The rationale for the application of PEEP during mechanical ventilation of the lungs of patients with ARDS is
to prevent alveolar collapse
, reducing injurious alveolar shear stresses and improving ventilation–perfusion matching, and thus, arterial oxygenation.
Why is PEEP increased?
Applying PEEP
increases alveolar pressure and alveolar volume
. The increased lung volume increases the surface area by reopening and stabilizing collapsed or unstable alveoli. This splinting, or propping open, of the alveoli with positive pressure improves the ventilation-perfusion match, reducing the shunt effect.
What is the best ventilation mode for ARDS?
As a treatment,
prone position ventilation
results in significantly better oxygenation than mechanical ventilation applied in the supine position in ARDS patients [46].
What should PEEP be for ARDS?
In the ARDS Network study, patients ventilated with lower tidal volumes required higher levels of PEEP (
9.4 vs 8.6 cm water
) to maintain oxygen saturation at 85% or more. Some authors have speculated that the higher levels of PEEP may also have contributed to the improved survival rates.
What does high PEEP mean on ventilator?
Application of unnecessary high PEEP (i.e., when PEEP does not result in lung recruitment)
increases transpulmonary pressures
, forcing West Zone 3 lung regions to Zones 2 and 1. This phenomenon increases dead space ventilation, resulting in hypercapnia when minute ventilation remains constant.
What is a normal PEEP level?
Applying physiologic PEEP of
3-5 cm
water is common to prevent decreases in functional residual capacity in those with normal lungs. The reasoning for increasing levels of PEEP in critically ill patients is to provide acceptable oxygenation and to reduce the FiO
2
to nontoxic levels (FiO
2
What is a potential complication of high PEEP?
Pulmonary barotrauma
is a frequent complication of PEEP therapy. Pneumothorax, pneumomediastinum, and interstitial emphysema may lead to rapid deterioration of a patient maintained on mechanical ventilation with an already compromised respiratory status.
How long can you stay on a ventilator with ARDS?
ARDS patients may require ventilation for long periods of time. On average this is
seven to 14 days
. Beyond this time, doctors may suggest a tube be placed directly into the windpipe through the neck (tracheostomy) by a surgeon. Usually the doctor believes it may take weeks more to recover from ventilator support.
How do you set PEEP in ARDS?
- Ventilate with a CPAP of 35 cmH
2
O for 45 seconds. - Then, set a PEEP of 20 cmH
2
O. - If a minimum tidal volume of 5 ml/kg cannot be achieved, decrease PEEP by 2 cmH
2
O until you get your minimum tidal volume. - Then, decrease PEEP by 2 cmH
2
O every 20 minutes.
What are the three stages of ARDS?
In ARDS, the injured lung is believed to go through three phases:
exudative, proliferative, and fibrotic
, but the course of each phase and the overall disease progression is variable.
What is the highest PEEP level on a ventilator?
PEEP of
29
appears to be the highest tolerated PEEP in our patient. We noted an initial rise in blood flow across all cardiac valves followed by a gradual decline.
What is a normal PEEP setting on a ventilator?
This, in normal conditions, is
~0.5
, while in ARDS it can range between 0.2 and 0.8. This underlines the need for measuring the transpulmonary pressure for a safer application of mechanical ventilation.
What is FIO2 normal range?
Natural air includes 21% oxygen, which is equivalent to F
I
O
2
of 0.21. Oxygen-enriched air has a higher F
I
O
2
than 0.21; up to 1.00 which means 100% oxygen. F
I
O
2
is typically maintained
below 0.5
even with mechanical ventilation, to avoid oxygen toxicity, but there are applications when up to 100% is routinely used.
What is best PEEP?
Best or optimal PEEP will be defined as the
PEEP below which PaO2 /FIO2 falls by at least 20%
. If at least 20% Partial Oxygen tension (PaO2) PaO2 /FIO2 decrement is not obtained, then PEEP that will result in the highest PaO2 will be selected.
What are PEEP values?
Positive end-expiratory pressure (PEEP) is a value that can be
set up in
patients receiving invasive or non-invasive mechanical ventilation.
Does high PEEP lower blood pressure?
Results. In both groups, the increase in PEEP led to an increase in CVP and airway pressure. When PEEP was above 4 cm H
2
O in the hypertension group,
a decrease in blood pressure
and ScvO
2
, and an increase of heart rate were observed. These results indicated that cardiac output significantly decreased.
