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Small Animal Surgical Emergencies


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percentage of oxygenated hemoglobin, and, for sedentary patients, can be left in place for continuous monitoring (Figure 1.3). Many patients in respiratory distress will not tolerate the restraint necessary for arterial blood gas collection and thoracic radiographs, especially on presentation. If obtaining an arterial blood gas is feasible, findings may include decreased SpO2, decreased partial pressure of carbon dioxide (PaCO2) consistent with hyperventilation, increased PaCO2 consistent with hypoventilation, decreased partial pressure of oxygen (PaO2) consistent with hypoxemia, and an increased partial pressure of alveolar–arterial oxygen gradient P(A–a)O2). Calculation of the P(A–a)O2 gradient provides objective information on pulmonary function by removing the influence of ventilation on PaO2. When a patient is breathing 21% oxygen, the P(A–a)O2 should be less than 10–15 mmHg. When a patient is breathing 100% oxygen, the P(A–a)O2 should be less than 150 mmHg. If the P(A–a)O2 gradient is greater than 15 mmHg while breathing 21% oxygen, it is consistent with pulmonary dysfunction. For A–a gradient calculation, see the formula in Box 1.1.

Photo depicts continuous pulse oximetry assessment in a laterally recumbent dog receiving oxygen supplementation via nasal prongs.

      Preliminary evaluation of the ratio of SpO2 to fraction of inspired oxygen (FiO2) to the partial pressure of oxygen in arterial blood to FiO2 (PaO2/FiO2) showed good correlation between the two values in dogs. It is possible that with further investigation, the SpO2/FiO2 may become a reliable, less invasive alternative to determining PaO2/FiO2 [9].

      The partial pressure of alveolar–arterial oxygen (P(A–a)O2) gradient provides objective information on pulmonary function by removing the influence of ventilation on PaO2.

equation equation

       PAO2 = alveolar gas equation

       FiO2 = percentage of inspired O2

       Patm = atmospheric pressure (760 mmHg used at sea level)

       PH2O = water vapor pressure (53 mmHg 39°C for dogs/cats; 47 mmHg at 37°C in humans)

       R = respiratory quotient (approximately 0.8–0.9)

      Example Blood Gas

       PaCO2 = 24.2

       PaO2 = 59.5

       PAO2 = (0.21 × (760 – 53)) – (24.2/0.9)

       PAO2 = 121.6

       P(A–a)O2 = 121.6–59.5

       P(A–a)O2 = 62.1 (indicates hypoxemia is due to pulmonary dysfunction)

Photo depicts TFAST ultrasonographic appearance (still image) of a B-line, which is created by increased infiltrates in the pulmonary parenchyma allowing ultrasound penetration.

      The most important part of the cardiovascular assessment during emergency patient triage is the determination whether the patient is in shock. If shock is suspected, the type of shock and need for fluid therapy must then be determined. The common feature in all shock patients is inadequate cellular energy metabolism, which is