Subject Characteristics

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Continuous Positive Airway Pressure Therapy
By Ahmad Younis Professor of Thoracic
Medicine Mansoura Faculty of Medicine
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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)

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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'.
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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 )
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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.

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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.

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Non Invasive Positive Pressure Ventilation

• Noninvasive ventilation (NIV) refers to the
  provision of mechanical ventilation (MV) through
  the patients 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)

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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

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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.
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Mechanism of upper airway occlusion in
obstructive sleep apnea and its prevention by
continuous positive airway pressure pneumatic
splint effect.
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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.
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MODES OF PAP
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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.

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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.

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Top Normal pressure curve (pressure measured at
the mouth level) breathing at ambient ("0")
pressure airway pressure is _at_ -3 cm H2O at peak
of inspiration (I) and _at_ 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.
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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.

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Representative tracings of flow, tidal volume,
and airway pressure (Paw) during administration
of continuous positive airway pressure (CPAP) and
bi-level PAP
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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 after- load, 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.
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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.

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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.

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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.

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The nasal mask (left) and nasal pillows (middle)
and full face mask (left)
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Left Nasal pillows. Center. Total face mask.
Right Helmet.
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A Mouth piece devices B Mouthpiece with
lip-seal. C Patient using an angled mouthpiece
D Patient using mouthpiece with lip-seal .
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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.

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Measures for nasal mask ( height and width of
actual nose )
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Template for assessment of suitable mask size for
the patient 
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Examples of commercially available chin straps.
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Measures for full face mask ( height from under
lower lip to bridge of the nose and width of
mouth) 
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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.
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Forehead spacer designs to decrease the risk of
facial skin breakdown. Left Gel spacer. Center
Foam spacer. Right Adjustable forehead arm. 
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Facial skin breakdown secondary to mask used for
noninvasive positive-pressure ventilation.
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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.

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Separate exhalation device or exhalation port in
the circuit .
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CPAP machine.
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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.

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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.

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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
  end-exhalation. The amount of drop (Cflex 1, 2,
  3) is determined by a proprietary algorithm.

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• 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).

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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.
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B-Flex found in the BiPAP
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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 levelusually a low level of CPAPand 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 auto-adjusting
  pressure

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0
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Ramp
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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

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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

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• 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 non-cardiac) and COPD exacerbation.
• If the condition doesn't improve and CPAP is not
  effective, generally the next step is intubation
  and mechanical ventilation.

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• Medicare Coverage Guidelines for long term CPAP
• Face-to-face clinical evaluation by treating
  physician prior to sleep study
• 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.

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Posbiopsy procedure