Positive end-expiratory pressure (PEEP) is the pressure in the lungs (
alveolar pressure Alveolar pressure (Palv) is the pressure of air inside the lung Pulmonary alveolus, alveoli. When the glottis is opened and no air is flowing into or out of the lungs, alveolar pressure is equal to the atmospheric pressure, that is, zero cmH2O, cmH2 ...
) above
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
(the pressure outside of the body) that exists at the end of
expiration
Expiration or expiration date may refer to:
Expiration
Expiration may refer to:
*Death
*Exhalation of breath, breathing out
*Expiration (options), the legal termination of an option to take an action
*Shelf life, or the time after which a product ...
. The two types of PEEP are extrinsic PEEP (PEEP applied by a ventilator) and intrinsic PEEP (PEEP caused by an incomplete exhalation). Pressure that is applied or increased during an inspiration is termed
pressure support Pressure support ventilation (PSV), also known as pressure support, is a spontaneous mode of ventilation. The patient initiates every breath and the ventilator delivers support with the preset pressure value. With support from the ventilator, the p ...
.
Intrinsic (auto-) PEEP
Auto-PEEP is an incomplete expiration prior to the initiation of the next breath causes progressive air trapping (
hyperinflation
In economics, hyperinflation is a very high and typically accelerating inflation. It quickly erodes the real value of the local currency, as the prices of all goods increase. This causes people to minimize their holdings in that currency as t ...
). This accumulation of air increases alveolar pressure at the end of expiration, which is referred to as auto-PEEP.
Auto-PEEP develops commonly in high minute ventilation (
hyperventilation
Hyperventilation is irregular breathing that occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blood. ...
), expiratory flow limitation (obstructed airway) and expiratory resistance (narrow airway).
Once auto-PEEP is identified, steps should be taken to stop or reduce the pressure build-up.
When auto-PEEP persists despite management of its underlying cause, applied PEEP may be helpful if the patient has an expiratory flow limitation (obstruction).
Extrinsic (applied) PEEP
Applied PEEP is usually one of the first
ventilator settings chosen when
mechanical ventilation
Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air ...
is initiated. It is set directly on the
ventilator
A ventilator is a piece of medical technology that provides mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently. Ventilators ...
.
A small amount of applied PEEP (4 to 5 cmH
2O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse.
A higher level of applied PEEP (>5 cmH
2O) is sometimes used to improve hypoxemia or reduce
ventilator-associated lung injury
Ventilator-associated lung injury (VALI) is an acute lung injury that develops during mechanical ventilation and is termed ventilator-induced lung injury (VILI) if it can be proven that the mechanical ventilation caused the acute lung injury. In c ...
in patients with acute lung injury,
acute respiratory distress syndrome
Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin colo ...
, or other types of hypoxemic respiratory failure.
Complications and effects
Positive end-expiratory pressure can contribute to:
* Decrease in
**systemic venous return, cardiac output, cardiac index
**pulmonary capillary wedge pressure (PCWP), preload, arterial blood pressure
* Increase in:
**Intrathoracic pressure, RV afterload (CVP and PAP)
**lung functional residual capacity
*Pulmonary
barotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in tensio ...
can be caused. Pulmonary barotrauma is lung injury that results from the hyperinflation of alveoli past the rupture point.
* The effects of PEEP on intracranial pressure (ICP) have been studied. Although PEEP is hypothesized to increase ICP due to impedance of cerebral blood flow, it has been shown that high PEEP does not increase ICP.
*Renal functions and electrolyte imbalances, due to decreased venous return metabolism of certain drugs are altered and acid-base balance is impeded.
History
John Scott Inkster, an English
anaesthetist
Anesthesiology, anaesthesiology, or anaesthesia is the medical specialty concerned with the total perioperative care of patients before, during and after surgery. It encompasses anesthesia, intensive care medicine, critical emergency medicine, ...
and physician, is credited with discovering PEEP.
When his discovery was published in the proceedings of the World Congress of Anaesthesia in 1968, Inkster called it Residual Positive Pressure.
See also
* (CPAP)
*
*
References
Respiratory system procedures
Intensive care medicine
Modes of mechanical ventilation
Respiratory therapy