Bi-level Positive Airway Pressure
BY
AHMAD YOUNES
PROFESSOR OF THORACIC MEDICINE
Mansoura faculty of medicine
Non-invasive ventilation
• Non-invasive ventilation refers to the application of
ventilatory assistance without the use of an invasive
airway.
• In the vast majority of cases therapy will be
delivered with positive pressure devices , although
a few individuals still use negative pressure
devices.
• Negative pressure devices present a number of
difficulties with regard to home ventilation including
bulkiness, fit ,comfort, they can induce significant
upper airway obstruction , rendering therapy
ineffective.
Non-invasive ventilation
• Positive pressure therapy may be delivered with
either volume or pressure preset ventilators .
1-Volume preset ventilation delivers a stable tidal
volume irrespective of the patient’s pulmonary
system mechanics (compliance, resistance and
active inspiration) .
2- Pressure preset ventilation delivers a set
pressure during inspiration and expiration, and
changes in the patient’s pulmonary mechanics
directly influence the flow and the delivered
tidal volume .
What is a mode
• A mode of mechanical ventilation has three essential
components :
1- The control variable (the mechanical breath goal e.g. a
set pressure or a set volume )
2- The breath sequence
3- The target scheme
• Inspiration is an active process ,driven either by the
patients effort ,the ventilator or both .
• The machine can control only the volume (and flow) or
the pressure given.
• The breath can be described on the basis of what
triggers the breath what limits it (the maximum value of
a control variable)and what ends (cycles ) it.
Modes of ventilation
• Volume controlled breath is triggered by the patients or
by the machine , limited by flow and cycled by volume.
• Pressure controlled breath is triggered by the patients
or by the machine , limited by pressure and cycled by
flow or time.
The breath sequence
1- Control mode (timed) : all breaths are controlled by the
machine (but can be triggered by the patient)
2- Assisted mode (spontaneous) :all breaths are
spontaneous .
3- Assisted /control (spontaneous/ timed): patient can take
spontaneous breaths between mandatory breaths .
The target scheme
• The ventilator settings and programming that
dictate its response to the patients lung
compliance ,lung resistance ,and respiratory
effort.
• The regulation can be
1-simple as controlling pressure in pressure
controlled mode or
2- can be based on a complicated algorithm as in
dual mode of ventilation ( AVAPS).
Non-invasive ventilation
• Most studies evaluating these two modes in patients with
chronic respiratory failure have shown equivalent effects
with respect to maintaining nocturnal gas exchange and
improving daytime blood gases.
• Due to lower cost and greater patient comfort , most
patients in the majority of centres are now prescribed
pressure preset devices, mostly commonly , bi-level
machines.
• Volume ventilators are recommended for patients with the
most severe respiratory failure including those with
tracheostomy and when continuous or near continuous
ventilatory support is needed.
• A switch from pressure to volume preset ventilation may
also be required in patients who are adherent to pressure
preset ventilation but who fail to respond to treatment .
Non-invasive ventilation
• Volume preset ventilators are usually set in an
assist/control or control mode of support.
• No difference in blood gas improvement, lung
function or compliance with therapy was seen
between the two modes.
• Pressure preset ventilators may be set in an
assist (“spontaneous”) mode where each breath
is patient triggered; an assist/control
(“spontaneous / timed”) mode where breaths
may be patient or machine triggered; and a
control (“timed”) mode where all breaths are
machine triggered only .
Non-invasive ventilation
• The spontaneous mode has been used in patients able
to trigger the ventilator consistently, whereas the
spontaneous/timed mode is used when the ability of the
patient to trigger the device reliably is reduced due to
poor or absent inspiratory flows being generated (e.g.
respiratory muscle weakness, drive to breathe is
reduced or absent, or specific characteristics of the
patient’s pulmonary mechanics), where the goal of
therapy is to control the respiratory pattern .
• The pressure settings used in bilevel devices include
the inspiratory positive airway pressure (IPAP) and
expiratory positive airway pressure (EPAP), with the
difference between the two determining the level of
pressure support
Bi-level Positive Airway Pressure
• Bi-level PAP (BiPAP) was developed in mid 1990's by
Respironics Corporation, trademarked 'BiPAP'.
• Since BiPAP is a trademark, other companies use
different terms, such as 'bilevel', VPAP (variable positive
airway pressure), and "duo."
• One internet ad shows 4 different bilevel machines from
4 different manufacturers; only Respironics' machine is
"BiPAP."
• Whereas CPAP sets a single pressure above the
ambient pressure, BiPAP sets two pressures above the
ambient, a higher (IPAP) and a lower (EPAP), e.g., 10/5
cm H2O . Note that both pressures are always above
ambient.
Pressure curve when BiPAP = 10/5 cm H2O; now the pressure is
higher on inspiration than on expiration, but both pressures are above
ambient.
NOTE: BiPAP is equivalent to PSV (pressure support ventilation) +
PEEP (positive end-expiratory pressure) in the intubated patient; in
that situation PEEP is the same as EPAP.
Bi-level Positive Airway Pressure
• Bi-level Positive Airway Pressure therapy with a variable
pressure setting would conceivably decrease the amount of
pressure against which the patient exhales, thereby
decreasing abdominal muscle recruitment and consequent
respiratory discomfort during the expiratory cycle
• During the inspiratory cycle, the greater level of pressure
assist would combat the inspiratory flow limitation suffered
by the upper airway . An additional benefit with bi-level PAP
is the greater tidal volume ( VT) and unloading of the
respiratory muscles, when compared to CPAP.
• The difference between the IPAP and EPAP could be
considered as pressure support level that could augment
the inspired VT. This feature can be exploited to combat
“non-obstructive” hypoventilation that may occur due to a
host of conditions.
Bi-level Positive Airway Pressure
• In adults, the maximum IPAP setting for bi-level PAP is not to exceed
30 cm H2O, and the minimum difference between IPAP and EPAP level
should not be < 4 cm H2O.
•A transition from CPAP to bilevel PAP is encouraged when the CPAP
level approaches 15 cm H2O. This is because exhalation against CPAP
levels approaching 15 cm H2O can be uncomfortable for most patients.
•Bi-level PAP therapy was not superior to conventional CPAP therapy
from an adherence standpoint.
•The cycling of the device from IPAP to the EPAP and vice-versa may
be triggered by the spontaneously breathing patient (spontaneous
mode) or by a set respiratory rate programmed into the device (timed
mode).
•The sensitivities or the triggering threshold for causing the device to
cycle in the spontaneous mode may be based on pressure, flowcontour, hardwired timing, or a proprietary combination of such
measures.
Rise time , trigerring and cycling
Bi-Flex comfort feature
Ramp comfort feature
Bi-level Positive Airway Pressure
• Dys-synchronous cycling between the patient and the device can be
uncomfortable and could lead to hyperinflation and further dyssynchrony.
• In some older devices the triggering sensitivities could be adjusted
by the physician, but in most modern bi-level PAP devices for home
use the technology has veered in favor of automation and higher
levels of sensitivity.
• The rate of pressurization from EPAP to IPAP level (the “rise time”)
can be adjusted to climb more briskly or more slowly. Such a feature
may need to be adjusted for individual patient comfort .
• Some reports suggest that a brisk response (or shorter rise time)
may have some inherent oscillatory behavior that may set the stage
for “emergent” central ,However, the effect of rise time on emergent
central apneas has not been demonstrated in clinical studies outside
of mathematical or bench models.
Autotitrating bilevel devices
• A recent innovation is that of autotitrating bilevel devices.
The algorithms of these machines are designed to
automatically titrate pressure support levels, and in some
devices EPAP, based on minute ventilation or flow targets.
• There is mounting evidence for the use of these devices in
managing sleep disordered breathing in patients with
central sleep apnea / Cheyne–Stokes respiration .
• There is currently a paucity of data and clinical experience
with the algorithms and technology to automatically titrate
ventilatory support in patients with chronic respiratory
failure . Consequently, it is not possible to make
recommendations about the role and effectiveness of
autotitrating bilevel devices for chronic respiratory failure at
the present time
The administration of a backup rate (timed mode) during bilevel PAP therapy may be considered under 2 circumstances.
1- The backup rate could be considered in patients with alveolar
hypoventilation, with or without chronic respiratory insufficiency
(elevated arterial PCO2 ) of various etiologies, which is primarily
aimed at increasing minute ventilation (VE) and resolving the
hypoventilation.
2- Another circumstance would be to treat central sleep apnea or
prevent the appearance of emergent central apneas in patients
undergoing PAP therapy for OSA.
• In both cases, the choice of the backup rate seems arbitrary and is
probably best guided by polysomnography resolution of central
apneas or persistent hypoxemia due to alveolar hypoventilation
(SpO2 < 88% in the absence of obstructive hypopneas or apneas as
an indirect measure of hypoventilation).
• In general, a backup rate set at 2 breaths below the patient’s
spontaneous rate during calm wakefulness breathing with titration
upwards at 2-breath increments can be considered.
Auto-bilevel positive airway pressure with a
minimum (EPAP) of 6 cm H2O and a maximum
(IPAP) of 25 cm H2O.
Principal Indications
• Non-acute setting:
1) When CPAP doesn't work for sleep apnea.
2) For patients with chronic CO2 retention who
also have sleep apnea ( OHS).
3) For patients with neuromuscular disease who
need some assistance with nocturnal
ventilation.
• Acute setting: Pulmonary edema or COPD
exacerbation, when there is CO2 retention and a
desire to avoid endotracheal intubation.
How is the pressure applied non-invasively?
• Same as with CPAP, but machine used is designed to deliver BiPAP.
S9 VPAP S Bilevel
VPAP 111
What kind of mask is used?
• Same as for CPAP
SOMNOvent auto-S/ST
BiPAP S/T
The nasal mask (left) and nasal pillows (middle) and full
face mask (left)
Medicare Coverage Guidelines
Same criteria for CPAP
1. Face-to-face clinical evaluation by treating physician prior
to sleep study
2. Medicare-covered sleep test that shows AHI 15 event/hr. or
higher, or AHI 5-14 events/hr. with documentation of
excessive daytime sleepiness, impaired cognition, mood
disorders or insomnia or hypertension, ischemic heart
disease, or history of stroke and CPAP has been tried and
proven ineffective .
• Note that there are additional criteria for continued
coverage, including a face-to-face evaluation between the
31st and 90th day of treatment.
VOLUME-TARGETED BiPAP
• Volume-targeted bilevel positive airway pressure (VTBPAP) has been developed in which the IPAP-EPAP
difference is automatically adjusted to deliver a target
tidal volume.
• VT-BPAP has the potential advantage of automatically
varying the PS to deliver a targeted tidal volume if the
condition of the patient changes. For example, if
respiratory muscle strength declined and the tidal
volume decreased, the device would deliver higher PS
to return the delivered tidal volume to the targeted level.
• VT-BPAP can be used in the S, ST, or T mode.
• VT-BPAP device is available (Average Volume Assured
Pressure Support [AVAPS], Philips-Respironics).
BiPAP AVAPS "Average Volume Assured Pressure
Support," is a variant of BPAP that automatically
adjusts pressure support to meet changing patient
needs while maintaining a target tidal volume.
Ideal body weight
• Estimated ideal body weight in (kg)
Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.
Females: IBW = 45.5 kg + 2.3 kg for each inch over 5
feet.
• Estimated adjusted body weight (kg)
If the actual body weight is greater than 30% of the
calculated IBW, calculate the adjusted body weight
(ABW):
ABW = IBW + 0.4(actual weight - IBW)
• The IBW and ABW are used to calculate medication
dosages when the patient is obese.
• This formula only applies to persons 60 inches (152 cm)
or taller.
VOLUME-TARGETED BPAP
• Comparing BPAP and AVAPS (both in the ST mode) in
patients with OHS. AVAPS resulted in a slightly higher
ventilation and lower PaCO2 without any better sleep
quality or quality of life measures compared with BPAPST. On AVAPS, the minute ventilation was greater than
on BPAP but sleep quality was comparable between the
two NPPV modes.
• When VT-BPAP is used, the purpose of a
polysomnography PAP titration is to select a level of
EPAP that eliminates obstructive events (obstructive
apnea and hypopnea) and document that the device
does deliver adequate tidal volumes.
Intelligent Volume Assured Pressure
Support ( iVAPS )
• Intelligent. Automatic. Personalized.
• Maintain a preset target alveolar minute ventilation
• Monitors delivered ventilation
• Adjusts pressure support
• Provides an intelligent backup breath
Two mechanisms independent of one another
1-Variable Pressure Support to guarantee Alveolar
Ventilation
2- iBR: intelligent Back-up rate
VPAP™ ST with iVAPS
Why Alveolar Ventilation?
• Gas exchange only occurs at alveolar level
• We have a continuous demand for a supply of
O2 and removal of CO2
• Conducting airways do NOT participate in gas
exchange
Anatomical Dead space
• Inspired/expired air remaining in conducting
airways
• Not involved in gas exchange
• Correlation between patient’s height and dead
space (Vd)
• Height is used to calculate anatomical dead
space (Vd) for each breath of air (Tidal Volume)
• Example dead space volume (Vd) : 120 ml for
height 175 cm or 70 inches
Anatomical dead space in relation to
height of the patient
Alveolar Ventilation
• Vt (500ml) – Vd (120ml) = alveolar ventilation for one
breath
• 500 - 120 = 380 ml participates in gas exchange for each
breath
• Vta x RR (respiratory rate) = Va (minute alveolar
ventilation) = 0.380 x 15 = 5.7L/min
Benefits Of Alveolar Ventilation
• Supply of O2 (PaO2) .Normal = 80 – 100 mm Hg
• Removal of CO2 (PaCO2) . Normal = 35 – 45 mm Hg
• Alveolar ventilation provides necessary gas exchange to
satisfy metabolic demand
As alveolar ventilation drops , iVAPS rapidly increase pressure
support until target Va is reached, and as alveolar ventilation
increase , iVAPS rapidly decrease pressure support .
Intelligent back up rate (iBR) stays out of the way at 2/3 spontaneous rate
whenever the patient spontaneously triggers above 2/3 of the target . once
the patient rate reach minimum back up rate (2/3 of the target ) iBR increase
towards patient spontaneous rate to maintain alveolar ventilation .Once
spontaneous trigering returns, iBR drops back to 2/3 of the target /
spontaneous rate.
Auto-TriLevel
• The auto-TriLevel principle by Weinmann combines two
proven types of therapy – auto-CPAP and BiLevel – into
a synthesis that offers the most therapy effectiveness.
Your benefits with these products:
• Therapeutically effective maximum and mean pressures
that are lower than BiLevel with the same tidal volume
for fewer side effects such as leakage.
• It‘s like a new titration every day – adjusts to patient‘s
high variability .
• Effortless titration and monitoring .
Auto-TriLevel
• IPAP: inspiratory pneumatic
splinting of the airways
(ventilation)
• EPAP: easier exhalation at a low
expiratory pressure level for a
pleasant breathing sensation
• Additional end-expiratory
pressure (EEPAP): required
minimum pressure for adequate
splinting of airways during phase
when risk of collapse is highest
• PDIFF (Δ IPAP-EPAP): needoriented ventilation support by
means of changes between
inspiratory (IPAP) and expiratory
(EPAP) pressure levels
Auto-TriLevel
• Reduced mean and maximum therapy pressure
under TriLevel: Results of a bench test
comparison with BiLevel therapy.
• SOMNOvent auto-ST is the world‘s first automatic
BiLevel device that permits goal-oriented therapy
settings(SCOPES).
• With the combination of the autoTriLevel principle and
the automatic trigger WMtrak, this device delivers the
greatest effectiveness, reliability and breathing comfort
– simply the fastest therapy results.
• Particularly for cases of complicated SDB, SOMNOvent
auto-S, convinces with its intelligent combination of
automatic BiLevel S therapy and auto-CPAP.
Auto-TriLevel
• Auto-bilevel spontaneous (SOMNOvent auto-S ).
• Auto-bilevel spontaneous/timed (SOMNOvent
auto-ST ).
• Anti-cyclic modulated ventilation (SOMNOvent
auto-CR ).
ASV is a variant of BPAP that was developed to treat
Cheyne-Stokes central apnea. Both ASV and BPAP
devices with a backup rate are approved for use with
patients with central apnea and complex sleep apnea
ASV is BiPAP with a twist. The IPAP and EPAP can vary,
depending on the patient's needs.
In some ASV-type machines , the EPAP is fixed and only the
IPAP changes; in others both can change.
Basically, in ASV one or both pressures is continously
adjusted, so that the ventilation delivered to the patient
'adapts' to the situation.
SomnoVent CR
Respironics autoSV
ResMed VPAP Adapt SV
The top graph is pressure and bottom is flow. Note that EPAP is set at
5 cm H2O. The IPAP is variable. When central apnea ensues , the
machine senses less air flow and ratchets up the IPAP, eventually
reaching the pre-set limit of 15 cm H2O. The prescription for this
patient would read: "IPAP 5, PS 3-10."
A peak flow target is established around the 4-minute
average and the machine changes the air delivery as
needed, to deliver 95% of the target, as shown below.
Dynamic pressure support inversely proportionate to peak flow
Periodic breathing treated with BiPAP auto SV
Trilevel ASV uses three different pressure levels over the
course of the breathing cycle. The IPAP pressure provides
the inspiratory splint and ventilation. Expiratory pressure
is varied between a lower level at the start of expiration
(EPAP) and a higher level at the end of expiration (EEPAP).
Confusing Points Clarified
• BiPAP is used for non-invasive ventilation. It is
designed to augment alveolar ventilation because it
delivers two pressures, one higher IPAP and one lower
EPAP; however, both IPAP and EPAP are above ambient
presure.
• BiPAP is the same as PSV + PEEP in the intubated
patient.
• BiPAP is actually a trademark of Philips Respironics,
and so cannot be used in advertising by other
manufacturers. ResMed Corporation, for example, uses
the term "Bilevel" instead of BiPAP.
• Many machines are on the market that can deliver
BiPAP as somnovent ST .
Confusing Points Clarified
• Also confusing is that BiPAP comes in several 'modes' - all variations on the simple two pressure model:
• S (Spontaneous) Mode. The device triggers IPAP when
flow sensors detect spontaneous inspiratory effort and
then cycles back to EPAP.
• T (Timed) Mode. Here the IPAP/EPAP cycling is purely
machine-triggered, at a set rate, typically expressed in
breaths per minute.
• S/T (Spontaneous/Timed) Mode. Here the machine
triggers to IPAP on patient's inspiratory effort, but there
is also a 'backup" rate. This rate is set to ensure that
patients still receive a minimum number of breaths per
minute if they fail to breathe spontaneously. However,
this is not a ventilator mode and will not provide life
support for the continously apneic patient.
Confusing Points Clarified
• While BiPAP is generally better than CPAP for patients
with CO2 retention, or who need augmentation in
alveolar ventilation, there is no rule of thumb about
which BiPAP mode is 'best'. That can only be
determined with a careful titration of pressures in the
hospital or sleep lab.
• BiPAP AVAPS machine designed specifically for
patients with hypoventilation disorders (e.g., restrictive
thoracic disorders, obesity hypoventilation syndrome,
some cases of central apnea and COPD). Not to be
confused with ASV, AVAPS is not for complex sleep
apnea or sleep apnea unresponsive to CPAP and BiPAP
(which are the indications for ASV).