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2 is Not 2 is Not 2
The fundamental flaw in perception when providing long-term oxygen therapy(LTOT) to a patient
Brian W Carlin, MD, FCCP, FAARC, Robert McCoy, BS, RRT, FAARC, Ryan Diesem, BA

The Reality – 2 liters per minute continuous flow is not equal toa 2 setting on an intermittent flow (IF) device. A 2 setting on one
intermittent flow device is not equal to a 2 setting on a different
intermittent flow device. Therefore, for oxygen delivery devices:
2 is not 2 is not 21.

T
sy
va

Fundamentals of oxygen therapy
Oxygen is the fuel that drives life. Every cell requires the properamount of oxygen to function properly and without proper
oxygen levels, complications occur.2

The maximum FiO2 of a variety of portable oxygen
systems, utilizing intermittent flow at 20 breaths/min
providing
supplemental oxygen, it cannot be assumed that thevaries greatly.*

oxygen device will provide adequate oxygenation due in partthe variability of the devices, oxygenation must be measured at
all patient activity levels due to the variability in performance ofdifferent oxygen therapy equipment.3*Although research exists, more research is needed to explore recent product impr
the market.

Oxygen is a drug that needs to be prescribed,
delivered and monitored like any other drug.
The maximum FiO2 of a variety of portable oxygen systems, utilizing intermittent flow at
20 breaths/min varies greatly.*
The maximum oxygen dose of portable oxygen systems, utilizing intermittent flow at 20
breaths/min varies greatly.**Although research exists, more research is needed to explore recent productimprovements and new additions to the market.

Normal oxygenation occurs naturally in a healthy body withhealthy lungs, yet when lung disease compromises lung function,
hypoxemia occurs. Supplemental oxygen therapy is provided
to maintain normal oxygen level, yet can only be effective if
given in adequate doses to sustain effective oxygenation. When
Dr Carlin practices pulmonary, critical care, and sleep medicine in western
Pennsylvania. He is active within several national organizations including
the American Association of Cardiovascular and Pulmonary Rehabilitation,
CHEST, and the American Thoracic Society. He is the current chair of the
National Lung Health Education Program and is a member of the National
Board for Respiratory Care. Robert McCoy is the Managing Director ofValley Inspired Products Inc. Ryan Diesem is the Research Manager of Valley
Inspired Products Inc.

Respiratory Therapy Vol. 13 No. 1 Winter 2017-2018n

Oxygen is the only drug that has been shown tomaintain and prolong life of patients with chroniclung impairment.
Reference: Continuous or nocturnal oxygen therapy in hypoxemic
The maximum
oxygendose of portablechronic
obstructive
pulmonarydisease:oxygena clinical trial. Nocturnal Oxygen
Therapy
Trial Group.
Intern Med 1980;93(3):391-398.
systems, utilizing
intermittent
flow atAnn
20 breaths/min

varies greatly.*

Hypoxemia and comorbidities
Cor pulmonale
When oxygen is not provided at therapeutic levels, the body willcompensate. The pulmonary vasculature will divert blood flow toareas of the lung that have effective oxygen levels. If this is notpossible, pulmonary blood vessels will constrict causing blood toback up into the heart and peripheries of the body.

Polycythemia
The blood will compensate by producing more hemoglobin
to increase the oxygen carrying capacity of the blood. This
thickening of the blood impacts circulation.

29

efficiency of oxygen delivery and conserves oxygen.

mia and comorbidities

monaleGeneral cellular dysfunction
xygen is not provided at therapeutic levels, the body will compensate. The pulmonary vasculature will
All other organs in the body will slow their function in theood flow to areas of the lung that have effective oxygen levels. If this is not possible, pulmonary blood
4
response
to tolowlevels.
will constrict
causing blood
backoxygen
up into theheart and peripheries of the body.

Intermittent oxygen delivery options (provides oxygen when the patient is inhaling and turns off withexhalation):• Demand flow allows for oxygen delivery at the same flow rate as prescribed oxygen which is usually 2
WhyLPM.
different intermittent flow devices are not the same
Hybridflow allows
for a higher
peak firstflow of oxygen
the explaining
beginning of a breath
returns2
to the flowat• thesame
setting,
thestepatin
2thenis notrate prescribed.
Pulse
volume• Pulsedose provides a higher peak flow at the beginning of a breath and cycles off when the volume ofis delivered.
Thisappropriate
keeps the volume doseof oxygenthroughout
a range of breath rates.
Pulseoxygenvolumeat anisconsistent
the key
to effective• Minute volume delivery is a fixed delivery of oxygen for one minute. If respiratory rate increases, theoxygenation.
The
volumeofoxygendeliveredtogasvolume of gas delivered will decrease to maintain the fixed minute volume. exchange

hemia
Basically, the body does not function well without therapeutic
od will compensate by producing more hemoglobin to increase the oxygen carrying capacity of the blood.
units in the lung (alveoli) is how effective oxygenation occurs.
oxygenlevels,which begins a downward progression of bodykening of theblood impacts
circulation.
different intermittent flow devices are not the same at the same setting, the first step inIntermittent
flow (IF) oxygen delivery devices are highly variablemechanics to the point where patients will reduce activity, retain Why
explaining 2 is not 2.
cellular dysfunction
in delivering consistent volumes of oxygen. Dose settings are notsecretions and eventually develop chest infections requiringr organs in the body will slow their function in the response to low oxygen levels.
Pulse volume

consistent in delivering known volumes of gas. Gas volume, gas

medical intervention. These occurrences are the exacerbations

Pulse volume at an appropriate dose is the key to effective oxygenation. The volume of oxygen delivered to gasdeliveryflow,
gasdeliveryin the first
half
of inspiration
andexchangeunitspeakin the lung(alveoli)
is how
effective oxygenation
occurs.
Intermittent
flow (IF) oxygen
deliverydevicesare highlyof
variabledelivering
consistent volumes
oxygen. Doseoxygenation.
settings are not consistent
the purity
theingas
all contributetoofeffective
Withinto become the frequent flyers that cost healthcare systems
delivering known volumes of gas. Gas volume, gas delivery peak flow, gas delivery in the first half of inspiration andy, the body does not function well without therapeutic oxygen levels, which begins a downward
any change in these parameters, the FiO2 will change and impact
penalties under the ACA.
sion of body mechanics to the point where patients will reduce activity, retain secretions and eventually the purity of the gas all contribute to effective oxygenation. With any change in these parameters, the FiO2 will
and impact
effective oxygenation.
effective
oxygenation.
chest infections requiring medical intervention. These occurrences are the exacerbations that occur withchangethat occur
with oxygen-deprived
patient
and
cause
them
Reference: Pierson
DJ. Pathophysiology
and clinical effect of chronic
hypoxia.
RespirCare 2000;45(1):39-51.

deprived patientand causethem tobecome the frequent
flyers that costflow
healthcare
systems penalties
Historyof theevolutionof continuous
oxygenhe ACA.

Max FiO2% per Breath

Max Pulse Volume per Breath in mL

therapy to intermittent flow oxygen delivery

15 BPM

100
90
80
70
60
50
40
30
20
10
0

20 BPM

30 BPM45

15 BPM

20 BPM

30 BPM

Continuous(CF) ofoxygenwas flow
the original
methodtoof
40
History of theflow
evolution
continuous
oxygen therapy
35
oxygen therapy
due to thesimplicity
of delivery and limitation ofintermittent
flow
oxygen delivery
30
technology. The limitation is CF wastes oxygen by delivery flow
25
ous flow (CF)oxygenwastheoriginal
methodofoxygentherapyduetothesimplicity
ofdeliveryandwhen the patient is exhaling and pausing between breaths. The
20n of technology. The limitation is CF wastes oxygen by delivery flow when the patient is exhaling andUnit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Unit 8 Unit 9
Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Unit 8 Unit 9
fixed
flow
also
allows
for
FiO2
to
drop
when
respiratory
rate
between breaths. The fixed flow also allows for FiO2 to drop when respiratory rate increases shortening
increases
shortening
inspiratorytime.
ory time.
Above:
Maximum
pulse andvolumesand FiO2
ofsystems
different
Pulse respiratory
systems at
different
Above:
Maximum
pulse volumes
FiO2 of different
Pulse
at different
rates.
respiratory rates.

Inspiratory time
Inspiratory time is the window of opportunity for therapeutic gas to be delivered to gas exchange units in the lung.
AsInspiratory
a patient breathes faster,
timethe window of opportunity becomes shorter and the gas must be delivered quickly tobe therapeutic. Demand units were not effective in delivering oxygen therapeutically due to fixed/low peak flow
Inspiratory
timeis the window of opportunity for therapeutic
delivery. Minute volume devices typically have a higher peak flow, which will allow gas to be delivered quickly, yet
withincreased
breath rate, oxygenvolumesdecrease with
an impact
on FiO2
gasantobe delivered
to gasexchangeunits
in thelung. As a patient

VIP graph of flow delivery reference 2013 article

VIP graph of flow delivery reference 2013 article

breathes faster, the window of opportunity becomes shorter andthe gas must be delivered quickly to be therapeutic. Demand
units were not effective in delivering oxygen therapeutically due
to fixed/low peak flow delivery. Minute volume devices typicallyhave a higher peak flow, which will allow gas to be delivered
quickly, yet with an increased breath rate, oxygen volumes
decrease with an impact on FiO2.

iagram of a Above:
respiratory
flow cycle
relationship to
continuous-flow
supplemental
oxygen, indicating the sections ofDiagramof ainrespiratory
flow
cycle in relationshipto continuous-flowhing patternsupplemental
that useful oxygenis delivered.
oxygen,indicating the sections of the breathing pattern that useful

Pulse Delivery Flow Profiles
Pulse Delivery Flow Profiles
Set2

oxygen is delivered.
ous flow, oxygen conserving options:
Transtracheal oxygen - a method of bypassing the upper airway and reduces dead space which allows
improved use of oxygen and improves patient compliance due to elimination of cannula irritation.

20

14

Oxygen Delivery (LPM)

16• Transtracheal oxygen – a method of bypassing the upper
airway and reduces dead space which allows improved use ofoxygen and improves patient compliance due to elimination ofcannula irritation.
• Reservoir oxygen systems – utilizes a 20 mL reservoir tostore oxygen between breaths improving efficiency of oxygen
delivery and conserves oxygen.

• Demand flow allows for oxygen delivery at the same
flow rate as prescribed oxygen which is usually 2 LPM.
• Hybrid flow allows for a higher peak flow of oxygen at
the beginning of a breath then returns to the flow rateprescribed.
• Pulse dose provides a higher peak flow at the
beginning of a breath and cycles off when the volumeof oxygen is delivered. This keeps the volume ofoxygen consistent throughout a range of breath rates.
• Minute volume delivery is a fixed delivery of oxygenfor one minute. If respiratory rate increases, thevolume of gas delivered will decrease to maintain the
fixed minute volume.

Set6

30BPM

40BPM

12
10
8
6
4
2
0
Each Section = 1 second

Above: Flow profiles of 3 pulse dose systems showing oxygen delivery in one second.
Above: Flow profiles of 3 pulse dose systems showing oxygen delivery in one second. The first 60% of an inspiratory cycle is
The first 60% of an inspiratory cycle is considered delivered to gas exchange units in theconsidered delivered to gas exchange units in the lung, the rest occupies dead spacelung, the rest occupies dead space.
Triggering sensitivity
Triggering sensitivity is important to allow gas delivery in the early part of inspiration. The first segment of apatient’s breath goes to gas exchange units in the lung; the remainder of the gas will occupy dead space and notparticipate in gas exchange, therefore, is wasted. If an intermittent flow device is slow to sense a patients breathe,the volume of gas that is delivered when the device does sense a breath will be delivered later in the breathingcycle and may have some of the gas occupying dead space. If devices attempt to be as sensitive as possible, yet anasal cannula is an open system, which causes variability in the devices ability to sense a breath. Cannula
placement, tidal volumes, inspiratory flow rates and mouth breathing are also causes for a device to be slow totrigger or miss an inspiration.

Triggering sensitivity

Triggering sensitivity is important to allow gas delivery in theearly part of inspiration. The first segment of a patient’s breathgoes to gas exchange units in the lung; the remainder of the gas
will occupy dead space and not participate in gas exchange,
DeviceVariability
therefore,
is wasted. If an intermittent flow device is slow to
All intermittent flow oxygen delivery devices are different in design and function. The ability to control and deliver
sense
a patient’s
breath,thevolumeof gasthatpatterns.
is delivered
oxygentherapeuticallydepends on thecapabilities ofthe device
and the patientsbreathing
IF system
designs attempt to provide therapeutic oxygen in a device that is convenient for the patient to use.
when the device does sense a breath will be delivered later inConsiderations for therapeutic oxygen delivery
the breathing cycle and may have some of the gas occupying• Amount of source gas available to deliver to the patient.
Compressed
and liquid oxygen
systems havemostasavailable
source gas on
deado space.
IFgasdevices
attempt
tothebesensitive
asdemand.
possible, yeto Portable oxygen concentrators are limited by their oxygen product capabilities in one minutea nasal(limited
cannulais an onopen
system, which causes variability inoxygen availability
demand).
• Dose settings with a range of oxygen volumes. The greater the dose volume, the greater the FiO2
thedevices ability to sense a breath. Cannula placement, tidal
potential.
•

30

Set4

20BPM

18

Continuous flow, oxygen conserving options:Intermittent oxygen delivery options (provides oxygen
when the patient is inhaling and turns off withexhalation):

10BPM

Triggering sensitivity.

Respiratory Therapy Vol. 13 No. 1 Winter 2017-2018nvolumes, inspiratory flow rates and mouth breathing are also
causes for a device to be slow to trigger or miss an inspiration.

Device Variability
All intermittent flow oxygen delivery devices are different indesign and function. The ability to control and deliver oxygentherapeutically depends on the capabilities of the device and thepatients breathing patterns. IF system designs attempt to provide
therapeutic oxygen in a device that is convenient for the patient
to use.

Considerations for therapeutic oxygen delivery• Amount of source gas available to deliver to the patient.
◼ Compressed gas and liquid oxygen systems have the mostavailable source gas on demand.
◼ Portable oxygen concentrators are limited by their oxygen
product capabilities in one minute (limited oxygen
availability on demand).
• Dose settings with a range of oxygen volumes. The greater thedose volume, the greater the FiO2 potential.
• Triggering sensitivity.
• Peak flow capabilities that allow for oxygen to be delivered
quickly, the higher the peak flow capability the faster theoxygen can delivered in therapeutic range.
• Consistent oxygen delivery with variable breathe rates; minutevolume delivery of IF devices reduces pulse volume withfaster breath rates.

Considerations for patient convenience/compliance• Device weight – the heavier the device the less likely thepatient will use the device consistently.
• Device operating time – if a device does not operate as long asa patient will be away from home, travel outside the home will
be limited or the patient may not use the device consistently
while away.
Issues:◼ Gas contents for a liquid oxygen or compressed oxygen
cylinder.
◼ Oxygen production (concentrator) battery weight, battery
exchange.
• Ease of use – complicated user interface will limit a patient’s
use of the device.
• Esthetics – a portable oxygen system that looks like anindustrial product will prevent a patient from using the device
consistently in public places. Also, oxygen is perceived as alast resort option by patients which prevents some patientsfrom using an oxygen system in public.
• Carrying options, straps carts, etc. – if a device is difficult toincorporate into a normal use similar to purses, backpacks orother standard devices that are carried, the portable oxygen
may not be utilized.

Summary
Therapeutic oxygen delivery is necessary to prevent
complications, hospitalizations and increased overall healthcare
cost. Oxygen is a drug that needs to be assessed correctly,
prescribed effectively, delivered therapeutically and monitoredconsistent to insure patient benefits. Delivery options for oxygentherapy are different and need to be evaluated on a patient at
all activity levels to insure effective oxygenation. A 2 setting on
one oxygen delivery devices is not the same as the 2 setting on
another oxygen delivery device. Patient compliance with LTOT
requires the combination of therapeutic oxygen delivery with asystem that will allow a patient the ability to do normal actives ofRespiratory Therapy Vol. 13 No. 1 Winter 2017-2018
ndaily living. To prevent to complications of hypoxemia describedin this paper, therapeutic oxygen delivery is the most essential
component of LTOT.

Conclusion
New oxygen delivery systems are available to address the needsof LTOT patients who desire to maintain a normal lifestyle while
using portable oxygen equipment. Newer home oxygen systems
have become available that address the patient’s lifestyle needs,
yet may not provide therapeutic oxygen with all activities,
therefore: Clinicians must recognize that when prescribing
oxygen therapy, they must either completely understandthe capabilities and limitations of the devices they will beprescribing or have a skilled clinician titrate the oxygen dose at
all activity levels on the device the patient will be using.

References
1

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Respir Care 2000;45(1):95-103
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