Understanding Decompression Injuries

Disclaimer: I am neither a doctor nor am I a scientist. This article is intended to be an overview of a very complicated and complex medical/scientific subject. If you believe yourself or another to be suffering from a decompression or another dive-related injury, stop reading immediately and call the Divers Alert Network Emergency Hotline at (919)-684-9111 or seek emergency medical care without delay.

Decompression Injury (DCI) is a term that describes a number of different injuries that one could sustain while SCUBA diving. While it is important to be aware of the risks that adventure sports like SCUBA diving can impose upon us, it is also relevant to point out that the majority of diving injuries occur due to diver error. To best mitigate potential for injury, it is important to always dive within your training and experience. PADI offers a number of courses that can expand your training and experience, so be sure you are taking advantage of the educational opportunities available before conducting riskier SCUBA adventures.

The two most common forms of DCI are an arterial gas embolism (AGE) and decompression sickness (DCS). Before we can break down the differences between them, we need to have a basic understanding of how our bodies respond to SCUBA diving.

Physiology 101

Oxygen is the fuel for our bodies. Every muscle, fiber, and tissue that we have relies on a steady supply of oxygen in order to function. We add fuel to the machine of our bodies through breathing. We inhale the air around us which then travels into our lungs where the gas is then filtered into the blood stream. Oxygenated blood (blood that is infused with oxygen) then travels around our bodies dropping off little oxygen packages like the mail carrier. Also like a mail carrier, when oxygen packages are dropped off, other packages are picked up that contain, among other things, the gasses that we cannot metabolize so that they can be exhaled and expelled from our bodies.

Everyone knows about carbon dioxide (CO2), a toxic gas that makes up a lot of our exhale, but the gas we need to be aware of for SCUBA diving is nitrogen. Nitrogen makes up almost 80% of the air that we breathe, but is not a gas that our bodies can absorb. At the surface, this isn’t a problem. Our bodies are well adapted to push out the nitrogen with each exhale we make and there is no risk of it getting “stuck” inside of us. Diving changes that due to the increased pressure (partial pressure) on the mix of gasses we are breathing. This increase in pressure causes nitrogen to get shoved into our cells and tissues. That’s not a problem, but since our bodies cannot absorb those nitrogen bubbles, we need to practice safe, conservative diving habits in order to off gas that nitrogen correctly. Slow ascents, safety stops, excellent buoyancy control, and adequate surface intervals will all assist your body in off gassing nitrogen and will lessen your risk of a DCI.

So, now that we have a basic understanding of the on gassing and off gassing process, lets look at what results of improper or incomplete off gassing.

Arterial Gas Embolism (AGE)

An AGE is the more serious and dangerous of the two main types of DCI and can be generally considered the result of improper off gassing.

When we are diving, is important to always be in control. In control of our decent at the start of a dive, in control of our buoyancy during the dive, and in control of our ascent at the end of a dive (or any time we are ascending). The maximum safe rate of ascent is 1 foot per second, or 60 feet per minute.

Maintaining a 1ft/sec (or slower) ascent rate enables our body to process, flush out, and properly off gas the nitrogen in our cells. Ascending at a faster-than-safe rate can result in the nitrogen bubbles in our cells expanding beyond a size that will allow them to squeeze through our bodies for exhalation. When one of these bubbles gets stuck, it causes an AGE and blocks the blood flow. Remember the ship that got stuck in the Suez Canal a few years ago? That’s what is happening when you experience an AGE.

Symptoms of an AGE often include dizziness, confusion, chest pain, and loss of consciousness and will be experienced within relatively close proximity to the dive.

Treatment for an AGE typically includes oxygen and hyperbaric therapy. This will “crush” the nitrogen bubbles and allow them to be properly off gassed. Delays in treatment may result in long-term injury and loss of bodily functions.

Decompression Sickness (DCS)

DCS (also known as “the bends”) is the most common form of DCI. While it is not as serious as an AGE, it is not to be taken lightly. Having personally witnessed divers experiencing symptoms of DCS, I can assure you that it is not something to be trivialized.

DCS is essentially the result of incomplete off gassing. Luckily for divers everywhere, achieving complete off gassing is fairly straight forward and you will be or have been taught the three simple steps in your Open Water Diver Course:

1. Dive planning
   Whether you are using a dive computer to plan your dives or you are using an abacus and the US Navy Dive Tables, your dive should always have a plan that you do not deviate from. Stay within the limits of your certification and do not exceed the “No Deco Time” either displayed on your dive computer or plotted on the dive tables. Plan your dive and dive your plan!

2. Safety stop
   Three to five minutes, that’s all that is asked of you. Hell, I spent more time than that trying to find my keys this morning, I can certainly spare 5min hanging out at 15-20ft to allow for my body to get the last little bit of in-water off gassing completed. Always always complete a 3-5min safety stop at a depth of 15-20ft at the end of each dive and save the last third of your tank to ensure that you have enough breathing gas to perform your safety stop.

3. Surface interval
   Just because you ascended at a safe rate, performed your safety stop, and were excellent in your safe diving practices doesn’t mean that all the nitrogen has been processed out of your body. In order to prevent nitrogen oversaturation, it’s important to allow for an hour or more between dives. This will not only keep you safer, but will allow for more bottom time on ensuing dives!

Common symptoms of DCS include joint pail, skin rashes, neurological symptoms, and in severe cases even death. Unlike the more immediately experienced symptoms of an AGE, symptoms of DCS may not present themselves until several hours (or longer) after the dive.

Similar to an AGE, treatment includes oxygen and hyperbaric therapy, usually consisting of several multi-hour sessions in a recompression chamber over the course of several days.

Preparing for Calamity

Even on objectively safe, responsible, and conservative dives, accidents can happen. It is important to be prepared for catastrophe, and you can prepare yourself to accurately respond to DCI’s with proper training. In the PADI curriculum, courses like Emergency Oxygen Provider, Rescue Diver, and the catalog of Emergency First Response Courses will empower you with the knowledge development and practical application needed to be the best dive buddy you can be!