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PEER REVIEWED 46 JULY/AUGUST 2018 metabolic acidosis or those that have received certain medications (e.g., opioids or corticosteroids). Quantification of pulmonary function can provide more objective data to support the decision to supplement oxygen. Potential tools include measurement of pulse oximetry or arterial blood gas analysis. Oxygen saturation below 93% and an arterial partial pressure of oxygen below 70 mmHg should prompt oxygen supplementation. 1 These monitoring modalities may be inappropriate in animals with profound respiratory distress and rarely change the decision to provide oxygen in more severely affected patients. As mentioned above, it is often reasonable to provide oxygen to critical patients, even if other interventions are ultimately needed to stabilize them. Consequently, oxygen supplementation is often provided while other procedures are performed (e.g., obtaining vascular access, performing pericardiocentesis). Specific noncardiopulmonary disease processes (such as traumatic brain injury) may actually benefit greatly from oxygen supplementation. HOW SHOULD OXYGEN BE SUPPLEMENTED? Several options exist for providing supplemental oxygen. Whenever possible, the least stressful method should be considered, but this should be balanced with the ability to provide as much oxygen as needed with each method ( TABLE 2 ). For short-term oxygen supplementation, it is generally unnecessary to humidify the oxygen; however, long- term exposure of the respiratory epithelium to dry air may promote the development of respiratory infection. Humidification is easily achieved by bubbling oxygen through sterile saline or water. Flow-by Oxygen An easy method to provide supplemental oxygen is to hold oxygen tubing close to an animal's face ( FIGURE 2 ). This modestly enriches the fraction of inspired oxygen (FiO 2 ), but potentially only a few TABLE 1 Causes of Hypoxia HYPOXIA CATEGORY MECHANISM EXAMPLES Hypoxic hypoxia Insufficient oxygen available to lungs Low FiO 2 (e.g., anesthesia machine failure) Hypoventilation (e.g., coral snake envenomation, drug overdose) Ventilation perfusion mismatch (e.g., pulmonary disease) Anatomic shunting (e.g., patent ductus arteriosus) Diffusion impairment (e.g., pulmonary fibrosis) Anemic hypoxia Reduced hemoglobin content Immune-mediated hemolytic anemia Hemorrhage Circulatory hypoxia Cardiovascular impairment Hypovolemic shock Anaphylaxis Septic shock Cardiac tamponade Massive pulmonary thromboembolism Systolic failure (e.g., dilated cardiomyopathy) Histotoxic hypoxia Cells incapable of using oxygen Cyanide toxicity Mitochondrial dysfunction TABLE 2 Average Achieved FiO 2 Associated With Oxygen Supplementation Technique SUPPLEMENTAL OXYGEN TECHNIQUE AVERAGE FIO 2 ACHIEVED (%) Flow-by oxygen 25–40 Facemask 35–60 Oxygen hood 30–50 Oxygen cage 21–60 Unilateral nasal line 30–50 Bilateral nasal lines 30–70 Intubation (anesthesia machine) 100 Intubation (mechanical ventilator) 21–100 Adapted from Sumner and Rozanski. 3

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