Oxygen is one of the most basic drugs we have. In many acute illnesses, such as acute respiratory infections, asthma, fetal asphyxia, and shock, the availability of an oxygen supply can save a patient's life. It becomes especially important during resuscitations, in the operating room, or when treating cardiopulmonary illnesses and any illness (including acute mountain sickness) at altitude.
In austere medical situations, industrial (or research or aviation) oxygen can be used instead of medical oxygen. Oxygen gas is produced from the boiling-off of liquid oxygen, so it would appear that industrial oxygen is the same as medical oxygen. However, there is an ongoing controversy about whether there is any difference between four kinds of oxygen that are sold: aviation, medical, welding, and research. They are all at least 99.5% pure (usually 99.9% pure), and all are produced from an identical—often the same—system. Any humidity present in medical oxygen is added at the bedside. Purity is not an issue, since the purity required for welding is more critical than that for breathing. The major differences between medical oxygen and industrial oxygen are how it is filtered and the amount of liability insurance paid by the manufacturer. Microscopic filtration is used to remove air particles from both, but medical oxygen is run through filters that can also remove bacteria, and so is considered sterile.8–10
Oxygen often comes in bulky, expensive cylinders. It may be difficult to identify which cylinders contain oxygen. The international standard requires oxygen cylinders to be painted white. In the United States, however, they are green, and in British Commonwealth countries, they are usually black with white shoulders. Industrial oxygen cylinders may be painted almost any color, so don't rely on the cylinder's color to identify its contents.11 Note that you may see one of two terms used in descriptions of flow rates, either the term psi (pounds-force per square inch) or psig (pounds-force per square inch gauge; i.e., pressure related to the surrounding atmosphere). For medical purposes, they are generally equivalent. In this book, I will use the term "psi."
Oxygen cylinders vary in size from the small portable D or E cylinders (which supply 1 to 10 hours of oxygen) to the larger stationary M, H, or K cylinders (which, at very low flow rates, supply oxygen for up to 56 hours). The duration depends on the oxygen flow rate. For example:
- D cylinder: 350 L @2200 psi (23 min @ 15 L/min)
- E cylinder: 625 L @ 2200 psi (42 min @ 15 L/min)
- M cylinder: 3000 L @ 2200 psi (200 min @ 15 L/min)
- H and K cylinders: 6900 L @ 2200 psi (690 min @ 10 L/min; ~33 hours @ 3 L/min)
Therefore, it is helpful to know how much oxygen each type of cylinder commonly contains, and how long it will last.
Oxygen concentrators extract the nitrogen from room air to produce 95% oxygen. They do this by using zeolite granules to adsorb the nitrogen from compressed air.12 Zeolite crystals can be expected to last at least 20,000 hours—about 10 years' use.10
Concentrators are available in sizes ranging from domestic models with flows of up to 4 L/min to very large installations that supply an entire hospital. They typically deliver 2 to 5 L/min of oxygen.13 Oxygen concentrators require 350 to 400 W of electric power and can run off a small gasoline generator, a solar- or wind-powered system with battery storage, or a domestic or commercial power source.14 However, the machine's power requirements must match the available power supply.
The price to purchase an oxygen concentrator is about half that of purchasing a 1-year supply of oxygen in cylinders.10 The cost (electricity) to run them, regardless of the oxygen flow, is about 2.5 p/hr (UK) or 5 ¢/hr (US). This is much cheaper than using cylinder oxygen, which costs from 10 p/hr (UK) or 20 ¢/hr (US) at a flow rate of 0.5 L/min up to £1.00/hr (UK) to $2/hr (US) at 5 L/min.10
Oxygen concentrators can be used to supplement oxygen to anesthetized patients, but the outlet pressure is insufficient to power an anesthesia machine.10 A flow splitter allows oxygen from a concentrator to be supplied to up to four separate sites simultaneously if required, depending on the concentrator's capacity and the patients' needs.12
The oxygen must be introduced upstream from the vaporizer in a drawover system or it will dilute the inspired vapor concentration.12 If added using a reservoir attachment above the vaporizer inlet, the 95% oxygen at a flow rate of 1 L/min produces a FiO2 of from 35% to 40%; a rate of 5 L/min produces a FiO2 of up to 80%.15
To increase the FiO2 even more and provide an improved margin of safety, prefill a large plastic sack (e.g., trash bag) with concentrator oxygen and then attach this reservoir to the inlet side of the draw over system during preoxygenation. Remove the empty sack as soon as preoxygenation and intubation are completed.16,17
Oxygen tents are not the best way to administer oxygen. But, when nothing else is available, the top of a plastic cake server with a hole cut out of the side for the neck works well as an oxygen tent for infants (Fig. 9-3).
Improvised pediatric oxygen tent.
High-pressure oxygen sources (25 or 50 psi) can be split for use by up to seven patients with commercially available devices. These can also be "jury-rigged" by knowledgeable respiratory therapists. Low-pressure oxygen sources (cylinders/concentrators) can also be split, depending upon the patients' needs.
For mouth-to-mouth resuscitation, make a shield by cutting out about half the length of the third (long) finger from a medical glove. Extend the part of the finger still on the glove into the patient's mouth, and stretch the remainder of the glove over the mouth and nose as a protective shield.18 This works, but a handkerchief draped over the mouth and nose might work as well or better to protect the rescuer from at least the "big stuff." With the new, "continuous" cardiopulmonary resuscitation (CPR), rescue breathing is taking a back seat to chest compressions, at least for cardiac events.
Often forgotten is that, if no other means is available, patients can be given mouth-to-tube ventilation through an ETT, an LMA, a tracheostomy tube, an esophageal obturator airway (EOA), a Combitube, a makeshift cricothyrotomy tube, or similar device. The problem is, other than covering the tube's end with a thin cloth (e.g., a handkerchief) to avoid contact with large amounts of blood or other secretions, none of these devices provides infectious protection to the rescuer.