When SCUBA diving goes wrong – Decompression Illness


Jonathan Morgan, MSIV

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Medical Student

Lake Erie College of Osteopathic Medicine-Bradenton

A 54 year-old male presents to your emergency department complaining of dizziness that started shortly after completing a dive. He is a biologist who was studying the nearby river. He reports that about 10 minutes after surfacing he became profoundly dizzy. He also reports nausea that has since resolved. He thinks his hearing is normal. He can walk, but stumbles sideways.

His companions administered oxygen immediately and called 911. He is currently alert, oriented, complaining of only dizziness. His vitals are: BP 130/70, Pulse 76, RR 14, Temp. 37.0 C, SpO2 98% on room air.

What do you need to know about his dive?

Basic information includes maximum depth of the dive, time at maximal depth, decompression or safety stops used, previous dives within 12 hours, and type of gas and equipment used. [1]
Our patient was diving using recreational SCUBA gear in a river. He was at a depth of 70 feet for 35 minutes. On ascension he used a 5-minute safety stop. HIs last dive was yesterday, with the same profile. According to his dive computer, no decompression stop was needed.

What can go wrong? Are “decompression illness” and “decompression sickness” the same thing? Do I have to remember the difference between type 1 and type 2 decompression sickness?

Current recommendations are to refer to any disorder caused by air bubble formation during decompression as “decompression illness” (DCI). The primary diagnoses covered by the umbrella of “DCI” are arterial gas embolism (AGE) and decompression sickness (DCS). [2]

Arterial Gas Embolism

  • Occurs during ascent, when expanding air in the lungs causes over-distention and subsequent alveolar rupture, allowing alveolar air to enter the arterial circulation. [2]
  • Alveolar rupture can also cause pneumothorax and subcutaneous emphysema. [1]
  • Generally, presents as a CNS disorder; can cause unilateral stroke-like symptoms, cognitive deficits, unconsciousness, or seizures. [1]
  • Arterial bubbles can cause occlusion of any artery, potentially leading to cardiac, respiratory or musculoskeletal symptoms, or to rhabdomyolysis. [1]
  • Depth threshold: Can occur in shallow water – as little as 3-5 feet. [2,3,4]
  • A history of breath holding during ascent can suggest the diagnosis, but underlying lung disease (asthma, blebs, etc) can also cause air trapping and AGE. [2]
  • Causes more than one third of recreational SCUBA deaths. [5]

Decompression Sickness (DCS)

  • Under pressure, high levels of nitrogen dissolve in body tissues: if the rate of ascent exceeds the body’s ability to exhale nitrogen, and nitrogen comes out of solution in the form of bubbles. [1]
  • The older understanding of DCS was that venous gas bubbles cause occlusion of blood vessels, leading to pain and tissue ischemia. Newer evidence suggests that endothelial damage and inflammatory cascades are a large part of the pathology of DCS. The result is capillary leak and extravasation of fluid volumes so large that hypotension can result. [1,2]
  • Symptoms include skin itching or rash; joint pain; constitutional complains of malaise, fatigue, or headache; neurologic symptoms; shock; or cardiac arrest. [1,2]
  • The diagnosis is entirely clinical, and essentially any new symptom after diving should be considered a case of DCS. [2]
  • Depth threshold: uncommon unless diving deeper than 30 feet. [2]
  • Symptoms may be delayed up to 24 hours, but usually present within 4 hours. [2]

Previously DCS was divided into “type 1” and “type 2” illness based on severity of symptoms, with type 2 being more serious. This classification system is poorly predictive of outcome, and its use is declining. [2]

How can I tell DCS from AGE?

Differentiation can be difficult or impossible, and combined presentations are possible, but the treatment is the same. [1] A history of breath holding during ascent, underlying lung disease, or rapid ascent can suggest AGE, but lack of this history is not definitive. [2,4]. Diagnosis of AGE generally requires CNS symptoms be present. [2]

What other problems can arise when diving?

  • Middle/inner ear barotrauma – history of difficulty equalizing during descent, tinnitus, hearing loss, and vertigo.
  • Alternobaric vertigo – transient vertigo due to difficulty equalizing
  • CO poisoning due to contaminated gas
  • Oxygen toxicity
  • Immersion pulmonary edema – occurs while at depth rather than on ascent
  • Aspiration

Our patient claims he followed a dive computer – shouldn’t he be safe from DCS?

NO. Most dive tables are derived from US Navy data that allow a 1-3% rate of DCS among young, very healthy divers. Do not be reassured by a diver who reports their dive was by the books – decompression illness can occur even within accepted “safe” dive profiles. [2]

What is the Treatment for DCI?

  • Call the Diver’s Alert Network’s (DAN’s) 24-hour hotline at 1-919-684-9111. A similar service to poison control, DAN can provide advice, coordinate resources, etc.
  • Arrange for hyperbaric therapy. DAN may be able to help locate an available chamber.
  • Address immediately life-threatening complaints: resuscitation/CPR/airway management as needed. Treat seizures with benzodiazepines (or barbiturates if benzos fail). [1]
  • Oxygen: 100% FiO2, or as close as possible. [5] Notice our patient’s SpO2 is on room air; not ideal. Supplemental O2 was quickly restarted
  • Imaging: CXR, primarily to rule out pneumothorax. Imaging beyond CXR is not very helpful and can delay time to decompression, but any size pneumothorax MUST be detected and treated (with a chest tube) before the patient goes to the chamber, since it can develop tension physiology with the pressure shifts of hyperbaric therapy. [1,5]
  • Provide IV fluids, as patients are often dehydrated; provide 1-2L in the first hour and 1.5 ml/kg/h maintenance. [1]
  • Keep the patient supine. [1,2]
  • Medications: Antiplatelet agents, anticoagulants, and steroids have all been suggested, but have limited supporting data. [1,6] Tenoxicam may be provided by the dive physician during recompression. [2,6]


Hyperbaric therapy is indicated in almost all cases of DCI. Initially mild symptoms may progress. Similarly, if symptoms of DCI seem to have resolved there is a risk for delayed decompensation, and the recommended plan is to refer any patient thought to have DCI for hyperbaric treatment, even if their symptoms are improving or resolved. [1]

While there are no randomized studies of hyperbaric therapy, it is a widely accepted therapy and there is some evidence that recovery is better if oxygen and hyperbaric therapy are provided more rapidly. [1] Even severe neurologic symptoms seem to respond well to hyperbaric therapy. [2]

I’m in the boonies and hours away from a chamber – still worth it? How do I get the patient there?

There is benefit to recompression even hours later. [1] There is no clear time cutoff; in cases of mild symptoms and long/dangerous transport a dive physician can be contacted to discuss the situation. [1] “Mild” symptoms include static or remitting limb pain, constitutional symptoms, rash, or NON-dermatomal sensory changes that are stable for 24 hours in the setting of an otherwise normal neurologic examination. [2]

Transport by fixed wing aircraft pressurized to sea level is ideal, but ground or helicopter transport is OK, so long as the helicopter tries to remain below 300 meters. It is not clear when the speed of air travel is worth the risk and expense, but this can be discussed by the receiving dive medicine physician. [1]

What happens in the dive chamber? How long is the patient going to be in there?

Most of this is the realm of the consulting hyperbaric physician, but it may be helpful to think ahead about possible logistic issues (for patients and for their families).

Recompression therapy proceeds according to specific recipes. As an example, “US Navy Table 6” is often used, and totals 285 minutes: 105 minutes breathing 100% O2 at 18 meters sea water (msw) and then 9 msw for 180 minutes, all with periodic 5 minute air breathing periods to prevent oxygen toxicity. There are other recipes, but little evidence to support one over another.

If symptoms do not totally resolve, treatments will likely be repeated (possibly daily) until there is a plateau in improvement, which in some severe cases has been 15-20 treatments. Staying near the chamber may be necessary: recommendations are for 2-6 hours of observation after treatment and spending 1 day within 1 hour’s travel time of the chamber. [2]

Critical patients present other issues. Equipment may not fit in the chamber, and fire risk is always a concern. All balloons must be saline filled. A central venous catheter may be needed to monitor CVP during pressure shifts, especially if the patient is ventilated. Due to inability to equalize pressures, intubated patients require paracentesis and a myringotomy or tympanostomy. [1]

So back to our patient – hemodynamically stable and dizzy. Does this patient have to go to a decompression chamber?

Post-diving vertigo can be difficult to diagnose. Possible etiologies include inner ear DCS, barotrauma with rupture of the TM, oval window, or round window, or cerebellar etiology. An abnormal neurologic exam, history of difficulty equalizing or strong Valsalva, or abnormal otoscopic exam with hemotympanum or drainage would suggest diagnoses other than inner ear DCS. [7]

If this is thought to be DCS, decompression therapy is indicated. [7] Keep in mind that symptoms can get worse, for example there is a case report of a patient presenting initially with vertigo and nystagmus who received hyperbaric treatment and one day later developed hypotension, respiratory distress, pulmonary edema, and pleural, pericardial, and peritoneal effusions. [8]

In our patient no history of difficulty equalizing could be elicited, there was no hearing loss, and the TM appeared intact without hemotympanum. In consultation with DAN and a receiving dive physician it was decided that this was likely inner ear DCS. The patient was transferred 4+ hours away by ground for recompression.


1. Tetzlaff K, Shank ES, Muth CM. Evaluation and management of decompression illness–an intensivist’s perspective. Intensive Care Med. 2003;29(12):2128-36. PMID: 14600806.

2. Vann RD, Butler FK, Mitchell SJ, Moon RE. Decompression illness. Lancet. 2011;377(9760):153-64.PMID: 21215883.

3. Tetzlaff K, Shank ES, Muth CM. Evaluation and management of decompression illness–an intensivist’s perspective. Intensive Care Med. 2003;29(12):2128-36. PMID: 11728772.

4. Hayden SR, Buford KC, Castillo EM. Accuracy of a SET of Screening Parameters Developed for the Diagnosis of Arterial Gas Embolism: The SANDHOG Criteria. J Emerg Med. 2015;49(5):792-8. PMID: 26371977.

5. Dickey LS. Diving injuries. J Emerg Med. 1984;1(3):249-62. PMID: 6491243.

6. Bennett MH, Lehm JP, Mitchell SJ, Wasiak J. Recompression and adjunctive therapy for decompression illness. Cochrane Database Syst Rev. 2012;5:CD005277. PMID: 22592704.

7. Gempp E, Louge P. Inner ear decompression sickness in scuba divers: a review of 115 cases. Eur Arch Otorhinolaryngol. 2013;270(6):1831-7.PMID: 231000085.

8. Gempp E, Lacroix G, Cournac JM, Louge P. Severe capillary leak syndrome after inner ear decompression sickness in a recreational scuba diver. J Emerg Med. 2013;45(1):70-3. PMID: 23602149.