Info Decompression & Treatment Simplified

Akimbo · Dec 11, 2017

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Visualizing Decompression

This section might be useful for anyone having trouble visualizing the processes involved in decompression. That probably includes most people who don't work with them in their profession or has total recall from their physics and physiology classes.

Outgassing Demos

We have all seen a soda bottle cap removed to demonstrate gas coming out of solution. But how does that compare to the real world of diving? The low-average pressure in a soda bottle at room temperature is about 2.5 ATM or a depth equivalent in seawater of 81' or 25M. That is a little extreme compared to what would happen to a recreational diver that has been at that depth less than an hour because they are not fully saturated or instantly shoot to the surface.

However, it is probably pretty close to an explosive decompression* incident for a saturation diver from that depth. I have had US Navy Diving Medical Officers describe the results of explosive decompression at autopsy as pulverized and gruesome.

* Explosive decompression is very rare and can happen when a diver surfaces very fast with a significant decompression obligation — getting entangled in a large lift bag or a hull failure in a decompression chamber for example.

Spatial Relationships
The cells that make up our tissues are too small for most of us to relate to, so this comparison may help.

This illustrates the relative difference in size between red blood cells, an alveolar sac, and the thickness of paper. There are about 700 million alveoli in an adult's lungs.

Red blood cells are pretty small, but Nitrogen Molecules are almost unimaginably smaller.

Imagine a small lake that fits inside a 400 meter or quarter mile track. Now imagine that the lake is 73M or 240' deep. There would be about 10 Trillion drops of water in that lake. That's how may Nitrogen Molecules would fit in the space of a red blood cell.

Hopefully these illustrations will help divers visualize how the far smaller diluent molecules can easily pass through various body tissues.

Gas Transfer in the Lungs
The volume of Oxygen metabolized by our tissues doesn't change with depth but does with activity; typically between 1 and 1.5 Liters/Minute. That's the volume of two bottles of wine! That brings up the question: How can that much gas volume exchange through membranes in our lungs every minute?

The answer is the deceptively large surface area packed into our lungs. Sources vary but most estimates of the internal surface area in our lungs range between 50 and 100 M² (540-1,076 Ft²). For reference, a tennis court is 188 M² (2,028 Ft²). The tissue membrane in each Alveoli is only one cell thick and there are about 700 hundred million of them.

The Driving Force
Gas transfer is driven by a process called Diffusion, which explains movement of atoms, molecules, and particles from a higher to a lower concentration. Human lungs allows Oxygen molecules to "diffuse" from the lungs to the blood stream while simultaneously diffusing CO2 from the blood to the lungs. Diluent will diffuse in and out of the blood stream depending on whether the diver is descending or ascending.

Solids May Not Be What You Think
The word porous rarely comes mind when thinking of a solid; but you wouldn’t think that if you were a Nitrogen or Helium molecule.

This image is of healthy human bone viewed under scanning electron microscope.

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Akimbo · Dec 11, 2017

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What Exactly is DCS?

US Navy does a pretty succinct job of defining DCS:

3-9.3 Decompression Sickness (DCS). A diver’s blood and tissues absorb additional nitrogen (or helium) from the lungs when at depth. If a diver ascends too fast this excess gas will separate from solution and form bubbles. These bubbles produce mechanical and biochemical effects that lead to a condition known as decompression sickness.

Reference: US Navy Diving Manual, Revision 7A, Volume 1, Page 3-46 or Acrobat (.pdf) Page 204. See the paragraphs following this excerpt for a much more complete discussion. This manual is written for Navy divers rather than medical professionals so it is pretty understandable. This link is for a free download, without copyright restrictions, and is about 14MB.

The mechanical effect primarily refers to partially or totally blocked blood flow; basically a "log jam" of diluent bubbles in our bloodstreams. Inflammation-like effects can also interfere with nerve function. Diluent gas (Nitrogen and/or Helium) normally leaves the body through the lungs fast enough to prevent DCS symptoms. The exact process is complex and not fully understood, but the part that divers really care about is restoring sufficient blood flow and alleviating symptoms, thus preventing damage.

“ Anyone can get DCS that dives deeper than 30'/10M, regardless of what your dive computer says. ”

Like most medical maladies, DCS is not totally predictable because of human and environmental variability — between individuals and from day to day. Fortunately, the two most important variables are easily and precisely measured; Time and Depth (pressure). The hard-to-predict part is how the body reacts to them and many other lesser variables that are known to influence decompression. Here are a few of them.

Physical Activity:
Heavy work increases diluent absorption, probably in excess of what your dive computer is assuming by default. Some dive computers incorporate heart rate monitoring and use predefined assumptions to adjust decompression algorithms automatically. Some other computers allow manual setting of exertion levels. This factor is prominently considered in US Navy decompression tables.

Thermal Stress:
Cold skin and lower core temperature restricts blood flow, which directly influences ingassing and outgassing rates. This factor is also addressed in instructions for US Navy decompression tables. Some dive computers adjust algorithms based on water temperature, which is not the same as your temperature(s). Decompressing when cold (a common problem due to low activity) decreases decompression efficiency. Surface-supplied divers using hot water heated wetsuits have been found to have increased DCS risk — probably because decompression algorithms never anticipated them to be effectively floating in a hot tub.

Health and Fitness:
This is especially true for vascular and pulmonary function. Many dive computers allow manually setting conservation factors that can partially account for physical fitness. Keep in mind that the greatest quantity of human testing and field data has been collected on healthy navy divers, mostly under the age of 40, and virtually all male. This does NOT imply that female divers are at greater or lesser risk; only that comparatively little data is available to justify a conclusion. See DAN Explores Fitness and Diving Issues for Women

Age:
Degradation of decompression efficiency increases with age. Some dive computers will adjust algorithms based on your birth date. Unfortunately very limited data is available to quantify how to adjust calculations due to individual variability. See Guidelines for Seniors

Hydration:
Inadequate hydration is believed to increase DCS risk. This is a very logical assumption when you realize the critical role that liquids play in gas transfer in the alveoli. Ultra-dry high pressure breathing gases exacerbates the problem. Unfortunately proving the hypothesis would be very expensive and hard to justify when you consider all the other reasons to stay hydrated. For obvious reasons, non-alcoholic and un-carbonated beverages are your best pre-dive choice.

Dive Profile:
The vast majority of decompression data is based on "square dive profiles" used on typical working dives — meaning the entire bottom time is spent at the maximum depth. The meandering profile of recreational divers can be a significant advantage especially when the deepest part of the dive is at the beginning and the diver gradually moves shallower. Shore, wall, and wreck dives can be planned to take advantage of this factor. This is one of the most effective arguments in favor of recreational dive computers. All dive computers continuously calculate decompression throughout the dive, effectively crediting time above your max depth.

Medications:
There are a few medications and supplements that are suspected of improving or compromising decompression efficiency. Probably more important is that some can mask DCS symptoms. See I’m Taking this Medication … Can I Dive?

Repetitive Dives:
Repetitive dives, especially over a period of days, increases DCS risk. There are tons of reasons but a good guess includes an accumulated underestimate of residual diluent in your tissues, contributed to by all these variables. There is also less experimental and quantitative data to verify every repetitive dive calculation.

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Akimbo · Dec 11, 2017

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DCS Treatment

“ DCS treatment is
conceptually pretty simple:
Reduce bubble size and
expedite elimination. ”

"Re-compressing" the diver will shrink the volume of bubbles in accordance with Boyle's Law, in addition to forcing some back into solution (think of a soda bottle). Increasing the PPO2 (Partial Pressure of Oxygen) accelerates the transfer of diluent gas from the bloodstream, across the alveoli, and into the lungs so it can exit the body. The major complication is raising the PPO2 too high and causing Oxygen Toxicity.

As discussed in the above link, Oxygen Toxicity or OxTox can cause convulsions, which will likely drown a diver if it happens underwater. Convulsions, though unpleasant, are easily managed in a dry decompression chamber with a trained attendant. Normally the DCS patient is breathing pure Oxygen and an attendant is breathing air from the chamber.

Another factor that favors chambers is the recommended threshold to avoid OxTox is about twice as in the water. Divers with Nitrox training are often surprised that the allowable PPO2 limit in a dry chamber is 2.8 ATA versus 1.4 in the water. That allows breathing pure Oxygen at 60' (18.3M). There are several treatment tables but the US Navy's Tables 5 and 6 are the most widely used around the world:

The green bands indicate periods of breathing pure Oxygen and the light blue bands are breathing air. Table 6 is very similar except there are more Oxygen periods at 60'.

Pure Oxygen solves another thorny problem. Since different tissues in the body absorb and release diluent gases at different rates, you can outgas in the "faster" tissues while "slower" tissues are ingassing. Any increase in diluent gas absorption will increase your decompression liability. That problem doesn't exist when breathing pure Oxygen because there is no diluent to absorb no matter what tissues are involved or where in the decompression cycle you are — even I can do the math on that!

DCS Treatment versus Therapy

There are two significant phases in DCS treatment; time-sensitive restoration of blood flow and therapy to accelerate healing of the damage left behind. OK, it is a little more complicated than that but it is the big-picture view that matters to divers.

The majority of dissolved diluent gas absorbed during a dive naturally leaves the body within about 2 hours and virtually all within 24 hours. Chamber treatment after this period is functionally closer to Hyperbaric Oxygen Therapy (HBOT) than the classic DCS treatment; even though some of the same tables are often used. New or similar symptoms can persist after initial chamber treatment but are largely caused by residual tissue damage and inflammation that often accompanies it.

The core principal behind HBOT is super-oxygenation of tissues. HBOT is primarily used to treat wounds, burns, gangrene, and Carbon Monoxide poisoning. Physicians would prescribe HBOT all the time to treat inflammation if the cost was competitive with Advil (a common Over-The-Counter Non-Steroidal Anti-Inflammatory medication).

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Akimbo · Dec 11, 2017

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DCS Diagnosis

“ The hard part isn’t operating the chamber. Accurate diagnosis is. ”

Here's the problem: Let's say there's a diver that is four days into a liveabaord trip diving the deep wrecks in Truk and has pain in their leg. Is that DCS, over-activity, or any number of other medical problems? Same scenario, but the diver collapses on deck after a long decompression? Is it DCS, a heart attack, a stroke, or an injury acting up from an old car accident? Slamming someone in a chamber for the wrong reason could delay lifesaving time-critical treatment.

DCS is diagnosed by medical professionals through a process of exclusion. Technically, it isn’t DCS until a doctor says it is; and even then it is literally an educated guess. The decision matrix for determining how to treat DCS after it is diagnosed is pretty involved, but understandable:

US Navy Diving Manual, Revision 7A, Figure 17-1. Chapter 17 - Diagnosis and Treatment of Decompression Sickness and Arterial Gas Embolism, Page 17-39 or Page 885 in the Acrobat file. As you can see selecting proper treatment is not a trivial process.

See

US Navy Diving Manual, Revision 7A, Appendix 5A, Neurological Examination, Page 5A-1 or Acrobat Page 931
Field Neurology for Divers, Alert Diver Online
@Doppler's The Five-Minute Neurological Exam: don’t leave home without it!

Personal Sidebar

I'm onboard a diving support vessel undergoing sea trials off Stavanger Norway when we get an emergency radio call from a hospital asking if we can treat an unconscious diver. A small boat pulls up alongside about half an hour later and a local doctor and the patient strapped on a stretcher are hustled below deck. I get in with them as the inside tender and the chamber is pressurized until the patient starts to regain consciousness.

The doctor was out of his element to say the least so I start the neuro-exam taught in the Navy. The IDs in his pocket said he was from the UK and was a commercial diver. The standard questions like "what's your name", "how old are you", and "where do you live" all matched up until I asked "how much do you weigh".

Keep in mind I'm a young Yank while the supervisor and most of the crew are Brits. I excuse myself and go into another lock, swing the hatch closed, and report that something is really wrong. This guy seems perfectly lucid but insists that he weighs 13 Stone! All I hear at the other end is laughter so I repeat it thinking that my voice shift at 165' on air is making me misunderstood. Even more laughter over the comms and I see some guys through the viewport holding their gut.

I'm starting to wonder if I'm too narked for the task when the British super finally comes on the phone and explains that the patient is fine, one Stone in the UK equals 14 Lbs or about 6.4Kg. That episode cost me the first round when we got on shore.

The worst part of the story is DCS was misdiagnosed.

Akimbo:
He left the chamber symptom free after several days of "treatment". I heard from the attending doc about a month later that he passed out again in Scotland. He had not been under pressure since we treated him and was diagnosed with some weird form (my words) of spinal meningitis. This is a case where he responded to treatment but had nothing to do with DCS.

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Akimbo · Dec 11, 2017

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Recognizing DCS Symptoms

Timely treatment can have a very positive impact on the severity of DCS symptoms as well as the speed and completeness of your recovery, independent of the time to onset of symptoms. Consider that carefully if you ever find yourself debating if your symptoms are DCS or not.

The symptoms can vary a lot so I encourage you to read the following excerpts selected from the US Navy Diving Manual, Revision 7A, Volume 5, to help you decide. See Chapter 17 - Diagnosis and Treatment of Decompression Sickness and Arterial Gas Embolism starting on Page 17-8 or Acrobat Page 854. I accentuated selected text in Red with a sans serif font to emphasize some of the more important points. Comments in Blue italics are added for context.

17-4 DECOMPRESSION SICKNESS

While a history of diving (or altitude exposure) is necessary for the diagnosis of decompression sickness to be made, the depth and duration of the dive are useful only in establishing if required decompression was missed. Decompression sickness can occur in divers well within no-decompression limits or in divers who have carefully followed decompression tables. Any decompression sickness that occurs must be treated by recompression. For purposes of deciding the appropriate treatment, symptoms of decompression sickness are generally divided into two categories, Type I and Type II. Because the treatment of Type I and Type II symptoms may be different, it is important to distinguish between these two types of decompression sickness. The diver may exhibit certain signs that only trained observers will identify as decompression sickness. Some of the symptoms or signs will be so pronounced that there will be little doubt as to the cause. Others may be subtle and some of the more important signs could be overlooked in a cursory examination. Type I and Type II symptoms may or may not be present at the same time.

17-4.1 Diagnosis of Decompression Sickness. Decompression sickness symptoms usually occur shortly following the dive or other pressure exposure. If the controlled decompression during ascent has been shortened or omitted, the diver could be suffering from decompression sickness before reaching the surface. In analyzing several thousand air dives in a database set up by the U.S. Navy for developing decompression models, the time of onset of symptoms after surfacing was as follows:

42 percent occurred within 1 hour.
60 percent occurred within 3 hours.
83 percent occurred within 8 hours.
98 percent occurred within 24 hours.

I find this excerpt especially important so it is included out of sequence and with maximum emphasis. Reference US Navy Diving Manual, Revision 7A, Volume 5, section 17-5.2, Guidance on Recompression Treatment, Page 17-14, or Acrobat Page 860.

Treat promptly and adequately.
The effectiveness of treatment decreases as the length of time between the onset of symptoms and the treatment increases.
Do not ignore seemingly minor symptoms. They can quickly become major symptoms.

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Akimbo · Dec 11, 2017

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Type 1 DCS

Divers with Type 1 DCS are at much lower risk of long term injury than those with Type II symptoms. However, Type I symptoms often progress to Type II so treat both with urgency.

Reference US Navy Diving Manual, Revision 7A, Volume 5, Page 17-9, or Acrobat Page 855.

17-4.2 Symptoms of Type I Decompression Sickness. Type I decompression sickness includes joint pain (musculoskeletal or pain-only symptoms) and symptoms involving the skin (cutaneous symptoms), or swelling and pain in lymph nodes.

17-4.2.1 Musculoskeletal Pain-Only Symptoms. The most common symptom of decompression sickness is joint pain. Other types of pain may occur which do not involve joints. The pain may be mild or excruciating. The most common sites of joint pain are the shoulder, elbow, wrist, hand, knee, and ankle. The characteristic pain of Type I decompression sickness usually begins gradually, is slight when first noticed and may be difficult to localize. It may be located in a joint or muscle, may increase in intensity, and is usually described as a deep, dull ache. The pain may or may not be increased by movement of the affected joint, and the limb may be held preferentially in certain positions to reduce the intensity (so-called guarding). The hallmark of Type I pain is its dull, aching quality and confinement to particular areas. It is always present at rest and is usually unaffected by movement.

Any pain occurring in the abdominal and thoracic areas, including the hips, should be considered as symptoms arising from spinal cord involvement and treated as Type II decompression sickness. The following symptoms may indicate spinal cord involvement:

Pain localized to joints between the ribs and spinal column or joints between the ribs and sternum.
A shooting-type pain that radiates from the back around the body (radicular or girdle pain).
A vague, aching pain in the chest or abdomen (visceral pain).

17‑4.2.1.1 Differentiating Between Type I Pain and Injury. The most difficult differentiation is between the pain of Type I decompression sickness and the pain resulting from trauma or other injury such as a muscle strain or bruise. If there is any doubt as to the cause of the pain, assume the diver is suffering from decompression sickness and treat accordingly. Frequently, pain may mask other more significant symptoms. Pain should not be treated with drugs in an effort to make the patient more comfortable. The pain may be the only way to localize the problem and monitor the progress of treatment.

17-4.2.2 Cutaneous (Skin) Symptoms. The most common skin manifestation of decompression sickness is itching. Itching by itself is generally transient and does not require recompression. Faint skin rashes may be present in conjunction with itching. These rashes also are transient and do not require recompression. Mottling or marbling of the skin, known as cutis marmorata (marbling), may precede a symptom of serious decompression sickness and shall be treated by recompression as Type II decompression sickness. This condition starts as intense itching, progresses to redness, and then gives way to a patchy, dark-bluish discoloration of the skin. The skin may feel thickened. In some cases the rash may be raised.

17-4.2.3 Lymphatic Symptoms. Lymphatic obstruction may occur, creating localized pain in involved lymph nodes and swelling of the tissues drained by these nodes. Recompression may provide prompt relief from pain. The swelling, however, may take longer to resolve completely and may still be present at the completion of treatment.

17-4.3 Treatment of Type I Decompression Sickness. Type I Decompression Sickness is treated in accordance with Figure 17-2. If a full neurological exam is not completed before initial recompression, treat as Type II DCS.

Symptoms of musculoskeletal pain that have shown absolutely no change after the second oxygen breathing period at 60 feet may be due to orthopedic injury rather than decompression sickness. If, after reviewing the patient’s history, the Diving Medical Officer feels that the pain can be related to specific orthopedic trauma or injury, a Treatment Table 5 may be completed. If a Diving Medical Officer is not consulted, Treatment Table 6 shall be used.

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Akimbo · Dec 11, 2017

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Type II DCS

Reference US Navy Manual, Diving Revision 7A, Volume 5, Page 17-11, or Acrobat Page 857.

17-4.4 Symptoms of Type II Decompression Sickness. In the early stages, symptoms of Type II decompression sickness may not be obvious and the stricken diver may consider them inconsequential. The diver may feel fatigued or weak and attribute the condition to overexertion. Even as weakness becomes more severe the diver may not seek treatment until walking, hearing, or urinating becomes difficult. Initial denial of DCS is common. For this reason, symptoms must be recognized during the post-dive period and treated before they become too severe. Type II, or serious, symptoms are divided into three categories: neurological, inner ear (staggers), and cardiopulmonary (chokes). Type I symptoms may or may not be present at the same time.

17‑4.4.1 Neurological Symptoms. These symptoms may be the result of involvement of any level of the nervous system. Numbness, paresthesias (a tingling, pricking, creeping, “pins and needles,” or "electric" sensation on the skin), decreased sensation to touch, muscle weakness, paralysis, mental status changes, or motor performance alterations are the most common symptoms. Disturbances of higher brain function may result in personality changes, amnesia, bizarre behavior, lightheadedness, lack of coordination, and tremors. Lower spinal cord involvement can cause disruption of urinary function. Some of these signs may be subtle and can be overlooked or dismissed by the stricken diver as being of no consequence.

The occurrence of any neurological symptom after a dive is abnormal and should be considered a symptom of Type II decompression sickness or arterial gas embolism, unless another specific cause can be found. Normal fatigue is not uncommon after long dives and, by itself, is not usually treated as decompression sickness. If the fatigue is unusually severe, a complete neurological examination is indicated to ensure there is no other neurological involvement.

17‑4.4.2 Inner Ear Symptoms ("Staggers"). The symptoms of inner ear decompression sickness include: tinnitus (ringing in the ears), hearing loss, vertigo, dizziness, nausea, and vomiting. Inner ear decompression sickness has occurred most often in helium-oxygen diving and during decompression when the diver switched from breathing helium-oxygen to air. Inner ear decompression sickness should be differentiated from inner ear barotrauma, since the treatments are different. The “Staggers” has been used as another name for inner ear decompression sickness because of the afflicted diver’s difficulty in walking due to vestibular system dysfunction. However, symptoms of imbalance may also be due to neurological decompression sickness involving the cerebellum. Typically, rapid involuntary eye movement (nystagmus) is not present in cerebellar decompression sickness.

17‑4.4.3 Cardiopulmonary Symptoms ("Chokes"). If profuse intravascular bubbling occurs, symptoms of chokes may develop due to congestion of the lung circulation. Chokes may start as chest pain aggravated by inspiration and/or as an irritating cough. Increased breathing rate is usually observed. Symptoms of increasing lung congestion may progress to complete circulatory collapse, loss of consciousness, and death if recompression is not instituted immediately. Careful examination for signs of pneumothorax should be performed on patients presenting with shortness of breath. Recompression is not indicated for pneumothorax if no other signs of DCS or AGE are present.

17‑4.4.4 Differentiating Between Type II DCS and AGE. Many of the symptoms of Type II decompression sickness are the same as those of arterial gas embolism, although the time course is generally different. (AGE usually occurs within 10 minutes of surfacing.) Since the initial treatment of these two conditions is the same and since subsequent treatment conditions are based on the response of the patient to treatment, treatment should not be delayed unnecessarily in order to make the diagnosis.

17-4.5 Treatment of Type II Decompression Sickness. Type II Decompression Sickness is treated with initial compression to 60 fsw (Feet of Seawater or 18.2M) in accordance with Figure 17-1. If symptoms are improved within the first oxygen breathing period, then treatment is continued on a Treatment Table 6. If severe symptoms (e.g. paralysis, major weakness, memory loss, altered consciousness) are unchanged or worsen within the first 20 minutes at 60 fsw, assess the patient during descent and compress to depth of relief (or significant improvement), not to exceed to 165 fsw (Feet of Seawater or 50.2M). Treat on Treatment Table 6A. To limit recurrence, severe Type II symptoms warrant full extensions at 60 fsw even if symptoms resolve during the first oxygen breathing period.

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Akimbo · Dec 11, 2017

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OK, I might be bent

“ If you only remember one thing
from this thread it should be:
Find the nearest chamber
to my next dive. ”

When in doubt, seek help. Here are a few options to consider depending on your situation:

Contact DAN (Diver's Alert Network) whether you are a member or not. They are one of the best-information resources for diving medical emergencies available to civilians in the world. International Emergency Hotline: +1-919-684-9111
Tell crew members if you are on a charter dive boat. Do NOT go below deck alone and try to "sleep it off".
Start breathing pure Oxygen as soon as possible.
Do NOT go in the water to perform IWR (In Water Recompression) unless you and support divers are well trained, you are properly equipped, and no chamber is within reasonable travel time.
Go to a local emergency room with experience treating divers.
Before you dive anywhere:
- Find the nearest chamber that accepts emergency DCS and AGE (Arterial Gas Embolism) cases. See Why Are Fewer Chambers Available for Emergencies?
- Know how to contact them and the local emergency phone number. For example, dial 911 anywhere in the US.

Sometimes, very mild/suspected DCS symptoms can be treated by breathing pure Oxygen on deck. There are very few medical conditions likely to be experienced by people healthy enough to dive that will be aggravated by Oxygen.

SAFETY WARNING
Oxygen increases the risk of fire! It isn't a combustible but makes almost everything burn faster, hotter, and at a lower ignition temperature.

Just in case your Advanced Nitrox course glossed over them, Google Oxygen Safety to review them. Here are some special precautions for divers:

Store Oxygen in well-ventilated spaces in case of leaks. Next to your water heater is a bad idea!
Only breathe Oxygen in well-ventilated spaces
Always check with the captain before bringing Oxygen onboard
NEVER take Oxygen stage bottles into your cabin and try to self-treat DCS. You could end up a crispy critter and burn the boat to the waterline!

Any properly equipped dive charter boat will have emergency Oxygen for this purpose. Dive boat crews "should" have emergency procedures in place to assist with appropriate treatment. Give serious consideration to going to an emergency room when shore diving, locally or traveling. It is most prudent to have someone drive you in case your symptoms suddenly progress. Call for an ambulance if symptoms are severe.

Reluctance to Inconvenience Others
DCS can be hard to diagnose so there is a natural reluctance to "sound the alarm" too soon, in addition to denial. Reluctance to inconvenience a boat load of divers on vacation also supports denial of symptoms. Just reverse the rolls. How would you feel if you knew a fellow diver ended up in a wheelchair because they were afraid that reporting symptoms would cost you a few dives?

A similar factor was elegantly handled by some of the best commercial diving supervisors I worked with. They would pull a new diver onboard off to the gas shack for a private conversation. It would begin with reviewing company policies that included sending a diver back to shore for a full medical checkup and a month off after a DCS treatment. It went without saying that the diver would lose a month or more of depth pay.

The super would go on to say something like "If you come up and tell me after a dive that you your knee hurts and a "chamber ride" always helps, it doesn’t qualify as reporting DCS symptoms. You get some O2 at 60' and I don't have to fill out a bunch of paperwork — wink-wink. Divers and supervisors both know how critical time-to-treatment is.

Of course, it is much different on a charter dive boat. Honestly reporting your suspicions to the captain would most likely trigger a neuro-exam, putting you on O2 (on deck), and monitoring you for more definitive symptoms. Recalling divers, pulling anchor, heading for shore, and the captain on the radio to the Coast Guard probably means your neuro-exam confirmed your suspicions and you did the right thing.

Medical Insurance
Your existing medical insurance may cover all or part of your chamber treatment because it is "the standard of care" for DCS. However, that insurance may only apply in your home country and your treatment may be delayed waiting for verification from your insurer. Many divers opt to purchase specialized insurance for divers from organizations like DAN (Diver's Alert Network) or another reputable provider experienced with diving accidents. They may end up being fully reimbursed by your health insurer, especially in your home country, but they will immediately guarantee payment and provide excellent advice to treating physicians so your treatment delays are minimized.

Evacuation Go-Bag
There are some things that will be needed whether the patient is heading to the hospital by Coast Guard helicopter or in a buddy's car. Crew members and dive buddies can try to assemble it if the patient can't. Ideally, the kit will be kept by a friend that accompanies the patient. Give it to an evacuation team member if the patient is unconscious and nobody can ride with them.

Dive computers are an invaluable resource for the medical team
Identification is required, especially passports outside your home country
Insurance cards. Don't forget the DAN card if the patient is a member
Cell phone, unless the patient is unconscious
Wallet or purse, unless the patient is unconscious
A really well-prepared diver will carry a small hard-copy summary of important medical information including their primary care physician's contact data and list of medications.

It's probably a good idea to assemble most of your go-bag yourself and let a buddy know where it is. DCS isn't the only reason you might need one.

Recommended Reading

In Denial Dealing with Denial, Getting Bends out of the closet

Tech Diving Magazine Issue 29, 6.3 MB free download, 33 pages, Dealing with Denial, Getting Bends Out of the Closet, Page 6.

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Akimbo · Dec 11, 2017

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Soapbox

I thought I should bare my soul so readers can assess my personal biases and perspectives. OK, maybe to vent a little steam at the same time.

Time to Treatment
Much of my career was in military and commercial diving. Policies and jurisdictions dictated that decompression chambers were onboard during all diving operations requiring decompression or with a significant potential for DCS (actual policies varied but that is the gist).

As a result, divers that expressed any suspicion of DCS symptoms were typically in the chamber at 60'/18M breathing pure Oxygen within 10 minutes. Several treatments involved Type II symptoms that were recognized by the dive crew... same result with no discussion. The important part of the story is every diver walked out of the chamber joking instead of requiring additional hyperbaric treatments and physical therapy. It is unknowable how many of these suspected cases were actually aches and pains caused by heavy work, but it is equally unknowable how may would have progressed to serious Type II cases with permanent or long term effects if treatment were delayed. I'm betting the answer is "most of them".

Unfortunately, most recreational divers are lucky to get in a chamber within 2-4 hours. However, you can usually administer pure Oxygen within minutes. There is no doubt that a treatment Table 5 or 6 is far more effective, but breathing nearly 5 times the PPO2 on deck is a HUGE improvement over breathing air — and will almost certainly improve your outcome.

If you consider that the primary cause of DCS is compromised blood flow, would anyone really think that restoring flow after hours will not cause damage? I have seen studies that compare outcomes between delayed treatment that exceeds 12 hours compared to 48 hours with marginal to no statistical difference. I don’t understand how that is materially different than keeping a tourniquet on a limb with an open wound for 12 hours and being surprised that there are just as many amputations as leaving it on for two days.

The point I am trying to make is to have a plan to minimize your time-to-treatment. Don’t contribute to the problem by hoping that it is really a pulled muscle instead of seeking help at your first suspicion. Oxygen is cheap and let professionals determine the best way to proceed.

Choosing Dive Computers

I am often concerned when I read that divers are looking for the least conservative algorithm for their dive computer. Granted, some percentage of divers will get bent staying within any decompression recommendation. After all, they are numerical predictions based on time, depth, historic probabilities, decompression theory, and incomplete information. It follows that the least conservative algorithms and settings will have highest probability of DCS and more serious symptoms. We're doing this for fun and getting bent isn't.

1% DCS Hit Rates?

You will hear statements like the US Navy designed their tables for a 1-3% frequency of DCS. Reality and logic doesn't bear this out. I don’t doubt that the diving tables were originally calculated based on a maximum failure rate in the 1-3% range, using assumptions and decompression theories known at the time. My observations as an ex-Navy diver and from performing and witnessing thousands of decompression dives using Navy tables through more than 50 years, is those numbers don't translate to modern recreational diving. I have even used several early and underdeveloped proprietary HeO2 tables and have never been bent.

Ask yourself, have you been bent once out of every 100 dives? For that matter, does anyone think that one out of 100 recreational divers gets bent in their lifetime? Does this pass the smell test?

Seriously, does anyone really think that a bunch of Navy Master Divers, Diving Officers, and Diving Medical Officers periodically review incidence reports and conclude that not enough divers are getting bent so tables must be changed until more than one out of 100 divers ends up in a chamber? I know the Navy and injuring divers is seriously bad for careers, up and down the line. Navy Divers are not combatants and shorter decompression times would not materially improve mission outcome.

Classifying DCS Hits

You will occasionally see terms like deserved and undeserved hits (as-in hit by DCS). I detest these terms but understanding their meaning has value. A "deserved hit" is when recommended decompression was not fully completed resulting in DCS, whether through forced, accidental, or intentional omission. Undeserved hits are when divers develop DCS even when decompression recommendations are properly completed (which includes NDLs and staged decompression regardless if it is derived from tables or computers). Nobody ever accused me of being "politically correct" but I find these terms to be ignorant and offensive.

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Info Decompression & Treatment Simplified

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1: Introduction

What is Decompression?

Contents

FAQ - Unfurled links in ScubaBoard posts

Akimbo

Just a diver

Visualizing Decompression

Outgassing Demos

Akimbo

Just a diver

What Exactly is DCS?

Akimbo

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DCS Treatment

DCS Treatment versus Therapy

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DCS Diagnosis

Personal Sidebar

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Just a diver

Recognizing DCS Symptoms

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Just a diver

Type 1 DCS

Akimbo

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Type II DCS

Akimbo

Just a diver

OK, I might be bent

Akimbo

Just a diver

Soapbox

Choosing Dive Computers

1% DCS Hit Rates?

Classifying DCS Hits

Similar threads

Info Decompression & Treatment Simplified

Please register or login

1: Introduction​

What is Decompression?​

Contents​

Just a diver

Visualizing Decompression​

Outgassing Demos​

Just a diver

What Exactly is DCS?​

Just a diver

DCS Treatment​

DCS Treatment versus Therapy​

Just a diver

DCS Diagnosis​

Personal Sidebar​

Just a diver

Recognizing DCS Symptoms​

Just a diver

Type 1 DCS​

Just a diver

Type II DCS​

Just a diver

OK, I might be bent​

Just a diver

Soapbox​

Choosing Dive Computers​

1% DCS Hit Rates?​

Classifying DCS Hits​

Similar threads

1: Introduction

What is Decompression?

Contents

Visualizing Decompression

Outgassing Demos

What Exactly is DCS?

DCS Treatment

DCS Treatment versus Therapy

DCS Diagnosis

Personal Sidebar

Recognizing DCS Symptoms

Type 1 DCS

Type II DCS

OK, I might be bent

Soapbox

Choosing Dive Computers

1% DCS Hit Rates?

Classifying DCS Hits