There are very few formal criteria for the use of oxygen in hospital. The American College of Chest Physicians and the
National Heart, Lung and Blood Institute has published the following recommendations for instituting oxygen therapy:
• cardiorespiratory arrest
• hypoxaemia (PaO2 < 8 0 kPa/60 mmHg or saturations < 90%)
• hypotension (systolic blood pressure < 100 mmHg)
• low cardiac output with metabolic acidosis
• respiratory distress (respiratory rate > 24 per minute).
Oxygen is also indicated in the perioperative period, in trauma or other acute illness, carbon monoxide poisoning, severe anaemia, and when drugs are used that may reduce ventilation, such as opioids.
In general, the devices available to deliver oxygen can be split into two categories depending on whether they deliver a proportion of, or the entire, ventilatory requirement (Figure 2.1; Table 2.1):
• Low flow devices deliver oxygen at less than the inspiratory flow rate, for example nasal cannulae and simple face masks (including masks with a reservoir bag). Although they are low flow, they can deliver a high concentration of oxygen. The oxygen concentration is variable.
• High flow devices deliver oxygen at above the inspiratory flow rate, such as Venturi masks. Although they are high flow, a low concentration of oxygen may be delivered. The oxygen concentration is fixed.
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