A Diver's Guide To Oxygen Therapy Apparatus

This is an electronic reprint and expansion of an article that appeared in Sources (Part 1: July/Aug. 1989, 30-35 & Part 2: Sept/Aug 1989, 72-74). This material is copyrighted and all rights retained by the author. This article is made available as a service to the diving community by the author and may be distributed for any non-commercial or Not-For-Profit use.

About The Author: Larry "Harris" Taylor, Ph.D. is a biochemist and Dive Safety Coordinator at the University of Michigan. He has authored more than 100 scuba related articles. His personal dive library is considered one of the best recreational sources of information in North America.
Copyright 2001-2004 by Larry "Harris" Taylor
All rights reserved.


Every diver has been told that recompression is the treatment of choice for a serious diving malady. However, since divers may dive in locations separated in time and space from recompression facilities, there is often an appreciable delay (12-40 hours, or more) between the onset of the first recognizable symptoms and admission to a recompression facility. Therefore, it is important for divers to accept the reality that they, on the dive site, as the first responders, determine the subsequent quality of life (if life continues) long before professional medical people see the victim. Divers must realize that in the field, without professional medical care, the administration of 100 % oxygen is the treatment of choice for dealing with most serious diving maladies.

Oxygen is often used in traumatic injuries to treat shock-associated hypoxia (lack of oxygen in the body tissues due to a decrease in blood circulation) or to supplement the breathing of those with chronic lung disease. The vast majority of oxygen equipment available to the public is designed to manage those particular problems. These devices have saved lives, and they will continue to do so, in situations that they were designed to manage. However, devices that were designed for home treatments are inadequate for the dive accident scenario. In diving problems, the key to successful management of the diving accident victim pending hyperbaric oxygen therapy is continued breathing of the highest possible concentration of oxygen en route to professional medical assistance.

A serious dive malady can be described as "bubble trouble." A large bubble(s) of gas, composed primarily of nitrogen, an inert gas, has formed and that bubble(s) interferes with normal body functioning. (Note: In decompression sickness a nitrogen bubble forms as the supersaturated nitrogen gas comes out of solution; in an air embolism the bubble initially is air (79 % nitrogen). However, the body’s metabolism uses the oxygen in the air bubble, so that eventually the bubble becomes almost all nitrogen. In decompression sickness, the bubble can form in almost any tissue. In a lung over pressurization event, the bubble of air is injected into the spaces around the lung or directly into arterial circulation. If the bubble enters the arterial circulation, the bubble generally first lodges in a capillary. Since blood flow is only one way, cells downstream from the bubble stop receiving nutrients and oxygen, while cell-toxic metabolic waste products begin to build-up. The result is that cells downstream from the bubble begin to die. Many cells (particularly those of the central nervous system), once dead, are never regenerated. If too many cells die, life is either impaired, or in the worst case, ceases.

Treatment for "bubble trouble" is to reduce the size of the bubble so that the bubble can no longer interfere with normal function or to move the bubble through the capillary and thus restore blood flow. This can be accomplished physically in a recompression chamber. The effect of increased pressure (typically, 165 fsw in air embolism cases and 60 fsw in decompression sickness) is to decrease the volume of the offending bubble. Decreasing bubble size can also be accomplished by the administration of a very high concentration of oxygen.

We use oxygen primarily not to treat trauma-associated hypoxia, but rather as a technique to denitrogenate" the body. Ideally, we wish to initially surround the offending nitrogen bubbles(s) with a pure oxygen environment. Since we begin with a bubble composed almost exclusively of nitrogen, if we surround the bubble with 100% oxygen, then nitrogen in the bubble will move out of the bubble into the nitrogen-poor surroundings. (Remember Daltons law of partial pressure and that all gases wish to remain uniform in concentration through the volume they occupy). The movement of nitrogen out of the bubble is controlled primarily by partial pressure differences. The greater the difference of partial pressure between the outside and inside of the bubble, the faster this movement of gas will occur. Movement of gas will continue until the partial pressure for the gas is the same inside as it is outside the bubble for all gas components within the bubble. If the bubble's surroundings can be kept at a high oxygen concentration, eventually the bubble will have little nitrogen present. Oxygen (having a higher concentration outside the bubble) will move into the bubble. However, The loss of nitrogen (moves out because of partial pressure gradient between inside and outside the bubble) and the consumption of oxygen by cellular processes cause the bubble to shrink in size. Ultimately, the bubble shrinks enough to restore normal function or, if in a capillary, move through the capillary and thus restore blood flow. In order for this process to work, the oxygen concentration administered to the diving accident victim must be exceptionally high, as close to 100% as possible. In other words, to be effective in reducing the bubble (thus, saving body functions or life itself), our oxygen administration equipment should be capable of delivering 100% oxygen while meeting 100% of the patient's respiratory requirements. (See Why 100% for a more detailed discussion.)

There is an enormous diversity of devices on the market for home utilization of oxygen. These devices vary in the amount and percentage of oxygen that can be effectively administered. Remember, the primary concern in the field management of a diving problem is the ability to deliver 100% oxygen to the patient. Let's examine the equipment available today.

CYLINDERS:

Cylinders are available in either aluminum or steel in a variety of sizes. Cylinders should be rated by D.O.T. for oxygen service and painted green. Merely painting a scuba tank green is not a good practice; Cylinders and all equipment rated for oxygen service undergo a special cleaning to insure that no grease or oily combustible material is present in the system. The cylinder should be equipped with a medical oxygen valve, which has two holes that mate to two pins on the oxygen regulator. These valves are commonly opened with a special wrench, although more expensive units will have a convenient handle. Some valves have a cylinder pressure gauge built-in, thus allowing the cylinder pressure to be monitored without having to put on the regulator. For divers, the minimum size should be a 412 liter (14.6 cu. ft.) steel D cylinder. The comparable aluminum cylinder is 415 liters. This will provide 30 to 40 minutes of 100% oxygen delivered by demand valve. It will also provide about 27 minutes of lower concentration oxygen when delivered to a constant flow device at a minimum flow rate of 15 Liters/minute (L/min). The standard kit now contains an aluminum Jumbo D (636.8 Liters; 22.4 cu. ft.) cylinder. This provides about 50 minutes of use by demand system and approximately 42 minutes of use at 15 Liters per minute. Also available is a larger E cylinder that has a volume of 680 liters (24.1 cu. ft.). Larger cylinders (3000 L) are available, but these cylinders are not very portable. Cylinders should be filled only with medical (U.S.P.) grade oxygen. Some people have filled oxygen bottles used in rescue training with compressed air because it is cheaper. Not only is this practice illegal, but also it could be dangerous, as compressed air is 79 % nitrogen. In an emergency, someone could get confused and administer compressed air (21 % oxygen) to a patient who desperately needs 100 % oxygen.

REGULATORS:

The preferred system is a demand mask system. These systems deliver oxygen only when the patient breathes (demands a gas supply) and thus, the patient most efficiently uses the gas in the cylinder. This efficiency, coupled with its ability to furnish nearly 100 % oxygen to the patient is why the demand system is the most desirable oxygen administration system available for use by divers in treating a serious "bubble trouble" event. A demand regulator (analogous to a scuba second stage) requires a high-pressure regulator (analogous to a scuba first stage). There are several of these devices available. The "first" and "second" stages can be purchased separately or combined as part of a demand valve system. Divers can consult their local hospital supply vendor for descriptions and specifics of available units. (In dealing with local vendors, the key word to remember is "demand"; some very good resuscitators on the market do not have the demand feature.) In addition, DAN has assisted in making available to divers a complete oxygen administration kit that includes a demand regulator system. Information on this system is available from DAN
The demand system is very similar to a scuba regulator. When the patient inhales, the second stage senses the decrease in pressure and initiates rapid gas flow. Since this system is sealed from the environment, this mask can deliver approximately 100 % oxygen to the patient. The demand mask system is the current preferred method of oxygen administration to a breathing patient for the management of a serious diving malady.

VARIABLE RATE/ CONSTANT FLOW SYSTEMS:

If a demand system is not used (they are expensive), then the next best option would be an adjustable-flow medical oxygen regulator capable of delivering at least 15 L/min. These regulators deliver a constant flow of oxygen at a rate that can be adjusted by the first responder. Additionally, many demand systems have a first stage that will only furnish gas to a second stage demand regulator. In this case, a separate regulator capable of delivering a minimum of 15 L/min will be needed for the pocket mask to cope with a non-breathing victim. Ideally, a regulator (like that contained within the DAN kit) should be purchased which will supply both a demand valve mask and a constant flow system. Most of the oxygen delivery systems discussed below will be utilized at minimum of 15 L/min, but you want a regulator able to deliver more than the minimum. Most regulators have two gauges: a cylinder pressure gauge and an oxygen flow meter. Simply turning a knob can vary the gas flow. Those regulators used with a cylinder whose valve contains a cylinder pressure gauge may only have a flow meter. Although these systems can, with the proper mask, deliver a reasonable concentration of oxygen, the continuous flow wastes much of the gas supply and is not nearly as effective or efficient as the demand valve in meeting the respiratory requirements of the diving accident victim.
All regulators should be rated for oxygen service and used only on oxygen cylinders. They should be inspected and serviced annually by a qualified technician.

FIXED RATE / CONSTANT FLOW SYSTEMS:

These units typically have a small (often disposable) gas bottles, an on-off valve, and a constant flow delivery of only 6 L/min. These devices often come with only a simple facemask. These units are not capable of delivering the desired high concentrations of oxygen needed to "denitrogenate" and as such, divers should consider them inadequate for their needs in dealing with any diving malady. Although these devices are the least expensive oxygen administration tools available, they are also the least desirable in terms of effectiveness in dealing with a diving "bubble trouble" emergency.

ADAPTORS:

There are commercial and homemade devices available for utilizing scuba regulators with medical oxygen cylinders. This defeats the primary purpose of safety standards that have historically been promulgated to prevent accidents. Many industrial or medical gases are chemically reactive. In addition, there are an abundance of different gases used in medicine. Having standards, which allow regulators to be used on cylinders of only one type of gas, prevents formation of dangerous chemical combinations arising from the mixing of these different gases. It also guarantees that the gas delivery system is chemically compatible with the gas being delivered. Finally, this set of standards insures that the gas being delivered is what you think it should be.
Oxygen is chemically reactive and can interact with a great many compounds. These oxidation reactions liberate heat, enough to initiate combustion or, in some cases, explosions. To prevent accidental chemical reactions from occurring, all oxygen equipment must be rigorously cleaned and degreased. Most scuba diving regulators are not kept scrupulously clean; thus, using a scuba regulator as an oxygen delivery device poses an element of fire risk. There has been at least one reported incident of a fire that occurred because of the use of a scuba regulator and a homemade adaptor on an oxygen cylinder.
There is always a group of divers looking for a way to "beat the system." In the Great Lakes we have divers diving well beyond sport diving depths. Many of these divers are "experimenting with their spinal cords" by using homemade oxygen decompression procedures in the water. Some of these divers are unaware of the risks of breathing 100% oxygen at depth. Although this population is, admittedly, small, an adaptor does provide a potential for abuse by those few people who wish to use oxygen for their in-water decompression procedures. In-water use of oxygen should remain outside the realm of traditional sport diving.
Some of these oxygen-to-scuba adaptors have proven of tremendous value in remote parts of the world. Most North Americans are not that isolated and can have ready access to proper equipment. Lastly, if you already have an oxygen cylinder, a suitable medical oxygen regulator and a demand valve are not much more in cost than the most often used adaptor.

DELIVERY MASKS:

The delivery systems discussed below may supply higher concentrations of oxygen in a clinical setting when used by clinical professionals, but, in the field, in an emergency use by the lay community, it is reasonable to believe the concentrations of oxygen delivered will be significantly less than text-book quoted values.

CONSTANT FLOW DELIVERY DEVICES: The mask used will determine the final concentration of constant flow oxygen that the patient breathes. The gas coming out of the cylinder is 100 % oxygen; the concentration of oxygen the patient actually breathes will depend on how much the oxygen is diluted with air or the patient's exhalation. The final concentration of oxygen delivered will be affected by the actual flow rate, the quality of the seal of the mask around the patient's mouth and nose, and the patient's rate and depth of breathing. In general, the higher the flow rate, the higher the concentration of oxygen the patient will breathe (and the shorter the time that the gas supply will last). The poorer the mask-patient seal, the lower the concentration of oxygen that the patient will receive. In the field, the flow rate and the quality of the mask seal are probably the most important elements in determining the actual concentration of oxygen delivered to the patient. Note that the concentrations of oxygen mask delivery systems listed below are practical values obtained by skilled medical personnel in a clinical setting. Values obtained in the field from highly stressed first responders will probably be lower.

NASAL CANNULA: This device delivers an unpredictable amount of oxygen ranging from 24-32 % at 1 - 6 L/min depending on how much the patient inhales through the mouth. Higher flow rates are uncomfortable for the patient. A high flow rate can quickly dry out the nasal mucosa and become rapidly uncomfortable.

SIMPLE FACEMASK: This device is probably the most commonly available to the public. It seals poorly and its large ventilation holes allow the oxygen flow to be diluted with air. The simple facemask at an oxygen flow of 6 L/min delivers approximately 35-40 % oxygen. Increasing the flow to 10 L/min may increase oxygen concentration to about 50 %. If the flow rate is less than 6 L/min (as cylinder nears empty), the patient may re-breathe much of his own exhalation and thus, the concentration of oxygen delivered will be low, possibly severely hypoxic.

VENTURI MASKS: This device utilizes a mechanical venturi effect to increase oxygen flow rate into the mask; this limits the dilution of the oxygen by air entering into the mask. There are different types of venturi masks available. Typically, these units deliver 24 - 28 % oxygen at 4 L/min and 35 - 40 % oxygen at 8 L/min. This mask should only be used in a clinical setting and should not be used in the field.

PARTIAL REBREATHER: This mask adds a reservoir bag to the simple facemask. This mask appears similar to a non-rebreather mask. However, it is missing a one-way valve between the reservoir bag and the mask. The reservoir bag fills with oxygen. When the patient breathes, much of the inhalation volume comes from the bag and thus, the oxygen concentration delivered is increased. However, with this system the patient's exhalation can mix with gas in the bag. At 6 L/min this system delivers 40-50 % oxygen; at 10-15L/min the partial rebreather can deliver approximately 60 % oxygen. These masks are often called medium concentration oxygen delivery masks.

NON-REBREATHER: This mask consists of a mask that has a reservoir bag attached. The bag is separated from the mask by a one-way valve that prevents air and patient exhalation from diluting the oxygen in the reservoir bag. When the patient inhales, the valve opens and the patient breathes primarily oxygen. There are also one-way valves that cover the holes on the mask to allow patient exhalation to escape without allowing large quantities of air to enter
the mask. Some masks have this one-way valve on both sides of the mask. These masks are prescription only. If both sides are covered and gas flow ceases, then the patient will not be able to breathe because the valves keep air from entering during inhalation. The common high oxygen concentration mask has a one -way valve on only one side so that if gas flow ceases, the patient can still breathe. At a minimum oxygen flow of 15 L/min, as long as the reservoir bag is kept filled and a good seal is maintained, this mask can deliver 60 - 75% oxygen to the patient
The systems described above are designed for use with a patient that is breathing. This accounts for roughly 90 - 95 % of all diving accidents. Since these devices require an inhalation effort from the patient to move the oxygen into the lungs, they will be ineffective in dealing with a non-breathing patient who is in probably the most desperate need of high concentrations of oxygen. The following devices are used for the non-breathing patient.

POCKET MASK: This device is the current suggested means of ventilating a non-breathing scuba diving accident victim. The oxygen line is hooked into a nipple on the mask, gas flow is started, and the rescuer performs mouth-to-pocket mask resuscitation. At 6 L/min the oxygen delivered will be about 35 %. At 15L/min this procedure, with a good mask seal, will deliver about 50 % oxygen to the patient. These units are used in conjunction with a small one-way valve assembly that diverts the patient's exhalation away from the rescuer. The valve also contains a filter to minimize risk of disease transmission between rescuer and patient. The valve assembly should be considered single-use.

SINGLE-USE POCKET MASKS: This disposable device is designed for use in C.P.R. The unit (InterTech # 008010, or equivalent) comes with a single use pocket mask that forms a good seal, a one-way valve to isolate the patient's breath from the rescuer, a short piece of respiratory tubing, and a mouthpiece to make breathing into the device a little easier and more comfortable. By adding a T-adaptor oxygen inlet (Airlife U/Adapit # 004081, or equivalent) and changing the length of respiratory tubing to longer than 12 " (the tubing acts as an oxygen reservoir; the longer the tubing, the higher the final concentration of oxygen that can be delivered), this new device can furnish more than 60 % oxygen to the patient at 15 L/min. Consult your local hospital supply vendor for parts and check your assembly with someone knowledgeable in oxygen administration to insure that the device is properly assembled.

MECHANICAL VENTILATOR: Many demand oxygen systems, as well as special mechanical resuscitators, can utilize oxygen pressure to force oxygen into the lungs. Some of these, particularly older models, do not have overpressure release valves. If too much gas is forced into the lungs, it is possible for the patient to suffer lung damage from the resuscitation effort. All mechanical ventilators require specialized training and therefore belong to the realm of the licensed medical professional. Sport divers, without special training should not utilize these devices. Remember, a primary concern of a first responder is to do no additional harm.

BAG VALVE MASK: This device stores oxygen in a bag that fills from an oxygen reservoir. The oxygen is delivered to the patient by squeezing the large bag. Properly used (which requires three or four hands and/or a lot of properly-supervised practice), this device can furnish nearly 100 % oxygen to the non-breathing patient. To be effective, they must be used in conjunction with an endotracheal airway and should not be used by rescuers who have not had proper training and practice to obtain this necessary skill. (Placement of an oral airway is most definitely a technique that requires training and clinical ability. Improper placement can injure or block the patient's airway. Those without clinical training and proficiency should not attempt Insertion of airway management devices.)

NASAL CANNULA ON RESCUER: One technique for administration of oxygen to an unconscious diver has the rescuer breathing oxygen delivered by a nasal cannula. After breathing oxygen, the rescuer then performs mouth-to-mouth resuscitation on the victim. Note that this technique certainly delivers a greater concentration of oxygen to the victim than mere mouth-to-mouth breathing. Since the nasal cannula can deliver at best about 32% oxygen to the rescuer, the actual oxygen concentration delivered to the patient will be probably between 20 - 30%. The effectiveness of this technique has not yet been demonstrated.

RECOMMENDATIONS FOR A DIVING ACCIDENT MANAGEMENT OXYGEN KIT:

1. Avoid all 6 L/min constant flow devices.

2. The DAN oxygen unit was assembled based on the advice of the hyperbaric medical experts at DAN It contains a single 415 L cylinder (41 minutes supply at 10 L/min. (DAN kits now primarily use an aluminum Jumbo D (636.8 Liters; approximately 50 minutes of gas supply for a demand inhalator)), a demand valve delivery oxygen system for breathing patients and a pocket mask for non-breathing patients. This kit represents the current state of the art for dealing with oxygen administration in a serious diving emergency. As such, the DAN kit (or its equivalent) represents the minimal amount of oxygen equipment that should be present on dive training sites. Dive training should NOT, in my opinion, occur with anything less than this equipment on site. Since many divers dive or train in remote locations and are more than 30 minutes from medical assistance, a second (or more) 415 L (or larger) cylinder is desirable. Divers should have enough gas supply on hand to treat an injured diver for the amount of time it takes for the local site professional emergency response team to travel to the dive site.

INSTRUCTORS PLEASE NOTE: In the US, the DAN oxygen kit is considered the standard-of-care in the diving community for treatment of diving accidents. To train with less than this is a liability risk that you should be unwilling to assume!

3. A reasonable emergency alternative to the demand system, would be one (or more) D or E cylinder, a variable flow (15 L/min) medical oxygen regulator, a high concentration (non-rebreathing) oxygen delivery mask for breathing patients, and either the Laerdal or single-use modification pocket mask described above for a non-breathing patient. I tell my students to carry a non-rebreather mask in their traveling first aid kit. So, if they are in a situation where the only oxygen supply is constant flow and a simple facemask, substitution of the non-rebreather mask for the simple facemask can immediately boost the oxygen concentration given to the patient.

4. For those who already have oxygen cylinders and possibly some oxygen administration equipment, possible additions include:

a. A demand valve and mask with appropriate first stage. Consult your local hospital supply vendor or DAN for advice. Many of these devices contain a lever or trigger for positive pressure mechanical ventilation. If your demand system has a trigger, do not use this trigger unless you have received training in its use. Improper use (especially with older mechanical ventilators) could damage patient's lungs and lead to increased patient injury or death.

b. For those who already have an oxygen regulator capable of delivering 15 L/min and cannot afford a demand mask, a non-rebreathing mask (Hudson # 1059, or equivalent) is a necessary alternative. This mask properly used, will deliver about 60 - 70 % oxygen at 15 L/min. The mask sells for between $ 3 - 6. But remember, for denitrogenation we need the highest possible concentration of oxygen, so, although this system is better than nothing, all efforts should be made to supply accident management kit with a demand system.

c. One of the pocket mask assemblies described above.

d. A rugged carrying case to protect the oxygen unit from rough handling and the environment. Cases with O-rings to insure watertight integrity are recommended for use in marine environments.

Local hospital supply vendors or DAN can be exceptionally helpful to you when you assemble the oxygen administration portion of your emergency response kit. Make certain that you discuss your needs with a respiratory therapist, not just a salesperson. Explain that your oxygen use will be emergency field management of a scuba diving injury, and that your desire is to furnish the highest possible concentration of oxygen with only a limited supply of gas to a scuba diving accident victim. They may also inform you about any local legal restrictions on oxygen equipment or utilization. Note that oxygen used in aircraft, in very small cylinders (like those sold by mail-order), or by rescue personnel for emergency use only are exempt from prescription requirements. (Many local vendors, however, will be more comfortable if you obtain a prescription for your oxygen unit. My personal prescription states that the oxygen unit is only for emergency applications in a diving accident.) Regardless of what you decide to carry in your emergency response kit, remember that people save lives; equipment merely helps. (In an emergency, divers should utilize whatever is available to the best of their abilities within the limitations of their training and the tools assembled.) All the above equipment is useless; unless you (and your buddy) know how to use the life saving tools you will carry with you to the dive site. Thus, you should seek out the training of a knowledgeable dive rescue or oxygen administration instructor who can teach you the proper use of oxygen administration devices. Oxygen administration is a skill that can be easily learned, under proper supervision. Practice now could prevent a later problem from becoming a catastrophe.