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70 Cards in this Set
- Front
- Back
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Measuring Atmospheric Pressure
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1.Atmospheric pressure is measured with a barometer
2.Height of the mercury in the column represents the downward force of atmospheric pressure. 3.Torr is used also in measuring pressure. 4.1mm Hg = 1 torr 5.Sea Level average atmospheric pressure is 760mm Hg |
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Clinical Pressure Measurements
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Aneroid barometer are common in homes
-Consists of a box with a flexible, spring-supported top that responds to external pressure changes. Activates a geared pointer, which gives a reading -EX: Used to measure blood or airway pressure at bedside -Strain-gauge pressure transducers measures electronically -pressure change will expand or contract a diaphragm connected to electrical wires and the change of electricity measures electrical flow |
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Properties of Gases
Partial pressure |
the pressure exerted by a single gas in a gas mixture
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Properties of Gases
Dalton’s law |
the partial pressure of a gas in a mixture is proportional to its percentage in the mixture
Ex: a gas making up 25% of a mixture would exert 25% of the total pressure or 0.25 fractional concentration |
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Properties of Gases
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- Air consists of approx 21% oxygen and 79% Nitrogen
- To get the partial pressure of each gas, multiply its fractional component by the total pressure (assuming the normal atomospheric pressure of 760 torr) - PO2=0.21x760=160 torr - PN2=0.79x760=600 torr - 600+160= 760torr |
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Properties of Gases
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- In contrast, high atmospheric pressures increase the PIO2 in an air mixture
- Pressures above atmospheric are called hyperbaric pressures- commonly occur only in underwater and in special hyperbaric chambers - Ex: Depth of 66ft under sea, water exerts a pressure of 3atm, or 2280mmHg (3x760) - 3 times the PO2 at sea level! |
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Solubility of Gases in Liquids
(Henry’s law) |
- The volume of gas dissolved in a liquid is a function of its solubility coefficient and its partial pressure
- High temperature decreases solubility and low temperatures increase solubility - Ex: open can of soda may still fizz if left in the refrigerator but quickly goes flat when left out at room temperature - *Temperature changes kinetic energy. As a liquid is warmed energy is increased. This increases the escape of molecules and pressure. |
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Gas laws
Boyle’s law |
the volume of gas varies inversely with its pressure
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Gas laws
Charles’ law |
the volume of gas varies directly with its temperature
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Gas laws
Gay-Lussac’s law |
the pressure exerted by a gas varies directly with its absolute temperature
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Gas laws
Combined gas law |
interaction of the gas laws mentioned above
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Critical Temperature and Pressure
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- For every liquid, there is a temperature abouve which the kinetic activity of its molecules is so great that the attractive forces cannot keep them in a liquid state – critical temperature
- It is the highest temperature at which a substance can exist as a liquid - The pressure needed to maintain equilibrium between liquid and gas phases of a subatance at this critical temperature is the critical pressure |
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Liquid Oxygen
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- Is produced by seperating it from liquified air mixture at a temperature below its boiling point
- After Oxygen is seperated from air, the liquid must be sotred in containers below boiling pt. |
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Fluid Dynamics
hydrodynamics. |
The study of fluids in motion
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Fluid Dynamics
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- The pressure exerted by a liquid in motion depends on the nature of the flow itself.
- A progressive decrease in fluid pressure occurs as the fluid flows through a tube due to resistance. |
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Fluid Dynamics
Laminar flow |
fluid moving in discrete cylindrical layers or streamlines
- Poiseuille’s law – predicts pressure required to produce a given flow - *Fluids flwoing in a laminar pattern, the driving pressure will increase whenever the fluid viscosity, tube length, or flow increases. - Also, greater pressure will be required to maintain a given flow if the tube radius decreases |
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Fluid Dynamics
Turbulent flow |
loss of regular streamlines; fluid molecules form irregular eddy currents in a chaotic pattern (not laminar!)
Change from Laminar to turbulent is caused by -Fluid density (d) -Increased -Viscosity (v)-Increased/decreased -Tube radius ®- Increased -In combination theses factors determine Reynold’s number |
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Fluid Dynamics
Transitional Flow |
-A mixture of laminar and turbulent flow
-Flow in the respiratory tract is mainly transitional in nature -The pressure is determined by the pressure generated by laminar and turbulent flow -Laminar mostly affected by fluid viscosity, as where -Turbulent, fliud density is the key factor |
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Cross-Sectional Area
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-Velocity of a fluid moving through a tube at a constant flow varies inversely with the available cross-sectional area- Law of continuity
-Application of nozzles or jets in fluid streams, are simply narrow passages n a tube design to increase fluid viscosity. -Ex: garden hose nozzle -In respiratory jets are used in equipment, including pneumatic neublizers and gas entrainment or mixing devices |
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Fluid Dynamics
The Bernoulli effect |
-Fluid passing through a tube, that meets a constriction, experiences a significant pressure drop.
-Fluid that flows through the constriction increases its velocity while the lateral wall pressure decreases. |
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Fluid Dynamics
Fluid entrainment |
-The velocity of a fluid (gas) can increase greatly at the point of a constriction.
-This can cause the lateral pressure to fall below atmospheric pressure. -If an open tube is placed distal to the constriction, another fluid can be pulled into the primary flow stream (fluid entrainment). |
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Fluid Dynamics
Air Injector |
device designed to increase the total flow in a gas stream.
-A pressurized gas, Oxygen, is the primary flow source -This gas passes through a nozzle, beyond which is an air entrainment port. The negative lateral pressure created at the jet orifice entrains air into the gas stream. -Thereby, increases total output of the system |
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Fluid Dynamics
Air Injector |
-*The entrained air depends on the diameter of the jet orifice and size of the entrainment ports
-*The larger the entrainment ports, the greater is the volume of air entrained and higher is the total output flow -*The larger the jet results in a lower gas velocity and less entrainment -*So a small jet will boost the velocity, entrained volume and total flow |
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Fluid Dynamics
The Venturi and Pitot tubes |
-A Venturi tube is a modified entrainment device.
-It widens just after its jet or nozzle. -This helps restore fluid pressure back toward prejet levels. -Provides greater entrainment than the air injector -Help keep the % of entrained fluid constant, even when the total flow varies. -However, any buildup of pressure downstream from the entrainment port decreases fluid entrainment -A Pitot tube (modified Venturi Tube) lessens the effect of downstream pressure on fluid entrainment |
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Fluid Dynamics
Fluidics and the Coanda effect |
-Fluidics is a branch of engineering that applies hydrodynamics principles in flow circuits.
-(Fluidic devices have no moving parts, they are very dependable) -The Coanda effect (wall attachment) is observed when fluid flows through a small orifice with properly contoured downstream surfaces. |
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States of Matter
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Solids – have a high degree of internal order; their atoms have a strong mutual attractive force
Liquids – atoms exhibit less degree of mutual attraction compared with solids Gases – weak molecular attractive forces; gas molecules exhibit rapid, random motion with frequent collisions |
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States of Matter (cont.)
Internal energy of matter |
Potential Energy - energy of position
Kinetic Energy - energy of motion |
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States of Matter (cont.)
Internal energy and temperature |
The two are closely related
Absolute zero = no kinetic energy Temperature scales Kelvin Celsius |
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States of Matter (cont.)
Heat and the First Law of Thermodynamics |
Energy can be neither created nor destroyed.
Energy gain by a substance = energy lost by surroundings. |
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States of Matter (cont.)
Heat transfer |
When two objects of different temperature coexist, heat will move from the hotter object to the cooler one until they are equal.
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(Oxygen Therapy)
General goals and clinical objectives |
1. Correct documented or suspected acute hypoxemia.
2. Decrease the symptoms associated with chronic hypoxemia. 3. Decrease the workload hypoxemia imposes on the cardiopulmonary system. |
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Correcting Hypoxemia
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1. oxygen corrects hypoxemia by raising alveolar and blood levels of oxygen
2. *The most tangible objective of oxygen therapy, and the easiest to measure and document 3. Hypoxemia is defined as a PaO2< 60mmHG or an SaO2 < 90% on Room Air |
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Decreasing the Symptoms of
Hypoxemia |
Additionally, oxygen therapy can help relieve the symptoms associated with certain lung
disorders Patients with Chronic Obstructive PulmonaryDisease (COPD), interstitital lung disease These patients report less dyspnea when receiving supplemental oxygen May improve mental function with patients with chronic hypoxemia |
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Minimizing Cardiopulmonary
Workload |
*Cardiopulmonary system compensates for hypoxemia by increasing ventialtion and cardiac output
*This reduced workload is important especially when the heart is already stressed by disease or injury, as in myocardial infarction, sepsis, or trauma |
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Minimizing Cardiopulmonary
Workload cont. |
*Hypoxemia causes pulmonary vasoconstriction and pulmonary hypertension
*Pulmonary vasoconstriction and hypertension increase workload on the right side of the heart *Patients with chronic hypoxemia, this increased workload over a long term can lead to right ventricular failure (cor pulmonale). *Oxygen therapy can reverse pulmonary vasoconstriction and decrease right ventricular workload |
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Oxygen Therapy (cont.)
Assessing the need for O2 therapy |
Laboratory documentation
PaO2, SaO2, SpO2 Specific clinical problem e.g., patient suspected of carbon monoxide poisoning Clinical findings at the bedside Tachypnea, tachycardia, confusion, etc. |
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Oxygen Toxicity
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Precautions and hazards of supplemental O2
Oxygen toxicity Primarily affects the lungs and central nervous system Determining factors include PO2 and exposure time. Prolonged exposure to high FIO2 can cause infiltrates in the lung parenchyma. |
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Oxygen Toxicity
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Effects on the CNS, including tremors, twitching, and convulsions (hyperbaric pressure)
Bronchopneumonia: Patchy infiltrates appear on CXR and more prominent in the lower fields (100% oxygen at sea level) |
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Oxygen Toxicity
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An exudative phase results from alveolar fluid buildup, leads to low ventilation/perfusion ratio, physiologic shunting, and hypoxemia
In end stages, hyaline membranes form in the alveolar region, and pulmonary fibrosis and hypertension develop. |
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Oxygen Toxicity
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Studies show 50% of oxygen for extended periods show no major damage
Goal is to use lowerst possible FIO2 compatible with adequate tissue oxygenation *Rule of Thumb: limit patient exposure to 100% oxygen to less than 24 hours whenever possible. High FIO2 is acceptable if the concentration can be decreased to 70% within 2 days and 50% or less in 5 days |
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Precautions and hazards of supplemental O2 (cont.)
Depression of ventilation (read this p.871*******) |
Occurs in COPD patients with chronic hypercapnia Primary cause of hypoventilation when given oxygen is due to the suppression of the hypoxic drive
These patients normal respond to a high CO2 which is there stimulus to breath due to a lack of oxygen sensed by peripheral chemoreceptors Given a high oxygen and raising there PO2 suppress these chemoreceptors, depress their ventilatory drive and elevates PCO2 |
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Retinopathy of Prematurity
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ROP also called retolental fibroplasia, is an abnormal eye condition that occurs in some premature or lowbirth-weight infants who receive supplemental
oxygen Excessive blood oxygen level causes retinal vasoconstriction, which leads to necrosis of the blood vessels Scarring often leads to retinal detachment and blindness *Keep infants PaO2 < 80mmHg to minimize damage |
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Precautions and hazards of supplemental O2 (cont.)
Absorption atelectasis(Read Carefully p. 872) |
Can occur with an FIO2 above 0.50
Increase of diffusion into the blood, causes a drop in pressure in the alveoli, and causes the lungs to collapse *Because collapsed alveoli are perfused but not ventialted, absorption atelectasis increases physiologic shunt and worsens blood oxygenation. Patients breathing small tidal volumes are at the greatest risk. |
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O2 delivery systems: design and
performance |
Three basic designs exist-
Low-flow systems, Reservoir systems, &High-flow systems |
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Low-flow systems
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provide part of a pts inspiratory gas flowneeds.
The remainder of the gas the pt inhales comes from room air, so the FIO2 varies Variation of the FIO2 is dependent on the pts tidal volume (depth of breathing), andrespiratory rate |
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Low-flow systems
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Provide supplemental oxygen directly to the airway at a flow of 8L/min. or less
Because the inspiratory flow of a healthy adult exceeds 8L/min, the oxygen provided by a low-flow is Always diluted with air Resulting in a low and variable FIO2 Equipment includes: Nasal Cannula, nasal catheter, and the transtracheal catheter |
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Low-flow systems
Nasal cannula |
Delivers an FIO2 of 0.24 to 0.40
Used with flow rates of ¼ to 8 L/min This fills the anatomic reservoir (nasopharyn & oropharynx) FIO2 depends on how much room air the patient inhales in addition to the O2. Device is usually well tolerated. |
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Low-flow systems
Transtracheal catheter |
Surgically places a Teflon catheter in the trachea between the second and third tracheal ring through the neck by a physician
Uses 40% to 60% less O2 to achieve the same PaO2 by nasal cannula Used with flow rates of ¼ to 4 L/min Complications such as infection are possible, high cost, mucus plugging |
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Rule of Thumb: Low-Flow Oxygen
Devices |
For patients with a normal rate and depth of breathing, each liter per minute of nasal oxygen increases the FIO2, approx. 4%
Ex: Patient using a nasal cannula at 4L/min has an estimated FIO2 of approx. 37% (21+16) |
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Reservoir Systems
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Devices to maintain FIO2 levels at lower flow rates
Using a small reservoir, oxygen flow may be reduced wihout affecting oxygen delivery Good for ambulation and exercise Reservoir cannulas, masks and nonrebreathing circuits In principle, enclosure systems, such as tents and hoods, operate as head-or-body surrounding reservoirs |
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Reservoir Systems
Reservoir cannula(p.878) |
Designed to conserve oxygen
Nasal reservoir-stores oxygen in a small membrane reservoir during exhalation. Decreases the flow needed for a given FIO2 Pendant reservoir-helps hide the reservoir under their clothing The extra weight can cause injury to ears and face Can reduce oxygen use as much as 50% to 75% Humidification usually not needed |
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Reservoir Systems
Reservoir masks |
Most commonly used reservoir systems
Three types Simple mask Partial rebreathing mask Nonrebreathing mask |
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Reservoir Systems
Simple Oxygen Masks |
Disposable plastic mask designed o cover the mouth and nose
The mask gathers and stores oxygen between patient breaths The patient exhales directly through open holes or ports in the mask If oxygen input flow cease, the patient can draw in air through these holes |
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Reservoir Systems
Simple Mask cont. |
Input flow range for adults is 5-10L/min
*If more flow needed switch to a high-flow device, if flow is too low, the mask volume acts as dead space and causes CO2 rebreathing The holes can entrain room air, so FIO2 is variable |
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Reservoir Systems
Partial Rebreathing Mask |
Has a reservoir bag attached to the mask
*This mask contains no valves, so during exhalation source oxygen enters the bag As implied, the pt rebreathes part of his exhaled gases The bag fills with oxygen, as the patient inhales a mixture of oxygen and air is inhaled |
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Reservoir Systems
Partial Rebreather Mask cont. |
As long as the oxygen input flow keeps the bag from collapsing during inhalation, CO2 rebreathing is negligible
Typically up to 70% of oxygen Oxygen flow is adjusted so that the reservoir bag is not allowed to fully collapse duringinspiration |
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Reservoir Systems
Nonrebreathing Mask |
Prevents rebreathing with one-way valves added to
the masks exhalation port(s) and between the mask and the reservoir bag The one way valve between the mask and bag help to prevent exhaled gas from mixing with oxygen in the bag The one way valve on the exhalation port closes during inspiration to prevent room air from entering the mask 70% FIO2 and flow should be set at 10L/min or > |
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Reservoir Systems
Nonrebreathing Reservoir Circuit |
Can provide a full range of FIO2 (21%-100%)
and deliver the prescribed concentartion to both intubated and nonintubated pts Contains a blending system to premix air and oxygen It is then warmed and humidified Flows into a inspiratory volume reservoir Egan p. 880 |
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High-flow systems
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Supply a given O2 concentration at a flow equaling or
exceeding the patient’s peak inspiratory flow Use air-entrainment or blending system Can ensure a fixed FIO2 FIO2 (fraction of inspired oxygen) (expressed as a decimal) |
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High-flow systems
Air-Entrainment Systems |
Direct a high-pressure oxygen source through a small nozzle or jet surrounded by air-entrainment ports
Venturi effect entrains the room air, mixing the oxygen with it. Size of the oxygen jet and entrainment ports, differeing oxygen concentrations may beobtained |
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High-flow systems
Air-Entrainment Systems |
The size of the jet or port determines the air to oxygen ratio and thus the FIO2…Ratio of air entrainment to oxygen flow may be calculated
Liters of Air Entrained/Liters of Oxygen Also= (1.0-FIO2)/(FIO2-0.21) FIO2= desired oxygen concentration Using a 24% venturi device. What is the air to oxygen entrainment ratio Table 2-1 on p70 in White |
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High-flow systems
Total Flow (air and oxygen) |
1. must know the air to oxygen ratio
2. know liter flow of oxygen Total Flow= Liters of Air + Liters of Oxygen An entrainment mask is set at 24%. The oxygen flow to the mask is 3L/min. What is the total flow (air and oxygen) to the patient? |
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High-flow systems
Air Entrainment Mask |
FIO2 is regulated by selection and changing of the jet adapter
The smallest jet or port provides the highest oxygen velocity and thus the most air entrainment and the lowest FIO2 The largest jet or port provides the lowest oxygen velocity and thus the least air entrainment and the highest FIO2 |
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High-flow systems
Air-Entrainment Nebulizer |
Pneumatically powered air-entrainment nebulizers are
similar but have an additional humidification and temperature control Humidificaton is achieved through production of aerosol at the nebulizer jet Temperature control is provided by an optional heating element Combined, these features allow delivery of particulate water (in excess of needs for body tempterature and pressure, saturated) to the airways |
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High-flow systems
Air-Entrainment Nebulizer |
Unlike AEMs, these have fixed orifices (ports)
Fixed to deliver 100, 70, and 40% Used only when output flow meets or exceeds the patients inspiratory demand And can not increase nebulizer output flow by means of increasing oxygen input (12-15L/min) |
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Air-Entrainment Nebulizer
Assessing if flow meets the patient’s needs |
1. Simple visula inspection- as long as you can see mist escaping throughout inspiration, flow
is adequate to meet the patients needs 2. compare the nebulizer flow to the patients peak inspiratory flow Peak inspiratory Flow is 3x minute volume. The nebulizer flow needs to exceed this to ensure flow and FIO2 |
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High-flow systems
Blending Systems |
Separate pressurized air and oxygen sources are input, and the
gases are mixed either manually or with a precision valve(blender) Allows a precise control over both FIO2 and total flow output Can provide flow well in excess of 60L/min Qualifies as a true fixed-performance delivery devices In adults, gas from a blender us delivered through an opensystem, like an aerosol mask or T tube, or with a closed nonrebreathing system Mixing Gases Manually: Separate air and oxygen flowmeters must be adjusted for the desired FIO2 and flow |
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High-flow systems
HIOX |
Disposable high FiO2 delivery mask developed to
deliver high oxygen concentrations (80% at a 8L/min) consistently with less room air entrained No air entrainment ports or one-way valves covering exhalation holes Contains a manifold consisting of 3 one-way valves The reservoir contains pure oxygen during inspiration |
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High-flow systems
Vapotherm |
High-flow oxygen therapy system capable of delivering flows from 5-40L/min with humididty and heat (95% RH)
Water enters the gas stream as water vapor Temperature ranges from 35-43 degrees Celsius Can be used with a nasal cannula or transtracheal catheter |
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High-flow systems
Oxygen Blenders |
Oxygen and air are mixed and delivered with precise control over the relative concentration
Alarm system to warn of low pressure Always check the O2 with a calibrated oxygen analyzer at least once per shift Oxygen analyzer kept in line always when being used with neonates |
