Positive end expiratory pressure
A positive end-expiratory pressure ( PEEP , English positive end-expiratory pressure ) is a parameter in artificial ventilation. It describes a positive pressure in the lungs at the end of the exhalation (expiration). It is generated by a PEEP valve. A common unit of measurement for PEEP is millibars .
With artificial positive pressure ventilation , the most commonly used form of controlled ventilation, the pressure conditions in the lungs differ from those in normal breathing. For inhalation, air is pressed into the lungs with pressure. For exhalation, this applied pressure is removed and the pressure in the lungs adapts to the ambient air pressure again. If you look at the pressure conditions at the end of exhalation, for a moment the pressure in the lungs is the same as in the environment. The end-expiratory pressure difference compared to the environment is zero. In order to achieve a positive pressure in the lungs at the end of the exhalation and to hold it until the next inhalation, a PEEP valve is required. It prevents the pressure drop during exhalation from reaching ambient air pressure. The end-expiratory pressure difference compared to the environment then remains positive.
As a result of a PEEP, the mean airway pressure and the functional residual capacity and thus the gas-exchanging surface are increased. It can help prevent the alveoli from collapsing, thus preventing atelectasis . In addition, PEEP can reduce the work of breathing in the case of ventilation that supports spontaneous breathing. In addition, the oxygen saturation of the blood can be improved in many cases .
By increasing the pressure in the chest, PEEP reduces the return of venous blood to the heart , which can decrease cardiac output . Conversely, a back pressure arises in the upper and lower vena cava with corresponding increases in pressure in upstream organs. Depending on the level of the PEEP, this can damage the brain , liver , kidneys and other organs.
In virtually any mechanical ventilation, a moderate PEEP is at least used, for example in the treatment of drowning or diving accident , as well as in smoke - or carbon monoxide - intoxication . PEEP is also used in the treatment of pulmonary edema .
During operations on the neck ( goiter resection , thyroidectomy , carotid desobliteration, etc.), PEEP prevents air from entering large veins accidentally opened and thus preventing dangerous air embolism .
In the case of awake patients, a mask can also be used as part of mask CPAP . Here, too, there is a risk of stomach overinflation, albeit significantly less.
Relative contraindications for PEEP are obstructive airway diseases that tend to develop an intrinsic peep , such as asthma . Since the airway obstruction means that the expiration time is not sufficient for a complete pressure equalization, a positive pressure remains in the alveoli beyond the constriction.
Advantages and disadvantages
If the systems are carefully adapted, the disadvantages of the positive pressure in the exhalation phase are outweighed by advantages.
- Enlargement of the functional residual capacity , thereby increasing the gas exchange area , ventilation- perfusion ratio, reduced intrapulmonary shunts , increased oxygenation
- Avoidance of atelectasis
- Improvement of lung compliance
- Reduction of pulmonary edema
- Risk of barotrauma if the PEEP level is too high
- Increased right ventricular afterload
- Increase in intracranial pressure
- Wolfgang Oczenski, Harald Andel, Alois Werba: Breathing - breathing aids: breathing physiology and ventilation technology. Georg Thieme Verlag, 2012. ISBN 9783131520494 .
- Robert F. Schmidt , Florian Lang, Manfred Heckmann: Physiologie des Menschen. with pathophysiology . 31st edition. SpringerMedizin Verlag, Heidelberg 2010, ISBN 978-3-642-01650-9 , p. 715 .
- Rolf Dembinski: Non-invasive forms of ventilation. In: Anesthesia & Intensive Care Medicine. Volume 60, June 2019, pp. 308-315, here: pp. 312 f.
- Rolf Dembinski: Non-invasive forms of ventilation. In: Anesthesia & Intensive Care Medicine. Volume 60, June 2019, pp. 308–315, here: p. 312.