Decompression Sickness – StatPearls – NCBI Bookshelf

Jeffrey S. Cooper; Kenneth C. Hanson.

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Last Update: September 2, 2022.

Continuing Education Activity

Decompression sickness (DCS) occurs when dissolved gasses (usually nitrogen or helium, used in mixed gas diving) exit solution and form bubbles inside the body on depressurization. DCS occurs from underwater diving decompression (ascent), working in a caisson, flying in an unpressurized aircraft, and extra-vehicular activity from spacecraft. Proper decompression procedures during diving can help decrease DCS. Experts have classified DCS as Type I with symptoms involving only the skin, musculoskeletal system, or lymphatic systems; and Type II with symptoms that involve the central nervous system. This activity reviews the presentation of decompression sickness and highlights the role of the interprofessional team in its management.

Objectives:

• Review the etiology of decompression sickness.

• Describe the presentation of decompression sickness.

• Summarize the treatment of decompression sickness.

• Outline the importance of improving care coordination among interprofessional team members to improve outcomes for patients affected by decompression sickness.

Access free multiple choice questions on this topic.

Introduction

Decompression sickness (DCS) occurs when dissolved gasses (usually nitrogen or helium, used in mixed gas diving) exit solution and form bubbles inside the body on depressurization. DCS occurs from underwater diving decompression (ascent), working in a caisson, flying in an unpressurized aircraft, and extra-vehicular activity from spacecraft. Proper decompression procedures during diving can help decrease DCS. Experts have classified DCS as Type I with symptoms involving only the skin, musculoskeletal system, or lymphatic systems; and Type II with symptoms that involve the central nervous system.

Etiology

DCS is bubble formation, growth, and elimination caused by a reduction in ambient pressure that results in inert gasses, usually nitrogen, that are dissolved in solution within tissues of the body. Individuals that breathe air in a pressurized environment reach a state of equilibrium/saturation of gas. This dissolved gas will be driven out of solution when leaving a higher-pressure environment to a lower pressure environment, such as ascending from depth during self-contained underwater breathing apparatus (SCUBA) diving, leaving a caisson worksite, or ascending to altitude in an unpressured aircraft. There are individual factors identified as possibly contributing to an increased risk of DCS. These include dehydration, patent foramen ovale,[1] previous injury, cold ambient temperature, high body fat content, and alcohol consumption. Type II decompression sickness (neurological symptoms) is thought to occur from right-to-left shunting of venous bubbles.[2]

Epidemiology

The incidence of decompression sickness, fortunately, is rare. Estimates for sports diving are three cases per 10,000 dives. The incidence among commercial divers can be higher ranging from 1.5-10 per 10,000 dives. As expected, the incidence depends on the length and depth of the dive.[3] The risk for DCS is 2.5 times greater for males than females.

Pathophysiology

The pathophysiology of DCS is due directly to the formations of bubbles coming out of solution. Tissue damage results from multiple mechanisms including blockage of blood flow and vascular spasm.[4] Gas bubbles also cause endothelial damage resulting in activation of the intrinsic clotting cascade with platelet activation. Inflammatory mediators are released and with increased endothelial permeability development of edema, which leads to tissue ischemia.[5]

History and Physical

The initial evaluation of a patient suspected of DCS should include a detailed history and physical exam. For a conscious patient, get the details of exposure, including onset, duration, and progression of symptoms. For a diver with DCS, it is vital to determine the patient’s dive profile and gas mix.[3] An ear exam should look for signs of barotrauma. The patient should have a detailed neurological exam. 

DCS occurs most frequently in the shoulders, elbows, knees, and ankles. Joint pain (“the bends”) accounts for most cases, with the shoulder being the most prevalent site. Neurological symptoms present in 10% to 15% of DCS cases with a headache and visual disturbances being the most common symptoms. Skin manifestations are a feature in about 10% to 15% of DCS cases. Pulmonary DCS (“the chokes”) is quite rare in divers and much less frequently seen in aviators because of oxygen pre-breathing protocols. Bubbles in the skin or joints result in mild symptoms, larger numbers of bubbles in the venous blood may cause lung damage, and bubbles involving spinal cord function may lead to paralysis, sensory dysfunction, or death. If there is a cardiac right-to-left shunt, (e.g., a patent foramen ovale), venous bubbles could potentially enter the arterial circulation, resulting in an arterial gas embolism.

DCS should be suspected if related symptoms occur following a drop in pressure within 24 hours of diving. The diagnostic confirmation is if the symptoms are relieved by recompression. Magnetic resonance imaging (MRI) or computed tomography (CT) can occasionally identify bubbles in DCS, but they are not good at determining the diagnosis and certainly cannot be used to rule out DCS.

Evaluation

DCS is a clinical diagnosis. As the goal for treating all patients with symptomatic DCS is hyperbaric oxygen (HBO), with emphasis placed on recompression, there should be no delay in treatment for further diagnostic workup. The one exception is a chest x-ray, as untreated pneumothoraces are an absolute contraindication for HBO.[3]

Treatment / Management

All decompression sickness cases should have initial treatment with 100% oxygen until HBO therapy is available. Neurological, pulmonary, and mottled skin lesions should be treated with HBO therapy even if seen several days after development. Fluid administration is indicated, as this helps minimize dehydration. The recommendation to administer aspirin is no longer valid, as analgesics may mask symptoms. Patient placement is in the supine position or the recovery position if vomiting occurs. The Trendelenburg position and the left lateral decubitus position (Durant’s maneuver) may be potentially beneficial if air emboli are suspected, but these positions are no longer recommended for extended periods, owing to concerns regarding cerebral edema. If the patient experiences an altered mental status or is unconscious, initial management should focus on the treatment and stabilization of ABCs, (airway, breathing, and circulation). Patients should receive HBO treatment as soon as possible.

Patients that need evacuation to a definitive treatment center by aeromedical transport should fly on pressurized aircraft. If unpressurized aircraft, such as helicopters, are the only means of transport then flight altitude should be limited to 300 m or 1000 ft if possible. [3]

Differential Diagnosis

Vertigo can indicate inner ear or vestibular decompression sickness wherein bubbles form in the perilymph fluid of the cochlea.[6] However, other diving-related causes merit consideration, as recompression and hyperbaric oxygen can cause worsening of some of these conditions. Inner ear barotrauma, in particular, would be a contraindication to compression as high-pressure gas may be forced into the cochlea causing further trauma on decompression. Alternobaric and caloric vertigo should be differentiated from decompression sickness by history. Cerebral arterial gas embolism affecting the midbrain or cerebellum can also present as inner ear decompression sickness but receives similar treatment.[1]

The differential diagnosis for divers should also consider that the stress of diving can exacerbate chronic medical problems. Consider cardiac disease for patients with chest pain and exacerbation of intrinsic lung disease for shortness of breath. Other considerations include pain from previous musculoskeletal injury and stroke and hypoglycemia for altered mental status.  Further concerns include drowning or near-drowning and thermal stress.[3]

Treatment Planning

There are a variety of hyperbaric chamber treatment protocols for decompression sickness. These differences are based on such things as the severity of the insult and the availability of oxygen. There are also in water recompression protocols. The usual US treatment protocol is a US Navy Treatment Table 6 done with oxygen pressurized to 2.8 atmospheres absolute (ATA). In water, recompression is a relatively high risk but is a consideration if there would otherwise be significant delays to treatment, logistical difficulties, or other problems. It requires appropriate training, equipment, and pre-planning. Immediate treatment at the surface with oxygen is beneficial for improving outcomes and decreasing recompression treatments.   

Treatment of DCS employing the US Navy Treatment Table 6 with oxygen at 18m is the standard of care. Significant delay to treatment, transportation difficulties, and facilities with limited experience may lead one to consider on-site treatment.  Surface oxygen for first aid is shown to improve the efficacy of recompression and decreased the number of recompression treatments required when administered less than four hours post-dive. In-water recompression (IWR) to 9m, breathing oxygen is one option that has shown success over the years. IWR is not without risk and requires certain precautions. IWR would only be suitable for an organized and disciplined group of divers with suitable equipment and practical training in the procedure.

Prognosis

Having had decompression sickness may place patients at increased risk for future similar events. Prognosis is severity dependent and also dependent on such factors as the time to recompression, availability and time to surface oxygen, and supportive care.

Complications

Decompression sickness can cause long-term damage. Central nervous system lesions in the spine and brain may occur.

Deterrence and Patient Education

The risk of decompression sickness is reducible in several ways. Divers should avoid flying within 24 hours after their last dive and longer no-fly periods may be required based on dive profiles and guided by decompression tables or computers. The use of oxygen-enriched gas can also ameliorate risk if used on “air tables.” Using a more conservative dive table or dive computer setting will likewise reduce risk. Isobaric decompression, breathing oxygen at depth, likewise can lessen the inert gas burden and reduce decompression sickness risk. 

Cold exposure, heavy exercise, recent alcohol use, and dehydration all increase risk and should be avoided. Preliminary research also shows that exercise several hours before diving may be protective while exercise after diving may increase the risk of DCS.[7]

Pearls and Other Issues

The treatment of DCS is with 100% oxygen, followed by recompression in a hyperbaric chamber.[8] In most cases, this will prevent long-term effects. However, permanent injury from DCS is possible. To prevent the excess formation of bubbles leading to decompression sickness, divers limit their ascent rate. The recommended ascent rate used by popular decompression models is about 10 meters (33 ft) per minute.

Enhancing Healthcare Team Outcomes

The management of patients with decompression sickness best done with an interprofessional team. Early identification and referral to a hyperbaric center are important for good outcomes from serious decompression sickness. In water, treatments need a well-trained and organized team approach.[9][10] Divers should have oxygen for immediate administration in the case of DCS. The Divers’ Alert Network provides referrals to hyperbaric facilities and 24/7 consultation with hyperbaric trained physicians and other providers.

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References

1.

Livingstone DM, Smith KA, Lange B. Scuba diving and otology: a systematic review with recommendations on diagnosis, treatment and post-operative care. Diving Hyperb Med. 2017 Jun;47(2):97-109. [PMC free article: PMC6147252] [PubMed: 28641322]

2.

Clarke JR, Moon RE, Chimiak JM, Stinton R, Van Hoesen KB, Lang MA. Don’t dive cold when you don’t have to. Diving Hyperb Med. 2015 Mar;45(1):62. [PubMed: 25964043]

3.

Pollock NW, Buteau D. Updates in Decompression Illness. Emerg Med Clin North Am. 2017 May;35(2):301-319. [PubMed: 28411929]

4.

Geng M, Zhou L, Liu X, Li P. Hyperbaric oxygen treatment reduced the lung injury of type II decompression sickness. Int J Clin Exp Pathol. 2015;8(2):1797-803. [PMC free article: PMC4396314] [PubMed: 25973070]

5.

Hall J. The risks of scuba diving: a focus on Decompression Illness. Hawaii J Med Public Health. 2014 Nov;73(11 Suppl 2):13-6. [PMC free article: PMC4244896] [PubMed: 25478296]

6.

Mitchell SJ, Doolette DJ. Pathophysiology of inner ear decompression sickness: potential role of the persistent foramen ovale. Diving Hyperb Med. 2015 Jun;45(2):105-10. [PubMed: 26165533]

7.

Madden D, Thom SR, Dujic Z. Exercise before and after SCUBA diving and the role of cellular microparticles in decompression stress. Med Hypotheses. 2016 Jan;86:80-4. [PubMed: 26804603]

8.

Chin W, Joo E, Ninokawa S, Popa DA, Covington DB. Efficacy of the U.S. Navy Treatment Tables in treating DCS in 103 recreational scuba divers. Undersea Hyperb Med. 2017 Sept-Oct;44(5):399-405. [PubMed: 29116694]

9.

Mitchell SJ, Bennett MH, Bryson P, Butler FK, Doolette DJ, Holm JR, Kot J, Lafère P. Consensus guideline: Pre-hospital management of decompression illness: expert review of key principles and controversies. Undersea Hyperb Med. 2018 May-Jun;45(3):273-286. [PubMed: 30028914]

10.

Walker, III JR, Murphy-Lavoie HM. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): May 1, 2023. Diving in Water Recompression. [PubMed: 29630272]

Disclosure: Jeffrey Cooper declares no relevant financial relationships with ineligible companies.

Disclosure: Kenneth Hanson declares no relevant financial relationships with ineligible companies.

Decompression Sickness – Harvard Health

What is it?

Decompression sickness, also called generalized barotrauma or the bends, refers to injuries caused by a rapid decrease in the pressure that surrounds you, of either air or water. It occurs most commonly in scuba or deep-sea divers, although it also can occur during high-altitude or unpressurized air travel. However, decompression sickness is rare in pressurized aircraft, such as those used for commercial flights.

When you scuba dive with compressed air, you take in extra oxygen and nitrogen. Your body uses the oxygen, but the nitrogen is dissolved into your blood, where it remains during your dive. As you swim back toward the surface after a deep dive, the water pressure around you decreases.

If this transition occurs too quickly, the nitrogen does not have time to clear from your blood. Instead, it separates out of your blood and forms bubbles in your tissues or blood. It is these nitrogen bubbles that cause decompression sickness. The condition is called the bends because the joint and bone pains can be so severe they double you over.

What happens inside your body during decompression sickness is similar to what happens when you open a carbonated drink. When you open the can or bottle, you decrease the pressure surrounding the beverage in the container, which causes the gas to come out of the liquid in the form of bubbles. If nitrogen bubbles form in your blood, they can damage blood vessels and block normal blood flow.

Factors that put you at higher risk of decompression sickness include:

• Heart muscle birth defects, including patent foramen ovale, atrial septal defect, and ventricular septal defect
• Being older than 30
• Being female
• Low cardiovascular fitness
• High percentage of body fat
• Use of alcohol or tobacco
• Fatigue, seasickness or lack of sleep
• Injuries (old or current)
• Diving in cold water
• Lung disease

Someone with an abnormal hole or opening in the heart from a birth defect is at especially high risk of developing serious symptoms from decompression illness. Because bubbles create high blood pressure in the lungs, blood and bubbles from your veins may flow more readily through the heart’s opening. This means your blood can re-circulate into arteries without first getting oxygen. An opening in the heart can also allow a relatively large air bubble (called an air embolism) to circulate into your arteries. An air embolism can cause a stroke.

People with asthma or another lung disease may have thin-walled air pockets in their lungs called bullae. These pockets do not empty quickly when the persons exhales. As they return to the surface after a deep dive, air in the bullae may expand. If a bulla ruptures, it could cause a collapsed lung or allow a large air bubble (air embolism) to enter the arteries.

Symptoms

Symptoms of decompression sickness include:

• Joint pain  
• Dizziness
• Headache
• Difficulty thinking clearly
• Extreme fatigue
• Tingling or numbness
• Weakness in arms or legs
• A skin rash

Diagnosis

Your diving history and symptoms are key factors in diagnosing decompression sickness. Blood tests and joint X-rays usually do not show any signs of the problem.

Expected duration

Joint pain, the most common symptom from decompression sickness, can last for days or weeks.

Prevention

To minimize the risk of decompression sickness while diving:

• Dive and rise slowly in the water, and don’t stay at your deepest depth longer than recommended. Scuba divers typically use dive tables that show how long you can remain at a given depth.
• Do not fly within 24 hours after diving.
• Don’t drink alcohol before diving.
• Avoid hot tubs, saunas or hot baths after diving.
• Make sure you are well hydrated, well rested and prepared before you scuba dive. If you recently had a serious illness, injury or surgery, talk to your doctor before diving.

Some people should avoid diving altogether, or should consider special risks. If you have a heart defect, it is not safe to dive. If you have asthma, a history of a ruptured lung at any time in your life or another lung disease, discuss diving safety with a doctor before deciding whether to dive. A person who requires insulin to treat diabetes may have wide swings in blood glucose levels during a dive, and caution is advised. Avoid diving if you have a groin hernia that has not been repaired, since expanding gas in the hernia can cause symptoms.

Treatment

Emergency treatment for decompression sickness involves maintaining blood pressure and administering high-flow oxygen. Fluids also may be given. The person should be placed left side down and if possible the head of the bed tilted down.

The optimal treatment is the use of a hyperbaric oxygen chamber, which is a high-pressure chamber in which the patient receives 100% oxygen. This treatment reverses the pressure changes that allowed gas bubbles to form in the blood stream. The treatment drives nitrogen back into its liquid form so that it can be cleared more gradually from the body over a period of hours.

It is not recommended that divers with decompression sickness attempt to treat themselves with deep diving.

When to call a professional

If you experience symptoms of decompression sickness after scuba diving or flying, get to a doctor as soon as you can. Hyperbaric treatment is most successful if given within several hours after symptoms start.

Prognosis

Most cases of decompression sickness respond well to a single treatment with hyperbaric oxygen. Your doctor may suggest repeated treatments if you continue to experience symptoms, especially neurological symptoms.

Additional info

Undersea & Hyperbaric Medical Society

https://www.uhms.org/

Nitrogen Narcosis: What Divers Need to Know

By Megan Danny November 18, 2022

Nitrogen narcosis is a mysterious condition that affects scuba divers and, in rare cases, even freedivers. There are other names for nitrogen narcosis: “deep delight”, “martini effect” and “deep intoxication”. However, on a dive boat, you will most likely just hear something like: “ Have you ever been anesthetized? »

What is nitrogen narcosis?

Simply put, it is the anesthetic effect caused by breathing compressed gas at depth, usually nitrogen. The National Institutes of Health (NIH) gives a more detailed definition.

Divers should be able to recognize the symptoms of nitrogen narcosis in themselves or their dive buddy. According to experts from the Divers Alert Network (DAN), the most common symptoms include the following:

• Impaired normal thought process
• Difficulty concentrating
• Drowsiness
• Self-confidence and euphoria
• Feeling of fear

How does nitrogen anesthesia feel?

First of all, nitrogen narcosis deprives you of the ability to reason and make intelligent decisions. At the same time, when you just go with the flow, not making any decisions and not completing any tasks, you may not realize that you have some kind of mental disorder. Many divers have been exposed to anesthesia without even knowing it.

Next comes the feeling of euphoria. Divers liken the feeling to being slightly drunk or getting a dose of “laughing gas” (nitrous oxide) from the dentist, but nitric narcosis works a little differently for everyone. Some divers, myself included, feel anxiety and pessimism instead of joy.

At this point, if the diver is unaware that he is under anesthesia and continues to descend, he may begin to have difficulty with physical coordination. Now the situation is getting very dangerous. Further descent to the depth can cause hallucinations, fixation on some individual obsessions, stupor and much more.

What you can do to detect nitrogen narcosis

Recognizing and avoiding intoxication at depth is an important safety skill. That’s why the PADI ^® Deep Diver Specialty Course includes an activity that allows divers to measure and evaluate the disturbances in normal thinking that occur with increasing depth. You will complete a task on the surface that requires reflection, such as a math problem or solving a simple puzzle. Personally, I liked to use one of these toys with holes of various shapes (where you need to insert figures in the form of a circle, triangle, etc.).

Under water, the instructor will ask you to repeat the task at a depth of at least 18 m, but with slight differences. If on the surface the instructor asked you to subtract two large numbers, then under water these numbers will be different. I usually ask my students to fold triangular shapes into a ball on the surface, and then fold the shapes into a circle underwater.

Your instructor will record how long it will take you to complete both tasks. As you go deeper, you may find that the task seems more confusing or takes longer to complete. The purpose of this activity is to help you understand how nitrogen anesthesia can affect you. This is one of several important things you will learn in the PADI Deep Diver course.

Other frequently asked questions

Is nitrogen narcosis the same as decompression sickness?

No, it’s not. Both conditions are caused by breathing compressed air that includes nitrogen, but decompression sickness and nitrogen narcosis are not the same thing. Learn more about how to spot decompression sickness.

At what depth does nitrogen narcosis occur?

Every human body is different. Some people love spicy food, while others can’t stand it. I’ve been bitten by mosquitoes on six continents, leaving red spots, and my partner is completely immune. Nitrogen anesthesia is no different. Some divers feel the effect as early as 30 meters, while others feel nothing until they reach the recreational limit of 40 meters.

You might be wondering if the use of a gas mixture with a lower nitrogen content, such as enriched air, reduces the risk of anesthesia ? According to recent research, no. In addition, when using enriched air at depths below 30 meters, there is a risk of oxygen intoxication. Learn more on the PADI Enriched Air Diver course.

How is nitrogen anesthesia treated?

The diver or his dive buddy must first recognize the symptoms. The next step is to ascend slowly until the diver feels normal again.

How long does nitrogen anesthesia last?

The diver should begin to feel normal within a few minutes after ascending to a shallower depth. If symptoms persist, stop diving and seek medical attention.

Is it possible to experience anesthesia while freediving?

According to Akim Ladhari, PADI AmbassaDiver™ and founder of Blue Immersion Freediving, nitrogen narcosis can happen to freedivers too. Most often this happens when diving to a depth of more than 70 meters.

Why does nitrogen narcosis occur?

Scientists haven’t figured out the cause completely, 100 percent, but they have identified some factors that increase the likelihood of its occurrence:

• Depth
• Fatigue
• Drinking alcohol before diving
• Cold water/hypothermia
• Nervousness

The easiest way to avoid nitrogen narcosis is to limit your diving depth to 30 meters or less, especially if you feel tired, anxious or have had a drink the day before. In the PADI Deep Diver Specialty Course, you will learn how to recognize and prevent nitrogen narcosis, as well as many other useful things.

Experience deep diving with a PADI Instructor. Watch the video below or contact your Instructor or PADI Dive Center/Resort for more information.

LEARN MORE ABOUT THE DEEP DIVER COURSE

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Nitrogen poisoning | it’s… What is nitrogen poisoning?

Example of tunnel vision in case of nitrogen poisoning

Nitrogen poisoning , nitrogen anesthesia , deep disease – narcotic effect of nitrogen on the central nervous system (depression of higher functions of the brain). Occurs when diving to depths of more than 40 meters with apparatus with compressed air.

Causes

High partial pressure of nitrogen in the breathing gas mixture. The toxic effect of nitrogen depends on individual sensitivity. When using air as a breathing mixture, nitrogen toxicity begins to manifest itself from a depth of 45 m (nitrogen partial pressure 4.3 kgf / cm²) and has an intoxicating and hypnotic effect, like alcohol or ether, so this disease is often referred to as nitrogen “narcosis”.

Signs

At a depth of 60-80 m, excitation, causeless gaiety, memory impairment, dizziness, decreased efficiency and quick wits are observed. At a depth of 80-100 m, a disorder of coordination of movements occurs, arousal increases, visual and auditory hallucinations appear. A swimmer-submariner is capable of performing ridiculous, inappropriate (inadequate) actions. At depths of more than 100 m, “narcotic” sleep is possible. Fatigue, an increase in the content of carbon dioxide in the inhaled air, cooling contribute to the early manifestation of the toxic effect of nitrogen.

The above depths apply to professional divers, while an ordinary (untrained) swimmer may show signs of nitrogen poisoning as early as 40 meters.

Mechanism of action

The biochemical mechanism has not yet been studied in detail, but it is believed that the narcotic effect of nitrogen is due to the dissolution of gas in fats, as well as the “sticking” of nitrogen molecules to the membranes of nerve cells.

First aid

First aid in the event of nitrogen poisoning consists in lifting the victim to the surface or to a shallower depth. During the ascent from the depth, the nitrogen “intoxication” quickly disappears without any residual effects.

Prevention

• Identification of divers who are hypersensitive to the toxic effects of nitrogen.