Positive End Expiratory
Pressure
Dr Muhammad Asim Rana
Description
• The ventilator applies a positive pressure at end
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exhalation, thus supra-atmospheric pressure is
maintained throughout the breathing cycle.
When applied during spontaneous breathing the
term CPAP is used
When applied to a mechanically ventilated
patient the term PEEP is used
When applied to end of exhalation the term
END-EXPIRATORY POSITIVE AIRWAY
PRRESSURE is used
• From a physiological point of view PEEP,
CPAP & EPAP are identical
• Different acronyms are delivered from the
controls of the equipment used to provide
them.
Advantages
1. Recruits & stabilizes the collapsed alveoli
2. Increases the FRC & prevents expiratory collapse
3. Improves oxygenation in conditions associated with
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diffuse alveolar collapse & hypoxemia
Used to decrease inspiratory work of breathing with
auto-PEEP
Decreases lung injury chances by maintaining
minimum lung volume (minimizes shear forces
associated with repetitive collapse & recruitment of
injured alveoli)
• Positive end-expiratory pressure (PEEP)
has lung protective effects during
mechanical ventilation in isolated lungs,
and in intact and open-chest animals.
• In intact healthy rats, edema and hemorrhage
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from ventilation with excessive lung volumes
were substantially reduced when PEEP was used
In a dog lung injury model lung injury was
caused by ventilation with large Vt and low
PEEP.
This injury was reduced in animals ventilated
with smaller Vts and higher PEEPs despite
similar EILVs.
• The effect of end-expiratory atelectasis on
lung injury was evaluated in a rabbit
surfactant-deficient model. Rabbits
ventilated with negative end-expiratory
pressure demonstrated greater alveolar
capillary permeability, reduced lung
compliance, and worse gas exchange than
rabbits ventilated with PEEP.
• These and other studies provide convincing
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evidence that PEEP has lung protective effects
during mechanical ventilation.
However, PEEP also can contribute to lung injury
by raising EILV unless Vt is simultaneously
reduced.
Moreover, PEEP may cause circulatory
depression from increased pulmonary vascular
resistance and decreased venous return.
Disadvantages
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Can impair cardiac output
Increases risk of barotrauma esp,>15 cm
Increases intracranial pressure
Decreases renal & portal blood flow
Can complicate data collection in pts of RHF
Increases extra vascular lung water
increases dead space if excessive
May increase inspiratory work of breathing if
over distention occurs
Indications
1. Hypoxia with FiO2 > 0.5 in pts with
diffuse B/L infiltrates (ARDS, Pul edema)
2. Cardiac surgery to prevent post operative
mediastinal bleeding
3. Post operative atelactasis
Determining the optimal level of
PEEP
• Determining the optimal level of PEEP in
individual patients represents a difficult
and tenuous balance between potential
lung protective effects and deleterious
effects on the lung and other systems.
• Some investigators have used static or
quasi-static pressure-volume curves of the
respiratory system to explain the effects of
ventilation at low EELV, to predict the
effects of ventilation with higher PEEPs
and EELVs, and to identify the best PEEP
to apply during Conventional Ventilation to
achieve lung protection.
• The slope of the pressure-volume
relationship represents compliance of the
respiratory system. Compliance in the
lower portion of the curve increases as
airway pressure and volume rise,
representing gradual recruitment of
atelectatic portions of the lung.
• This interpretation is supported by
improved arterial oxygenation53 and CT
evidence of increased lung aeration in
ARDS patients.
• The midpoint of the portion of the pressure-volume
curve with increasing slope is frequently labeled “Pflex”
and may represent the inspiratory airway pressure and
volume where many lung units are open.
• The mid-portion of the pressure-volume
curve appears to be virtually rectilinear.
This region of approximately constant
compliance has been interpreted to
represent a range of airway pressures and
lung volumes in which little or no further
recruitment occurs.
• Some workers have advocated setting
PEEP to approximately Pflex plus 2 cm
H2O to prevent the closure of unstable
lung units during expiration and, thus, to
prevent injurious shear forces from
ventilation with insufficient EELV.
• This recommendation is supported by the
results of studies suggesting that CV with
PEEP that is less than Pflex may cause
VALI.
Setting PEEP
• TECHNIQUE 1
• Begin at about 5 cm of H2O & increase in steps
of 2 cm H2O until optimal PEEP is achieved–
i.e,
PaO2>60,FiO2<0.5, hemodynamic stability
Achieving max static compliance of lungs
Intrapulmonary shunt fraction < 15%
Maximum VO2 (O2 consumption per unit of
time)
TECHNIQUE 2
• Sedate/paralyze the patient. Patient
should not be making any respiratory
excrsions
• Suction the respiratory secretions
• Ensure tight endotracheal/TT cuff seal
• Increase FiO2 to 1.0
• Deliver single breath via ventilator to
make patient achieve projected TLC
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Disconnect patient from ventilator
Allow patient to exhale to FRC
Take a super-syringe (filled with 1.0 FiO2)
Inflate lungs with 100 ml of O2 at a time pause for
2-3 seconds & measure Pel.
Keep inflating with 100 ml of O2 at each step until a
volume of 25 ml/kg is injected or airway pressure of
35 cm of H2O is reached or SaO2 starts falling <
87%
An inflation curve plotting press & vol is made
Best PEEP is slightly above lower inflection point.
Thank You