickness of the fluid or some
  other cause of adhesiveness between the fluid and
  the container.
• Water vs. Ketchup
• FRICTION Surface resistance to relative motion
  caused by the rubbing of one object or surface
  against another.
• DENSITY Mass per unit of volume (mg/L)

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Pressure and Flow of A Fluid

• The pressure exerted by a static fluid is the
  same at all points along a horizontal tube.
• When flow occurs, the pressure drops as a tube
  becomes further from the source of the pressure.
• Gas flow in a plumbing system.

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No Flow
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Flow
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Types of flow

• A. Laminar
• B. Turbulent
• C. Transitional

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Laminar Flow

• Smooth movement in a parabolic pattern through a
  smooth tube of fixed size.
• Poiseuilles Law defines the pressure required to
  produce a flow under these conditions
• Flow pattern found in distal airways.

Velocity is greater at the center than along the
walls due to friction.
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Poiseuilles Law

• P Driving pressure (to move gas through a tube)
• fluid viscosity (n)
• tube length (l)
• flow (?)
• radius (r)

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Poiseuilles Law

• Consider an endotracheal tube
• If I need the same gas flow, what must happen to
  pressure (P) if I
• Increased length (l) needs ___________ pressure
• Decreased radius (r) needs ___________ pressure
• Decrease gas viscosity (n) needs ___________
  pressure
• If I increase the gas flow (?), what must happen
  to pressure (P)? ___________

A. 5 L/min.
B. 5 L/min.
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Turbulent Flow

• Molecules moving in many directions.
• Multiple eddy currents.
• Requires a greater driving pressure.
• Poiseuilles Law no longer applies.
• Flow pattern found in larger airways.
• Laminar flow become turbulent at a Reynolds
  Number gt2000.
• Dimensionless number

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Reynolds Number

• v linear velocity (distance/time)
• d fluid density (weight/volume)
• r tube radius (size of opening)
• h fluid viscosity (thickness, stickiness)

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Reynolds Number
What would allow gas to move freely in many
directions? (more turbulent)

• v linear velocity _____
• d fluid density ________
• r tube radius ________
• h fluid viscosity _______

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Transitional Flow

• A mixture of laminar and turbulent.
• Similar to what is happening in the majority of
  the respiratory tract.

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Fig 6-21
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Oxygen Therapy
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Oxygen Equipment

• If the alveolar oxygen is low (?PAO2), the
  arterial oxygen (PaO2) will also be reduced.
• The goal is to increase the alveolar oxygen level
  (PAO2)by providing supplemental oxygen to the
  patient.
• Four Categories of Oxygen Delivery Equipment
• Low Flow
• Reservoirs
• Enclosures
• High Flow

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Estimating Patient Flow Needs

• One of two methods can be used to determine the
  patients inspiratory flow rate and therefore the
  minimum flow needed by the device.
• OR

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Example Patient Flow Needs

• Minute Ventilation 8 L/min
• Tidal Volume 0.4 L
• Respiratory Rate 20 bpm
• Insp. Time 1 sec

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Low Flow Oxygen Delivery Systems

• Devices
• Nasal Cannula
• Nasal Catheter
• Transtracheal Catheter (SCOOP)

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Low Flow Systems and Inspiratory Flow

• Device does not meet patient entire inspiratory
  flow needs.
• Patients needs to draw in additional gas.
• HAS NOTHING TO DO WITH THE FLOWMETER SETTING!
• Provides low oxygen concentrations (22-45).
• Some people include Reservoir Systems in this
  category as well.
• Simple masks, Partial rebreathers,
  Non-rebreathers, Reservoir cannulas

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Flow Needs

• Adults typically have an inspiratory flow of 24 -
  30 L/min.
• Low flow devices provide ¼ 8 L/min. of 100 O2.
• Flow difference must come from room air (21) or
  reservoir (gt21).

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Oxygen Concentration

• Low flow devices have air oxygen mixing at the
  patients airway.
• O2 concentration is variable and depends on the
  patients respiratory pattern.
• A higher O2 concentration is achieved when
  breathing is at a slower rate and a slow flow.
• Less room air is brought into the system.
• A lower O2 concentration is achieved when
  breathing is at a higher rate rapid flow.

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Oxygen Delivery Devices

• High-Flow Systems

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FIO2 vs. FDO2

• The D stands for delivered.
• Technically speaking, oxygen devices deliver a
  specific amount of oxygen.
• What is actually inspired is related to how
  much air is entrained and dilutes the oxygen
  flow.
• Likewho cares?

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High Flow Oxygen Delivery Systems

• Devices
• Air-entrainment mask (venturi)
• Air-entrainment nebulizer
• Aerosol Mask
• Tracheostomy Collar
• T-Bar
• Face Tent
• Blender
• Dual Flowmeters

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Air Entrainment Nebulizer

• Oxygen source
• Flow meter
• Nebulizer with sterile water
• Large bore tubing
• Drain bag
• Patient interface
• Aerosol mask
• Trach collar
• Face tent
• T-bar)

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Fluid Entrainment

• Air entrainment masks nebulizers use a method
  of fluid mixing known as fluid entrainment.
• First fluid flow determines the amount of a
  second fluid that will be drawn into the first
  fluid flow.

100 O2
21Air
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Methods of Fluid Entrainment

• Jet mixing principle
• Air entrainment mask
• Bernoulli principle
• Air entrainment nebulizers
• Both principles for fluid entrainment use the
  concept of
• Decreasing cross sectional area
• Increasing velocity of gas

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Law of Continuity
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Jet Mixing Principle

• The net effect is an increase in total flow.
• This can result in a very precise amount of
  oxygen and air mixing.

Fig 38-13 Page 882
Source Gas (Oxygen)
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Factors Affecting Air Entrainment

• The amount of air that is entrained is dependent
  on two factors
• Size of the jet orifice
• Size of the entrainment ports
• Air-entrainment masks work by altering one of
  these factors.

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Jet Orifice Size

• Smaller jet opening causes increased velocity of
  main gas causing more entrainment of air.
• FIO2 decreases
• Total gas flow increases

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Size of Entrainment Ports

• Larger ports allow more air to be entrained
• FIO2 decreases
• Total flow increases

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AirOxygen Mixing
Set O2 AirO2 ratio Liters of air mixing with 1 liter of 100 O2 Total flow
100 01 1
80 0.31 1.3
70 0.61 1.6
60 11 2
50 1.71 2.7
40 31 4
35 51 6
30 81 9
21 251 26
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Altering FIO2

• Oxygen flow remains constant and is set by RCP
  with a flow meter.
• Air flow changes based on
• Jet size
• Port size
• More air dilutes oxygen flow and decreases FIO2.

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What will happen to FIO2 when

• I decrease the size of the jet? ____________
• I increase the size of the jets? ___________
• I decrease the size of the ports? __________
• I increase the size of the ports? ___________
• I decrease the oxygen flow? _____________
• I increase the oxygen flow? ______________
• I pinch the aerosol hose? _______________
• (Back pressure against air entrainment)

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Bernoulli Effect

• Fluids have three types of energy
• Potential Energy (the driving pressure)
• Kinetic Energy (the energy created by a mass of
  fluid moving at a specific velocity)
• Because the mass is never changing, it is
  directly proportional to the velocity of the
  fluid.
• Pressure Energy (the energy exerted on the walls
  of the tube)
• This radial pressure is also known as lateral
  wall pressure.

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Bernoulli Effect
1700 1782

• As fluid flows through a tube, the pressure
  within the tube decreases over the length.

1700 27 July 1782
1700 27 July 1782
1700 27 July 1782
Fig 6-24 Page 115
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Bernoulli Effect

• Fluid velocity increases as the fluid travels
  through a constriction.

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Bernoulli Effect

• According to the First Law of Thermodynamics,
  energy cannot be lost.
• If the forward velocity is increasing (kinetic
  energy goes up), and potential energy is
  unchanged (the tube is level), the pressure
  energy (lateral wall pressure ) would have to be
  decreasing.
• The smaller the constriction, the higher the
  velocity and lower the lateral wall pressure.

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Bernoulli Effect
Velocity increases, Lateral wall pressure
decreases.
Fig 6-25 Page 115
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Venturi Principle
1746 - 1822

• If gas flowing through a tube meets a small
  enough constriction, the pressure will drop to
  sub atmospheric and actually entrain a second gas
  (fluid).

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10
-5
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Venturi Masks

• Venturi masks dont work on the Venturi
  principle they work on jet mixing.

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Nebulizer Function

• 1. Based on Bernoulli Venturi principles
• Main gas flow (usually oxygen)
• Entrains liquid to create aerosol particles
• 2. Based on jet mixing principle
• Main gas flow (usually oxygen)
• Entrains air which lowers the FIO2

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AirOxygen Mixing
Set O2 AirO2 ratio Liters of air mixing with 1 liter of 100 O2 Total flow
100 01 1
80 0.31 1.3
70 0.61 1.6
60 11 2
50 1.71 2.7
40 31 4
35 51 6
30 81 9
21 251 26
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AirO2 Ratio example

• 40 O2 has an AirO2 ratio of 31
• Oxygen flow 1L/min Air entrained 3 Liters/min
• Total flow 4 L/min
• O2 flow meter 10 L/min Air entrained 30 L/min
• Total flow 40 L/min

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Calculating the AirO2 Ratio

• FIO2 of 35
• AirO2 ratio 4.61 or approximately 51

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Calculating the AirO2 Ratio

• The Magic Box

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Calculating Device Flow

• What is the airO2 ratio for an air entrainment
  mask at FIO2 40?
• Ratio for 40 is 31
• If the O2 Flowmeter is set at 8 L/min
• Then the entrained air will be 8x3 24 L/min
• Total flow (air O2) (8 24) 32 L/min

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Practice

• Sibbersons Practical Math For RC
• Ch 4 Device Flow Rate, Sample Problems Third
  Set, pgs. 49-53.
• Practice problems, pgs 54-55

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Is the Device Flow Adequate?

• Can the device be classified as a high flow
  system?
• Will it meet or exceed the patients inspiratory
  flow?
• Will the FIO2 be stable?
• Will the patient pull in room air and lower the
  FIO2?

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Peak Inspiratory Flow

• Peak Inspiratory flow (PIF)
• The fastest speed at which the patient draws gas
  into the respiratory tract during inspiration.
• Normal adult PIF is 24 30 L/min.
• Can be as high as 60 100 L/min.
• Device flow must meet or exceed PIF to be
  considered a high flow device.

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Estimating Patient Flow Needs

• One of two methods can be used to determine the
  patients inspiratory flow rate and therefore the
  minimum flow needed by the device.
• OR

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Which calculation to use?

• Choose your calculation based on the information
  given.
• Example
• Given information is Vt .5L (500 mL) and rate 12
• Which formula ___________________________
• Example
• Given information is Vt .5L and tI is 0.9 sec
• Which formula? __________________________

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Example Patient Flow Needs

• Minute Ventilation 8 L/min
• Tidal Volume 0.4 L
• Respiratory Rate 20 bpm
• Insp. Time 1 sec

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Is the device flow adequate?

• Device flow was 32 L/min
• Patient needs 24 L/min
• Device gt patient set FIO2 delivered
• FDO2 FIO2
• Device flow lt patient flow lower FIO2 then set
  delivered
• FDO2 ? FIO2

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Example
Air entrained
O2 Flowmeter
Device flow
Aerosol tubing
(O2 mist)
H20 entrained
Drain bag
Mask
Nebulizer
Device flow should meet or exceed inspiratory flow
Inspiratory flow
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Will patient receive set FIO2?

• Patient flow
• Tidal volume .5L
• Rate (f) 20
• Insp. time 1 sec.
• IE 12
• Min.Vent. Vt x f __
• Patient insp. Flow ____

• Device flow
• FIO2 60
• O2 flow 8 L
• AirO2 ratio ______
• Total flow _______

Will patient receive set FIO2? NO.
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Gas Mixing Using Two Flowmeters

• Sometimes is may be necessary to blend oxygen and
  air together to obtain a desirable FDO2.
• The formula is

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Gas Mixing Using Two Flowmeters

• Example If an air flowmeter is set at 6 L/min
  and the oxygen flowmeter is set at 2 L/min,
  calculate the FDO2.

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Practice

• Sibbersons Practical Math For RC
• Ch4 Inspiratory Flow Rates, Sample Problems
  First Second Set, pgs. 47-49.
• Practice problems, pgs 53-54
• Ch 12 IE Ratio, Sample Problems Eighth Set,
  pgs 146-147
• Practice Problems, pg. 156

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Device flow vs. Patient flow

• Sibbersons Practical Math For RC
• Ch4 Patient Device Flow Comparison, Sample
  Problems Fourth Set, pgs. 51 - 52.
• Practice problems, pgs 55 - 57

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ASSIGNMENTS

• Egan - Reading Assignments
• Ch 6 Fluid Dynamics, pgs. 112-117
• Ch 38 Oxygen Delivery, pgs. 872-88
• Ch 34 Mini Clinis, pgs. 882, 885, 887 888
• 7

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ASSIGNMENTS

• Sibbersons Practical Math For RC
• Ch4 Inspiratory Flow Rates, Sample Problems
  First Second Set, pgs. 47-49.
• Practice problems, pgs 53-54
• Ch 12 IE Ratio, Read Only pgs. 146-151

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ASSIGNMENTS

• Sibbersons Practical Math For RC
• Ch 4 Device Flow Rate, Sample Problems Third
  Set, pgs. 49-53.
• Practice problems, pgs 54-55
• Ch 4 Device Flow vs. Patient Flow, Sample
  Problems Fourth Set, pgs. 51-52.
• Practice problems, pgs 55-57