METHODS OF OXYGEN ADMINISTRATION
Various types of oxygen delivery devices are available. With a ﬂow rate of 6 to 10 L/min of 100% oxygen, it is possible to achieve inspired oxygen concentrations (Fio2) of up to 95%. The actual Fio2 depends on the system used and the oxygen ﬂow rate relative to the patient’s respiratory rate and tidal volume.
The nasal cannula (nasal prongs) is perhaps the most common mode of oxygen delivery and can provide 30% to 50% oxygen with ﬂow rates of 6 to 8 L/min; higher ﬂow rates may cause nasal irritation. The simple mask ﬁts over the mouth and nose, and exhaled gas escapes via side ports. Carbon dioxide may accumulate if the oxygen ﬂow rate is too low. Simple masks deliver an Fio2 of 35% to 50% with a ﬂow rate of 6 to 10 L/min. The partial rebreathing mask is similar to the simple mask but has a reservoir bag. On inspiration, oxygen from the bag is mixed with air entering via the exhalation ports. The oxygen ﬂow rate is adjusted so that the bag does not collapse with inspiration; most of the exhaled gas escapes via exhalation ports. Partial rebreathing masks deliver an Fio2 of 50% to 70% with an oxygen ﬂow rate of 6 to 10 L/min.
The nonrebreathing mask is a modiﬁcation of the partial rebreathing mask and incorporates one-way valves between the mask and the reservoir bag and at the exhalation ports. Thus, oxygen is inspired only from the bag, and exhaled gas may escape via the ports. The oxygen ﬂow rate is adjusted so that the bag does not collapse. The nonrebreathing mask can deliver an Fio2 of up to 95%.
The Venturi mask is used to deliver a ﬁxed low concentration (24%-40%) of oxygen. The Venturi mask works on the principle of air entrainment; 100% oxygen is directed through a tube in a center jet stream, which pulls in room air through side ports. The relative amounts of air and oxygen are determined by the size of the jet and side ports. Venturi masks deliver oxygen concentrations of 24%, 28%, 35%, or 40%. The amount of air entrained by the Venturi mask is high, and this ﬂushes the environment around the patient’s face—preventing rebreathing—and maintains a ﬁxed oxygen concentration over a wide range of oxygen ﬂow rates and independent of the patient’s rate of ventilation, thus minimizing the danger of inadvertently supplying too much oxygen.
Disadvantages of the Venturi and other masks include difﬁculty with talking, eating, washing, expectoration, and administration of aerosol medications. The nasal cannula and Venturi mask are best suited for administering the low concentrations of oxygen necessary to minimize carbon dioxide retention in patients with chronic obstructive pulmonary disease. The nasal cannula is more comfortable and does not interfere with eating, washing, or expectorating. However, the actual Fio2 depends on the amount of ﬂow relative to the patient’s demand and the amount of air taken in through the mouth or nose.
The T tube and tracheostomy collar (also available in a Venturi mode) are used to deliver supplementary oxygen to patients with tracheostomies (see Plate 5-21).