Medical Gas Therapy
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The overall goal of oxygen therapy
to maintain adequate tissue oxygenation while minimizing cardiopulmonary work
the three specific clinical objectives for oxygen therapy
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
define cor pulmonale
enlargement of the right ventricle of the heart due to disease of the lungs or of the pulmonary blood vessels
the 4 major harmful effects of oxygen therapy
O2 toxicity, depression of ventilation, retinopathy of prematurity, absorption atelectasis
basic characteristics of low-flow systems
supply O2 @ 8 L/ or less, don't meet pt's inspiratory flow needs so pt draws room air resulting in low & variable FiO2 (amount depends on pt's inspiratory flow rate, tidal volume, and the O2 flow delivered)
at what point is humidification needed for nasal cannula?
over 4 L/min
what is the most common liter flow and resultant FiO2s for nasal cannula?
1-5 L/min, there is a 4% increase in FiO2 for every 1 L/min so the pt's FiO2 from room air is .21 and if @ 2 L/min, will be .21 + .08 = .29
basic characteristics of a transtracheal catheter
deliver O2 directly into the trachea through a small bore catheter that is surgically inserted into the trachea; uses 40-60% less O2 flow than cannula so no humidification necessary; O2 builds up in trachea during expiration & is taken in during inhalation
what is the cause and procedure for when there is no gas flow felt coming from the cannula
- cause = flow meter not on or system leak
- procedure = adjust flow meter, check connections
what is the cause and procedure for when the humidifier pop-off is sounding
- cause & procedure
- obstruction distal to humidifier - find and correct obstruction
- flow is set too high - use alternative device
- obstructed naris - use alternative device
what is the cause and procedure for when pt reports soreness over lip or ears
irritation or inflammation caused by appliance straps - loosen straps or place cotton balls at pressure pints or use an alternative device
what is the cause and procedure for when the pt is mouth breathing
habitual mouth breathing or blocked nasal passages - switch to a simple or venturi mask
define reservoir systems
Provides a mechanism to gather and store oxygen between patient breaths.
- Classified as a variable performance device, however can be a fixed performance device as long
- as the stored volume equals or exceeds the patient’s tidal volume and there are not any air leaks.
Consist of the reservoir cannula and reservoir masks.
characteristics of a simple mask
cover mouth and nose with the body of the mask gathering & storing O2 between pt breaths; exhaled air escapes through holes in its body. If O2 input is interrupted, air is drawn through these holes and around the mask edge. Flows of 5-12 L/min, minimum of 5 L/min to prevent rebreathing of CO2, FiO2 35-50%, chosen when moderate FiO2 are needed for a short time
characteristics of partial rebreather mask
- Has a 1 liter reservoir bag
- which increases the reservoir volume therefore increases the FiO2 over a simple
- The bag is open to the flow
- of exhalation gases and does allow the first portion of the exhaled gases to
- enter the reservoir, thus the rebreathing of air
- At flows between 6 – 10
- L/min FiO2’s are between 35 – 60 %
characteristics of a nonrebreather mask
- Like the partial rebreathing mask it has a 1
- liter reservoir bag, however it also has a series of one-way valves.
- A one way valve between the
- bag and mask prevents exhaled gas from returning into the bag. One way valves
- placed on the exhalation ports will prevent entrainment of room air
- In concept a leak-free mask
- with competent valves and adequate flow should deliver 100% source gas.
- A truly fixed performance
- situation is difficult to achieve, however the nonrebreather mask will
- provide the highest FiO2 of the reservoir mask, with FiO2 around 70+%
approximate FiO2 achieved with simple mask
35-50% @ 5-12 L/min
approximate FiO2 achieved with partial rebreathing mask
35-60% @ 6-10 L/min
approximate FiO2 achieved with nonrebreathing mask
if the patien is constantly removing mask....
the causes can be claustrophobia (use alternative device) or confusion (use restraints)
if no gas flow can be detected with the reservoir mask...
either the flowmeter is not on (so turn it on) or there is a system leak (check connections)
if the humidifier pop-off is sounding...
either there is an obstruction distal to the humidifier ( find and correct the obstruction), the input flow is too high ( omit humidifier if treatment is short term), or there is a jammed inspiratory valve ( fix or replace valve)
if the reservoir bag collapses when the patient inhales...
the flow is inadequate so increase the flow
if the reservoir bag remains inflated throughout inhalation...
there is either a large mask leak (correct leak) or the inspiratory valve is jammed or reversed (repair or replace the mask)
if erythema develops over face or ears...
irritation or inflammation due to appliance or straps (provide skin carem use an alternative device, or place cotton balls on affected areas to act as a buffer between the skin and equipment)
describe high flow systems
Also known as fixed performance devices
- High flow systems supply a given oxygen concentration at a flow that equals or exceeds
- the patients inspiratory flow, thus ensuring a stable FiO2
In order to meet variations in patient’s inspiratory demands, a high flow device should provide at least 60 L/min total flow
- There are two major categories of high flow devices:
- –Air Entrainment Systems
- –Blending Systems
what is the minimum flowrate that high flow systems should be capable of delivering?
how do air entrainment systems operate
Directs a high-pressure oxygen source through a small nozzle or jet surrounded by air entrainment ports
- As the oxygen flows through the restricted orifice the velocity increases.
- The increased velocity pulls in or entrains room air through the air entrainment port
What 2 factors affect the amount of air entrained?
jet size or orifice and the air entrainment port size
what effect does the jet size have on the way the air entrainment system operates?
the smaller the jet the higher the velocity, the high the velocity the more air entrained so the lower the FiO2 and the greater the total output flow
what effect does the air entrainment port size have on the system?
the larger the air entrainment port the more air entrained so the lower the FiO2 and the greater the total output flow
What formula is used to calculate the air to oxygen ratio?
Liters of air divided by the liters of O2 = (100-%O2) / (%O2-21)
%O2 = [(Air flow x 21) + (O2 flow x 100)] / total flow
what is the air to oxygen ratio for 40% oxygen?
what is the air to oxygen ratio of 60% oxygen?
what is the effect of down stream flow resistance on air entrainment devices?
Any resistance to flow distal to the jet will result in less air entrained, therefore the delivered oxygen concentration will be increased.
However total flow will also be decreased, therefore if the total flow does not meet the patients needs the patient will inhale room air and the delivered oxygen concentration may actually be lower than what is being delivered.
how can extra humidification be added to the venturi mask:?
- The best way to add humidification to a venturi
- mask is to use an air entrainment nebulizer connected to the mask with the nebulizer connected to an air flowmeter
air entrainment mask vs air entrainment nebulizer
- AEMs :
- indicated for patients with
- high or changing ventilatory demands needing a stable low – moderate FiO2
- The most common problems
- with AEM’s are:
- Providing sufficient total output flow to ensure a stable FiO2. Providing extra humidification
- Pneumatically powered nebulizer
Provides additional humidification and heat control
The oxygen jet serves two purposes, entrainment of air and also to entrain water into the jet stream producing an aerosol
Heat can also be added
Device of choice for delivery of oxygen to patients with artificial tracheal airways by either a T-piece (Briggs Adaptor) or trachcollar
Due to increase resistance to flow the maximum oxygen input flow is between 12-15 L/min
what are the two ways to assess adequacy of flow by an air entrainment nebulizer
A visual inspection to see if mist escapes from the T tube (in which case the pt's inspiratory flow needs are being met) and also to compare it to the pt's peak inspiratory flow (during tidal breathing is ~3x minute volume) and as long as it exceeds this amount, the inspiratory flow needs are being met.
what are the 5 ways to achieve higher output flow for AENs
1) add open reservoir to expiratory side of T tube 2) provide inspiratory reservoir with one-way expiratory valve 3) connect 2+ nebulizers together in parallel 4) set nebulizer to low concentration; bleed-in oxygen; analyze, and adjust 5) use a commercial dual-flow system
when is it approriate to use a blender system?
when air-entrainment devices cannot provide a high enough O2 concentraion or flow and if the power goes out and the treatment cannot be administered without the power being on
How do you calculate the oxygen and air settings to achieve a specific FiO2 and flow rate when manually blending O2 and air?
- O2 flow = [Total flow X (O2% - 21)] / 79
- Air flow = Toal flow - O2 flow
- to manually mix air and oxygen to provide a pt with 50% O2 at a total flow of 60 L/min.
- O2 flow = (60x(50-21)) / 79
- O2 flow = 22 L/min
- Air flow = 60 L/min - 22 L/min
- Air flow = 38 L/min
So 22L of O2 and 38L of air should be blended together
what are the 3 types of oxygen enclosure devices?
hood, tent, incubator
what are the key features of an oxygen hood?
- best method for controlled oxygen therapy to infants, covers only the head so the rest of the body is free to be cared for, Oxygen is delivered to the hood via either a heated air entrainment nebulizer of a blending system with a heated humidifier, and a minimum flow of 7 L/min should be set in order to prevent
- accumulation of carbon dioxide
what are the key features of an oxygen tent?
Air conditioned or cooled by ice to provide a comfortable temperature within a plastic sheet canopy, Major problem is that frequent opening and closing of the canopy causes wide swings in oxygen concentration, and because of variability of FiO2 and inability to produce high FiO2’s tents are used primarily to provide pediatric aerosol therapy to children with croup or cystic fibrosis
what are the key features of an incubator?
high infection risk, completely enclose the pt, wide swings in O2 concentration due to the opening and closing of the unit to care for the pt.
nitric oxide therapeutic benefit
potent pulmonary vasodilator, by causing smooth muscle relaxation in the pulmonary capillary system. This improves blood flow to ventilated alveoli which helps reduce pulmonary vascular resistance
He's value as a therapeutic gas and the purpose?
based on the low density and is used to decrease the WoB in pts with large airway obstruction by decreasing the turbulence of flow in the airways which int urn requires a reduction in the driving pressure needed to move air flow past the obstruction
What concentration should He/O2 be?
80/20 or 70/30
how should heliox be delivered?
non-rebreather or simple mask
since an O2 flowmeter will be inaccurate when regulationg He flow, what conversion factor must be used to determine flowrate?
what are the common problems with He therapy?
ineffective for aerosol delivery, coughing less effectived b/c of reduced turbulent air flow, distorted speaking, and hypoxemia because of adding high levels of O2 decreased the effectiveness of the He.
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