Treating Decompression Sickness (The Bends)

Decompression sickness (DCS) is one of the most common problems reported to Divers Alert Network^® (DAN^®). Although scuba diving accidents are rare, it’s important to know how to handle suspected cases of DCS. Your ability to take appropriate action can make a difference in the life of someone you care about.

What is Decompression Sickness?

DCS, also known as the bends, describes a variety of injuries that result from inadequate decompression following exposure to increased pressure. This can occur following uneventful dives within accepted no-decompression limits but is more likely after dives that involve a rapid underwater ascent. DCS can also be prompted by ascending in an airplane too soon after diving. When there is a rapid decrease in surrounding pressure, nitrogen absorbed by the body at depth comes out of solution, creating bubbles in the bloodstream and/or body tissues.

Symptoms of DCS can occur immediately after surfacing or up to 24 hours later. On average a diver with DCS will experience symptoms between 15 minutes and 12 hours following a dive.

Symptoms of DCS

• Unusual fatigue
• Itchy skin
• Pain in the joints and/or muscles of the arms, legs or torso
• Dizziness, vertigo and ringing in the ears
• Numbness, tingling and paralysis
• Shortness of breath

Signs of DCS

• Blotchy rash
• Muscle weakness or paralysis
• Difficulty urinating
• Confusion, personality changes or bizarre behavior
• Staggering
• Coughing up bloody, frothy sputum
• Collapse or unconsciousness

How to Treat a Diver with Suspected DCS

If you suspect a diver has DCS, provide emergency oxygen right away. Next, determine the severity of their condition (emergency, urgent or timely) by following the guidelines below:

Emergency DCS

A diver who is profoundly dizzy, intermittently conscious, weak, walking with an abnormal gait or having trouble breathing is experiencing a serious medical emergency. Administer 100 percent oxygen, and arrange emergency evacuation to the nearest medical facility.

Always contact emergency medical services first, then contact DAN. Although a diver with severe DCS requires recompression, it is essential that he or she be stabilized at the nearest medical facility before transportation to a chamber.

Urgent DCS

A diver experiencing severe pain that is either constant or increasing should be placed on 100 percent oxygen and given fluids. The next step is to contact DAN or the nearest medical facility. Emergency air transportation may not be necessary in all cases. Do not give the diver analgesics (pain relievers) unless advised to do so by medical personnel.

After obtaining professional medical advice, conduct a neurological exam and write down as much information as you can about the diver’s recent diving activity. A neurological exam can be done by anyone; no medical experience or training is required. Simply follow the on-site neuro exam directions found here. Ask the diver about any diving activities within the past 48 hours, including depths, times, ascent rates, surface intervals, breathing gas used and any problems experienced during or after the dives.

Obtain as much info as you can without delaying transportation to a medical treatment facility. If time allows, the following additional information may aid medical professionals with diagnosis and treatment:

• Symptom onset times and progression after the diver surfaced from their last dive
• A list of all first aid measures taken (including times and method of oxygen delivery) and their effect on symptoms
• A description of any joint or other musculoskeletal pain including location, intensity and changes based on movement or weight-bearing maneuvers
• Photos of any rashes with a detailed description of their location
• Information about any traumatic injuries sustained before, during or after the dive

Timely Cases of DCS

Divers who do not have obvious symptoms or whose symptoms develop slowly over multiple days may have a “timely” case of the bends. Common signs and symptoms may include vague complaints of pain or abnormal sensations.

Follow the steps described previously under “Urgent DCS” to conduct a neurological assessment and collect information about the diver’s recent activity. Next, contact DAN or a medical professional, or go to the nearest medical facility for advice and further evaluation.

Denial: The Worst Symptom of DCS

Denial is arguably the worst “symptom” of DCS. Delayed treatment can lead to permanent injury and prolong (or even prevent) the diver’s full recovery. Emergency oxygen can cause symptoms to temporarily improve only to reappear later — it is no substitute for a medical evaluation. Always contact DAN or a medical professional with training in dive medicine in cases of suspected DCS — even if the symptoms and signs appear to have resolved. 

Be Prepared, Get Insured

Dive accidents can happen to anyone, not just newly certified divers. According to a recent DAN Annual Diving Report, nearly 600 divers contacted DAN with concerns about DCS, and divers with 21-60 logged dives were the most likely to report a diving incident. Learn more about the Top 5 Factors That Increase a Diver’s Risk of Getting the Bends.

Many medical insurance plans cover only the cost of hyperbaric treatments and not the cost of getting you to the chamber (the average cost for an air ambulance is around US$20,000). Ensure you have protection against the unexpected by purchasing DAN Dive Accident Insurance.  

Join DAN

The Bends – Chemistry LibreTexts

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The Bends is an illness that arises from the rapid release of nitrogen gas from the bloodstream and is caused by bubbles forming in the blood and other tissues when a diver ascends to the surface of the ocean too rapidly. It is also referred to as Caisson sickness, decompression sickness (DCS), and Divers’ Disease.

Introduction

As divers descend into the ocean, the external pressure on their bodies increases by about 1 atm every 10.06 m. To balance this it is necessary to increase the pressure of the air they breathe from tanks or pumped to them from the surface so that their chests and lungs do not collapse. Unfortunately, our bodies aren’t used to the pressurized air (because we normally breathe air under normal atmospheric conditions). With higher air pressure in the lungs Henry’s Law tells us that gases such as nitrogen, helium (when used in diving gas mixtures) and oxygen become increasingly soluble in the blood. Unlike oxygen which is metabolized, nitrogen and helium build up throughout the body When divers want to emerge from the water, they have to make sure they don’t ascend to the surface level too quickly because they risk numerous bubbles forming as the nitrogen/helium re-equilibrates, much as when a pressurized bottle of soda is suddenly opened. When nitrogen (N₂) gas forms bubbles, it accumulates and saturates the muscles and blood, causing pain. Called the Bends, this condition can also cause injuries involving the nervous system.

Figure taken with permission from Wikipedia Commons.

The solubility of a gas is the ability for the gas to dissolve in a solvent (in our case, blood, which although it contains organic components is essentially an aqueous solution). Both temperature and pressure affect the solubility of a gas.

The Solubility as a Function of Temperature

• In water solvents, the higher the temperature, the less soluble the gas is.
• In organic solvents, the higher the temperature, the more soluble the gas is.

The Solubility as a Function of Pressure

English chemist William Henry discovered that as the pressure increases, the solubility of a gas increases. Henry’s Law is then:

\[ C =k P_{gas} \]

where

• C=solubility of a gas in a solvent at a specific temperature,
• P_gas is the partial pressure of the gas, and
• k is Henry’s Law Constant

In the case of The Bends:

• If a diver goes deeper and deeper into the water, more nitrogen builds up in the bloodstream and other tissues.
• Following Henry’s Law; as the pressure increases, the solubility of nitrogen in the diver’s bloodstream increases.
• As a result, nitrogen from the compressed air stays in the bloodstream and other tissues
• However, since the diver is in a highy-pressurized environment, the excess N₂ can only be relieved when the diver ascends to levels with lower external pressure
• Ideally, this should happen during the diver’s gradual rise to the surface
• Unfortunately, sometimes , the diver ascends too quickly, resulting in the rapid formation of bubbles, which interfers with nerves, blood and lymphatic vessels and leads to excruciating joint pain and clotting.

Example \(\PageIndex{1}\):

Determine Henry’s Law Constant, k, with the information that the aqueous solubility of N₂ at 10 degrees Celsius is 11.5 mL N₂ / L and 1 atm.

\( k= \dfrac {11.5 mL N_{2}/ L}{\ 1 atm} \)

Now if the P_gas of N₂ increases to 5 atm:

\[ P_{N2}=\dfrac {C}{\dfrac {11. 5 mL N_{2}/ L}{\ 1 atm}} \]

\[ 5 atm=\dfrac {C}{\dfrac {11.5 mL N_{2}/ L}{\ 1 atm}} \]

Solve for C: C= 57.5 mL N₂ /L

Therefore, both examples show that as the the pressure increases from 1 atm to 5 atm, the solubility of the N₂ gas increases from 11.5 to 57.5 mL N_{2 /} L. This supports Henry’s Law.

Symptoms of the Bends

• Joint pain
• Fatigue
• Itching and rashes
• Coughing and chest pain
• Dizziness and paralysis
• Unconsciousness
• Death

Most symptoms occur 24 hours after decompression, but can occur up to 3 days after.

Prevention

• Ascending to the surface slowly (rate of 60 ft/min.)
  • The slower the diver surfaces, the more slowly the excess nitrogen is equilibrated and the lower the impact on the diver
• Spending time in a decompression chamber
  • Chambers that high-pressured divers are placed in.
  • Once in the chamber, the diver is immersed in a high pressure environment which is slowly reduced, minimizing any effect.
• Breathing a compressed air mixture of helium and oxygen with no nitrogen.
  • For deep dives, in addition to the Bends, excess nitrogen can lead to decreased mental function. This is called nitrogen narcosis.
  • Helium is less soluble in the blood stream and thus does not build up as much, providing a smaller threat to divers and is used for deep dives.

References

1. Petrucci, et al. General Chemistry: Principles & Modern Applications: Custom Edition for CHEM 2 (Hardcover). Upper Saddle River: Pearson Education, Inc., 2011.
2. Phatak, Uday. “Decompression Syndrome (Caisson Disease) in an Indian Diver.” Annals of Indian Academy of Neurology. Online-Only Journal. 13.3. 2010 n.pag. web. 30 May 2011.

Problems

1. What is Henry’s law?
2. How does Henry’s law relate to the Bends illness?
3. How does temperature affect solubility?
4. How does ascending to the surface make the bends less prevalent?
5. Why is breathing the compressed helium/oxygen mixture better than air with N₂?

Answers

1. \(C =k *P_{gas}\) (where C=solubility of a gas in a solvent at a specific temperature, P_gas is the partial pressure of the gas, and k is Henry’s Law Constant)
2. As the pressure increases, the solubility of gases in the diver’s bloodstream increases. Henry’s law states that the solubility of a gas increases when the pressure increases.
3. As temperature increases, the solubility of gases decrease in aqueous solutions. In organic solutions, the solubility of gases increases at higher temperatures.
4. When diver surfaces slowly, he/she will have a reduced impact of pain from the bubbles that form. Instead of rapidly forming and causing joint pain, the slow rise to the surface creates a steady loss of pressure, resulting in pain that is not as severe.
5. Helium is less soluble in the blood stream, providing a smaller threat to divers when they come up to the surface of the ocean. Fewer bubbles are formed, meaning that the divers encounter less pain as they ascend.

Contributors and Attributions

• Dhara Shah (UCD)
• Josh Halpern (LibreTexts)

The Bends is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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Diving fin selection

How to choose fins for scuba diving

Main function

Can I swim without fins? Undoubtedly. You can dive with a mask and without fins, enjoying the beauty of the underwater world.

But everything changes when we put on scuba gear. The weight of the cylinders under water is small, but the mass, i. e. the inertial force remains the same as on land – about 20 kg. In addition, rigid cylinders hinder freedom of movement.

The use of fins compensates for the difficulties encountered.

Properly fitted, comfortable and efficient fins make a big difference in a scuba diver’s comfort underwater.

The choice of the most suitable fin model depends on your tasks and your individual characteristics.

Fin elements

To assess the suitability of fins, we select two parameters:

• easy attachment to the leg;
• swimming efficiency.

The first is determined by the design of the foot pocket, the second by the design of the blade and the overall shape of the fin.

The variety of designs of galoshes comes down to two fundamental options: fins with closed and open heels.

The first ones are very comfortable when put on bare feet and provide the tightest connection between the fin and the foot.

Open heel fins with a strap are more comfortable to put on over wetsuit boots. They are also called adjustable. Modern models of adjustable fins allow you to tighten and loosen the strap right on your foot.

The variety of fin blade designs is very large.

For fins, as for any engine, efficiency is extremely important, i.e. the ratio of useful work to energy expended.

Under water, everything is measured by air: the more energetic the physical work, the greater its consumption. The more efficient the fins, the less air is needed to cover a certain distance.

Other things being equal, the efficiency of the fins and their suitability to your individual needs can change the air flow rate by 20 – 30%. Accordingly, the time spent under water will change by the same amount.

Long fins with blades made of thin, elastic and rather rigid plastic and rubber galoshes have excellent hydrodynamic properties.

In terms of speed, these fins outperform the vast majority of other models and are optimal for swimming without scuba gear. It is no coincidence that underwater hunters all over the world prefer fins of this design.

Scuba divers, on the contrary, rarely use them, as they lose to smaller fins in maneuverability. For swimming with the device, fins with shorter blades made of a similar material are produced.

Another way to increase efficiency is with windowed fins. What is their meaning?

During stroke, a zone of increased pressure is created on one side of the rowing surface, and a zone of reduced pressure on the other. The resulting eddy currents along the edges of the fin create additional drag.

Slots at the base of the blade allow water to pass through, reducing pressure differences and thereby reducing eddy currents.

This design does not increase the speed imparted by the fins, but reduces the effort during the stroke.

Significantly increases the efficiency of fins when using the tunnel effect.

During the stroke, a certain amount of water inevitably rolls to the sides, not participating in the creation of the forward movement of the diver.

If the inside of the fin blade is made of a softer material than the sides, the fin flexes during the stroke, creating a trough that orients the flow of water in the desired direction, thereby reducing the amount of water that rolls down empty.

Another way to create a tunnel effect is to divide the plastic blade with 2 – 4 longitudinal rubber grooves that allow transverse bending.

A variation of the tunnel effect is the spoon or ladle effect achieved by a wedge-shaped insert of softer material or rubber grooves of different lengths.

Today, tunnel effect fins are the most popular among scuba divers.

Choosing fins

How to choose fins? First, you need to make a choice between closed or open heel fins.

For swimming, speed swimming or spearfishing, it makes sense to choose the first option.

If you are serious about scuba diving, we recommend purchasing open-heel fins with adjustable straps and neoprene socks or boots, as without them, swimming with adjustable fins is extremely uncomfortable and often causes blisters.

Now about the choice of a specific model.

Overall design and color variations are important, but more important is the hydrodynamic properties of the fins.

Depending on your physique and physical abilities, one or another fin will be most comfortable for you.

We offer the following test to help you make the right choice. All you need is a swimming pool or an open body of water.

Put on your mask and fins, calm your breath and dive a fixed distance close to your limit on one breath. For someone it will be 25 m, for someone – 50 or more.

Relax and repeat the experiment with other fins. Choose those with which this exercise is given to you the easiest.

They don’t necessarily reach maximum speed, thereby reducing diving time, but they convert your energy into forward movement in the most beneficial way, which means they will be the best way to save air when diving.

Fins Instructions for use

If the fins do not have metal parts, it is not necessary to rinse them with fresh water after every sea dive, but it is advisable to do this before a long break in use.