Positive end-expiratory pressure
Encyclopedia
Positive end-expiratory pressure (PEEP) is the pressure in the lungs (alveolar pressure
) above atmospheric pressure
(the pressure outside of the body) that exists at the end of expiration. The two types of PEEP are extrinsic PEEP (PEEP applied by a ventilator) and intrinsic PEEP (PEEP caused by a non-complete exhalation).
). 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
), 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).
chosen when mechanical ventilation
is initiated. It is set directly on the ventilator.
A small amount of applied PEEP (3 to 5 cmH2O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse. A higher level of applied PEEP (>5 cmH2O) is sometimes used to improve hypoxemia or reduce ventilator-associated lung injury
in patients with acute lung injury, acute respiratory distress syndrome, or other types of hypoxemic respiratory failure.
, hypovolemia
, pulmonary embolism
, dynamic hyperinflation without airflow limitation, or a bronchopleural fistula
. It may also have undesirable consequences in patients undergoing prone ventilation.
Alveolar pressure
Alveolar pressure is the pressure in centimeters of water pressure held within the alveoli of the lungs during inspiration. The pressure value is the difference from atmospheric pressure, which is considered zero when establishing the value....
) above atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
(the pressure outside of the body) that exists at the end of expiration. The two types of PEEP are extrinsic PEEP (PEEP applied by a ventilator) and intrinsic PEEP (PEEP caused by a non-complete exhalation).
Intrinsic PEEP (Auto)
Auto (Intrinsic) PEEP — Incomplete expiration prior to the initiation of the next breath causes progressive air trapping (hyperinflationHyperinflation
In economics, hyperinflation is inflation that is very high or out of control. While the real values of the specific economic items generally stay the same in terms of relatively stable foreign currencies, in hyperinflationary conditions the general price level within a specific economy increases...
). 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
Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...
), 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 PEEP (Applied)
Applied (Extrinsic) PEEP — Applied PEEP is usually one of the first ventilator settingsModes of mechanical ventilation
Modes of mechanical ventilation are one of the most important aspects of the usage of mechanical ventilation. The mode refers to the method of inspiratory support. Mode selection is generally based on clinician familiarity and institutional preferences since there is a paucity of evidence...
chosen when mechanical ventilation
Mechanical ventilation
In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...
is initiated. It is set directly on the ventilator.
A small amount of applied PEEP (3 to 5 cmH2O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse. A higher level of applied PEEP (>5 cmH2O) is sometimes used to improve hypoxemia or reduce ventilator-associated lung injury
Ventilator-associated lung injury
Ventilator-associated lung injury is an acute lung injury that develops during mechanical ventilation and is termed ventilator-induced lung injury if it can be proven that the mechanical ventilation caused the acute lung injury. In contrast, ventilator-associated lung injury exists if the cause...
in patients with acute lung injury, acute respiratory distress syndrome, or other types of hypoxemic respiratory failure.
Indications
- Intrapulmonary shunt and refractory hypoxemiaHypoxemiaHypoxemia is generally defined as decreased partial pressure of oxygen in blood, sometimes specifically as less than or causing hemoglobin oxygen saturation of less than 90%.-Distinction from anemia and hypoxia:...
. - Decreased Functional Residual CapacityFunctional residual capacityFunctional Residual Capacity is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration...
(FRC) and Lung Compliance.
Contraindications
Contraindications — There are no absolute contraindications to applied PEEP. However, applied PEEP can have adverse consequences (especially at high levels) and should be used cautiously in patients who have intracranial abnormalities, unilateral or focal lung disease, hypotensionHypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
, hypovolemia
Hypovolemia
In physiology and medicine, hypovolemia is a state of decreased blood volume; more specifically, decrease in volume of blood plasma...
, pulmonary embolism
Pulmonary embolism
Pulmonary embolism is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream . Usually this is due to embolism of a thrombus from the deep veins in the legs, a process termed venous thromboembolism...
, dynamic hyperinflation without airflow limitation, or a bronchopleural fistula
Bronchopleural fistula
A bronchopleural fistula is a fistula between the pleural space and the lung. It sometimes develops following pneumonectomy or an infection.-External links:* http://www.cuhk.edu.hk/med/ans/Trainee%20Manual/Respiratory%20Problems/BRONCHOPLEURAL.pdf...
. It may also have undesirable consequences in patients undergoing prone ventilation.
Complications
- Decreased venous return —
- Barotrauma — Pulmonary barotraumaBarotraumaBarotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid...
is lung injury that results from the hyperinflation of alveoli past the rupture point. - Increased intracranial pressure — In people with normal lung compliance, PEEP may increase the intracranial pressure (ICP) due to an impedance of venous return from the head.
- Alterations of Renal Functions and Water Metabolism — When PEEP is applied kidneys function in eliminating wastes, clearance of certain drugs, and regulating fluid, electrolyteElectrolyteIn chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
, and acid-base balance is inhibited.