Decompression sickness should be suspected if any of the symptoms associated with the condition occurs following a drop in pressure, in particular, within 24 hours of diving. In 1995, 95% of all cases reported to Divers Alert Network had shown symptoms within 24 hours. An alternative diagnosis should be suspected if severe symptoms begin more than six hours following decompression without an altitude exposure or if any symptom occurs more than 24 hours after surfacing. The diagnosis is confirmed if the symptoms are relieved by recompression. Although MRI or CT can frequently identify bubbles in DCS, they are not as good at determining the diagnosis as a proper history of the event and description of the symptoms.

First aid is common for both DCS and AGE:

- Monitor the patient for responsiveness, airway, breathing and circulation, resuscitate if necessary.

- Treat for shock.

- Lay the patient on their back, or for drowsy, unconscious, or nauseated victims, on their side.

- Administer 100% oxygen as soon as possible.

- Seek immediate medical assistance, locate a hospital with hyperbaric facilities and plan for possible transport.

- Allow the patient to drink water or isotonic fluids only if responsive, stable, and not suffering from nausea or stomach pain. Administration of intravenous saline solution is preferable.

- Record details of recent dives and responses to first aid treatment and provide to the treating medical specialist. The diving details should include depth and time profiles, breathing gases used and surface intervals.

Immediate treatment with 100% oxygen, followed by recompression in a hyperbaric chamber, will in most cases result in no long-term effects. However, permanent long-term injury from DCS is possible. Three-month follow-ups on diving accidents reported to DAN in 1987 showed 14.3% of the 268 divers surveyed had ongoing symptoms of Type II DCS, and 7% from Type I DCS. Long-term follow-ups showed similar results, with 16% having permanent neurological sequelae.

Treatment for the "Decompression Sickness" and the "Arterial Gas Embolism" components of DCI may differ significantly. Refer to the separate treatments under those articles.

Professional divers are screened for risk factors during initial and periodical medical examination for fitness to dive. In most cases recreational divers are not medically screened, but are required to provide a medical statement before acceptance for training in which the most common and easy to identify risk factors must be declared. If these factors are declared, the diver may be required to be examined by a medical practitioner, and may be disqualified from diving if the conditions indicate.

Asthma, Marfan syndrome, and COPD pose a very high risk of pneumothorax. In some countries these may be considered absolute contraindications, while in others the severity may be taken into consideration. Asthmatics with a mild and well controlled condition may be permitted to dive under restricted circumstances.

Recompression treatment in a hyperbaric chamber was initially used as a life-saving tool to treat decompression sickness in caisson workers and divers who stayed too long at depth and developed decompression sickness. Now, it is a highly specialized treatment modality that has been found to be effective in the treatment of many conditions where the administration of oxygen under pressure has been found to be beneficial. Studies have shown it to be quite effective in some 13 indications approved by the Undersea and Hyperbaric Medical Society.

Hyperbaric oxygen treatment is generally preferred when effective, as it is usually a more efficient and lower risk method of reducing symptoms of decompression illness, However, in some cases recompression to pressures where oxygen toxicity is unacceptable may be required to eliminate the bubbles in the tissues that cause the symptoms.

A significant part of entry level diver training is focused on understanding the risks and procedural avoidance of barotrauma. Professional divers and recreational divers with rescue training are trained in the basic skills of recognizing and first aid management of diving barotrauma.

Treatment of diving disorders depends on the specific disorder or combination of disorders, but two treatments are commonly associated with first aid and definitive treatment where diving is involved. These are first aid oxygen administration at high concentration, which is seldom contraindicated, and generally recommended as a default option in diving accidents where there is any significant probability of hypoxia, and hyperbaric oxygen therapy (HBO), which is the definitive treatment for most incidences of decompression illness. Hyperbaric treatment on other breathing gases is also used for treatment of decompression sickness if HBO is inadequate.

As a general rule, any diver who has breathed gas under pressure at any depth who surfaces unconscious, loses consciousness soon after surfacing, or displays neurological symptoms within about 10 minutes of surfacing should be assumed to be suffering from arterial gas embolism.

Symptoms of arterial gas embolism may be present but masked by environmental effects such as hypothermia, or pain from other obvious causes. Neurological examination is recommended when there is suspicion of lung overexpansion injury. Symptoms of decompression sickness may be very similar to, and confused with, symptoms of arterial gas embolism, however, treatment is basically the same. Discrimination between gas embolism and decompression sickness may be difficult for injured divers, and both may occur simultaneously. Dive history may eliminate decompression sickness in many cases, and the presence of symptoms of other lung overexpansion injury would raise the probability of gas embolism.

If a patent foramen ovale (PFO) is suspected, an examination by echocardiography may be performed to diagnose the defect. In this test, very fine bubbles are introduced into a patient's vein by agitating saline in a syringe to produce the bubbles, then injecting them into an arm vein. A few seconds later, these bubbles may be clearly seen in the ultrasound image, as they travel through the patient's right atrium and ventricle. At this time, bubbles may be observed directly crossing a septal defect, or else a patent foramen ovale may be opened temporarily by asking the patient to perform the Valsalva maneuver while the bubbles are crossing through the right heart – an action which will open the foramen flap and show bubbles passing into the left heart. Such bubbles are too small to cause harm in the test, but such a diagnosis may alert the patient to possible problems which may occur from larger bubbles, formed during activities like underwater diving, where bubbles may grow during decompression. A PFO test may be recommended for divers intending to expose themselves to relatively high decompression stress in deep technical diving.

Dysbarism refers to medical conditions resulting from changes in ambient pressure. Various activities are associated with pressure changes. underwater diving is the most frequently cited example, but pressure changes also affect people who work in other pressurized environments (for example, caisson workers), and people who move between different altitudes.

Arterial gas embolism (AGE) is a complication of lung barotrauma of ascent. It occurs when breathing gas is introduced to the circulation on the arterial side via lung over-pressure trauma. AGE can present in similar ways to arterial blockages seen in other medical situations. Affected people may suffer strokes, with paralysis or numbness down one side; they may suffer heart attacks; they may suffer pulmonary embolism with shortness of breath and chest pain. It is often impossible to distinguish AGE from DCS, but luckily it is rarely necessary for physicians to be able to distinguish between the two, as treatment is the same. Sometimes AGE and DCS are lumped into a single entity, Decompression Illness (DCI).

Ultrasound is commonly used in the evaluation of people who have sustained physical trauma, for example with the FAST protocol. Ultrasound may be more sensitive than chest X-rays in the identification of pneumothorax after blunt trauma to the chest. Ultrasound may also provide a rapid diagnosis in other emergency situations, and allow the quantification of the size of the pneumothorax. Several particular features on ultrasonography of the chest can be used to confirm or exclude the diagnosis.

Computed tomography (CT, or "CAT scan") is not necessary for the diagnosis of pneumothorax, but it can be useful in particular situations. In some lung diseases, especially emphysema, it is possible for abnormal lung areas such as bullae (large air-filled sacs) to have the same appearance as a pneumothorax on chest X-ray, and it may not be safe to apply any treatment before the distinction is made and before the exact location and size of the pneumothorax is determined. In trauma, where it may not be possible to perform an upright film, chest radiography may miss up to a third of pneumothoraces, while CT remains very sensitive.

A further use of CT is in the identification of underlying lung lesions. In presumed primary pneumothorax, it may help to identify blebs or cystic lesions (in anticipation of treatment, see below), and in secondary pneumothorax it can help to identify most of the causes listed above.

Compartment syndrome is a clinical diagnosis made by a physician. It can be tested for by gauging the pressure within the muscle compartments. If the pressure is sufficiently high, a fasciotomy will be required to relieve the pressure. Various recommendations of the intracompartmental pressure are used with some sources quoting >30 mmHg as an indication for fasciotomy while others suggest a <30 mmHg difference between intracompartmental pressure and diastolic blood pressure. This latter measure may be more sensible in the light of recent advances in permissive hypotension, which allow patients to be kept hypotensive in resuscitation. It is now relatively easy to measure compartment and subcutaneous pressures using the pressure transducer modules (with a simple intravenous catheter and needle) that are attached to most modern anaesthetic machines.

Most commonly compartment syndrome is diagnosed through a diagnosis of its underlying cause and not the condition itself. According to Blackman one of the tools to diagnose compartment syndrome is X-ray to show a tibia/fibula fracture, which when combined with numbness of the extremities is enough to confirm the presence of compartment syndrome.

If the diver has not been exposed to excessive depth and decompression and presents as DON, there may be a predisposition for the condition. Diving should be restricted to shallow depths. Divers who have suffered from DON are at increased risk of future fracture of a juxta-articular lesion during a dive, and may face complications with future joint replacements. Because of the young age of the population normally affected, little data is available regarding joint replacement complications.

There is the potential for worsening of DON for any diving where there might be a need for decompression, experimental or helium diving. Physically stressful diving should probably be restricted, both in sport diving and work diving due to the possibility of unnecessary stress to the joint. Any diving should be less than 40 feet/12 meters. These risks are affected by the degree of disability and by the type of lesion (juxta-articular or shaft).

Prevention is a more successful strategy than treatment. By using the most conservative decompression schedule reasonably practicable, and by minimizing the number of major decompression exposures, the risk of DON may be reduced. Prompt treatment of any symptoms of decompression sickness (DCS) with recompression and hyperbaric oxygen also reduce the risk of subsequent DON.

Mild disease can be treated with fluids by mouth. In more significant disease spraying with mist and using a fan is useful. For those with severe disease putting them in lukewarm water is recommended if possible with transport to a hospital.

Taravana is a disease often found among Polynesian island natives who habitually dive deep without breathing apparatus many times in close succession, usually for food or pearls. These free-divers may make 40 to 60 dives a day, each of 30 or 40 metres (100 to 140 feet).

Taravana seems to be decompression sickness. The usual symptoms are vertigo, nausea, lethargy, paralysis and death. The word "taravana" is Tuamotu Polynesian for "to fall crazily".

Taravana is also used to describe someone who is "crazy because of the sea".

Prevention includes avoiding medications that can increase the risk of heat illness (e.g. antihypertensives, diuretics, and anticholinergics), gradual adjustment to heat, and sufficient fluids and electrolytes.

Acute compartment syndrome is a medical emergency requiring immediate surgical treatment, known as a fasciotomy, to allow the pressure to return to normal. Although only one compartment is affected, fasciotomy is done to release all compartments. For instance, if only the deep posterior compartment of a leg is affected, the treatment would be fasciotomy (with medial and lateral incisions) to release all compartments of the leg in question, namely the anterior, lateral, superficial posterior and deep posterior.

An acute compartment syndrome has some distinct features such as swelling of the compartment due to inflammation and venous occlusion. Decompression of the nerve traversing the compartment might alleviate the symptoms (Rorabeck, 1984). Until definitive fasciotomy can be performed, the extremity should be placed at the level of the heart. Hypotension should also be avoided, as this decreases perfusion pressure to the compartment. Supplemental oxygen also optimizes tissue and neural oxygenation.

A catastrophic illness is a severe illness requiring prolonged hospitalization or recovery. Examples would include coma, cancer, leukemia, heart attack or stroke. These illnesses usually involve high costs for hospitals, doctors and medicines and may incapacitate the person from working, creating a financial hardship. They are the type intended to be covered by high-deductible health plans. Research indicates that the unusual economic environment of the delivery of catastrophic illness care encourages the use of innovative therapies. Medicare contains a benefit for catastrophic illness.

Chronic critical illness is a disease state which affects intensive care patients who have survived an initial insult but remain dependent on intensive care for a protracted period, neither dying nor recovering. The most characteristic clinical feature is a prolonged requirement for mechanical ventilation. Other features include profound weakness associated with critical illness polyneuropathy, increased susceptibility to infection, metabolic changes and hormonal changes. There may be protracted or permanent delirium, or other marked cognitive impairment. The physical and psychological symptoms of the disease are very severe, including a propensity to develop post traumatic stress syndrome.

Strict definitions of chronic critical illness vary. One definition is the requirement for mechanical ventilation for 21 days or more. It is estimated that 5-10% of patients who require mechanical ventilation as part of their initial illness will go on to develop chronic critical illness. Overall prevalence has been estimated at 34.4 per 100 000 of the population. Most adult patients do not survive chronic critical illness, and furthermore even those who are discharged from hospital frequently die soon after discharge. One-year mortality in adults is 48-68%. However, children fare better with two-thirds surviving to 5 years or beyond.

Magnetic resonance imaging (MRI) and ultrasound are comparable in efficacy and helpful in diagnosis although both have a false positive rate of 15 - 20%. MRI can reliably detect most full-thickness tears although very small pinpoint tears may be missed. In such situations, an MRI combined with an injection of contrast material, an MR-arthrogram, may help to confirm the diagnosis. It should be realized that a normal MRI cannot fully rule out a small tear (a false negative) while partial-thickness tears are not as reliably detected. While MRI is sensitive in identifying tendon degeneration (tendinopathy), it may not reliably distinguish between a degenerative tendon and a partially torn tendon. Again, magnetic resonance arthrography can improve the differentiation. An overall sensitivity of 91% (9% false negative rate) has been reported indicating that magnetic resonance arthrography is reliable in the detection of partial-thickness rotator cuff tears. However, its routine use is not advised, since it involves entering the joint with a needle with potential risk of infection. Consequently, the test is reserved for cases in which the diagnosis remains unclear.

Electrophysiologic testing is an essential part of the evaluation of Anterior interosseous nerve syndromes. Nerve conduction studies may be normal or show pronator quadratus latency.⁠⁠

Electromyography (EMG) is generally most useful and will reveal abnormalities in the flexor pollicis longus, flexor digitorum profundus I and II and pronator quadratus muscles.⁠⁠

The role or MRI and ultrasound imaging in the diagnosis of Kiloh-Nevin syndrome is unclear.⁠

If asked to make the "OK" sign, patients will make a triangle sign instead.

This 'Pinch-Test' exposes the weakness of the Flexor pollicis longus muscle and the flexor digitorum profundus I leading to weakness of the flexion of the distal phalanges of the thumb and index finger. This results in impairment of the pincer movement and the patient will have difficulty picking up a small item, such as a coin, from a flat surface.