Positive end-expiratory pressure

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.^[1] The two types of PEEP are extrinsic PEEP (PEEP applied by a ventilator) and intrinsic PEEP (PEEP caused by a non-complete exhalation). Pressure that is applied or increased during an inspiration is termed pressure support.

Intrinsic PEEP (auto)

Auto (intrinsic) PEEP — Incomplete expiration prior to the initiation of the next breath causes progressive air trapping (hyperinflation). 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.^[2] When auto-PEEP persists despite management of its underlying cause, applied PEEP may be helpful if the patient has an expiratory flow limitation (obstruction).^[3][4]

Extrinsic PEEP (applied)

Applied (extrinsic) PEEP — is usually one of the first ventilator settings chosen when mechanical ventilation is initiated. It is set directly on the ventilator.

A small amount of applied PEEP (4 to 5 cmH₂O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse.^[5] 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.^[6]

Complications

Positive end-expiratory pressure can contribute to:

• Decrease in systemic venous return
• Pulmonary barotrauma 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. ^[7][8]
• Renal functions and electrolyte imbalances, due to decreased venous return metabolism of certain drugs are altered and acid-base balance is impeded.^[9]

History

John Scott Inkster an English anaesthetist and physician is credited with discovering PEEP.^[10]

See also

• Positive pressure ventilation
• Positive airway pressure

References

1. "Positive end-expiratory pressure (PEEP)". TheFreeDictionary.com. Citing: Saunders Comprehensive Veterinary Dictionary. 2007.
2. Caramez, MP; Borges, JB; Tucci, MR; Okamoto, VN; et al. (2005). "Paradoxical responses to positive end-expiratory pressure in patients with airway obstruction during controlled ventilation". Crit Care Med 33 (7): 1519–28. doi:10.1097/01.CCM.0000168044.98844.30. PMC 2287196. PMID 16003057.
3. Smith, TC; Marini, JJ (1988). "Impact of PEEP on lung mechanics and work of breathing in severe airflow obstruction". J Appl Physiol 65 (4): 1488–99. PMID 3053583.
4. Kondili, E; Alexopoulou, C; Prinianakis, G; Xirouchaki, N; et al. (2004). "Pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease". Intensive Care Med 30 (7): 1311–8. doi:10.1007/s00134-004-2255-z. PMID 15054570.
5. Manzano, F; Fernández-Mondéjar, E; Colmenero, M; Poyatos, ME; et al. (2008). "Positive-end expiratory pressure reduces incidence of ventilator-associated pneumonia in nonhypoxemic patients". Crit Care Med 36 (8): 2225–31. doi:10.1097/CCM.0b013e31817b8a92. PMID 18664777.
6. Smith, RA (1988). "Physiologic PEEP". Respir Care 33: 620.
7. Frost, EA (1977). "Effects of positive end-expiratory pressure on intracranial pressure and compliance in brain-injured patients". J Neurosurg 47 (2): 195–200. doi:10.3171/jns.1977.47.2.0195. PMID 327031.
8. Caricato, A; Conti, G; Della Corte, F; Mancino, A; et al. (March 2005). "Effects of PEEP on the intracranial system of patients with head injury and subarachnoid hemorrhage: The role of respiratory system compliance". The Journal of Trauma and Acute Care Surgery 58 (3): 571–6. doi:10.1097/01.ta.0000152806.19198.db. PMID 15761353.
9. Oliven, A; Taitelman, U; Zveibil, F; Bursztein, S (March 1980). "Effect of positive end-expiratory pressure on intrapulmonary shunt at different levels of fractional inspired oxygen". Thorax 35 (3): 181–5. doi:10.1136/thx.35.3.181. PMC 471250. PMID 6770485.
10. Craft, Alan (December 13, 2011). "John Scott Inkster". BMJ (obituary) 343: D7517. doi:10.1136/bmj.d7517.