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).