Decompression Sickness: The Bends
Decompression sickness is due to nitrogen bubble formation in soft tissue, usually associated with rapid ascent from diving depth without proper subsurface decompression stops. The mechanism of bends formation is reviewed below.
- Nitrogen gas tissue loads with depth and on-gassing occurs with the set. Off gassing on ascent.
- If there is Ascent from depth faster than bubble-free tissue off gassing will allow — bubbles will form.
- Resultant Bubble formation is in veins and soft tissues.
- Endothelial (vessel wall) damage occurs with clots, ischemia, and more. HBO is the treatment of choice.
- HBO results include pressure bubble reduction & O2/N2 gradient for gas defusion. HBO also prevents reperfusion injury (white blood cell adherance to blood vessel walls).
- Arterial bubble formation + venous bubble formation = decompression illness. Decompression illness is associated wtih arterial gas embolism (AGE), which results frequently in unconsciousness and seizure.
There are as many presentations of Decompression Sickness (DCS) or "The Bends" as there are people diving. There is no diagnostic test for this condition. Flexibility in your diagnostic skills and a high index of suspicion when combined with history and mechanism of injury are still the mainstay of the correct diagnosis. The general rule is that if you suspect decompression sickness, treat for decompression sickness with recompression — HBO.
Photo by Frederick Dennstedt, used under Creative Commons Attribution-ShareAlike 2.0 Generic license
Decompression sickness is divided into 2 types. TYPE 1 has symptoms that involve only joint, skin, lymph node and swelling. A good rule of thumb is if the pain is in the extremities it can be safely treated as Type I pain. If the pain is proximal to the extremities involving the trunk, it should be treated as Type II DCS requiring more prolonged recompression. These patients may present with dizziness, truncal numbness or tingling, motor weakness or paralysis or urinary retention. If pulmonary intravascular bubbling (chokes) occurs, the patient will develop symptoms consistent with pulmonary embolus and pulmonary edema with chest pain, tachypnea and cough. There are many factors which predispose to decompression sickness apart from a simple violation of the conventional dive tables. These include age, dehydration, heat and cold, prior history of decompression sickness, obesity, sex and multiple dive profile. Flying after diving rather than waiting the recommended 24 hours is a common etiology of DCS. Arterial gas embolism is an immediate life-threatening diving emergency which frequently occurs with diving ascent. On Ascent, air expands in the alveoli and if not properly vented, the alveoli will expand, forcing the gas bubbles directly into the capillaries were they will circulate and eventually embolize as the arterioles narrow. If this occurs in the CNS, the results will be unconsciousness upon surfacing with stroke type symptomatology, commonly complicated by seizure. The combination of venous and soft tissue bubble formation with arterial gas embolism is referred to as decompression illness.
- Administer oxygen high dose nonrebreather mask
- Administer intravenous fluids — normal saline
- Administer aspirin to inhibit platelet aggregation
- Administer narcotic analgesia
- If symptomatology of arterial gas embolism, place the patient in mild Trendelenburg
- If air transport is necessary fly at less than 1000 feet of elevation
Recompression therapy (HBO) in a hyperbaric chamber
is the treatment of choice.
Photo by Christopher Albans, used under Creative Commons Attribution-Share Alike 3.0 Unported license
An HBO Chamber at Doctors Medical Center
Patent foramen ovale (hole in the heart) exclusion is an important part of DCS treatment. This anatomical defect is found in up to 20% of the population. It predisposes to the development of arterial bubble formation and arterial gas embolism. Echocardiogram with bubble study is the diagnostic procedure utilized.
Prevention is the best medicine:
- Properly train and condition for your dive experience
- Maintain ideal body weight
- Do not trust your dive computer. Plan your dive utilizing the Navy dive tables
- A 3 minute decompression stop at 15 feet as recommended by DAN (Divers Alert Network) is requisite regardless of such need according to the tables
- Do not dive if you are fatigued, dehydrated, menstruating, pregnant or have a upper respiratory / sinus infection
- Do not mix alcohol and diving
- Do not breath hold during ascent
- Wait 24 hours before boarding any airplane