Oxygen masks

• Hudson-type masks or nasal 'spectacles' give an imprecise FIO2 and should only be used when hypoxaemia is not a major concern. Hudson-type masks do allow delivery of humidified gas (e.g. via an 'Aquapak'). Valves fitted to the Aquapak system do not deliver an accurate FIO2 unless gas flow is at the recommended level.

• Masks fitted with a Venturi valve deliver a reasonably accurate FIO2 (0.24, 0.28, 0.35, 0.40, 0.60) except in patients with very high inspiratory flow rates. These masks do not allow delivery of humidified gas but are preferable in the short term for dyspnoeic patients as they enable more precise monitoring of PaO2/FIO2 ratios.

• A tight-fitting anaesthetic mask and reservoir bag allows 100% oxygen to be delivered.

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