DAN, Can You Tell Me…

The DAN Medical Services team addresses a wide range of questions from members and non-members every day relating to diving health and safety. Over the past weeks, these questions have included intracranial hypertension, Bell’s palsy, the impact of taking supplements, pinched nerves and so much more! Here is a sample.

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DAN, can you tell me ….

Hi DAN, I have had a pinched nerve for a few days that is bothering my right thigh. I gave it a couple of days, but there is no real improvement. Last night we had some friends over and one mentioned it might be because of my wetsuit. Normally I dive in tropical water, but currently in cooler water, so I purchased a waterproof 5mm long wetsuit about 2 weeks ago. Do you think my pinched nerve has something to do with the wetsuit because it’s tight — a good fit rather than too small?

DAN Answer: The pain in your thigh in unlikely to be related to a snug-fitting wetsuit. This type of pain you describe, a pinched nerve feeling originates from deeper within the tissue. The pressure from a too-tight wetsuit is superficial. It is more likely related to lifting and maneuvering of heavy scuba gear or an injury.

 

Hi DAN, I have Bell’s palsy, partial paralysis on the right side of my face probably caused by an ear or throat infection. The infection is gone but the paralysis is still there. I am a commercial diver and was wondering if can I dive with this condition or if diving will make it worse?

DAN Answer: Bell’s palsy, as you are aware, causes unilateral facial weakness and pain. Although often transient, it can also be permanent. There are some risks to consider. Since pain and paralysis can also be symptoms of DCS, it can make the diagnosis and treatment of DCS more difficult. If your ability to blink on that side is decreased, you can develop corneal ulceration, which can be worsened by exposure to seawater and the extreme environment encountered in diving (wind, salty air, etc.). A common treatment for this condition is a drug called acyclovir (antiviral). It’s important to consider that this drug can lower the seizure threshold. With facial paralysis, there can be difficulty with firmly retaining a regulator in the mouth. This would be less of a risk for you with the helmet, but perhaps there are occasions when you use a regulator with a mouthpiece. It would be best to wait until you have completed all treatment, have had a recovery period, and have been cleared to dive by a doctor with dive-medicine experience.

 

Hi DAN, I’ve recently started a strength training program, and I am taking supplements to optimise my regimen. Are there any implications for diving regarding these supplements: Beetroot supplement 500 mg, Creatine 5gm, Beta alanine 4gm, Methylsulfonylmethane MSM 3gm, whey protein or fish oil?

DAN Answer: Supplements should not be an issue with diving. With that said, there are no research studies on the effects of supplements in the hyperbaric environment. Given that you are overall healthy and engage in regular exercise, the larger question is the potential side effects of the supplements.

The general recommendation is to be on any new medication or supplement for at least thirty (30) days to rule out any potential negative side effects or adverse reactions. Do discuss your desire to dive while taking these supplements with your health care provider.

Do you have a diving-related medical question? If so, send your question to DAN’s Medical Services team: https://www.diversalertnetwork.org/?a=medicemail.

Timeline of an Emergency Call

By Matias Nochetto, M.D.

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The DAN® Emergency Hotline receives an average of 5,200 calls per year. DAN medics and physicians work 24 hours a day, 365 days a year to provide emergency medical assistance to divers in need. No matter where they are or what they are doing, these dedicated medical professionals answer the call. The following is a timeline of a recent case that exemplifies how things unfold when a diver calls DAN in an emergency.

2:28 a.m. ET: Dutch Caribbean — Dive Resort
Mr. Smith, who is 56 years old, cannot sleep. His urge to urinate is painful, and upon sitting up in bed he realizes his legs are numb. He is unsure if he can even stand up. Something is wrong. He wonders, “Am I bent? How is this possible? I did everything right.” Mrs. Smith advises her husband to call DAN.

The DAN medical department has a tested and effective protocol that governs every call to the emergency hotline.

2:35 a.m. ET: Durham, North Carolina — Home of a DAN Medic
A DAN medic’s mobile phone rings. The operator passes along Mr. Smith’s name, phone number and location. Mr. Smith reports eight dives over the past two days and describes his symptoms. The DAN medic recognizes that this may be serious decompression sickness (DCS), which requires a timely response. The medic recommends that Mr. Smith seek an evaluation at the closest medical facility and call DAN once he is there so a medic can speak to the examining physician. Mr. Smith agrees to ask his dive buddy to help him get to the local clinic.

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2:45 a.m. ET
The DAN medic calls the hyperbaric chamber on the island to alert them of a possible case of DCS. This case will likely push the limits of the facility’s capabilities. The hyperbaric doctor on staff agrees this could be a spinal cord hit and alerts the staff.

3:05 a.m. ET: Dutch Caribbean — Medical Clinic
Mr. Smith and the evaluating physician call DAN for a consultation. The physician reports that his patient has bilateral lower-extremity weakness, decreased sensation and urinary retention. He agrees with DAN’s initial assessment that Mr. Smith likely has DCS. The DAN medic informs the physician that he has already alerted the local hyperbaric facility, and the physician arranges for an ambulance to transport the patient to the chamber.

3:45 a.m. ET: Dutch Caribbean — Recompression Chamber Facility
Mr. Smith requires assistance to get into the chamber because he cannot walk and has a urinary catheter in place. The hyperbaric physician had agreed to treat the diver, but upon examination he realizes the case requires a higher level of care than his chamber can provide. He administers an initial hyperbaric chamber treatment while the DAN medic begins arranging an evacuation to a better-suited facility.

4:05 a.m. ET: Durham, North Carolina — Home of a DAN Medic
The DAN medic contacts DAN’s medical director to brief him on the case; he concurs with the plan. The medic then contacts DAN TravelAssist, which arranges emergency medical evacuations, and briefs them on the case. It is determined that the most appropriate chamber facility for Mr. Smith is in Miami, Florida.

4:30 a.m. ET: Stevens Point, Wisconsin — DAN TravelAssist Headquarters
A DAN TravelAssist representative contacts Mercy Hospital in Miami, which agrees to receive the patient. They alert the treating physician at the chamber in the Dutch Caribbean that a medical evacuation is being arranged.

5:00 a.m. ET: Dutch Caribbean — Recompression Chamber Facility
Mr. Smith reports some improvement during the treatment. He is starting to feel his legs again but is still too weak to resume normal walking. The treating physician explains this is normal and is a good sign. This first treatment will be completed at 9 a.m. ET.

8:30 a.m. ET: Durham, North Carolina — DAN Headquarters
The medic is now at DAN headquarters. DAN TravelAssist confirms that an air ambulance has been contracted to conduct the evacuation, during which the aircraft will maintain sea-level pressure. They will be ready to take off from Ft. Lauderdale, Florida, at 9 a.m. ET and should arrive in the Dutch Caribbean at 12 noon ET.

10:00 a.m. ET: Dutch Caribbean — Recompression Chamber Facility
Mr. Smith has completed his first treatment, and the treating physician reports the patient has recovered some motor function and some sensation. Mr. Smith and his wife will be ready for the medical evacuation by noon.

11:30 a.m. ET: Dutch Caribbean — Airport
The treating physician, a nurse, a paramedic, Mr. Smith and his wife arrive at the airport, and the air ambulance jet lands soon afterward. After the jet refuels and personnel complete documentation, the patient, his wife, a flight nurse, paramedic, treating physician and the pilots board the plane, which takes off less than an hour after it landed.

3:35 p.m. ET
The air ambulance lands in Miami, where a ground ambulance is waiting on the tarmac. The travelers promptly clear immigration and customs under special emergency procedures.

4:15 p.m. ET
The ground ambulance travels 9 miles to Mercy Hospital in less than 20 minutes.

4:45 p.m. ET: Miami, Florida — Mercy Hospital
Mr. Smith is admitted to the hospital, and a hyperbaric medicine specialist receives him at the emergency department. The doctor and nurses perform examinations, draw blood, confirm the patient’s medical history, complete the necessary paperwork and contact DAN to confirm Mr. Smith’s insurance.

5:30 p.m. ET
The hyperbaric doctor initiates a second chamber treatment, a U.S. Navy Treatment Table 6.

10:30 p.m. ET
Following the treatment, Mr. Smith is tired but happy to be regaining strength. The hyperbaric specialist explains that he is doing well but that these cases are serious and need to be treated aggressively.

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Over the next two days Mr. Smith receives four U.S. Navy Treatment Table 5 hyperbaric treatments and has physical therapy between treatments. Medical staff remove the urinary catheter after the fourth Treatment Table 5. Mr. Smith still has residual weakness in both legs but can walk with less assistance.

In the next few days Mr. Smith has four U.S. Navy Treatment Table 9 regimens, and his residual weakness remains unchanged after each of the last three treatments. The treating physician realizes that Mr. Smith has reached a clinical plateau and that further hyperbaric therapy is of no value. Time and continued physical therapy are now the appropriate treatment.

After three months Mr. Smith recovers full strength in his left leg and has only a slight decrement in his right. After two additional months, the strength in his right leg also returns to normal.

© Alert Diver — Q1 Winter 2019

10 Things You Might Not Know About Decompression Illness (DCI)

By John Lippmann, Chairman and CEO of the Australasian Diving Safety Foundation (ADSF)

Remember that the term decompression illness (DCI) includes both decompression sickness (DCS) resulting from dissolved nitrogen (or another inert gas) being eliminated from a diver’s body tissues; and arterial gas embolism (AGE) which is caused by air entering the arterial blood because of a burst lung.

  1. DCI was first reported in 1667 in a snake – not a diver!
    Boyle (from Boyle’s Law) placed a viper in a vacuum and noticed a bubble forming in its eye.
  2. It’s possible to get a burst lung and subsequent DCI (arterial gas embolism) in as little as 1.2 m of water. If a diver fills his lungs with compressed air and surfaces without exhaling, there is enough pressure change in the first 1.2 m from the surface to over-expand the lungs sufficiently to cause a tear.
  3. Divers have suffered from DCS after ascending from depths as shallow as about 6-7 m. It used to be thought that one had to dive deeper than 10m before DCS was a risk, but this is now known to be untrue.
  4. Most divers (possibly around 90%) who get DCI have been diving within the limits of their dive computer or tables. However, the risk of DCI increases when a diver exceeds these limits. This indicates that the limits cannot accurately account for individual differences between divers and the various factors that can influence nitrogen uptake and elimination during a dive.  All divers should add conservatism to their decompression calculations, especially is the diving is purely recreational and dive time doesn’t need to be maximised.
  5. Bubbles form within divers’ bodies during or after many dives, especially repetitive and deeper dives. These bubbles can be detected using ultrasound and usually do not cause symptoms. Some divers “bubble” more than others. A slow ascent rate and doing a safety stop reduces the amount of bubbling and therefore the risk of DCI.
  6. Some divers are more susceptible to DCI than others. Divers with a patent foramen ovale (PFO),which is a common heart defect that can enable blood to flow across the heart, have a significantly higher risk of DCI (sometimes quoted as 2 to 8 times, depending on the size of the hole). Other factors such as being overweight, increasing age, lack of fitness and dehydration may also play a role although there is little hard evidence to support some of these beliefs.
  7. A mottled reddish/purple/bluish rash is an increasingly common sign of DCI and is often associated with the presence of a PFO. Skin-related DCI used to be relatively uncommon in recreational divers. However, over more recent years it has become far more common. Part of the reason for this could be the result of the more frequent and longer dives and shorter surface intervals enabled by dive computers.
  8. Oxygen first aid is often delayed, given using unsuitable equipment and for too short a period. Good oxygen first aid is very important in the management of DCI and this is often poorly done. To maximise the benefit, near-100% oxygen should be given from the time symptoms first occur, and continued until a diving doctor advises that it be stopped.
  9. Many dive operators in remote areas do not have access to a sufficient supply of oxygen to last until an injured diver receives appropriate medical care. It can sometimes take over 24 hours for an evacuation team to reach some remote locations so a large supply of oxygen is required. Check this out before you go on a dive trip to an area without good access to suitable medical care.
  10. About 120-150 divers are treated for DCI in Australia each year.

 

 

Whose Fault is it Really?

The Incident: A relatively inexperienced diver, armed with only an Open Water Certification that equipped him with a basic knowledge of skills and equipment (for diving to a recommended depth of 18m), decided to book himself on a wreck dive to 30m at a site known to have a strong current.

When making the booking, the diver expressed his lack of experience and apprehension about undertaking the dive, but the shop staff still booked him in for the dive.

The dive crew provided a dive brief, including depths and currents, and advice that the visibility may be poor. The diver was not assigned a buddy, rather told to stay with the group. This concerned him, but he followed along with the others. Diving without a buddy was considered normal as the divemaster was usually able to keep small groups together.

As advised, visibility on the bottom was poor, the group ended up separated, and the diver was left alone. Unable to locate the other divers, he panicked and made a rapid ascent to the surface where he lost consciousness and had to be retrieved from the water by the boat’s skipper.

As a result of the rapid ascent, he suffered a gas embolism and was lucky to survive.

Emergency

Who is responsible for this incident? 

Is it the dive crew who failed to provide buddy teams and lost contact with the diver? Is it the dive shop who allowed this inexperienced diver to book onto a dive he wasn’t qualified to do? Or is it the diver who knew better than anyone that he was not prepared to undertake this dive?

While everyone plays a part in this scenario, the diver needs to take substantial responsibility as he is ultimately responsible for himself. Firstly, he signed up for a dive, despite being apprehensive, as he knew it exceeded his experience and training. He then went along with the plan to dive without an assigned buddy, despite not being comfortable with this, and knowing from his training that it wasn’t right. At any time, the diver could have, and should have, aborted but he didn’t. However, in his defence, it is difficult for an inexperienced diver to judge what the demands of the dive may be.

Of course, the shop staff and the dive team also contributed significantly: The shop staff should have questioned the diver further and knowing the conditions didn’t match the diver’s training and experience, they should have signed him up to a more suitable dive. Further, the dive crew should have re-assessed his suitability for the dive. They should also have assigned buddy pairs, particularly in poor visibility.

Unfortunately, this scenario is not an uncommon story. I have previously written about knowing when to call a dive, yet divers continue to push their limits.

Bottom line: If you are not fully prepared for the dive, both mentally and physically, or you are not qualified or experienced to do the dive, abort. There is no shame in calling a dive. It is certainly not worth injuring yourself, or worse, to complete a dive.

 

Scott Jamieson

DAN World Regional Manager

Do You Know Your Oxygen-Delivery Masks?

By Patty Seery

When a dive accident occurs, prompt action can greatly improve the outcome — if the rescuers respond appropriately. Oxygen administration is a critical element of first aid for dive accidents, but there are several ways to do it. Oxygen units include various delivery systems, including tight-sealing oronasal masks for use with a demand valve or for resuscitation, non-rebreather masks and, possibly, a bag- valve-mask resuscitator, so divers should know the appropriate mask to use in each situation.

Oronasal (resuscitation) Masks
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The demand valve with tight-sealing oronasal mask (often referred to as a pocket-style or resuscitation mask) is the most versatile and effective delivery device in most circumstances. When used properly, it can deliver a high percentage of oxygen to breathing, responsive, injured divers. In addition, they can be used to provide oxygen-supplemented ventilations to unresponsive injured divers who are not breathing on their own. This mask can also be used with manually triggered ventilators, which are used to deliver 100% oxygen to divers who are not breathing on their own.

The resuscitation masks have air-cushioned edges that adapt to a variety of face shapes and elastic straps to facilitate a good seal. They also feature oxygen inlets for administering supplemental oxygen when using the mask to provide ventilations to a nonbreathing diver. These masks are reusable, provided they are cleaned, and their one-way valves are replaced.

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When using a resuscitation mask, rescuers should ensure a good seal by using the elastic strap and proper hand positioning. When the injured diver is breathing and responsive, the diver can help with maintaining the mask seal. Rescuers using the mask for CPR or to support inadequate breathing should use two hands to create an effective seal around the entire perimeter of the mask, while, at the same time, tilting the head back and supporting the jaw.

Non-rebreather Masks
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Non-rebreather masks are a first-aid option for distressed injured divers who are unable to activate demand valves effectively. These single-use, disposable masks feature an attached reservoir bag that captures the flow of oxygen to the mask to ensure a ready supply. These masks do not conform to faces as effectively as oronasal masks, however, so some oxygen escapes, and some ambient air enters the mask via perimeter gaps. As a result, injured divers using non-rebreather masks receive a lower percentage of oxygen compared with resuscitation masks.

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When using a non-rebreather mask, it is important to tighten the mask’s elastic strap and adjust the nosepiece, but there is not much more rescuers can do to improve the mask’s efficiency.

Non-rebreather masks use a continuous flow of oxygen, which exhausts the oxygen supply more quickly than with other means of oxygen delivery.

Bag Valve Masks
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Bag valve masks (BVMs), which are used only on divers who are unable to breathe adequately on their own, are devices that enable rescuers to provide ventilations — with or without supplemental oxygen. They may be disposable or re-usable. Using a BVM is less fatiguing for rescuers than delivering rescue breaths through oronasal masks. These masks come with flexible tubing that connects to continuous-flow outlets of oxygen units. They also have reservoir bags that collect oxygen and are capable of providing high concentrations to injured divers.

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Oxygen delivery using a BVM requires two rescuers: One rescuer maintains the mask seal and the injured diver’s open airway, while the other squeezes the bulb to deliver ventilations. The other primary disadvantage of BVMs is that, like non-rebreather masks, they deplete oxygen supplies relatively quickly.

Regardless of the mask used, a rescuer’s technique affects the concentration of oxygen delivered to the injured diver. To optimise oxygen delivery, be sure to seal the mask to avoid leaks, and continually monitor both the seal and the injured diver. Do not depend on the injured diver to keep the mask secure; their comfort, changes in their level of consciousness and fatigue can compromise mask seal.

Delivery Device Flow Rate: litres per minute (lpm) Inspired Percentage*
Resuscitation (Oronasal) Mask 10 – 15 lpm ≤ 0.45-0.65 (45%-55%)*
Non-rebreather mask 10 – 15 lpm ≤ 0.8 (80%)**
Bag valve mask 15 lpm ≤ 0.9-0.95 (90%-95%)
Demand Valve N/A ≤ 0.9-0.95 (90%-95%)

*May vary with respiratory rate
**Less variation with changes in respiratory rate
+ Delivery percentages vary with equipment and techniques used. This table summarises various oxygen-delivery systems and potential values of inspired oxygen with their use.

Part of being a responsible diver is understanding that different oxygen masks exist, serve a different function, and offer a different level of effectiveness in terms of oxygen delivery. Should you ever require oxygen you will be able to ask that a flowrate be set to the most effective level. Knowing, having, and using the correct mask and correct flowrate is very important in the first aid management of DCI.

Deeper Diving Incidents

The DAN Emergency Hotline recently received two calls for help from technical divers. While all diving carries some degree of risk, tech diving often involves diving deeper and managing higher-risk scenarios. Technical divers in real or simulated overhead situations rely heavily on complicated equipment and extensive training, and it can be harder for them to rectify issues in the water.

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The diver in this case was scheduled to perform a solo dive with a run time of four hours. The plan was for the diver to send up his SMB at the dive’s three-hour mark to indicate that he was okay and had arrived at his first deco stop. When the SMB was not launched on time a search commenced. Several local resources, including search-and-rescue and Navy personnel were involved in the search. Sadly, the diver was not located, and after seven days the search was called off.

Ireland

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A hyperbaric facility reported an incident with an Irish diver while they were treating him. The diver, a DAN Member, was doing a week of deep technical dives exploring the wrecks off the north coast of Ireland. The diver had been at a depth of 74m when he experienced an equipment failure that resulted in a failure to deliver gas, which precipitated a rapid unplanned ascent. The diver experienced an immediate onset of DCS symptoms, including full body pain, and was airlifted to the nearest chamber via helicopter.

Following a good response to recompression treatment the diver wanted to fly home just 72 hours after treatment. The treating physician wanted him to extend this preflight surface interval given the severity of the symptoms he experienced, so the diver called DAN to discuss the case further. The DAN representative advised the diver that 72 hours is considered the minimum time period following treatment and it would be wise to wait another few days to fly home.

This diver booked a flight after the call without extending his preflight interval and fortunately returned home without his symptoms worsening. Per DAN advice he sought a follow-up evaluation with a physician back home in Australia for review of symptoms and further treatment.

Review DAN’s Fast Fact about the risks of flying after diving.

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DAN COMMENT

It’s important for divers of all levels to assess the degree of risk they face on each dive and determine whether they have the experience, training and equipment to comfortably perform the dive with minimal risk. This is particularly important in technical diving, where equipment failures must frequently be dealt with in the water and returning to the surface for help is not an option. Remember that there is no shame in sitting a dive out if it gives you any hesitation at all — the dive will always be there, and you can come back to give it another shot as soon when you are ready. With deeper and more complex dives, your comfort in the water will affect the safety of your entire team in the water, and your buddy will rely on you to honestly and accurately assess your ability to perform during the dive for your buddy’s safety as well as your own.

Regarding post-treatment flight recommendations, there is some debate about how long divers should wait before flying home after a significant recompression treatment. Because of the statistically insignificant numbers of divers available to study there is little scientific data upon which to base a definitive recommendation. The consensus among many dive-medicine-trained physicians is that a 72-hour wait period before flying is adequate in most situations, but it is still up to the treating physician to recommend what they believe to be most prudent for each patient. Significant DCS symptoms and long or repeated recompression treatments may indicate a need for a longer no-fly period, and it is always in the patient’s best interest to follow the treating physician’s recommendations. For more information on post-treatment no-fly periods, or to have a DAN physician consult with your treating physician, visit DAN.org/Contact.

Lessons in Gas Management

A diver, realising it has gotten harder to breathe, checks her air gauge. The display shows “0.” She panics and bolts for the surface.

You may not realise it, but ineffective breathing-gas management while diving is a recurrent problem. During peak season, DAN Medicine speaks with at least two divers every week who have concerns about having made a “rapid ascent” after finding themselves low on or out of breathing gas.

In this post we review three separate incidents involving breathing gas management and discuss why running out of air occurs more frequently than you may realise.

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Diver No. 1

A 37-year-old male diver with approximately 30 lifetime dives was doing his first night dive. It was also his first cold-water and first drysuit dive. He was healthy and not taking any medications. The diver descended to 30m, breathing air and using a dive computer. He had some difficulty beginning his descent due to his failure to adjust his weight to compensate for the increased buoyancy of the drysuit. After some time at the bottom he checked his air gauges and found he had less than 20 bar remaining. He signalled to his buddy he was terminating the dive and began to ascend. Because of inexperience, the ascent was not fully controlled, and the diver reported feeling “close to panic.”

Planning sufficient gas reserves to account for unexpected problems helps ensure divers make it back to the surface with gas to spare. Deeper or more challenging dives require greater reserves.

After surfacing, he waited for his buddy, and they swam back to shore. Fortunately, the diver did not experience any symptoms.

Diver No. 2

A 72-year-old male with hundreds of lifetime dives, including several technical dives, was participating in a series of wreck dives with three buddies. He was not known to have any medical conditions or to be taking any medications; he was reportedly in good general health. The first dive was an uneventful wreck dive to 34m for 28 minutes. The second dive was planned as a shallower dive, and the diver’s three buddies descended ahead of him. His body was later found floating on the surface 800m from the initial descent area. One witness reported that the snorkel was in the diver’s mouth when his body was recovered. His weight belt was not in place, and his tank was empty. Circumstances indicated he made a buoyant emergency ascent. His computer recorded a nine-minute dive to 9m. Apparently, each of the four divers used a single tank (per diver) to make both dives. The autopsy findings were consistent with drowning.

Diver No. 3

The diver was a 24-year-old female with approximately 100 lifetime dives. She reported a history of regular exercise and good general health, and she denied taking any medications. Her dives were warm-water ocean dives hunting lobster. The first dive was along a reef structure at a maximum depth of 22m, and some time passed before she located her prey. Trying to capture one lobster required a short chase and raised her respiratory rate. The diver checked her gauge only when she became aware of increased breathing resistance. It displayed “0.” She admitted to panicking and swimming rapidly toward the surface. She failed to jettison her weights or inflate her BCD, which she would have to have done orally because of her empty cylinder. Other divers saw her struggling to keep her head above water and remove the regulator from her mouth. They helped her return to the dive boat, where she had difficulty breathing and coughed up pink, frothy sputum. Crew members provided oxygen and returned to shore, where emergency medical service personnel were waiting. She was transported to the hospital and diagnosed with seawater aspiration. She developed pneumonia and was hospitalised for two weeks, after which she was discharged with no residual problems.

Stuart Cove's Dive Bahamas, New Providence Island, Bahamas.

Discussion

The reasons behind bad gas management are numerous and varied. The first diver in this case study introduced new environmental factors (a night dive in cold water) and new equipment (a drysuit), and he failed to make adjustments for any of it. As a result, poor buoyancy control, unfamiliar equipment and stressful dive conditions increased his air consumption and reduced the volume in his tank faster than usual. He had an adequate gas supply to make a safe ascent, but his inexperience left him unable to control his ascent rate.

The second diver started his second dive with a practically empty tank, which was either an oversight or a bad decision. He followed his training in making a buoyant emergency ascent, though he clearly ignored it in failing to ensure he had an adequate gas supply at the start of the dive.

The third diver was involved in vigorous and distracting activities. These increased her respirations and sped up the depletion of her gas supply, which she did not monitor carefully. She failed to follow her training by not releasing her weights to increase her buoyancy at the surface.

Exertion, stress, anxiety and environmental factors can all increase respiratory rate. Wearing too much or too little weight can cause divers to work harder, increasing gas consumption. Regardless of factors, however, divers should monitor gas supply frequently and consistently.

Conclusion

When planning a dive, incorporate a breathing-gas limit in the plan. For example, a buddy pair might agree to head back to the exit point when the first diver has used a third or half of his breathing gas (not counting the reserve to be left in the cylinder at the end of the dive). Maintaining buddy contact can make a life or death difference. Safe diving practices and sharpening skills such as buoyancy control reduce the risk of a breathing-gas emergency but do not eliminate it completely.

Proper responses to breathing-gas emergencies rely on experience and skill recall. Establishing and practicing responses are essential; confidence in being able to use an alternate air source provided by a buddy can lead to a much better outcome. Through planning and practice, effective breathing-gas management can become second nature and reduce the likelihood of a diving emergency.

By Marty McCafferty, EMT-P, DMT