Dive Medicine

Most dive injuries come from two physical principles.

Boyle’s law (gas volume changes with pressure) explains barotrauma and arterial gas embolism (AGE).
Henry’s law (more gas dissolves under higher pressure) explains decompression sickness (DCS).

AGE and DCS together are called decompression illness (DCI). Suspected DCI is treated with 100% oxygen, fluids, lying flat, and early recompression in a hyperbaric chamber. Diving medicine expertise, such as the DAN hotline, should be contacted early.

Diving emergency: call DAN

+1-919-684-9111 (collect calls accepted, 24 hours a day)

Tell the operator you have a diving emergency. You will be connected directly or called back as soon as possible. Transport the diver immediately to the nearest medical facility for stabilization and assessment. Call the same number if you need evacuation help through DAN Travel Assist.

The physics behind dive injuries

Boyle’s law

At constant temperature, gas volume varies inversely with ambient pressure. Gas in the ears, sinuses, lungs, and equipment spaces compresses on descent and expands on ascent. This explains barotrauma and air embolism.

Henry’s law

The amount of gas dissolved in a liquid is directly proportional to its partial pressure. Divers absorb more nitrogen at depth, and bubbles can form on the return to the surface. This explains decompression sickness.

Barotrauma

Barotrauma is the most common diving-related injury. It happens when an air-filled space cannot equalize with changing ambient pressure. Descent can cause squeeze with mucosal swelling and bleeding. Ascent can expand trapped gas and rupture tissue.

Type	Key points
Middle ear (ear squeeze)	The most common disorder in divers. Pain begins at a pressure difference of about 60 mmHg. Above 90 mmHg, Valsalva can no longer equalize. Causes include upper respiratory infection, anatomy, wax, earplugs, or a tight hood. Findings range from pressure and pain to blood or fluid behind the eardrum and perforation. Sudden pain relief with vertigo and nausea can signal rupture. Treatment: decongestants, analgesics, antihistamines, and antibiotics if there is purulent discharge or perforation. Most perforations heal on their own. ENT follow-up is recommended.
Inner ear	Uncommon but serious. Rupture of the round or oval window causes tinnitus, vertigo, and hearing loss, and can be permanent. Initial treatment is complete bed rest with the head elevated for 7 to 10 days. Worsening function needs urgent specialist referral and sometimes surgery.
Sinus	The second most common diving disorder. The frontal sinus is most often affected. Headache, nosebleed, and localized sinus pain. Treat with decongestants, and antibiotics if there is purulent discharge. A one-way blockage on ascent can rupture the sinus and cause pneumocephalus, which requires admission, neurologic checks, prophylactic antibiotics, and oxygen.
Dental	Trapped air around infected roots or fillings causes toothache or tooth breakdown. One series found it in 66 of 709 (9%) experienced divers. Simple analgesia and dental follow-up. Avoid diving until the dental problem is fixed.
Lung squeeze (descent)	Lung volume falls below residual volume, causing pulmonary edema or bleeding. Uncommon in scuba divers, because the lungs are constantly refilled. More likely in breath-hold divers.
Pulmonary barotrauma of ascent	Alveolar rupture when transalveolar pressure exceeds 20 to 80 mmHg, possible from depths as shallow as 1 to 1.5 meters. Breath-holding on ascent raises the risk, but cases occur without lung disease or rapid ascent. See below.

Complications of pulmonary barotrauma of ascent

Pneumomediastinum: chest fullness, pleuritic pain to the shoulders, dyspnea, cough, hoarseness, difficulty swallowing, neck crepitus, Hamman’s sign. CT is more sensitive than X-ray. No specific treatment is needed. 100% oxygen speeds reabsorption. Always check for coexisting AGE.
Pneumothorax: occurs in about 10% of pulmonary barotrauma episodes, with subcutaneous emphysema in about 25%. Ascending with trapped pleural gas can cause tension pneumothorax. Decompress before any recompression. A history of spontaneous pneumothorax is a contraindication to diving.
Arterial gas embolism: see next section.

Mask squeeze is not covered in the source review and is not discussed here.

Arterial gas embolism (AGE)

AGE is the most serious complication of pulmonary barotrauma. Gas enters the pulmonary veins after alveolar rupture, or when venous bubbles overwhelm the lung’s filtering capacity, and then travels to the arterial circulation. Emboli commonly lodge in vessels of about 30 to 60 micrometers.

Timing: symptoms typically appear within 10 minutes of surfacing, usually almost immediately. Immediate loss of consciousness is highly suggestive.
Brain (most common): from subtle cognitive change or “feeling off” to focal deficits, seizure, loss of consciousness, apnea, and death.
Heart: ECG changes or arrhythmia from coronary embolism. Sudden cardiac arrest is more often due to air obstructing the central circulation.
Kidney: blood or protein in the urine, or renal failure.
Depth: AGE can occur in shallow water and is independent of how long the diver was at depth.

Decompression sickness (DCS)

What happens

Divers breathing gas under pressure absorb extra nitrogen. On ascent, tissue gas tension can exceed ambient pressure, and bubbles form. Bubbles can block vessels, compress or rupture tissue, damage the vessel lining, and trigger clotting and inflammation. Venous bubbles alone do not always mean DCS will develop.

Timing and risk factors

About 90% of patients develop symptoms within 3 hours of surfacing. A small percentage develop symptoms after 24 hours. In one study quoted in the notes, onset was within 6 hours in 99% (mean delay 62 minutes), and the shorter the delay, the more serious the symptoms.
DCS is highly unlikely with dives of 10 meters or less. Tables and computers reduce the risk but do not remove it.
Dive profile is the most important risk factor. Obesity, age, and sex have been proposed, but evidence is not agreed.
Right-to-left shunt (PFO): associated with a two- to fivefold increase in the risk of severe DCS, against an overall incidence of 4 to 6 per 10,000 dives. A larger PFO and a more mobile atrial septum raise the risk.
Flying and altitude after diving: wait 12 hours after a single dive per day. After multiple dives, or dives with decompression stops, consider waiting up to 48 hours. The review notes that optimal waiting times are not known. The same waits apply to going to altitude by car.

A note on classification: The older Type I (mild) and Type II (serious) system is still widely used and appears below. Current reviews describe DCS by the organ system affected and group DCS with AGE as decompression illness (DCI), because treatment is the same and the two can be hard to tell apart.

Type I DCS (mild)

Pain (the bends): in 70 to 85% of type I cases. A dull, deep, throbbing, toothache-like pain, usually near a joint or tendon. The shoulder is the most commonly affected joint. It starts mild and slowly intensifies, so many divers blame a pulled muscle. Upper limbs are affected about 3 times as often as lower limbs. Pain-related splinting reduces function, and the pain can mask neurologic signs.
Cutis marmorata: widespread mottling or marbling, or a purple-red papular rash, rarely with an orange-peel look. It usually begins with intense itching, then redness, then the purple rash. Once thought benign, it is now linked to gas emboli in skin capillaries and possibly brainstem effects on autonomic control. A very high rate of PFO has been reported in divers with this rash, and the review links it with more severe DCS.
Lymphatic: uncommon, causing painless pitting swelling. The mildest cases involve only skin or lymphatics.
General: loss of appetite and marked fatigue after a dive are sometimes counted as mild DCS.
Mild DCS features (useful for treatment decisions): fatigue, non-dermatomal skin sensory changes, rash, itching, isolated asymmetric limb pain, and swelling that is not progressing at 24 hours, with no spinal or central neurologic signs.

Type II DCS (serious)

Type II features pulmonary symptoms, hypovolemic shock, or nervous system involvement. Pain is present in only about 30%. Onset is usually immediate but can be delayed up to 36 hours.

Spinal cord: the most common site. Symptoms can mimic spinal cord trauma. Low back pain within minutes to hours can progress to weakness, paralysis, paresthesia, loss of sphincter control, and girdle pain of the lower trunk. Back pain after a dive is a poor prognostic sign. Bladder problems (neurogenic bladder) may be the main presentation and can be prolonged.
Prognosis: divers whose symptoms began within 30 minutes of surfacing had the worst outcomes, with less than 50% resolution after hyperbaric oxygen.
Why the spinal cord and brain are vulnerable: the lungs normally filter bubbles. A PFO or ASD can bypass this, and hypoxia can open lung shunts. In the white matter, venous drainage already has low oxygen content, so small additional emboli can damage the blood-brain barrier and axons (perivenous syndrome). Spinal cord swelling in a confined space can worsen ischemia.
Atypical pattern: symptoms can shift, do not follow peripheral nerve territories, and often show sensory-motor “dissociation,” which makes it hard to tell from traumatic nerve injury.

DCS by organ system (UpToDate estimates)

System	Features	Approx. frequency
Musculoskeletal	Deep, boring joint ache, often shoulder or elbow, usually unaffected by movement, no local tenderness	50 to 65%
Spinal cord	Weakness, numbness, paresthesia, girdle or back pain, urinary retention. Nervous system involvement overall is about 60% of DCS cases	Weakness 20 to 25%; numbness 20 to 30%; girdle/back pain 1 to 5%; bladder 1%
Cerebral	Memory loss, ataxia (“the staggers”), visual and behavior changes	5 to 10%
Skin	Itch, scarlatiniform rash, cutis marmorata	5 to 10%
Lymphatic	Localized swelling, peau d’orange	1 to 5%
Cardiopulmonary (“chokes”)	Dry cough, chest pain, wheeze, dyspnea. Severe cases can cause right heart failure (“air lock”) and collapse	1 to 5% (shock, coagulopathy under 1%)
Inner ear	Vertigo, nausea, vomiting, hearing loss, tinnitus. About 75% of cases have no other symptoms	Vestibular 10 to 20%; cochlear 1 to 5%
General	Malaise, fatigue, headache (not clinically significant alone)	20 to 40%

Long-term bone effect

Dysbaric osteonecrosis occurs in divers with large numbers of dives. It is a persistent problem and its mechanisms are not fully understood.

Evaluating a sick diver

Dive profile: maximum depth, bottom time, safety and decompression stops, breathing gas, ascent rate, missed stops, computer alarms, equipment problems, recent dives, altitude exposure, and prior DCS or AGE.
Timing: symptoms starting during descent or at depth are usually not DCS or AGE. Think barotrauma, immersion pulmonary edema, or unrelated illness.
Diagnosis is clinical. Imaging and blood tests do not confirm DCS or AGE and should not delay hyperbaric treatment.

What else can look like DCI?

The differential includes toxic seafood ingestion (ciguatera, paralytic shellfish poisoning, puffer fish) and marine animal exposure (coral contact, jellyfish sting). The source review lists these only as mimics and gives no treatment details. Other mimics include barotrauma, immersion pulmonary edema, cardiac events, near-drowning, and traumatic nerve or spine injury.

First aid and treatment of suspected AGE or DCS

On site

Oxygen as close to 100% as possible, usually with a non-rebreather mask
Keep the diver lying flat
Keep warm, avoid overheating
Hydrate: oral fluids for mild cases. IV isotonic crystalloid 500 to 1000 mL boluses if needed
Rapid transfer, ideally straight to a hyperbaric facility
Call DAN or a diving medicine expert

In hospital

Airway, breathing, circulation
Continue near-100% oxygen and fluids
Decompress any pneumothorax before recompression
Catheterize for urinary retention
Keep severely ill patients horizontal. Trendelenburg is no longer recommended
Consider DVT prophylaxis in severely ill, admitted patients
Steroids, aspirin, and lidocaine are not supported for routine use

NSAIDs: may be used for pain. In one trial of 180 divers, tenoxicam 20 mg for seven days reduced the median number of recompression treatments from three to two, with no effect on functional outcome.

Hyperbaric oxygen (HBO)

Recompression is the gold standard for AGE and DCS and should start as soon as possible. Delayed treatment can still help, and no delay makes it futile.
The hyperbaric physician sets the protocol and number of sessions. Minor cases may need one, severe cases a series.
How it works: removes nitrogen, shrinks bubbles, oxygenates ischemic tissue, and may reduce brain swelling and inflammation.
Risks: middle-ear barotrauma in about 2%. Oxygen-toxicity seizure in about 1 in 5000 to 1 in 10,000 treatments, which resolves when oxygen is removed. Rare: transient worsening of myopia, pulmonary oxygen toxicity, pulmonary barotrauma.
Some studies report complete symptom resolution in about 80% of DCS patients.

Fitness to dive

Decisions should be individualized by a physician trained in diving medicine.

Absolute contraindications (lung): COPD, lung bullae or cysts, cystic fibrosis, sarcoidosis, pulmonary fibrosis, history of spontaneous pneumothorax or pneumomediastinum.
Cardiac: conditions that can cause loss of consciousness or incapacity, including arrhythmia, ischemic heart disease, decompensated heart failure, and septal defects.
Asthma: the added barotrauma risk has not been quantified and may be smaller than once thought. Any lung history warrants physician evaluation before diving.
PFO: raises DCS risk, but the review gives no specific screening or closure recommendation.

Prevention

Learn and practice ear equalization techniques, and do not dive with a cold or blocked sinuses or ears.
Fix dental problems before diving.
Follow dive tables or computers, respect ascent rates and safety stops, and be cautious with repetitive dives.
Respect post-dive flying and altitude waiting times.
Never hold your breath on ascent.
Use a pre-dive checklist. A cluster-randomized trial reported fewer mishaps when checklists were used.

Sports medicine perspective

A diver with new shoulder, elbow, or joint pain after a dive can be mistaken for a rotator cuff strain or tendinopathy, which is exactly how early DCS is missed. Key clues for DCS are a deep, boring ache without tenderness that is not affected by movement, onset within hours of surfacing, and associated itching, rash, fatigue, or numbness. If in doubt after a dive, give oxygen and call for diving medicine advice before assuming a musculoskeletal cause. Musculoskeletal injuries from gear carrying, cold exposure, and repetitive finning are common in divers and are a reasonable explanation only once DCS is excluded.

Seek emergency help immediately for

Loss of consciousness, confusion, or any neurologic symptom within minutes of surfacing
Weakness, numbness, back pain, or trouble passing urine after a dive
Chest pain, breathlessness, or cough after a dive
Rash with itching, severe fatigue, or joint pain in the hours after a dive
Vertigo, hearing loss, or tinnitus after a dive

Give oxygen, keep the diver flat, and call DAN: +1-919-684-9111.

Disclaimer: This page is for educational purposes only and does not replace individualized medical advice or emergency care. Any diving emergency requires immediate oxygen, rapid evacuation, and contact with a diving medicine service.