Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 216

 A small gradient in oxygen partial pressure normally exists between the alveoli (A) and the arterial blood (a).

 This gradient is due to:Normal physiologic shunting of blood through bronchial and coronary veins that drain deoxygenated blood directly into the left side of the heart.Normal ventilation‐perfusion gradients within the lung.

 The magnitude of the gradient (A‐a) can be calculated using the alveolar gas equation and by measuring the PaO2.

 Knowledge of the magnitude of the difference in the P(A‐a)O2 can indicate whether a functional deficit in O2 exchange exists.

 The significance of a calculated gradient is, however, dependent on the FiO2.

 Examples:A normal horse breathing room air, the P(A‐a)O2 gradient is <10 mmHg.A normal horse breathing 100% O2 may have a gradient up to 70 mmHg.

 Increases in P(A‐a)O2 may be due to:Anatomical shunting.V/Q mismatching.Diffusion impairment due to a thickened alveolar‐capillary membrane.