Anest. intenziv. Med. 2025;36(1):22-28 | DOI: 10.36290/aim.2025.006

Alveolar-arterial oxygen difference in intensive careReview Article

Kutěj M.^{1, 2}, Haiduk F.^{1, 2}, Sagan J.^{3, 4}, Máca J.^{1, 5}

¹ Klinika anesteziologie, resuscitace a intenzivní medicíny, Fakultní nemocnice Ostrava a Lékařská fakulta, Ostravská univerzita, Ostrava

² Klinika dětské anesteziologie a resuscitace, Fakultní nemocnice Brno a Lékařská fakulta, Brno

³ Klinika infekčního lékařství, Fakultní nemocnice Ostrava

⁴ Katedra interních oborů, Lékařská fakulta, Ostravská univerzita, Ostrava

⁵ Ústav fyziologie a patofyziologie, Lékařská fakulta, Ostravská univerzita, Ostrava

The alveolo-arterial oxygen difference (P_(A-a)O₂) describes the difference between alveolar and arterial oxygen tension. The primary purpose of P_(A-a)O₂ is to distinguish between extra- and intra-pulmonary causes of hypoxemia. P_(A-a)O₂ has come to the forefront again in the context of the SARS-CoV-2 (COVID-19) coronavirus pandemic, where relatively simple methods of patient triage and therapeutic approaches have been sought. In the intensive care setting, where it is almost always obvious whether the cause of hypoxemia is extrapulmonary or intrapulmonary, the importance of P_(A-a)O₂ has shifted toward assessing the severity, dynamics, and therapeutic interventions for conditions associated with pulmonary impairment rather than to the initial differentiation between pulmonary and extrapulmonary causes of hypoxemia. This review article aims to present the body of published literature that addresses the use of P_(A-a)O₂ calculation in the intensive care setting.

Keywords: alveolo-arterial difference, alveolar-arterial gradient, alveolar gas equation, intensive care, ventilation-perfusion impairment, right-to-left shunt.

Received: January 8, 2025; Revised: February 21, 2025; Accepted: March 5, 2025; Prepublished online: March 26, 2025; Published: April 28, 2025  Show citation