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Multi-agency training day

From time to time we take part in ‘Multi-Agency Training Days’. These are full-scale tests of our systems and processes; they help ensure that the various agencies involved can effectively co-ordinate the response to different emergencies.

Decompression Illness Treatment Scenario

The day started with a call from a Police Dive Supervisor advising us of an incident; one of their divers had a rapid, uncontrolled ascent from a depth of 22 metres. Decompression Illness treatment was required quickly; the Police had informed the Coast Guard and a Sea King helicopter had been dispatched for pick-up.

This call was received by the Duty Supervisor at London Hyperbaric Medicine  based at Whipps Cross University Hospital.

Seaking landing in Epping Forest.

Seaking landing in Epping Forest.

Team clearing the area looking for foreign objects

Team clearing the area looking for foreign objects

Diving Emergency – A Logistical Response

When we receive a call of this nature, advising of a diving emergency coming to us by helicopter, the Hyperbaric Supervisor must inform various agencies:

Police

The police need to be contacted as they are responsible for crowd control at the landing zone (LZ) in Epping Forest; this is a public area that’s well used during summer months with picnicking families.

Ambulance

Ambulance crews need to be on site to transport the patient from the LZ to Whipps A+E

Forest Rangers

Epping forest rangers will open up the locked gates around the area to allow access for the ambulance and police, they also help with clearing the area.

Hyperbaric Crew

The hyperbaric crew need to be mobilised to get the chamber ready to receive the patient.

This all needs to be done in a very short space of time; a Sea King helicopter can fly from the South coast to the LZ in about 30 minutes.

Outcomes

The whole exercise can be stressful but also very rewarding when everything goes like clockwork just as it did on this day. The outcome was that the patient was transferred efficiently with no problems and minimal disruption.

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Infographic How, When and Where Sharks Attack

Sharks have been roaming our oceans for millions of years. But will they still roam our oceans in 50 years from now? Fisherman have been harvesting sharks like it was corn from a field whiteout any reluctance. Now we came to a point that many sharks species are endangered and on the brink of extinction.

Sharks are our friends

Luckily governments all over the word are waking up and bills are being passed to save sharks from extinction. Now we need to educate younger generations that sharks are not brutal men eaters and that a living shark is worth much more than a dead shark.

Many people still believe that sharks are a threat to humans, but they forget that vending machines kill more people every year in the US. We humans are a threat to sharks though and if we keep killing them we will take down a whole eco system which we so much rely on.

Please share and help preserve sharks for future generations.

When Sharks Attack

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5 Minute Neurological Exam

Any diver can follow this 5 minute Neuro

 

  1.                   Orientation.–  Does the diver know name and age? Location? What time, day and year it is? Note: even though the diver appears alert, the answers to the question may reveal confusion, so do not omit them.
  2.                   Eyes. – Have the diver count the number of fingers you display using 2 or 3 different numbers. Check each eye separately and then together. Have the diver identify a distant object. Tell the diver to hold his head still, or you gently hold it still, while placing your other hand about 18” in front of their face.  Ask the diver to follow your hand with his eyes. Move your hand up, down, side to side. The divers’ eyes should smoothly follow your hand and should not jerk to one side and return. Check pupils are of equal size. Note: Often AGE victims have different dilation in one eye than the other. Also look for Nystagmus (fluttering of the eyes either vertically or horizontally). This is a sign of neurological problems, with vertical fluttering being associated with more severe damage.
  3.                   Face. – Ask the diver to whistle. Look carefully to see that both sides of the face have the same expression while whistling. Ask the diver to grit his teeth. Feel the jaw muscles to confirm that they are contracted equally. Instruct the diver to close their eyes while you lightly touch your fingertips across the forehead and face to be sure sensation is present and the same everywhere.
  4.                   Hearing. – Can be evaluated by holding your hands about 2 feet from the diver’s ears and rubbing your thumb and finger together. Check both ears, moving your hand closer until the diver hears it. If the surroundings are noisy (i.e.: a crowed beach), the test can be difficult to evaluate. Ask bystanders to be quite and turn off unneeded machinery.
  5.                   Swallow reflex. – Instruct the diver to swallow while you watch the Adams apple to be sure that it moves up and down.
  6.                   Tongue. – Instruct the diver to stick out their tongue. It should come out straight in the middle of the mouth without deviating to either side.
  7.                   Muscle strength. – Instruct the diver to shrug the shoulders while you bear down on them to observe for equal muscle strength. Check the divers arms by bring the elbows up level with the shoulders, hands level with the arms and touch the chest. Instruct the diver to resist while you pull the arms away, push them back, up and down. The strength should be approximately equal in both arms in each direction. Check leg strength by having the diver lie flat and raise and lower the legs while you gently resist the movement.
  8.                   Sensory perception. – The divers eyes should be closed during this procedure. Check both sides by touching as done on the face. Start at the top of the body and compare sides while moving downwards to cover the entire body. The diver should confirm the sensation in each area before you move to another area.
  9.                   Balance and coordination. – Be prepared to protect the diver from injury when performing this test. Have the diver stand with feet together, close eyes and stretch out arms. The diver should be able to maintain balance if the platform is stable. Your arms should be around the diver, but not touching the diver. Be prepared to catch the diver who starts to fall. Note: If the diver is already messed up you may want to avoid this one. If he can’t stand check coordination by having the diver move an index back and forth rapidly between divers’ nose and your finger held approximately 18” from the divers face. Instruct the diver to slide the heel of one foot down the shin of the other leg. The diver should be lying down when attempting this test.  Check these test on both legs and observe carefully for unusual clumsiness on either side.

 Remember to note all your findings.

 

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Taravana: Can free divers get bent?

Can free divers get bent?

Can free divers get bent?

The classic study by Cross in 1965 looked at Polynesian island natives of the Tuamotu Archipelago,who habitually free dive many times in quick succession, usually for food or pearls and may make 40 to 60 dives a day to 30 or 40 metres. Taravana means to ‘fall crazily’ and his report listed 35 male divers. Twelve of them suffered from vertigo and one died. The ages ranged from 19 to 62, and the greatest depth dived was about 45 m. The islanders usually dived from a canoe or an outrigger and descended using a weight of about 4 to 6 kg attached to a line and wore goggles or a face mask. Divers would hyperventilate for 3 to 10 minutes before diving with a deep inhalation, followed by deep expiration accompanied by a long drawn “whoooeee” sound. Before the dive, the diver lowered himself into the water and continued to hyperventilate at a faster rate. Just before he dived, he raised himself out of water to the waist, took a deep breath and descended feet first holding the weight. Time on the bottom ranged from 30 to 60 seconds. Ascent time was no more than 20 seconds from depths of 30 to 39m. As soon as he reached the surface, the diver hyperventilated again for 3 to 10 minutes and then dived. The maximum duration of a dive, from surface to surface, was 2 minutes and 35 seconds. The average however, was 1 minute 30 seconds for a series of timed dives. The most common symptoms of Taravana were vertigo, nausea and ‘mental anguish’. Occasionally, vertigo was the only symptom. Some of these symptoms could be due to hypoxia, hypercarbia (high CO2 in the blood) and drowning, but are highly suggestive of decompression illness, especially the neurological symptoms.

Breath hold diving causing decompression illness was then reported in 1965 by Paulev, a Medical Officer in the Royal Danish Navy, after he spent 8 minutes at 20m as an attendant in a recompression chamber and then performed a number of breath hold dives in the submarine escape training tank (SETT) to 20m. Each descent took 20-25 secs, he would then sit or walk until he felt the need to breathe, at about 2 minutes, then he ascended to the surface, which took 10 – 15 seconds. Surface intervals were short (between a few seconds and 2 minutes) and he was in the water about 5 hours. During the last 2 hours, he experienced nausea, dizziness and belching and during the last 30 minutes, he developed pain in his left hip and right knee, with the right leg and the right arm weakness. Two hours after leaving the water he had chest pain, abdominal pain, pins and needles and numbness in the right hand and blurred vision. He was treated with USN Table 3 which was partially successful although a residual weakness of the right hand persisted. Three further cases have subsequently been treated in the Norwegian SETT and each one had been compressed in the hyperbaric chamber before breath hold diving. All experienced neurological symptoms and were successfully treated, which supported the diagnosis of decompression illness from breath hold diving.

 Question 1

Can I freedive after scuba diving?

Freediving after scuba is not safe. Although there are no clear guidelines, it is generally agreed that freediving can result in decompression illness after scuba diving, as a result of the above examples.

Question 2

Is it escaped gas or evolved gas?

The clinical pictures described above are more in keeping with the slower onset and less profound neurological problems associated with evolved gas decompression illness, that are dependent on the amount of absorbed nitrogen. Rather than the sudden onset severe neurological problems associated with escaped gas arterial gas embolism.

Question 3

Can submariners get DCI?

Submarines are pressurised to around 1 atm so there is no risk of decompression illness. However, if there is a breach in the hull, any ingress of water will pressurise the remaining space and make decompression illness more likely, especially if there is then escape to the surface. I have described how submariners can get decompression illness from evolved gas after repetitive breath hold dives in SETT, however they are actually more likely to get decompression illness in SETT from escaped gas from pulmonary barotrauma if they hold their breath on ascent.

Question 4

Can cetaceans get DCI?

There have been reports in Nature journal of bubbles in the tissues of cetaceans that have been stranded, suggesting that decompression illness is a problem in these air breathing mammals. Although the truth is more difficult to ascertain, as the stranding and the bubbles could be caused by cavitation from military sonar.

Question 5

What is the difference between deep water and shallow water black out?

These 2 terms cause confusion but are caused by the same thing, except for the depth at which it happens. The urge to breath is driven by the level of CO2 in the blood. That is, until the O2 drops to a low level, when the urge to breath is driven by O2. At depth, the level of O2 and CO2 are raised due to the increased pressure and breathing can seem comfortable. But on ascent from 10m to the surface (or 30m to 10m), the levels of both halve. If the O2 levels drop beyond that required for the brain to function, then black out will occur.

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BEST WRECK DIVING SPOTS IN THE UK

When it comes to wreck-diving, UK is probably one of the best dive destinations in the world. With thousands of ship wrecks scattered all across the isles, there is always a wreck an avid diver can explore in every known dive destination in the Kingdom. Some sites offer even more scenic spots and unique animal encounters under water that no other destinations can provide. Here’s a list of the top 7 dive sites in the UK.

Weymouth and Portland, Dorset
Weymouth has more than 120 wrecks within a 20-mile radius. The wrecks include warships, submarines, steam ships and freighters, among others. The most popular are the M2, the Salsette, the Avalanche, and the Aeolian Sky. Situated in the centre of the Jurassic Coast World Heritage Site, the area has an abundance of reef and ledge dives and are home to an amazing variety of marine life.

Plymouth, Devon
Plymouth is where experienced divers often explore the wreck of the HMS Scylla, a Leander-class frigate, sunk as an artificial reef in 2004. Also visible is the James Eagan Lane, a US Liberty ship that was sunk by a U-boat in World War 2. The area also has a smattering of shoals and reefs, in case divers opt for a change of scenery.

Porthkerris, Cornwall
Located on the eastern side of the Lizard Peninsula, the Drawna Rocks in Porthkerris boasts of the best shore dive in England. Just a short ride to nearby Manacles are numerous wrecks such as the Mohegan, the Volnay and the Spyridion, among others. Apart from the wrecks are pinnacles, drop-offs, reefs and an abundance of marine life. During the months of May to August, Porthkerris is visited by the second largest shark in the world, the Basking shark.

Skomer Island, Pembrokeshire, Wales
This is a marine reserve with a sharp drop-off that goes down to 45m. It is the site of the Lucy, a 52m intact coaster that sunk perfectly upright in 40m of water. It’s also home to frolicking grey seals, rare gorgonian fans (found in only a handful of areas in the UK), and various crustaceans.

Isle of Man
Located in the southwest of the Isle of Man is the islet Calf of Man, which hosts a dive site called the Burroo. This is rated as one of the top 50 dive sites in the world. Due to the strong tidal currents in the area, the marine life is abundant and diverse and may possibly be the best in all of the British Isles. There is an intact wreck of a Manx trawler, the Fenella Ann. Other wrecks worth seeing are the Ringwall, SS Liverpool and the Thracian. There is also an interesting cave worth exploring in the nearby Sugar Loaf dive site.

Farne Islands, Northumberland
This area is famous for its colony of 5,000 grey seals that often accompany divers. It offers scenic wrecks such as the Somali, Chris Christianson, Abyssinia, and Britannia. It also has a pinnacle, a wall, some reefs and rocks covered with soft corals and a huge, deep-water anemone, the Bolocera.

Scapa Flow, Orkney, Scotland
This is a natural harbour offering the best wreck diving in the UK. In the area are three battleships: the Markgraf, the Kronprinz Wilhelm and the Konig; and four light cruisers: the Coln, the Brummer, the Karlsruhe and the Dresden. These are popular wrecks among the 52 ships of the German High Seas Fleet that were scuttled near Cava at the end of World War 1. Due to their sizes, it usually takes several dives to view and appreciate just one wreck. Aside from these Dreadnoughts, there are also several wrecks of fishing boats, trawlers, cargo ships and a host of others scattered all over the harbour.

Divers will have their calendars full just navigating these 7 spots in the UK. There isn’t a lack of places to explore, and definitely not a shortfall in exciting things to see.

M2 submarine.

M2 submarine.

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DIVING GEAR TRENDS FOR 2013

If you’ve spent the summer diving and find your gear needing some kind of an upgrade, now is probably the best time to buy. Too late for summer yet too early for next year’s dive season, you can upgrade your gear with this year’s current prices now, and be ready for next year’s season with brand-new equipment. Here are some of the latest goods that manufacturers have put out for 2013.

Rec/Tec BCDs
If you like exploring, going deeper and staying longer underwater, or maybe even considering doing some technical diving, a number of recreational and technical BCDs have been put out to address those requirements. The options make the transition from heavy recreational diving to light technical diving much easier, since you would no longer need to keep two sets of BCs. These rec/tec BCDs can be rigged to accommodate 2 cylinders, have at least 40lbs. of buoyancy lift –great for keeping you afloat comfortably even with an extra-heavy load – and come with more heavy- duty D-rings for attaching various accessories like a survive-balloon, flashlight, reel, slate, etc. Moreover, they’re made with tough, durable material that can withstand very rugged use. Some of these are the Apeks Black Ice, Oceanic Probe HLC and the Tusa BCJ-8000 X-Wing.

FINS: Modified Paddles
Once you’re hooked on diving you’ll often want to go where there’s a strong current as that’s where the action is – you can see pelagics and a whole lot of fish activity. Having a stiff fin can make a difference when moving against a strong current. But this is often hard on the leg muscles and can be a huge strain on the ankles. A split fin will work better and give you the thrust you need with less effort on your legs. But sometimes a split fin gets bent and can be an inconvenience. This year, no new developments have been made on the split fin though, and they’re probably on their way out anyway. Manufacturers like Mares, Aeris and Cetatek instead are banking on the modified paddles which give the desired stiffness for the propulsion that’s needed, yet with a flexible blade design that’s more compact– giving a shorter, lighter fin that’s more portable and suited for air travel requirements. They’re more comfortable, to boot. [No pun intended. ]

DRYSUITS
We all know the feeling of finding our drysuits unable to withstand the stress of wear and tear – a puncture here, a laceration there, or any kinds of minor abrasions in the most unexpected places. Imagine a leaking drysuit causing problems with your buoyancy! Knowing this, manufacturers have come up with drysuits made of specialized heavy-duty material that can withstand all kinds of stress. Companies like Bare have incorporated a high-tenacity nylon/butyl/polyester tri-laminate in its Trilam Pro Dry model; Waterproof USA’s D7 tri-laminate body is covered with an outer shell made entirely of Cordura; while USIA is playing around with nano-composite materials, creating a composite fabric that’s supposedly 15 times stronger than steel and 40 percent tougher than aramid fibers like Kevlar and Nomex — yet still lightweight and flexible. All these promise to give you years of trouble-free diving.

LED Flashlights
Everyone knows LED lights provide the punch of a high-wattage lantern with only a minimal power requirement but with a longer lasting battery life. Manufacturers are now coming out with smaller-sized units, small enough to fit into BC pockets but strong enough to be a primary light source during night dives. Such is the Ikelite Vega . It provides the convenience of bringing a single flashlight both for day — lighting holes and crevices – as well night dives. The Under Water Kinetics Aqualight E-LED on the other hand has adjustable light beams that can double up as a fill light, a spot light or focus light, or a floodlight for underwater video or still photography.

Lastly, SIZE AND WEIGHT still do matter . In 2012 we saw innovations for smaller and lighter gear. This year, the trend continues. More and more divers travel worldwide, so the demand for lighter, more compact equipment continues to be addressed. Meanwhile, we in the dive community have never had it this good.

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Dangerous Marine Life

 Dr Oliver Sykes

Marine life in tropical waters that pose hazards to man can be divided into four general categories: Contact irritants and toxins, Injected toxins, Ingested toxins and Predators . This month I will cover contact irritants and toxins.

 

JELLYFISH, HYDROIDS and ANEMONES

All these animals possess nematocysts, a stinging apparatus that discharges on contact. Floating tentacles can retain active nematocysts, even after drying and there is a wide range of toxicity, from mild to severe.

Symptoms: Rapid onset of pain, varying from mild to severe. The rash is red, hot and swollen, usually linear. There is frequent pustule and vesicle formation and severe stings may cause muscle cramps, abdominal pain, fever, chills, nausea, vomiting, respiratory distress, and cardiovascular collapse. Fatalities are increased if there is pre-existing cardiac and respiratory disease. Box jellyfish (aka chironex, irukandji or sea wasp) may cause death in healthy individuals in less than 15 minutes.

Treatment: Use topical vinegar to neutralize undischarged nematocysts or sea water if copious volumes of vinegar are not available and then removal of remaining tentacles. Apply topical analgesics and steroids or intravenous versions if available. Treatment for shock or cardiac arrest may be required and therefore monitoring of pulse and blood pressure is required. Box jellyfish anti-venom is not universally available at all dive sites or smaller hospitals or clinics. Avoiding box jellyfish contact is of paramount importance. When diving in remote resorts in south-east Asia it is wise to ascertain the availability of anti toxin.

 

CROWN OF THORNS

This is the only known venomous starfish, its arms having large spines with venom producing integument.

Symptoms: Rapid onset of swelling, redness and pain.

Cleanse the wound and apply topical antibiotics. Give tetanus protection.

 

 

SEA URCHIN

Multiple slender spines puncture the skin and break off.

Symptoms: Immediate pain, joint pain, swelling and numbness.

Treatment: Remove spines, cleanse, topical antibiotics and tetanus protection. Soaking in hot water for 60-90 minutes is said to offer relief from the pain and swelling. Surgery is indicated for a foreign body reaction and if a joint capsule is punctured. Topical antibiotics and tetanus protection should be offered.

 

SEA CUCUMBER

Some species eject a visceral liquid.

Symptoms: Redness, itching and pain. If eyes are involved, symptoms are similar to chemical burns and blindness can occur.

Treatment: Copious irrigation of the affected area.

 

SPONGES

Three species of sponges produce a rash on contact, including the red-beard sponge, fire sponge and poison-bun sponge.

Symptoms include: redness, joint pain and swelling.
Treatment: symptomatic with soothing lotions and topical steroids.

 

CORAL:

Coral may cause abrasions that become infected but there are no toxins associated with coral. Fire coral is not actually coral. It has nematocysts and is more closely related to jellyfish. On close inspection, fire coral has tiny hair like tentacles, unlike coral.

 

 

Question 1: What is shock?

Shock is a medical term for poor organ perfusion. The casualty looks pale, has a weak pulse, low blood pressure and may be drowsy or confused. There are many causes of this, but severe decompression sickness, arterial gas embolism, severe bleeding or anaphylaxis are the likely causes in divers. The treatment requires intravenous fluid resuscitation and needs medical support urgently.

 

Question 2: What is anaphylaxis?

Anaphylaxis is a life threatening reaction which is rare but can occur due/ as a result of to medications, commonly penicillin or stings, such as bee stings. Therefore it is possible to have an anaphylactic reaction to any of the above sea animals. The symptoms come on within minutes of exposure and include wheeze, itching, redness, confusion, drowsiness and shock.

 

Question 3: How do I treat anaphylaxis?

This may be indistinguishable from a severe jelly fish sting, but the treatment is the same. Therefore remove the cause, apply oxygen and intravenous fluid resuscitation but also adrenaline. People who are known to suffer anaphylaxis often carry adrenaline around with them. Also known as epinephrine, the injection is known as an epi-pen. Steroids, such as hydrocortisone and anti-histamines, such as chlorpheniramine, are used to prevent the reaction recurring. This is a life-threatening condition and patient’s should be taken to hospital for stabilisation or observation if responding to emergency treatment

 

Question 4: How do I avoid getting stung?

Find out about the dive site beforehand. Jellyfish appear seasonally and most others are rooted to the spot or at least move slowly. The best plan is not to touch anything but a thin wet suit is very effective at preventing stings. Be careful when it comes to washing the suit afterwards, as the nematocysts will still be active!

 

Question 5: What is Irukandji syndrome?

Irukandji syndrome is similar to anaphylaxis and is produced by a small amount of venom from a box jellyfish. There are muscle cramps, severe pain, a burning sensation in the skin and face, headaches, nausea, restlessness, sweating, vomiting, an increase in heart rate and blood pressure, and psychological phenomena such as the feeling of impending doom. The syndrome is delayed for 5–120 minutes and the treatment is symptomatic, with anti-histamines and anti-hypertensive drugs used to control inflammation and high blood pressure; intravenous opiates are used to control the pain. Irukandji are usually found near the coast, attracted by the warmer water, but blooms have been seen as far as five kilometres offshore. When properly treated, a single sting is normally not fatal, but two people in Australia are believed to have died from Irukandji stings in 2002.

 

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Decompression Modelling

Dr Oliver SykesScuba diving may seem a long way from the class room and the point of theory may not be obvious, but it can be vital in making important decisions, especially about decompression models (aka tables). This article will outline some important theory and hopefully remind you that no dive profile is completely safe. Bear in mind that a model is only as good as it has been verified to be and there are too many factors involved to guarantee prevention of DCI.

A fundamental problem in the design of decompression models is that the rules that govern a single dive and ascent do not apply when bubbles already exist, as these will delay nitrogen elimination and equivalent decompression may result in decompression illness (DCI). Therefore repetitive diving, multiple ascents within a single dive and surface decompression procedures are significant risk factors for DCI.

The ideal dive profile creates the greatest possible gradient for nitrogen elimination from the tissues without causing bubbles to form. However it is far from clear whether this is possible. Some decompression models assume that stable bubble micro nuclei always exist. However, the dissolved phase decompression models are based on the assumption that bubble formation can be avoided. The bubble models make the assumption that there will be bubbles, but there is a tolerable total gas phase volume or a tolerable gas bubble size and limit the maximum gradient to take these tolerances into account. A number of empirical modifications to dissolved phase models have been made since the identification of venous bubbles by ultrasound in divers soon after surfacing.

Building Bert’s observation that dissolved nitrogen causes DCI, the first model that was verified experimentally, was developed by Haldane and is based on the following principles and concepts:

  • Nitrogen dissolves into tissues and becomes completely saturated after a certain amount of time. (Henry’s law)
  • The degree of saturation is determined by the ambient pressure, so that a given tissue above atmospheric pressure contains more nitrogen than the same tissue at 1 atmosphere.
  • The difference between the ambient pressure and a tissue’s partial pressure is called the pressure gradient.
  • On ascent, the partial pressure may be higher than the ambient pressure. But the body can tolerate some amount of pressure gradient without DCI.
  • If the pressure gradient becomes too high, the dissolved nitrogen cannot be eliminated quickly enough (by exhalation) and nitrogen bubbles form.
  • Partial pressure is the fraction of the total pressure that a single gas exerts in a mixture.
  • Tissue compartments are areas of the body that absorb gas at different rates and are categorized by how fast they uptake gas. Haldane introduced the concept of halftimes and suggested 5 tissue compartments with half times of 5, 10, 20, 40 and 75 minutes.

Tissue compartments do not correspond to anatomic tissues but one compartment will on gas and off gas at the same rate. Fast tissues on-gas and off-gas in shorter half-times than slow tissues. Areas that are well supplied by blood, such as the lungs and abdominal organs, absorb nitrogen faster than other tissues. Slower tissues include fat, fatty marrow and cartilage and saturation is reached when the pressure gradient is 0. This means after one half-time a compartment is 50% saturated, but it is not 100% saturated after two half-times, since each time the pressure gradient is halved. After two half-times a compartment is 75% saturated. After three, 87.5%. Four, 93.8 and for simplicity, we say a compartment is 100% saturated after 6 half-times.

How large can a gradient become before it’s a problem? Haldane assumed from his observations that the gradient could be a maximum of twice ambient pressure for all tissues. He assumed that an ascent from 30m (4 bar) to 10m (2 bar), or from 10m (2 bar) to the surface when saturated would not cause DCI. This was very conservative for shallow dives and not conservative for deep dives. In the 1960s Robert D. Workman of the U.S. Navy Experimental Diving Unit revised Haldane’s model with further experimental work to allow each tissue compartment to tolerate a different amount of supersaturation which varies with depth. This required a standardised ascent rate, which he took to be 18m per minute. His work allowed greater flexibility and safety to be built into tables for a range of depths and he introduced the term “M-value” to indicate the maximum amount of supersaturation each compartment could tolerate at a given depth. There are M-values for each compartment for each decompression stop. In no-decompression diving, however, we only have to be concerned with the values for the pressure at the surface. The PADI recreational dive planner grew out of Workman’s work and this is the reason why 18m per minute is the ascent rate required. The precise algorithms used in dive computers and tables are proprietary and therefore not available, but the PADI recreational dive planner now has a long safety history and is a useful benchmark.

We now have a complete model for predicting how nitrogen moves in and out of the tissues and at what point this process becomes a problem. However it remains a model and is therefore not true for every dive for every diver. So keep it conservative and stay within the limits of your computer!

 

PADI Recreational Dive Planner

rdp

 

 

 

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Clearing your Ears In Water and Other Pressurised Environments.

As a diver, clearing your ears may be second nature. However we all had to learn at some stage and damage to your ears from over forceful clearing techniques is possible. So a quick reminder of the many techniques available may be useful.

The theory:

Your ears have an external tunnel that ends with a flexible ear drum. Imagine a real drum that gets compressed if you increase the pressure around it. (See a. in Figure 1.) The frame of the drum is like your skull and the skin of the drum is like your ear drum. Thankfully your ears differ significantly from a real drum! (See Ear anatomy picture below) For example, ach ear has a tube (See b. in Figure 2), which runs from behind the ear drum to the back of your throat. To stop your ear drum being pushed inwards, you need to increase the internal pressure behind your ear drum. You can do this by actively pushing air up these tubes. Unfortunately these tubes can work like flutter valves, hence can get stuck closed if you try too hard or allow the pressure to get too great before clearing your ears. Blockage can also occur when you have a cold and diving may not be possible. So you must not dive if you can’t clear your ears.

The external water pressure on the drum (Figure 1) and internal pressure generated by you (Figure 2):

 

The Techniques:

Try any of the techniques below early and often but perhaps start with 1. and  2. Everyone does it differently and works out which method works best for them. You will know when you have been successful when your ears “pop” and your hearing and perhaps balance returns to normal. Some of these are easier, in a recompression chamber rather than when diving.

1.         Swallowing, which is known as the Toynbee manoeuvre, drinking, sucking sweets, yawning, coughing, blowing your nose are all things we are used to doing and can be useful.

2.         Pinch your nose, close your mouth and try to blow out of your ears gently. Too hard will not work and can do damage. Watch other divers if you need to know how hard to try. This is known as the valsalva manoeuvre.

3.         The Lowry technique involves using all the above.

4.         Edmonds technique involves rocking the lower jaw from left to right and up and down and forwards and backwards, so that the lower teeth project in front of the upper teeth.

5.         Edmonds 2 advice: “Block your nose, close your mouth, then suck in your cheeks then puff them out quickly.”

6.         Try an otovent. (In chamber only) Occlude one nostril and blow up the balloon with the other nostril.  [youtube]

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7.         A difficult one to describe is the Frenzel manoevre. This involves closing the mouth and nose and push the back of your tongue up to the roof of your mouth as you swallow.

8.         Some people get good at clearing their ears and can do it without seeming to do anything. This is an advanced technique not discussed here, but everyone started off by holding their nose and blowing gently out of their ears!

Blocked or painful ears are very common while the pressure is increasing and difficulty clearing your ears is nothing to be ashamed of, but pain is a sign of possible barotrauma and definitely to be avoided. Some people simply find it difficult, but the longer and deeper you leave it, the less likely you will be able to clear your ears.

Ear Anatomy

 

(Kindly reproduced from Wikipedia)

Question 1: Who was Valsalva?

He was a 17th Century Italian anatomist, who described this method for expelling pus from the middle ear through a perforated ear drum.

Question 2:

Can I cause a perforated ear drum by clearing my ears too hard?

Yes, but this thankfully only happens rarely and is probably most commonly associated with a pre-existing weakness in the ear drum. Round window rupture and disruption of the middle ear bones are also possible and barotrauma is possible from as little as 2m. Grommets are artificial tubes placed in the ear drum to allow passive ear clearing, but completely preclude diving. Perforated ear drums seem to me to be most commonly caused by jumping into water ‘ear first’

Question 3:

Can I use decongestants to help clear my ears?

Definitely avoid these and do not dive if you cannot clear your ears. If the medications wear off, the ‘reverse block’ may cause barotrauma, intense dizziness and prevent ascent due to pain.

Question 4:

How can I be sure that I am clearing my ears properly?

Practise gently in water and follow the advice from your instructor. If clearing your ears is still causing pain, avoid diving with an upper respiratory infection. Try descending feet first to reduce venous congestion and using the anchor chain to fine tune to the speed of descent. Small ascents may relieve a blockage due to the flutter valve effect. Finally, there may be a correctable cause and a visit to your doctor may be useful.

Question 5:

How can I tell the difference between inner ear DCI and inner ear barotrauma?

This is an important question as the treatments are entirely different. Inner ear DCI requires recompression, but this will worsen inner ear barotrauma. However both may present with dizziness, nystagmus, (eye flicking) nausea, vomiting and unsteadiness. Both are serious conditions and require assessment by a doctor experienced in diving medicine. Inner ear barotrauma is more likely when symptoms begin on compression, with a shallow dive profile and forceful ear clearing. There may be associated ear barotrauma signs and symptoms, such as pain, fullness, unable to clear your ears and red/damaged ear drum.

Whereas the symptoms of inner ear DCI may start after the beginning of the ascent from longer, deeper, mixed gas dives and there may be signs and symptoms of neurological DCI, such as numbness and weakness in the limbs

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Seasickness

Diving from a liveaboard off Pemba, The Green Island, is apparently amazing. However I spent 3 days in bed, feeling very green. Kitting up just once was hell. While some get benefit from being underwater and rush to get in, even the small wave motion underwater was enough to make me feel like vomiting. Everyone who has hearing and a functioning vestibular system is susceptible to motion sickness. Numbers are roughly split into 1/3 that are highly susceptible, 1/3 suffer in rough conditions and 1/3 only in extreme conditions. The books always discuss an imbalance between the 3 sensory modalities for spatial awareness. These include proprioception, which is joint position sense, vision and the vestibular system, which is the sense of movement and balance. However there is also clearly a psychological input. Once begun, seasickness is more difficult to get rid of, but it is also catching and distraction may help reduce it. Hence remedies tend to work better if in place before the motion and the thoughts get out of hand. If I was away for longer, I may have managed some diving as often sea sickness gets better after 2-3 days at sea.

 

Hyoscine, meclizine and cinnarizine (stugeron, TM) work by reducing vestibular inputs and can be sedating. Most people do not have any serious problems with these medications; however there is the possibility of side effects, drug interactions and effects on pre-existing medical conditions. Therefore these medications should be discussed with a doctor before diving. Carl Edmonds recommends the trial use of any medication that cause drowsiness to ensure no untoward reactions and to dive shallower than 18m to avoid narcosis. For this reason alcohol must also be avoided. The most common side effects of seasickness medications are:

·        Drowsiness

·        Headache

·        Dizziness

·        Agitation

·        Poor concentration

·        Fast heart rate

·        Dry mouth

·        Blurred vision

·        Difficulty passing urine

·        Stomach and gut upsets

 

Closing your eyes, or looking at the horizon, reduces the conflict between balance and visual inputs, which is worsened by going below deck. Lying down along the boat’s centre line, toward the stern and minimizing head movements, reduces proprioceptive input by incurring the least complex movements. However it’s also the best place for a smelly engine and for navigating the boat. So may incur the wrath of those still capable of useful function and compound the demoralising effects of seasickness.

 

An approach that involves different mechanisms to prevent sea sickness may work well. For example, chewing fresh ginger, good hydration and acupressure are safe with cinnarizine. The acupuncture point known as Pericardium 6, traditionally has been used to help relieve nausea. It is located on the inside of the wrist, about the length of 2 fingernails up the arm from the centre of the wrist crease. Many travel stores sell wrist bands with built in buttons designed to apply acupressure to this point, which has no significant side effects.

The following nutritional tips may help reduce symptoms, improve overall health and should be considered before taking medications:

·        Avoid spicy, greasy, or fatty meals, alcohol and hangovers

·        Don’t overeat

·        Drink plenty of water.

·        Dry crackers and carbonated drink (such as ginger ale) may help

Peppermint tea, black horehound, biofeedback, cognitive behavioural therapy, hypnosis and breathing exercises have also worked for some people. Probably through relaxation. However no treatments are known to be effective in all cases and if symptoms do not resolve soon after arriving on dry land then it’s time to phone the doctor.

 

Finally, dehydration is worth a special mention as it is common, associated with sun and alcohol, and can predispose sufferers to sea sickness, vomiting and more dehydration. The outflow from the stomach (pyloric sphincter) may also stay constricted and stop oral fluids and drugs from reaching their site of action. Hence intravenous, intramuscular or rectal routes may be required to correct the imbalance of electrolytes in the blood and the increased risk of decompression illness. Dehydration is definitely one predisposing factor to avoid.

 

Questions

1) I recently went on a day trip to complete my Advanced Open Water course with the Deep dive. On the way to the site I suffered with seasickness and one of the other divers advised that I didn’t do the deep dive as I was more likely to get bent on the dive because I was seasick. I did complete the dive in the end and had no decompression sickness symptoms afterwards but wanted to know if this was really true and whether I was taking a risk doing the dive?

 

There is no reason why seasickness would directly cause decompression sickness. However dehydration and poor concentration due to sedative medications, rushed kitting up or feeling unwell can contribute to an increased risk. So if you are a seasickness sufferer, then you should be aware of these problems and minimise the effects before diving.

 

2) I suffer occasionally from seasickness and have seen other divers use all sorts of patches and natural remedies. I don’t like to take medicines so I’m keen to know whether these more natural methods really work?

 

Patches for seasickness are usually hyoscine, which avoids the oral route and generally provides a low dose for longer than tablets. There is no guaranteed cure for seasickness, so I cannot say what will work for you, but it is worth trying a range of remedies. Examples of the more natural remedies with the best evidence are probably ginger and acupuncture. A review of the use of ginger in American Family Physician journal in 2007, described 4 trials of its use in motion sickness. 2 trials showed there was benefit and 2 did not. For acupuncture, there does not seem to be any serious reviews for its use in motion sickness. However there are many similarities with post operative nausea and vomiting, for which there is some significant trials and reviews that suggest there may be some benefit.

 

3) Do I need to take sea sickness tablets before I go on the boat or can I take them if I start to feel sick?

Sea sickness tablets are for prevention, not cure. Hence are best taken before leaving the land in order to give the medications time to work. For precise timings, read the information sheet that comes with all over the counter medications. Different drugs will take different times to work, but at least an hour will be required before significant benefit and probably more for full benefit. Once you feel sick, medications are much less likely to work, if at all. So take them early and read the information sheet.

4) Should I eat something before taking sea sickness tablets?

Seasickness tablets do not have to be taken with food but can be. If you are likely to feel sea sick, then eating small amounts before travelling may be a good idea and good hydration prior to travelling is a must.

5) Can I take sea sickness tablets if I’m pregnant?

Hyoscine, meclizine and cinnarizine (stugeron TM) are not advisable in pregnancy. As with most medications, there is little research into the effects on pregnancy. However, if you have taken seasickness tablets while pregnant, then speak to your doctor. On balance, long term effects are very unlikely. A few grams of ginger and wrist bands are safe.

 

References:

Am Fam Physician. 2007 Jun 1; vol. 75(11) pp. 1689-91

Ginger: an overview.

White B

 

Br J Anaesth. 2009 May; vol. 102(5) pp. 620-5

P6 acustimulation effectively decreases postoperative nausea and vomiting in high-risk patients.

Frey UH, Scharmann P, Löhlein C, Peters J

 

J Neurosurg Anesthesiol. 2010 Apr; vol. 22(2) pp. 128-31

Electroacupoint stimulation for postoperative nausea and vomiting in patients undergoing supratentorial craniotomy.

Wang XQ, Yu JL, Du ZY, Xu R, Jiang CC, Gao X

 

Anaesthesiol Scand. 2009 Nov; vol. 53(10) pp. 1341-7

Effect of P6 acustimulation on post-operative nausea and vomiting in

patients undergoing a laparoscopic cholecystectomy.

Frey UH, Funk M, Löhlein C, Peters J

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