Adaptive servo-ventilation
(Anticyclic Modulated Ventilation)
BY
AHMAD YOUNES
PROFESSOR OF THORACIC MEDICINE
Mansoura Faculty of Medicine
Adaptive Servo Ventilation
• Adaptive servo-ventilatio (ASV) is a form of "BiPAP". The difference
is that ASV varies IPAP and/or EPAP to adjust ventilation as needed
by the patient.
• With traditional BiPAP the pressures are set and don't vary.
• At some point in the late 1990s ResMed Corporation developed an
ASV machine, and had it tested in heart failure patients with CheyneStokes respiration. C-S respiration, often occurs during sleep in
patients with congestive heart failure.
• The first clinical article to appear on ASV was Teschler H, et al.
Adaptive pressure support servo-ventilation: a novel treatment for
Cheyne-Stokes respiration in heart failure. 2001.
• Over the next decade more articles appeared showing that ASV
could treat not only Cheyne-Stokes respiration, but a syndrome that
wasn't even recognized in 2001: Complex Sleep Apnea.
Principal Indications
1) Central sleep apnea unresponsive to CPAP or BiPAP.
2) Complex sleep apnea.
BiPAP sets two pressures above the ambient, a higher (IPAP) and a
lower (EPAP), e.g., 10/5 cm H2O. In BiPAP the higher pressure is
experienced on inspiration and the lower pressure on expiration.
Note that both pressures are always above ambient.
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.
Autobilevel positive airway pressure with a
minimum (EPAP) of 6 cm H2O and a maximum
(IPAP) of 25 cm H2O.
BiPAP AVAPS
ASV is a variant of BPAP that was developed to treat CheyneStokes central apnea.
Both ASV and BPAP devices with a backup rate are approved for
use with patients with central apnea and complex sleep apnea
The ASV device responds to variation in flow by increasing
PS when flow and ventilation are low and decreasing PS
when flow is high
.
Servoventilation devices
• Three servoventilation devices are in current clinical use
:VPAP-AdaptSV (ResMed Corp, San Diego, CA) ,BiPAPAutoSV (Respironics, Murraysville, PA) and SomnoVent CR
• Algorithms of action for either VPAP-AdaptSV ,BIPAP
AutoSV or SomnoVent CR are proprietary and not
accessible to the medical community.
SomnoVent CR
Respironics autoSV
ResMed VPAP Adapt SV
What kind of mask is used?
• ResMed specifies their brand of full face mask for the
ResMed VPAP Adapt SV machine.
• ResMed VPAP Adapt SV: EPAP [expiratory positive airway
pressure] = 7.0 cm H2O, Minimum PS [pressure support] =
4.0 cm H2O, Maximum PS = 13.0 cm H2O, via ResMed
Quattro Full Face Mask (mask recommended by ResMed
with this machine), with heated humidity.
• Respironics autoSV: EPAP [expiratory positive airway
pressure] = 7.0 cm H2O, Minimum PS [pressure support] =
4.0 cm H2O, Maximum PS = 13.0 cm H2O. Respironics
states their machine can be used with virtually any mask.
• Note: Respironics has an upgraded version of auto SV,
called autoSV Advanced. The auto SV Advanced machine
allows the EPAP to vary along with the PS (pressure
support) level. In the auto SV you would set a lower and
higher EPAP, e.g., EPAP-min = 7, EPAP-max = 12.
Medicare Coverage Guidelines
• for Central sleep apnea, defined as:
1. Study showing AHI > 5 events/hr. and
2. Central apneas/hypopneas greater than > 50% of the
total apneas/hypopneas, and
3. Central apneas or hypopneas >=5/hr., and
4. Symptoms of either excessive sleepiness or disrupted
sleep.
• for Complex sleep apnea
CompSA is a form of central sleep apnea specifically
identified by the persistence or emergence of central
apneas or hypopneas upon exposure to CPAP or Bilevel device when obstructive events have disappeared.
These patients have predominantly obstructive or mixed
apenas during the diagnostic sleep study occurring at
>= 5 times per hour. With use of a CPAP or Bi-level, they
show a pattern of apneas and hypopneas that meets the
definition of CSA described above.
ASV is a CONFUSING term, for several reasons.
1) It is a manufacturers' proprietary trade mark, owned by ResMed
Corporation. ResMed was the first company to come out with this
type of 'smart' machine, which is designed for treatment of central
sleep apnea and complex sleep apnea.
2) Another equipment company, Philips Respironics, has come out with
a competing machine for the same set of conditions. Respironics
calls its machine BiPAP-autoSV, which stands for 'automatic servo
ventilation.' Obviously this is also 'ASV' but Respironics can't market
their machine as 'ASV' and they always use the term "autoSV".
3) The algorithms that govern these machines are both proprietary,
which means they can't be duplicated by any other machines on the
market.
4) The manufacturers use a variety of abbreviations, often without
explanation, in their brochures and web sites. Sometimes they use
"EEP" (end-expiratory pressure) to indicate what is more commonly
called "EPAP" (expiratory positive airway pressure), and "PS"
(pressure support) to indicate "IPAP" (inspiratory positive airway
pressure).
In summary, ASV-type machines are an evolving technology, and the
terminology is not as well defined as it is with BiPAP and CPAP.
Adaptive servo-ventilation
• Central sleep apnea (CSA) and periodic breathing is frequently—but
not only—found in patients with chronic heart failure (Cheyne-Stokes
respiration,CSR) due to ischemic heart diseases, dilated
cardiomyopathy or arterial hypertension.
• Different studies showed a proportion of up to 50% of heart failure
patients affected with sleep-disordered breathing. However, many of
these patients do not only present with central disturbances or
periodic breathing but also suffer from obstructions of the upper
airways .
• CPAP is the treatment of choice for obstructions of the upper airways
during sleep. CPAP attenuates central breathing disturbances during
sleep and improves heart function and quality of life in heart failure
patients with OSAS .CPAP has been shown to reduce the figures of
central disturbances by 50%.
• ASV has been developed to more effectively improve CSA/CSR.
Adaptive servo-ventilation
• The algorithms of ASV increase the pressure during
hypopneas and reduce it during hyperventilation.
• ASV has been shown to improve respiratory disturbances
in patients with CSA/CSR, complex sleep apnea and mixed
sleep apnea, and to be significantly more effective than
CPAP, bi-level therapy, non-invasive ventilation, and
oxygen
• For patients with OSA, auto-adjusting CPAP (APAP)
devices were developed with the aim of achieving optimal
adaptation of the treatment pressure to the actual
requirement of the patients.
• APAP reduces the treatment pressure substantially and is
preferred by patients.
• combination of adaptive servo-ventilation and
automatically adjusting CPAP might be the optimal
treatment for patients with both Cheyne-Stokes respiration
and OSAS.
What are the principal uses in the ACUTE SETTING?
• ASV via face mask is not used in the acute setting.
• ASV as a ventilatory mode in intubated patients is used occasionally.
One study (Intensive Care Med. 2010 Aug;36(8):1371-9. Epub 2010 May
26. Adaptive support ventilation versus conventional ventilation for total
ventilatory support in acute respiratory failure. Iotti GA, et. al.) found that
"Comparison between ASV and CV [controlled ventilation] resulted either
in similarities or in minor differences. Except for excessive Vt in a few
obstructed patients, all differences were in favor of ASV.“
• ASV is currently used almost exclusively in the NON-ACUTE SETTING
setting, for patients with 'complex sleep apnea'. CompSA, Thus, ASV is
indicated for situations when CPAP or BiPAP has failed.
• Even so, it remains somewhat unsettled about when ASV should be
used, how effective it is, and how to follow up such patients.
Principal Indications
• There are two principal indications:
1)Central sleep apnea
2) Complex sleep apnea.
• Central sleep apnea can basically be divided into
Cheyne-Stokes (C-S) and non-Cheyne Stokes
breathing.
What kind of mask is used to deliver
ASV?
• ResMed recommends their full face mask. Shown below is the
ResMed Quattro Pro full face mask.
ResMed VPAP Adapt SV:
• Backup rate: 12 breaths/minute
• Rise time: (the time it takes the device to change from EPAP to
IPAP. Settings range from 1 [fastest] to 6 [slowest]. The range
of values corresponds to 1/10 seconds, so that a rise time of 4
= 0.4 seconds)
• Inspiratory time: 2 seconds (range is 0.5 to 3.0 seconds)
• EPAP [expiratory positive airway pressure] = 7.0 cm H2O
• Minimum PS [pressure support] = 4.0 cm H2O
• Maximum PS = 13.0 cm H2O
• Maximum pressure for device (generally <=30 cm H2O)
• Mask: ResMed Quattro Full Face Mask (recommended by
company for their ASV machine), with heated humidity
Rise time
Costs
• ResMed's VPAP Adapt SV is probably the same price as
Respironics AutoSV machine, which is $5800.
• In addition there is the cost of the mask, and also the sleep
studies needed before any machine can be prescribed.
Respironics AutoSV
• ASV" as a label and a particular
methodology to adjust pressures was
patented by ResMed.
• A few years later, another large equipment
manufacturer, Philips Respironics, came out
with their own ASV-type machine; they call it
"autoSV."
• Auto SV is also an adaptive servo ventilator
device that uses a different algorithm to
adjust bilevel pressures.
• A newer model is called Auto-SV Advanced.
The device tracks flow. "The flow signal is analyzed and a target flow is
calculated. If the patient reaches the flow target, the device does not offer
any additional pressure support. If the patient does not reach the flow target
the device will dynamically change pressure support breath to breath .The
device tracks peak flow over a 4-minute cycle, as shown below.
•
A peak flow target is established around the 4-minute average and the
machine changes the air delivery as needed, to deliver 90% of the target,
as shown below.
Below is the pressure curve from Repironics regular AutoSV
machine, taken from a Respironics bronchure .
Principal Indications
1-Central sleep apnea
2-Complex sleep apnea
What kind of mask is used to deliver
ASV?
• Respironics states any mask used for
CPAP should work with their auto SV
machine.
• Below is the Respironics Comfort Gel
full face mask.
Respironics AutoSV
• Respironics currently has TWO devices, the
regular AutoSV and the AutoSV Advanced.
• Respironics recommends that physcians
now prescribe ONLY the AutoSV Advanced,
so it seems likely that the regular machine
will be phased out soon.
• Regular Auto SV
For the regular AutoSv you can use the
same prescription example as listed under
ResMed.
SOMNOvent CR
SOMNOvent CR
• Respiratory disturbances are detected based on the
analysis of actual minute ventilation, flow profile and
snoring.
• The minute ventilation is compared with the
average minute ventilation in a moving window
• The treatment mode is called anticyclic modulated
ventilation (ACMV).
The difference between IPAP and EPAP defines the tidal
volume. The EEPAP varies automatically due to the level
of the upper airway obstruction
Variation of treatment pressures during Cheyne-Stokes respiration. During
hypopneas the difference between IPAP and EPAP progressively increases,
while there is no inspiratory pressure support during hyperventilation. When
the patient breathes normally the pressure is relieved in expiration. The user
has to set the lower level of the EEPAP and the upper limit of the IPAP.
Screen-shot of a patient treated with ACMV.
SOMNOvent CR
• Device which combines automatic CPAP and
adaptive servo-ventilation proved to effectively
suppress all types of upper airway obstructions,
such as snoring, obstructive apneas and
hypopneas. Moreover, central respiratory
disturbances including periodic breathing were
deleted , and sleep quality improved.
• The results did not differ whether or not patients
suffered from cardiovascular diseases.
The device incorporates different features for
treating breathing disturbances non-invasively.
• It automatically adapts the positive airway pressure at the end of the
expiration, as this period of the breathing cycle is critical for the
opening of the upper airways.This component represents the
automatic CPAP mode which has proven effective in the treatment of
OSAS.
• In periods of normal breathing the expiratory pressure is relieved.
• The device applies varying tidal volumes which are defined by the
difference between IPAP and EPAP (pressure level in the early
expiration period). Thus, periodic breathing is overcome by
increasing the tidal volume during central hypopneas and decreasing
it during hyperventilation.
• Mandatory breaths are applied if there is complete cessation of the
airflow due to central apneas.
• The back-up frequency has been designed to avoid inducing
hypoventilation.
• While apneas can be identified undoubtfully in most
cases, central and obstructive hypopneas might be
difficult to discriminate based on standard
polysomnographic parameters.
• Esophageal pressure is hardly accepted in clinical
settings and re-evaluation studies.
• Therefore, we scored central hypopneas based on the
analysis of the inspiratory flow curve and the pattern of
the effort parameters.,
• One important advantage of the here presented
algorithm is the automatic discrimination between
obstructive and central disturbances and the
consecutive automatic adaptation of the end-expiratory
pressure.
• Many patients with OSAS present with at least a minor
portion of central disturbances, and CPAP or bi-level
therapy may induce CSA/CSR.
• The co-existence of obstructive and central
disturbances likely represents the common
pathophysiology . Thus, central apneas have been
found to be frequently accompanied by upper airway
occlusion ; periodic breathing in hypoxic conditions
results in upper airway narrowing .
• In heart failure, there is evidence for an overnight shift
in predominance of obstructive apneas to central
apneas .
• Similar to upper airway obstructions, central apneas
increase in the supine position and can be reduced
under CPAP treatment. For these aspects a trial of CPAP
can be recommended as first step in the treatment of
patients with co-existing obstructive and central
disturbances.
Complex sleep apnea syndrome
• Several studies have shown that central apnea
activity may disappear with continued CPAP use in a
subset of patients.
• Based on that, it has been postulated that in a
subset of patients, ‘‘complex sleep apnea’’ may then
merely reflect difficulty adjusting to the PAP with
repeated ‘‘transitional’’, sleep-onset central apneas,
inadequate titration or over titration of PAP, or
substantial mask leak.
• There are a number of patients with complex apnea
patients who continue to have central apnea activity
even after years of CPAP use
• If complex sleep apnea ("Comp SA") is a result of CPAP,
BiPAP may be tried, though it is not usually successful.
When Comp SA doesn't respond to BiPAP, or is a result
of BiPAP in the first place, there are two choices:
a) Continue CPAP or BiPAP to treat the OSA, hoping that
the central apneas will remit over time (they sometimes
do);
b) Start the patient on ASV.
• There is no clear standard about when to start ASV on
patients who manifest Comp SA.
• Mask type and size is best determined in the sleep lab,
when a patient is being titrated on an ASV machine.
Conclusions
• ASV is a way station on the road to newer and smarter
machines.
• Expense (about $6000 per machine) limits their wider
use, but no doubt these machines will become cheaper
and at some point replace our basic CPAP/BiPAP units.
• Despite the fact that the proprietary algorithms are
rather opaque, three machines seem to work well in
their stated objectives of treating central sleep apnea
and complex sleep apnea.
• As such, they compete in the market for treatment of
these conditions.
• From the standpoint of the sleep medicine specialist,
neither machine is clearly superior or inferior.
Conclusions
• Since ResMed was first out with an ASV machine, most
of the articles in the medical literature are based on
ResMed's device, but there are now several publications
for autoSV and Somnovent CR as well.
• More importantly, this is a rapidly evolving field, and
new machines will likely appear soon, from these three
companies as well as other competitors.