Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 215

 The partial pressure of oxygen in the alveoli can be determined using a simplified version of the alveolar gas equation:FiO2 = Fraction of inspired oxygen ≈ 0.21.PB = Atmospheric pressure (760 mmHg at sea level).PH2O = Water vapor pressure (mmHg) in airway (~50 mmHg at body temp of horse).R = Respiratory gas exchange ratio (~0.8).

 This calculation emphasizes the significance of FiO2 and PaCO2 on the alveolar gas partial pressure.

 Clinically, this equation highlights the significance of O2 supplementation for patients with impaired ventilation.

Example 1. Horse breathing room air (21% O₂) with a PaCO₂ = 35 mmHg.

Example 2. Horse breathing 100% O₂ with a PaCO₂ = 35 mmHg.

Example 3. Anesthetized horse hypoventilating on room air (PaCO₂ = 70 mmHg)

 Although this horse is hypoxemic, a PaO2 of <60 mmHg is fairly typical for anesthetized horses breathing room air.

 This example emphasizes how an increase in PaCO2 affects PAO2 and hence PaO2.

Example 4. Anesthetized horse hypoventilating on 100% oxygen (PaCO₂ = 70 mmHg)

 This example emphasizes the importance of providing O2 during anesthesia to prevent hypoxemia.