Transcript Subject Characteristics


Continuous Positive Airway
Pressure Therapy
By
Ahmad Younis
Professor of Thoracic Medicine
Mansoura Faculty of Medicine
AMBIENT AIR PRESSURE
• It is the pressure around us wherever we are, at
sea level or the top of a high mountain.
• The weight of earth's atmosphere creates 'air
pressure', which we don't feel because it's evenly
distributed throughout our lungs.
• This pressure can be expressed in several
different units of measurement based on the
following conversions: 1 mmHg = 1.36 cmH2O =
0.133 k Pa (kilo-pascal) = 1.33 hpa (hecto-pascal)
In this figure , blue is mercury, and the distance
from 'B' to 'A' is the barometric or air pressure. If
the open pan of mercury is at sea level then the
height of the column (from 'A' to 'B') is 760 mm Hg
and the sea level air pressure is said to be '760
mm Hg'.
The ambient air pressure decreases with altitude, simply because as
you go higher, there is less quantity of air to weigh on the surface.
This is shown in this figure , where PB is the barometric pressure at
a given altitude. (PO2 is the partial pressure of oxygen at that altitude )
Mechanisms of breathing
• We breathe by contracting respiratory muscles
(mainly the diaphragms) to expand the thorax
and thereby create a slightly negative airway
pressure relative to ambient pressure.
• This slightly negative pressure -- about -3 cm
H2O at rest -- allows fresh air to enter our lungs
and supply the blood with oxygen.
• Then we relax the respiratory muscles, and in
so doing exhale to create a slightly positive
pressure relative to ambient (+3 cm H2O); this
allows stale air full of carbon dioxide to leave
our lungs and enter the atmosphere.
To simplify the numbers for these pressure changes we
always reference ambient pressure to zero. This has two
great advantages:
1-We don't have to use large numbers to show the change
in airway pressures during breathing;
2-Though the ambient pressure changes with altitude
(lower the higher up you go), zero as the reference point
can be used at any pressure. In other words, since the
ambient pressure is distributed evenly thoughout out
lungs, zero can be the reference point for any altitude.
Non Invasive Positive Pressure Ventilation
• Noninvasive ventilation (NIV) refers to the
provision of mechanical ventilation (MV) through
the patient’s upper airway by means of a mask
without the use of an invasive artificial airway
(endotracheal tube or tracheostomy) .
• NIV has long been used as the standard method to
treat patients with chronic respiratory failure (CRF)
related to chest wall diseases, neuromuscular
disorders, or central hypoventilation .
• It has been shown to be effective in treatment of
different forms of acute respiratory failure (ARF)
Non Invasive Positive Pressure
Ventilation for SDB
• Studies have shown CPAP to increase upper
airway size, especially in the lateral dimension.
• Positive intraluminal pressure expands the
upper airway (pneumatic splint) and increase in
lung volume due to CPAP (due to a downward
pull on upper airway structures during lung
expansion “tracheal tug”), may also increase
upper airway size and/or stiffen the upper
airway walls, making them less collapsible
Positive airway pressure (PAP) can
1-Bring the AHI down to below 5 to 10/hr in the
majority of patients.
2-Improves arterial oxygen saturation and
decreases respiratory arousals.
3-Increase the amount of stage N3 and stage R.
NB :
1-An occasional patient with very severe apnea
will have a large REM or stage N3 sleep rebound
on the first night of PAP treatment.
2-The most difficult problem with PAP treatment is
that adherence is suboptimal in a large
percentage of patients.
Mechanism of upper airway occlusion in obstructive sleep
apnea and its prevention by continuous positive airway
pressure: “pneumatic splint” effect.
Change in the upper airway of a normal individual after
application of CPAP of 0 cm H2O (A) and CPAP of 15 cm H2O (B).
The airway increases in size mainly in the lateral dimension.
MODES OF PAP
CPAP
• CPAP was developed in 1981 by Professor Colin
Sullivan (Royal Prince Alfred Hospital in Sydney,
Australia) for treating patients with severe sleep
apnea.
• Within a few years, CPAP was commercially
available in the U.S., and replaced tracheostomy
as treatment of choice for severe OSA.
• Without doubt ,CPAP was the catalyst for
widespread development of sleep labs to diagnose
OSA and for the evolution of sleep medicine as a
recognized medical specialty.
CPAP
• With CPAP the patient is exposed to an airway pressure
above the ambient or room air pressure, which is always
referenced to zero.
•A CPAP of 5 cm H2O means the patient is continually
breathing against an airway pressure 5 cm H2O above the
ambient or 'zero' pressure.
•The pressure curve looks the same as if breathing at
ambient pressure, so that inspiratory and expiratory
pressure are still below and above the baseline,
respectively.
• Because the pressure is set at some specific level above
ambient (usually in the range of 5 to 15 cm H2O) CPAP can
be thought of as 'uni-level' positive airway pressure
(though it is never called that), to distinguish it from bilevel
positive airway pressure or BiPAP.
Top: Normal pressure curve (pressure measured at the
mouth level) breathing at ambient ("0") pressure; airway
pressure is @ -3 cm H2O at peak of inspiration (I) and @ +3
cm H2O at peak of expiration (E).
Bottom: Pressure curve when CPAP = 5 cm H2O; the
baseline pressure against which the patient breathes is
raised 5 cm H2O above ambient.
CPAP as the name implies, requires the airway
pressure to be constant between inspiration and
expiration.
• Such a pressure is achieved by a servo-controlled air compressor
that maintains the airway pressure as closely to the prescribed
pressure despite the pull (inspiration) and push (exhalation) of the
patient.
• The maintenance of such pressure within an FDA-specified
pressure range (for example, ± 1.5 cm H2O of the set pressure) is
necessary as a quality-assurance measure that would ensure that
the device maintains a certain prescription pressure for the patient.
• Such a pre-specified error range is generally greater with larger
tidal volume (VT) or inspiratory effort from patient, faster
respiratory rate, and at higher prescription pressure settings,
because the device would need to be more rapidly responsive to
the perturbations in the airway pressure at such extremes to
maintain the pressure at the prescribed level.
Representative tracings of flow, tidal volume, and airway
pressure (Paw) during administration of continuous positive
airway pressure (CPAP) and bi-level PAP
Physiological effects of positive airway pressure (PAP) therapy. PAP therapy splints
the upper airway (black crosses and arrows), achieves positive intra-thoracic pressure
(white crosses), decreases venous return, increases lung volume, decreases afterload, and can increase cardiac output. The bidirectional vertical arrows signify the
traction on the upper airways affected by the increase in end-expiratory lung volume.
Such a traction effect can assist in the splinting open of the upper airway.
CPAP treatment
• Non-acute setting: Treatment of obstructive
sleep apnea.
• Acute setting: Pulmonary edema or COPD
exacerbation, when there is hypoxemia but not
CO2 retention.
Note: CPAP by face mask = PEEP in the intubated
patient.
BiPAP treatment
• Non-acute setting
1) When CPAP doesn't work for OSA (need high pressure
or not tolerant due to high expiratory pressure).
2) For patients with chronic CO2 retention who also have
OSA.
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
indotracheal intubation.
Note: BiPAP by face mask = PSV + PEEP in the intubated
patient.
How is the pressure applied
non-invasively?
• Via a tight fitting mask attached in such a way
that air can be blown into the nose or the nose
and mouth.
• The mask connects to a hose that is attached to
a CPAP machine .
• The mask choices are the same whether the
patient is using CPAP or BiPAP.
• Generally there are 3 types: nasal mask, nasal
pillows, and full face mask.
The nasal mask (left) and nasal pillows
(middle) and full face mask (left)
Left: Nasal pillows. Center. Total
face mask. Right: Helmet.
A: Mouth piece devices B: Mouthpiece with lip-seal.
C: Patient using an angled mouthpiece D: Patient
using mouthpiece with lip-seal .
Interfaces
• Nasal pillow masks are often better tolerated
than traditional nasal masks by patients with
claustrophobia and are useful in patients with a
mustache or edentulous patients who have no
dental support for the upper lip.
• For patients who have severe nasal congestion
or open their mouths during PAP treatment,
oronasal (full face masks) and oral interfaces
are available
• If the patient gets up to use the bathroom during
the night, we encourage disconnection of the
hose from mask rather than taking off the mask.
Masks that are removed in the middle of the
night are often not replaced.
Measures for nasal mask ( height and width of actual nose )
Template for assessment of suitable
mask size for the patient
Examples of commercially available
chin straps.
Measures for full face mask ( height from under lower lip
to bridge of the nose and width of mouth)
A: Mask with inflatable cushion. B: Mask with foam-filled cushion. C:
Mask with inner lip that fits to the face when pressure is applied to the
mask. D: Mask with a gel-filled cushion.
Forehead spacer designs to decrease the risk of facial skin
breakdown. Left : Gel spacer. Center: Foam spacer. Right:
Adjustable forehead arm.
Facial skin breakdown secondary to mask used
for noninvasive positive-pressure ventilation.
Rebreathing
• The interface can affect the degree of rebreathing
during NPPV if the ventilator circuit has a leak port
for exhalation.
• In a lung-model study, a lower volume of
rebreathed CO2 with the exhalation port in the
mask is found as compared to the exhalation port
in the circuit. also an oronasal mask with the
exhalation port in the mask decreased the total
dynamic dead space, compared to having the leak
port in the circuit.
• With a nasal mask, the patient can exhale through
the mouth, which should decrease rebreathing.
Separate exhalation device or
exhalation port in the circuit .
CPAP machine.
Confusing Points Clarified
• CPAP does not, technically, provide
'ventilation' to the patient.
• It sets a single higher ambient pressure
against which the patient breathes, but
does not augment alveolar ventilation.
• If your goal is to improve someone's
PaCO2 non-invasively (i.e, to treat
hypercapnia), CPAP is not the method of
choice; instead, BiPAP is recommended.
Another clarification about CPAP is that it is a generic term,
not any manufacturer's trademark, like BiPAP and ASV.
• It is offered on machines from multiple
companies, all of whom may use the term 'CPAP'.
• Manufacturers may embellish their CPAP with little
twists which are patented, and seldom adequately
explained. An example is Respironics' CFlex and
CFlex+. They are 'pressure relief' modes that
abruptly drop the pressure in the transition from
inspiration to expiration, to a sharper degree than
would occur with passive exhalation.
• CFlex comes in 3 levels, 1, 2 and 3, representing
roughly 1, 2 or 3 cm H2O drop in pressure. CFlex+
is supposed to be an advance over regular CFlex.
Flexible Pressure
Two manufacturers of PAP devices have
developed flexible PAP
1- Philips-Respironics provide several comfort
options (Cflex, Cflex+, and Aflex)
2- ResMed devices offer expiratory pressure relief
(EPR).
In Cflex, expiratory pressure drops at the start of
exhalation but returns to the set CPAP at endexhalation. The amount of drop (Cflex 1, 2, 3) is
determined by a proprietary algorithm.
• Cflex+ adds a smoothing of the transition from
inhalation to exhalation.
• Aflex is a form of APAP that provides a 2 cm
H2O lower end-expiratory pressure than the
inspiratory pressure (in addition to the features
of Cflex*
A form of expiratory pressure relief is available
For both BPAP and autoBPAP devices, (Biflex).
The technology provides a smoothing of
transition from IPAP to EPAP as well as
expiratory pressure relief during the EPAP cycle
(Biflex 1, 2, 3).
C-Flex+ is new enhancement to comfort relief for advanced CPAP
units (REMstar Pro and Auto) when in fixed CPAP mode. Like C-Flex,
C-Flex+ provides flow-based pressure relief at the beginning of
exhalation. Like A-Flex, C-Flex+ softens the pressure transition from
inhalation to exhalation to provide additional comfort in fixed-CPAP
mode.
B-Flex found in the BiPAP
Ramp
• Most PAP devices, with the exception of certain
APAP devices, allow the patient to trigger the
ramp option.
• In the ramp option, the pressure starts at a
preset level—usually a low level of CPAP—and
then slowly increases to the treatment pressure
(CPAP) over the set ramp time
• Some APAP devices have a “settling time” at a
low pressure before the device starts autoadjusting pressure
0
Ramp
Humidification
• Most PAP devices come with the option of an
integrated heated humidification system.
• They can be used in the cool humidity mode if desired.
• Heated humidity can deliver a greater level of
moisture than cool humidification and may be
especially useful in patients with mouth leak or nasal
congestion.
• Mouth leak can cause a dramatic fall in relative
humidity and a loss of humidity from the upper
airway/CPAP system, thus drying the nasal or oral
mucosa.
• Use of heated humidification is recommended to
improve CPAP utilization.
In the clinical guidelines for titration, having HH available
for titration was recommended
OXYGEN AND YOUR PAP UNIT
• Your tubing is connected to the large end on
the tee adapter and the small tubing from your
oxygen system is connected to the small
nipple on the tee adapter.
• Always turn your CPAP or bi-level
unit ON before turning ON the
oxygen flow.
• Always turn OFF the oxygen before
turning OFF the CPAP or bi-level unit
In the ACUTE SETTING
•CPAP is used for patients with low oxygen saturation in
whom O2 at ambient pressure (nasal cannula, loose fitting
face mask) is not sufficient.
•The increased ambient pressure provided by CPAP 'recruits'
or opens up more alveoli, allowing supplemental oxygen to
better oxygenate the blood.
•Conditions commonly treated with CPAP in the ACUTE
SETTING include pulmonary edema (cardiac and noncardiac) and COPD exacerbation.
•If the condition doesn't improve and CPAP is not effective,
generally the next step is intubation and mechanical
ventilation.
Medicare Coverage Guidelines for
long term 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.
• Note that there are additional criteria for continued
coverage, including a face-to-face evaluation between the
31st and 90th day of treatment.
Posbiopsy procedure