The Bends (Decompression Sickness)
The Bends is the slang term used for decompression sickness. It was coined because one of the effects of getting decompression sickness is joint pain which can cause the sufferer to bend up in pain. You are more likely to hear divers referring to ‘getting bent’ than you are likely to hear, ‘having decompression sickness’ but they mean the same thing. Don’t let the name fool you though; joint pain is just one of many manifestations of this condition.
- What Causes Decompression Sickness (DCS)?
- When Was The Bends First Discovered
- Can DCS Be Predicted?
- What Are The Signs And Symptoms Of DCS?
- What To Do If You Think You Have The Bends?
- What Is The Treatment For Decompression Sickness?
- Recompression Chamber
- How Can You Prevent DCS? How Do You Avoid Getting The Bends?
- Safety Stops
- Ascent Speeds
- Sawtooth profiles
- Circulatory System Changes
- General Health
- How Can You Prepare For An Incident Of Decompression Sickness?
- Can You Be Predisposed To DCS?
- Can You Get Decompression Sickness If You Dive Using Nitrox?
- What Is A Decompression Dive?
- What Is Nitrogen Narcosis?
- What Is A Saturation Diver?
- Why Don’t Sea Creatures Such As Dolphins Get Decompression Sickness?
- Can You Get Decompression Sickness When Freediving?
- What Are Silent Bubbles?
- What Is The Difference Between DCS And DCI?
- What Is A Lung Over-Expansion Injury?
What Causes Decompression Sickness (DCS)?
Most commonly divers breathe air when scuba diving. Air is made up of 21% oxygen and 79% nitrogen. Humans need oxygen to survive, but the nitrogen is not used and, on land, this would be exhaled. When you dive, the weight of the water surrounding you exerts a pressure; the deeper you go, the greater the force.
This increased pressure forces the nitrogen into your tissues rather than being expelled as it would on land. The deeper you dive and the longer you dive the more nitrogen you absorb.
Decompression sickness is caused when the tissues are unable to unload this nitrogen build up safely. Much the same way as soda fizzes when you open a can and release the pressure if you reduce pressure on your tissues too quickly the nitrogen will release into the bloodstream in the form of bubbles. It’s the nitrogen bubbles getting stuck that cause the signs and symptoms associated with decompression sickness.
When Was The Bends First Discovered
Decompression sickness was first observed in miners returning to the surface as far back as the 1800s. These observations initialized what today we refer to as decompression theory. Fast forward a hundred years, and the first tables were created to predict and therefore avoid decompression sickness for military divers.
As recreational diving developed from military diving, these were the only tables available for use. It wasn’t until the mid-1980s that a recreational dive planner became available for the average person diving for pleasure.
Can DCS Be Predicted?
Today there are a few variations on algorithms. However, all of these are only frameworks that offer guidelines that work most of the time. They are just a mathematical extrapolation of a theory. They do not track anything physical in your body which is why conservatism is always emphasized when dive planning.
It is impossible to determine how many divers who follow established dive planning protocols and observe all contributing factors still get the bends. Regardless, even including those that have somehow flouted the rules, the incidence of decompression sickness is still quite low.
Most divers never experience it, even scuba diving instructors that make 600 dives a year safely stay the right side of a decompression chamber door.
While decompression sickness is a risk, it is a very low risk as long as you follow the rules.
What Are The Signs And Symptoms Of DCS?
Because the severity of decompression sickness is linked to nitrogen load as well as the cause and speed of unsafe off-gassing, symptoms will vary. Blotchy skin rash and itching, numbness, tingling, joint pain, swelling, dull ache, dizziness, weakness, fatigue, staggering, a tendency to favor one side of the body, paralysis, unconsciousness, and death can all be attributed to decompression sickness.
Symptoms occur from ten to fifteen minutes after surfacing and anywhere up to 12 hours later.
No matter what the symptoms are or how minor they seem a diver should always stop diving and seek medical assistance.
What To Do If You Think You Have The Bends?
The first response is to breathe 100% oxygen and while doing so get to a medical facility with a recompression chamber.
What Is The Treatment For Decompression Sickness?
Divers suspected of decompression sickness should be administered 100% oxygen as soon as possible. Oxygen helps the body eliminate the excess nitrogen. Medical personnel at the recompression chamber will then be able to determine the next course of action. For milder cases where oxygen was administered straight away, it’s possible that no further treatment will be required.
If further treatment is required the diver will need to be recompressed. The chamber essentially puts the diver under pressure as if they were going back to depth. Increasing the pressure allows the body to re-absorb the nitrogen bubbles and gives their body another chance to safely off-gas the nitrogen while the pressure is slowly reduced.
The patient is given 100% oxygen during their pressurization to further assist in getting rid of the nitrogen. The severity of the case will determine how many re-pressurizations the patient needs.
It should be noted that the speed of response to an incident of decompression sickness is critical not only to the success of treatment but also the length of the treatment. If you suspect decompression sickness, administer oxygen straight away, there is no harm in doing so.
It’s far better to arrive at a recompression chamber, breathing oxygen and subsequently be cleared of any diagnosis than wander along 6 hours later, ‘when you are sure.’ Decompression sickness, when treated promptly, rarely has any residual effects.
Divers suspected of decompression sickness should be administered 100% oxygen as soon as possible. Oxygen helps the body eliminate the excess nitrogen.
How much does it cost to treat decompression sickness?
The cost of treatment is difficult to determine because it does depend on where you are in the world, how the chamber is run, who operates it and how you get to the facility. If you need a helicopter ride, then you could be into thousands before you arrive at the chamber. A single treatment can cost around $5000 and you might need more than one.
How Can You Prevent DCS? How Do You Avoid Getting The Bends?
Be Conservative And Dive Within Your Limits!
When you learn to dive you are taught to plan a dive within no decompression limits using a mathematical table. A no decompression dive is a dive on which you can ascend straight to the surface without having to make decompression stops to allow excess nitrogen to be released.
Most people then purchase a dive computer which is a device that calculates your no-decompression limit for you based on your depth and time underwater. Regardless of the method used it is essential to remain conservative and never dive to the limit; dive tables and dive computers are just an extrapolation of an algorithm, and neither can track anything physical in the divers body.
A decompression stop and a safety stop are two different things. A safety stop is a pause added in for conservatism by divers making a no-decompression dive. This stop usually takes place at 5m and lasts for 3 minutes. The theory is that it allows that little extra time for excess nitrogen to be released.
The dive table will tell you to make a safety stop when you have made a dive that has resulted in a high nitrogen load, when you have dived to 30m or deeper, or when other factors of increased risk exist. Practically divers do them on every dive but know that they can be omitted in the case of an emergency.
Why at 5m? At the surface, the surrounding pressure is 1 bar, by 10m the pressure has doubled to 2 bar. The pressure doesn’t double again until 30m which means that the greatest pressure increase and decrease happens between 10m and the surface. It makes sense to pause halfway through this zone to allow a little more off-gassing.
The faster you ascend, the quicker the surrounding water pressure decreases. Ascend too quickly, and your body may struggle to eliminate nitrogen safely. Some scuba diving agencies recommend a speed of 18m per minute but most now recommend 9m per minute, and this is most likely what your dive computer will be set for.
A sawtooth profile is where a diver descends, ascends, descends, and ascends again in a jagged fashion. There’s no research to back this up, but it’s generally agreed that diving like this would be tempting fate. It feels counterintuitive, and a smooth profile of one descent and one ascent has to cause less physical disruption.
The most significant contributing factor in cases of decompression sickness is dehydration. Being dehydrated means that your blood is thick which causes your circulation system to be sluggish. A sluggish circulatory system will not efficiently get rid of nitrogen.
A few factors exacerbate the incidence of dehydrated divers. Firstly divers on holiday tend to visit countries hotter than their own which means they are not accustomed to the amount of water they need to drink in the new climate. Caffeinated drinks and alcohol dehydrate further; water is what you need.
Further, the air in a divers tank is dry which means the body needs to moisten it; this uses the body’s resources. Finally, the pressure change associated with diving fools your body into believing there is too much fluid which causes the diver to urinate, reducing hydro reserves further.
Circulatory System Changes
Your body unloads nitrogen via its circulatory system so anything that interferes with how this functions can have an impact on your body’s ability to off-gas. This is why divers who are working hard underwater or those diving in very cold water should be extra conservative with their dive plan. Similarly, post-dive vigorous exercise is discouraged as is post dive alcoholic beverages.
Smoking changes your blood pressure and pulse, but it also introduces carbon monoxide which your blood will bond with more readily than oxygen, and this disrupts gas exchange. To offset this preference for carbon monoxide, smokers have more red blood cells which means their blood is thicker and therefore flows slower and not as effectively to the peripheries. Smoking also constricts blood vessels which again slows down the circulatory system.
You don’t have to be super fit to scuba dive but you should keep an average level of fitness, be well rested and observe a healthy diet. This lifestyle not only ensures that you keep your circulation system running smoothly but that you can comfortably make a surface swim in full gear.
Being out of breath and having little stamina will not just affect your body’s response to nitrogen loading and efficient off-gassing but it will directly affect your ability to cope in an emergency situation.
Fat more readily absorbs nitrogen than other tissues, and someone who is overweight has a higher proportion of fat. Apart from increased absorption, the problem associated with bubble formation in fatty tissue is that there is no associated joint pain. This means that bubbles can enter the bloodstream and be carried to the heart and lungs undetected which can cause severe forms of decompression sickness.
If you feel unwell or are sick, the general recommendation is not to dive until you are better.
You will hear it said that divers should not get a massage post dive as this can cause decompression sickness. The theory being that massage could dislodge micro-bubbles which could join to form larger bubbles which can become problematic.
In reality, this is highly unlikely; the diver would need to have undertaken multiple dives to a high nitrogen loading or made decompression dives and then gone straight into a very intense deep tissue massage. The more significant risk here is associated with the diver becoming immediately sedentary and laying down with a high nitrogen load which would impede circulation. (Sunbathers and post dive snoozers take note!)
Flying or ascending to altitude after diving can cause decompression sickness because in both instances the surrounding pressure is reducing and any remaining nitrogen will come out of solution. The general rule is to wait 24 hours after surfacing before ascending to altitude.
How Can You Prepare For An Incident Of Decompression Sickness?
The correct response to an incident is vital; having a clear plan in place will expedite treatment and having the right insurance will mean there are no holdups in the chain of treatment.
When diving with an operator, understand their emergency assistance protocols. When diving from a boat or shore, there should be emergency oxygen available.
- Do you know where it is?
- Do you know how to use it?
- Are you certified to administer it?
- How will you alert emergency response?
- Is it the ship’s radio or is it by mobile phone and what is the number?
Having all the required information at your fingertips will make for an efficient response. If you are diving independently of an operator, you need to consider a plan for yourself which includes buying an emergency oxygen kit.
Diving insurance specifically covers you for recompression treatment and the costs involved in getting you to that facility. The closest facility may not be very close at all and transfer could include a helicopter journey or speedboat response.
You will find that some holiday insurance policies include diving too but they might restrict you by depth and activity so check the small print. It is possible that your dive operator provides insurance or allows you to buy cover for the chamber local to them. If you dive at home and regularly, holiday insurances don’t cover you, so you are better off seeking out annual coverage just for diving.
Look at the D.A.N. (Divers Alert Network) site for your country of residence or Dive Master Insurance. Dive Master Insurance even offers single day insurance which is excellent for those who just dive now and again. What you choose will depend on the location and circumstances in which you are diving as well as how often you dive.
For what you pay to dive, the cost of insurance is negligible, and even though the incidence is low, its just not worth the risk, you should not be diving without it.
Can You Be Predisposed To DCS?
There is a common heart condition that can make you more susceptible to decompression sickness. A PFO (patent foramen ovale) is the hole in the heart between the left and right chambers which in 75% of cases closes after birth. If the hole hasn’t closed your blood loaded with nitrogen could miss your lungs and go straight back into the arterial system.
If this happens your body just lost the chance to offload the gas which has a knock on effect as it circulates again, still loaded, and unable to carry the next load of nitrogen. Unfortunately, the way most people find out they have a PFO is by getting the bends. The good news is that there is an operation available to seal the hole.
Can You Get Decompression Sickness If You Dive Using Nitrox?
Nitrox is air that has been enriched with oxygen. The most common blend increases the oxygen content from 21% in air to 32%.
Nitrox blends reduce the diver’s exposure to nitrogen and therefore mean that the diver can dive for longer. However, the diver is still loading nitrogen and has no less risk than a diver breathing air.
What Is A Decompression Dive?
A decompression dive is a dive that requires the diver to stop on the way to the surface to let excess nitrogen escape. They will have a plan to follow which may include several stops on the way to the surface. More commonly the diver will breathe a nitrox blend as they get closer to the surface.
The increased oxygen helps their body to get rid of the nitrogen faster. Often their last stop is made breathing 100% oxygen at 6m depth, and they will continue breathing this until they are out of the water.
For divers who plan to dive to a depth where nitrogen narcosis would impair them, tri-mix is often breathed instead. This gas is a blend of oxygen, nitrogen, and helium. The helium replaces some of the nitrogen so that the diver’s mind is clearer however as helium is a lighter gas it is less forgiving when off-gassing. A diver using trimix benefits from a clearer mind but has no less decompression risk.
What Is Nitrogen Narcosis?
The other side effect of nitrogen absorption is narcosis which is a drunk-like state. While this is not harmful in itself, the euphoria can cause a disregard for safety. Ascend, and symptoms will subside.
What Is A Saturation Diver?
Saturation divers are paid to work underwater. Rather than decompress after each dive, they spend their whole time under pressure. So as an example, they might work under pressure for two weeks during which time they would live in a pressurized habitat. At the end of their two weeks, they would depressurize. Working and living like this means that they only put their bodies through decompression once.
Why Don’t Sea Creatures Such As Dolphins Get Decompression Sickness?
Humans and fish are entirely different and whereas fish do not suffer from decompression sickness they can die by being brought to the surface too quickly. They have something called a swim bladder which allows them to regulate their buoyancy in the water. Pull them up quickly and it will expand which can cause their stomach to come out of their mouths and their eyes to pop.
Ocean-going mammals, even though they are air breathers, still function a little differently from humans. Dolphin’s lungs, for example, are capable of holding more oxygen than humans but they can also process more gas.
A human can exchange 15 liters per second whereas a dolphin can exchange 130 liters. Also remember that a dolphin is not breathing compressed air from a tank but rather, breath holding, like a free diver.
Can You Get Decompression Sickness When Freediving?
Technically, yes. Very advanced freedivers making long and deep dives could load enough nitrogen to become symptomatic. Historically, pearl and sponge divers free dived for their booty, and again, after constant exposure, some showed signs of decompression sickness.
However, these are extremes and making a few surface dives while snorkeling is unlikely to cause a problem. The only caveat to this is if you have been scuba diving and had a nitrogen load in your body. Rapid decent and ascent, in this case, would not be advised as it would interrupt your body’s off-gassing and potentially cause microbubbles to join.
What Are Silent Bubbles?
Silent bubbles or micro-bubbles are tiny bubbles of nitrogen that exist in everyone post dive. On their own, they do not cause a problem.
What Is The Difference Between DCS And DCI?
Decompression illness is a term which covers both decompression sickness and lung over-expansion injuries. The name was brought into use to help divers offering first aid to injured divers. Emergency oxygen should be administered in both cases, and at the first response stage of an emergency, it is not necessary to diagnose which problem the diver has.
What Is A Lung Over-Expansion Injury?
A diver breathes air at a pressure that is equivalent to that surrounding them. As long as a diver does not hold their breath, breathing pressurized air is not a problem.
However, if a diver were to hold their breath and ascend or have a condition that would cause ineffective air exchange in the lungs or pockets of the lungs to stick together, then the air in their lungs would expand, and this can rupture the lungs and allow bubbles to enter the bloodstream. Air bubbles can block blood supply and cause a stroke or card