A Diver's Guide To Oxygen Therapy Apparatus
by
Larry
"Harris" Taylor, Ph.D.
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.
All rights reserved.
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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 Dalton’s 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 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.
Tank wrench,
standard valve & valve with handle
Typical constant flow system
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.
DAN Oxygen
Inhalator Valve
Typical Variable Rate/Constant Flow
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.
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.
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.
Nasal
Cannula
Simple Face Mask
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.
Venturi Mask
Partial Rebreather or Medium Concentration Mask
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:
Non-Rebreather Mask
Pocket Mask w/Oxygen Inlet & One-way Valve
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 lone-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. (See High
Concentration Delivery Mask for discussion and image)
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.)
Bag
Valve Mask
Set of Endotrachael Airways
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.
Author’s DAN
Kit (with second demand system)
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.
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Credit:
Photography of oxygen equipment by the author using his personal arsenal of oxygen delivery equipment
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 (See Alert Diver, Mar/Apr, 1997, p. 54) is considered
one of the best recreational sources of information in North America.
All rights reserved.
Use of these articles for personal or organizational profit is specifically denied.
These articles may be used for not-for-profit diving education