Dive Medicine

Preparation for Dive Travel

The Divers Alert Network (dan.org) provides a valuable service to the dive traveler. Over the years the network has been updating dive injury and fatality statistics. The information is clearly useful in determining who might be at greater risk for dive injury. Fortunately, we as medical providers are also blessed with data that can be found in the subscriber-funded newsletter Undercurrent . The number of dive accidents is on the rise, according to last year's report, but fatalities have remained approximately the same. DCS incidents are down from the previous year's high of 91, and now DCS is hovering at 56 incidents (2014 statistics). Undercurrent goes on to reference statistics related to older divers:

Five deaths involved divers who suffered heart attacks while in the water (out of 16 fatalities), and the average age of these divers was 60. In the last 2 years, nine in-water diving fatalities were attributed to medical causes in divers aged 50 or over. This number is significantly higher than the average age of non-medical fatalities, which is 42 years.

The British Sub-Aqua Club (BSAC) quoted these statistics in its Annual Diving Incident Report for 2014. The report goes on to say, “Older divers are advised to take account of the increased likelihood of a medical event when considering the type of diving in which they engage, and those diving with them should be more aware of the increased risk.” The physician advising a dive traveler is in an excellent position to help reduce this number.

Divers usually do not ask for medical clearance unless it is required by the dive resort. Issues such as asthma, obesity, heart disease, and physical disability may limit a diver's tolerance for unanticipated adversity encountered on a dive, and there are well-defined parameters a physician can use to determine who may be at risk. That said, “fitness to dive” is a notoriously difficult issue to determine with certainty. Dr. Tom Neuman, of San Diego, California, has been quoted as saying, “It is probably more important to ask if someone has ever run out of gas on the freeway than to ask about most medical conditions.” This comment is in reference to the well-known fact that some divers will run out of breathing gas in their SCUBA tank while diving due to inattention to air consumption. The ensuing emergency ascent is often not survived due to pulmonary barotrauma leading to air embolism. What is needed is a no-nonsense approach to dive fitness that could be applied to all divers whether they travel or not. It is essential to know what type of diving the traveler has planned. Will it be a low-stress dive vacation in warm, clear, tropical waters or is it going to be adventure diving in a cave or in deep shipwrecks in the North Atlantic using rebreather technology?

The most recent dive accident statistics indicate a number of other near-miss incidents. The most recently compiled causes of death include rapid ascent due to problems with buoyancy control or out-of-air situations, equipment problems, and solo diving or snorkeling. Medical history obtained after a fatality has revealed surprisingly consistent findings over the years. Cardiovascular disease is always the most prevalent, present in over 10% of all fatalities (13.6% in 2009, 12% in 2010) and this is still true today.

Most reports list “drowning” as a cause of death because that is all the coroner can confirm at autopsy. It takes experience and skill to tell the difference between a fatality in the water caused by drowning and one that is caused by air embolism. If the diver makes an emergency ascent due to an out-of-air situation or other problem causing panic in the water, air in the lung expands at a faster rate than can be safely exhaled. Pulmonary barotrauma, sometimes called “pulmonary overpressure injury,” allows a small amount of air to enter the pulmonary arterial system. Within three heartbeats this air is transmitted to the brain, causing momentary confusion or loss of motor control. The diver can no longer protect the airway, and the final common pathway for death is indeed drowning, but the antecedent cause is “air embolism,” and before that it is running out of air to breathe.

Scuba diving can be divided into several categories depending on the physical and technical demands of the anticipated dive and the remoteness of the dive location. This easily breaks down into three manageable categories:

• Recreational diving for the beginner or occasional diver in warm, clear water breathing compressed air, the maximum depth limited to 100 ft of seawater.

• Advanced deeper, multiday diving often using Nitrox (also known as enriched air nitrox). Nitrox refers to a modified breathing gas with a higher concentration of oxygen than is found in air (21%). The oxygen concentration is higher in order to lower the concentration of inert gas and lower the risk of DCS. The diver gets to dive longer, but the trade-off is that diving must be done at a shallower depth due to the potential for CNS oxygen toxicity.

• Technical diving, usually done with either multiple tanks or rebreather technology and requiring long decompression times before surfacing. Often the dives are deep and penetrate into caves or sunken vessels where there is no possibility of direct return to the surface. The dive sites are often in remote locations with virtually no access to medical care or a hyperbaric treatment facility.

In actuality there are many other subsets of diving. To name a few, there is the instructor, commercial diver, scientific diver, engineer, seafood harvester, public safety diver (usually performed by police and fire departments), military diver including marine mammal training for guard duty, and unexploded ordinance removal diving. The care of most of these fall under the general category of occupational medicine, and physical requirements are much more rigorous and are usually specified by the agency responsible for certification of the diver. It is beyond the scope of this chapter to review the requirements of each one.

Concerning a diver's “fitness to dive,” Dr. Richard Moon has stated that:

• 1.

  A diver should be able to do the “work” of diving. That is, to breathe, swim, and exercise underwater. Note here that some dives are more work than others, but if a diver is called on to rescue his or her partner, intense physical exertion will be required. This is why the minimum standard of physical fitness for any type of diving is the ability of the diver to achieve 13 metabolic equivalents (METS) or better of exercise, running on a treadmill. This is only one of many different ways in which physical fitness can be assessed. Each test of cardiovascular fitness has its strengths and weaknesses; one of the easier, cost-effective tests to administer in a medical clinic is the Harvard step test. This test is designed to work best for healthy individuals of normal weight. One of the weaknesses of the test is that it does not accurately predict fitness swimming or diving or apply to anyone with a partial disability or who is markedly overweight. Disadvantages include Biomechanical characteristics. They vary between individuals. For example, considering that the step height is standard, taller people are at an advantage as it will take less energy to step up onto the step. Body weight has also been shown to be a factor. Testing large groups with this test will be time consuming. Those in the latter categories will have trouble performing up to their physical potential with a Harvard step test. A bicycle ergometer can also be used, but its availability is somewhat limited.

• 2.

  A diver should not be unusually susceptible to barotrauma, which is pressure-related damage to the ears, lungs, or gastrointestinal tract. Barotrauma is the most common injury for any class of diving but happens most often to the novice diver.

• 3.

  A diver should not be susceptible in any way to loss of consciousness caused by seizures, hypoglycemia related to insulin-dependent diabetes, or heart block.

• 4.

  A diver should not have any disease that diving (exercising underwater) could make worse. This includes sinus or middle-ear disease, previous labyrinthine window rupture, or heart failure.

• 5.

  If female, a diver should not be pregnant, as the risk of bubble-related birth defects (decompression injury) is thought to be significant.

• 6.

  A diver should not be “overly” susceptible to DCS. There are 24 known variables that affect an individual's susceptibility to DCS at any given time. Some of these factors are increasing age, first day of menses, previous undeserved DCS, fatigue, dehydration, vigorous exercise at depth underwater, or heart disease such as an atrial septal defect or a patent foramen ovale.

Decompression Sickness

DSC goes hand in hand with physical fitness and an individual's “fitness to dive.” Microscopic bubbles are formed constantly in the body under normal circumstances from heterogeneous sources and are known to be present to a greater extent when a diver becomes fully saturated with inert gas. It has been known for many years that clinical symptoms of decompression sickness are determined by the body's ability to withstand and tolerate the effect of bubbles and not by the presence of bubbles themselves. Vascular bubbles produced by “provocative diving” (diving in a manner more likely to produce DCS) can cause disruption of the vascular endothelium. This in turn triggers a cascading sequence of events, the first of which is believed to be activation of white blood cell (WBC) adhesion molecules on the surface of the endothelium. WBCs adhere at the site of injury and trigger a chain of events resulting in increased permeability of the vessel, localized tissue edema, and intravascular plasma loss. Vessel occlusion ultimately results from a combination of bubble obstruction and circulatory sludging (localized intravascular dehydration). This in turn results in tissue hypoxia and release of inflammatory cytokines (signaling molecules), including the very important class of molecules called eicosanoids. The inflammatory cascade caused by WBC adhesion also fosters the production of newly discovered microparticles (MPs) in the bloodstream. These MPs are small fragments of membranes and nucleic acids (also termed “cellular dust”) that arise from the damaged endothelial tissue. The magnitude of MP production is highly variable and to some extent genetically mediated. This means that some individuals are more likely to get DCS on any given dive due to genetic variability. This finally explains the phenomenon of the “bends prone” individual. It is known but not well understood that diving leads to the activation of genes that are mainly triggered by hyperoxia. While some individuals are more prone to DCS, others (especially those who dive frequently) are rather immune to the effect of bubbles in the circulatory system. This is termed “DCS acclimatization” or the “work-up” dive effect. In some individuals, repeated exposure to high levels of inert gas can trigger an adaptive immunoinflammatory response by modulation of nuclear factors.

If tissue damage occurs and progresses, excitatory neurotransmitters are released, and ultimately reperfusion injury occurs. This is progressively irreversible tissue damage from reactive oxygen species (chemically reactive molecules containing oxygen). If DCS is allowed to progress untreated, the injury also triggers apoptosis (programmed cell death), the final and irreversible outcome of untreated DCS.

Overt DCS is an outward manifestation of this highly variable and multifaceted inflammatory disorder. Aerobic exercise can reduce bubble formation in animals and humans. The mechanism for this is probably the effect of nitric oxide liberated by exercise, but this is not known with certainty. What is known for certain is that the addition of nitric oxide in test animals who have been subjected to potentially lethal dives results in survival with no neurological injury. Nitric oxide has the ability to remove vascular bubbles; this raises the question of whether medication can potentially help treat DCS.

A thorough diving history and physical examination might uncover risk factors, but the examining provider needs to know what to look for. Certainly, a genetic predisposition for the inflammatory response associated with bubble formation is something that could be suspected only after multiple episodes of undeserved DCS. Fortunately, there are many guidelines available for determining a diver's fitness, and to a large extent the risk to any individual diver depends on the type of diving he or she will be doing.

A helpful strategy for quickly assessing a diver's risk is simply to review the medications the diver has taken recently. Certain medications are not recommended during diving, but, more importantly, some drugs signal the presence of medical or psychological conditions that should be taken into account when clearing someone for diving. Table 11.1 lists potentially problematic drug classes along with specific problems encountered in each class. The author has used this table for a number of years at the National Oceanic and Atmospheric Administration (NOAA) Physicians Training Course in Undersea and Hyperbaric Medicine lecture on the effect of medications and diving.

If a diver has normal exercise tolerance for age, a normal pulmonary function test with no evidence of significant reversible obstruction, low risk of heart disease, and no evidence of diabetes or other chronic or debilitating diseases, then you are well on the way to granting unrestricted clearance. A diver's psychological profile should be included in your assessment; the diver should not have a history of disabling anxiety, psychosis, or suicidal ideation. Psychological fitness to dive is much more difficult to define in some individuals, and occasionally it is necessary to get clearance from a mental health provider when unsure of the diver's safety in the water. Of course, the diver should not be taking any significantly problematic medications.

Some dive resorts provide appropriate warnings regarding possible dangers encountered while diving at the resort, but more often than not it is difficult to actually obtain up-to-date information. Some resorts suppress bad or conflicting news so as not to deter potential customers. It is well known that the Centers for Disease Control (cdc.gov) offers advice regarding food and water precautions and malaria prophylaxis, but it is more difficult to get information regarding in-water hazards such as serious marine envenomation, which is the fourth highest cause of dive injury as reported by DAN. Assessing the safety of dive sites for the beginner, disabled, or older diver is not possible until the diver is actually at the location. To stay up-to-date on a host of other dive safety issues, it is useful to have access to the monthly DAN newsletter, Safety Stop . Another monthly publication, Undercurrent ( www.undercurrent.org ), is probably the best source for this type of information and has a large, searchable database online with specific information about most dive resorts. There is also region-specific jellyfish information, constantly updated with an online database for Mediterranean waters, that is free for all interested users: the CIESM Jellywatch Program ( www.ciesm.org/marine/programs/jellywatch.htm ). The Commission Internationale pour l’Exploration Scientifique de la Mer Méditerranée, or simply the Mediterranean Science Commission, is an intergovernmental body with 23 member states that border the Mediterranean coast; using Jellywatch anyone can easily track population blooms of stinging jellyfish in a region of interest during a specified period of time. This is quite significant in light of fatal or severely disfiguring aquatic envenomation from jellyfish such as the Sea Nettle and the Box Jellyfish to name a few.

I find it valuable to remind travelers about dive accident insurance and travel insurance before the trip. Dive accident insurance can be literally purchased at the last minute from several sources, but this is not the case with travel insurance. Just to remind you, if a dive accident were to occur, especially if hospitalization, hyperbaric treatment, and a pressurized air ambulance is needed, the cost would be in the hundreds of thousands of dollars. Travel insurance is also useful to have, as it is not unusual for travel to an exotic dive location to cost many thousands of dollars. Divers often do not recognize that once the first arrangement for a trip has been made, whether a payment is involved or not, that day becomes what the insurance industry terms “the deposit date.” Travel insurance needs to be purchased immediately once the first arrangement has been made or else it is often simply not available.

An up-to-date diver's first-aid kit is highly recommended, especially when diving in remote locations. This is a fairly comprehensive list; the actual contents needed may vary depending on where the diving will take place. The following items are recommended (* indicates items that requires doctor's prescription):

• 1.

  Concise medical problem list of the individual diver for emergency use (with emergency phone numbers)

• 2.

  Assortment of water-resistant generic adhesive dressings, moleskin, chlorhexidine 4% surgical soap, 2-inch-wide elastic bandage, mupirocin* ointment, folding scissors

• 3.

  White wine vinegar and disposable razor for jellyfish stings

• 4.

  Prophylactic eardrops for swimmer's ear (otitis externa) containing acetic acid 2% (many over-the-counter products are available for this). Drops are best applied before and after a day of diving, as long as the drops are allowed to stay in the ear for a contact time of 5 minutes

• 5.

  Neomycin*, polymyxin B, hydrocortisone generic otic drops or ofloxacin otic* for treatment of swimmer's ear

• 6.

  Melatonin for jet lag (circadian rhythm sleep disorder)

• 7.

  Loperamide for traveler's diarrhea. Azithromycin* (for treatment of severe symptoms or infection)

• 8.

  Sunscreen with sun protection factor (SPF) 15 for normal sun sensitivity and SPF 30 or above for those unusually sensitive to the sun or who have a history of skin cancer (reapply often if swimming)

• 9.

  Insect repellent containing greater than 35% N,N -diethyl-meta-toluamide (DEET) or CDC recommended equivalent. Reapply three times a day

• 10.

  Hand sanitizer

• 11.

  Personal medications and 1% hydrocortisone ointment or stronger if allergic reaction to bug bites have occurred in the past. Consider acetaminophen and diphenhydramine

• 12.

  Birth control (condoms).