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Dive  Medicine

Most diving accidents or illnesses are related to the effect of depth/pressure on gases in the body; examples are decompression sickness, nitrogen narcosis, oxygen toxicity, arterial gas embolism and CO2 retention. Dysbaric osteonecrosis is an example of the effects on the bones and joints of bubbles from decreased pressure in a nitrogen saturated diver.
GtB Dive Medicine Cardiopulmonary Test
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Dont's for Divers

  • Don't dive into a submerged pool or into the shallow end of a pool. 
    Nine of ten diving injuries occur in six feet of water or less.  
  • Don't dive off the side of a diving board--dive straight ahead
  • Don't dive from the edge across the narrow part of a pool without
    having at least 25 feet of clear dive path in front of you.
  • Don't run and dive.  That can give you the same impact as a dive
    from a board
  • Don't do a backdive
  • Don't try fancy dives or dives with straight vertical entry
  • Don't dive at or through objects such as inner tubes
  • Don't put diving equipment on a pool that wasn't designed for it.
  • Don't dive from retaining walls, ladders, slides, or other pool equipment.
  • Don't dive into unfamiliar bodies of water.  Remember, 3 of 4
    diving accidents happen in natural bodies of water like lakes and rivers.
  • Don't swim and dive alone
  • Don't drink and dive.  The slowing effects of alcohol or drugs on
    reaction time can be extremely dangerous in diving.

Decompression Sickness  (DCS)

The label 'decompression sickness' (DCS) was introduced in place of "Caisson disease". Problems resulting from nitrogen leaving the body when ambient pressure is lowered i.e. coming up. Decompression sickness can be classified as either Type 1 or Type 2.
The different classification reflects the effect, and therefore the severity, of the condition. Diagnosing Decompression sickness as one (or both) of just two categories does not enable proper identification or discrimination. However, for the sake of completeness, the two types are described here.
GtB Decompression Sickness  (DCS)

Type 1 DCS can occur when bubbles affect the tissues around skeletal joints. Symptoms usually include unilateral (on one side of the body) discomfort or pain in one or more joints. The areas most often affected are the knees, elbows and shoulders.

Decompression sickness might also present as a skin (cutaneous) disorder. Nitrogen bubbles can cause mottling, lumps or a rash. "Skin bends", as they are colloquially termed, are more common during hyperbaric chamber 'dives' and when diving using a dry suit. Although not usually in them selves serious, skin symptoms may indicate the presence of problems elsewhere. A particularly serious cutaneous sign of DCS is 'cutis marmorata' marbling, in which an area of skin becomes pale with dark mottling. This is associated with considerable development of inert gas bubbles within the body.

If left untreated, Type 1 DCS may progress to Type 2.

Type 2 decompression sickness reflects involvement of the Central Nervous System (CNS) and / or the cardio-respiratory system. More than half of those diagnosed with DCS will be classified as Type 2.Cerebral symptoms arise from interruption of the blood supply to the main part of the brain, and include confusion, reduced mental function and unconsciousness. Involvement of the cerebellum may lead to tremors, loss of balance ("staggers") and a lack of co-ordination (ataxia). Balance may also be affected by damage to the vestibular part of the inner ear.

Spinal DCS may present as back pain, paresthesia (pins and needles), paralysis and loss of urinary sphincter control - resulting in either incontinence or retention.

As discussed already, the formation of small inert gas bubbles does not necessarily lead to the development of DCS. Likewise, when bubbles become trapped in the tiny blood vessels around the lungs' alveoli (air sacs), problems do not always arise. In fact, it is thought that their accumulation in this area may increase the rate that the gas is excreted from the body (Edmonds et al, 1993). However, if too many bubbles collect, breathing will become adversely affected ("chokes"). Symptoms include breathlessness, tachypnoea (increase in breathing rate), chest pain and coughing. Although symptoms may resolve, this should be regarded as a life-threatening condition as it may progress to fatal respiratory collapse.
PFO (Patent foramen ovale) is a persistent opening in the wall of the heart which did not close completely after birth (opening required before birth for transfer of oxygenated blood via the umbilical cord). This opening can cause a shunt of blood from right to left , but more often there is a movement of blood from the left side of the heart (high pressure) to the right side of the heart (low pressure).
GtB PFO Patent foramen ovale
People with shunts are less likely to develop fainting or low blood pressure with diving than are obstructive valve lesions (such as mitral valve stenosis or aortic stenosis), but are more likely to develop fluid accumulation in the lungs from heart failure and severe shortness of breath from the effects of combined exercise and water immersion.

Ordinarily, the left to right shunt will cause no problem; the right to left shunt, if large enough, will cause low arterial O2 tension (hypoxia) and severely limited exercise capacity. In divers there is the risk of paradoxical embolism of gas bubbles (passage of bubbles into the arterial circulation) which occur in just about all divers in the venous circulation during decompression.

Blood can flow in both directions with Intra-atrial shunts at various phases of the cardiac cycle and some experts feel that a large atrial septal defect (PFO) is a contra-indication to diving. In addition, a Valsalva maneuver, used by most divers to equalize their ears during descents and ascents, can increase venous atrial pressure to the point that it forces blood containing bubbles across the PFO into the arterial circulation. Thus the usual filtering process of the lungs is by-passed.

Nitrogen narcosis

Nitrogen narcosis is a dangerous condition that can affect scuba divers, especially when diving deeper than 30 meters. The exact mechanisms behind nitrogen narcosis are still to be explored, but it has to do with nitrogen gas affecting the nerve transmissions in the body during high pressure. Since the air inhaled by scuba divers contains a large amount of nitrogen (just like the air that we breathe above the surface every day), nitrogen narcosis was the first type of gas narcosis experienced by scuba divers, hence the name. The effects of nitrogen narcosis are similar to the effects of anesthetic gas or alcohol. It can be hard for the effected diver to realize that he or she is developing nitrogen narcosis, since the level of intoxication will increase gradually. If you suspect that you or your buddy is suffering from nitrogen narcosis, you should immediately begin your ascent to shallower depts. The effects of nitrogen narcosis will usually wear of as soon as you reach shallower depths, even if they are far from the surface.

Swimmer's Ear

The most common symptom of outer ear inflammation or infection, known as swimmer’s ear or otitis externa, is discomfort/pain that may worsen with pulling on the ear.
Occasionally, outer ear infections can be caused by a fungal infection. The fungal infection usually occurs on top of an existing bacterial infection, often after antibiotic treatment kills off some of the bacteria, which makes it easier for the fungi to grow. Ear infections can also be caused by fungi alone, especially in moist, warm climates. .

GtB Swimmers Ear

Treatment of swimmer's ear
Swimmer's ear, when properly treated by a physician, usually clears up within seven to 10 days.  Antiseptic or antibiotic ear drops should be the front-line treatment for people suffering from swimmer's ear, while restraint should be exercised in using oral antibiotics.

Preventing Swimmer's Ear
Prevention and treatment of dive-related earache depends upon whether the cause is in the external auditory canal or middle ear space.  When the problem is within the external ear canal, preventative steps include the application of drops that protect ear tissue and inhibit the growth of harmful microorganisms.

Recipe for Homemade Swimmer's Ear Drops:
  1. 1 Bottle (I used a condiment bottle purchased in the
    WalMart kitchen aisle for 97¢)
  2. Label bottle with handy dandy label maker (optional)
  3. Place equal parts vinegar & rubbing alcohol in bottle
  4. Give bottle a little shake & turn yourself about
    (again, turning is optional)
  5. Place a couple drops in each ear after swimming
  6. That's it - easy peasy!


Jellyfish-related deaths are rare, but the sting they inflict is extremely painful. Most known deaths from jellyfish are attributed to the man-of-war. Other jellyfish can inflict very painful stings as well. Avoid the long tentacles of any jellyfish, even those washed up on the beach and apparently dead

Portuguese man on war

Although it resembles a jellyfish, the Portuguese man-of-war is actually a colony of sea animals. Mainly found in tropical regions, the Gulf stream current can carry it as far as Europe or Africa. The Portuguese man-of-war resembles a large pink or purple balloon floating on the sea.

GtB Portugese man on war
The floating portion of the man-of-war may be as small as 15 centimeters, but the tentacles can reach 12 meters in length. The huge tentacles are actually colonies of stinging cells. These tentacles inflict a painful and incapacitating sting, but the sting is rarely fatal.
  • Pick off any visible tentacles with a gloved hand, stick, or anything handy, being careful to avoid further injury.
  • Rinse the sting thoroughly with salt or fresh water to remove any adhering tentacles.
  • Apply ice for pain control.
  • Irrigate exposed eyes with copious amounts of room temperature tap water for at least 15 minutes. If vision blurs, or the eyes continue to tear, hurt, swell, or are light sensitive after irrigating, see a doctor.
  • For persistent itching or skin rash, try 1 percent hydrocortisone ointment four times a day, and one or two 25 milligram diphenhydramine (Benadryl) tablets every 6 hours. These drugs are sold without prescription. Diphenhydramine may cause drowsiness. Don't dive, drive, swim or surf after taking this medication.

Scorpion Fish

Pain relief is a high priority in Scorpion fish stings. To ease pain, soak the wound in non scalding hot water for 30 to 90 minutes. (Victims in pain may not be able to tell if water is too hot.

Someone else should test the water temperature on his or her own hand first.) Heat inactivates at least one of the toxins in the venom, and thus relieves some of the pain. If pain returns an hour or more later, try the heat soaks again. While soaking, remove any protruding pieces of the spine or skin from the puncture.
GtB Scorpion (King Lion) Fish
Do not apply a tourniquet, ice, or pressure bandage. To clean the wound, gently pull the edges of the skin and scrub with clean gauze or a cloth soaked in clean, fresh water. Victims of infected Scorpion fish stings should see a doctor. If a victim shows any signs of a serious reaction, consider it a medical emergency.

The public is being asked to capture or kill these fish as they pose a serious threat to our beautiful Barrier Reef or report any sightings to the Hol Chan Marine Reserve office.

Further reading

This links provide more Dive Medicine related information.
Scubadoc's Diving Medicine Online Sitemap
Divers Dan Alert Network  Diving Medicine Frequently Asked Questions
To avoid accidents with Dangerous Creatures, please check out our Danger Creatures Page.

Guide to Belize,  September 2021



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