DEPTH Blog

If a gas not containing any oxygen is breathed, consciousness is rapidly lost with no increase whatever in the rate of breathing. Haldane had witnessed the effects first-hand down in the coal mines of South Wales: “Thus it is a common experience with miners going into an atmosphere of nearly pure fire damp [methane, CH4], or climbing up so that their heads are in the gas; they drop suddenly as if they were shot.” The response to rapidly halving the oxygen level breathed is actually an increase in pulse rate and blood flow, not an increase in the rate of breathing. The increase in pulse rate had first been recorded by Glaisher and Coxwell in their epic ascent from Wolverhampton gas works; it had risen from 70 on the ground to 100 at altitude.

Drysuits provide the greatest form of passive thermal protection for the diver. They are designed as one piece suits with a waterproof zipper for entering and exiting and have attached boots and seals at the diver’s wrists and neck to provide a dry internal environment. The suits are normally designed so a wide variety of insulating undergarments may be worn beneath them. These undergarments trap a layer of air providing the primary protection against cold. Too much air trapped in the drysuit can create buoyancy problems because the air forms a “bubble” that will move inside the suit, but some air is needed in order prevent the suit material from compressing and catching skin in the folds and causing a suit squeeze. A suit “squeeze” can be uncomfortable but is avoidable by adding a small amount of air to remove any suit wrinkles.

The term “sinus” can mean any channel, hollow space, or cavity in a bone, or a dilated area in a blood vessel or soft tissue; most often sinus refers to the four, paired, mucus-lined air cavities in the facial bones of the head. The same kind of membrane lines the sinuses and nose, so nasal infections spread easily to the sinuses. In sinusitis, mucous membranes inflame and swell, closing sinus openings and preventing infected material from draining. If nasal inflammation, congestion, deformities, or masses block sinus openings, the sinus lining swells and inflames, absorbing pre-existing gas that forms negative pressure. When blockage occurs during descent, the relative vacuum in the sinus increases the risk of damage. Hemorrhage into the sinus and then into the divers mask may occur.

Basic underwater navigation by means of simple observation or use of a compass and depth gauge remains a fundamental and essential skill for all divers. For most short excursions, these are the only instruments needed. Even when using advanced navigation instruments, basic navigation skills provide an important backup.

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An experienced open-circuit diver was trying the “latest, greatest” rebreather during an introductory dive experience. After a few minutes of cursory instruction, she entered the water and began her grand adventure. Descending gradually to 15 fsw (5 msw), she kept close watch on her gauges.

Cave diving is a specialized form of diving that can be performed in both inland freshwater caves and oceanic “blue holes.” To scientists, caves offer new laboratories for research. In cave diving, the emphasis should be placed on developing the proper psychological attitude, training in specialized techniques and life-support systems, dive planning, and the selection of an appropriately trained buddy diver.

We will always face the problem in a given patient, and with any condi­tion, of not knowing how much benefit is possible from using more oxygen in treatment. This dilemma is far from being unique to the use of oxygen, it also applies to the use of drugs. The answer is simple—it needs professional medical assessment of the response of an individual in order to titrate treat­ment and monitor the actions of interventions and this is actually the practice of medicine. The reliance on one-size-fits-all protocols for hyperbaric oxygen treatment, and even more so for drug treatment, dictated by reimbursement policy, is unscientific, absurd, and must be resisted. The importance of indi­vidualising treatment is now being recognised by the pharmaceutical industry, which is now advocating the use of gene profiling, for example, in drugs used against breast cancer. It must also be remembered that if the monitoring of side effects in trials is not undertaken responsibly, adverse media publicity can result in the failure of drug; with investment in the billions, drug develop­ment has become a very risky business. The contrast with hyperbaric oxygen treatment, which simply extends the envelope of normal healing, could not be greater, and we all use oxygen in the same way. Properly used, the risk associ­ated with hyperbaric oxygenation is not from the oxygen itself, it is from the minor changes in pressure on the ears. In fact, the risk to the patient is from not using it.

Death from bone marrow and fat embolism is rare and, obviously, af­ter minor trauma exceedingly rare, although there will undoubtedly be many cases that have not been published and many others that will have gone un­recognised. Deep venous thrombosis and pulmonary embolism after aircraft flights were thought to be rare but, with publicity, emergency departments close to major airports reported that they have seen such patients regularly over many years. This is known as the finder effect. Nevertheless, the odds against death from minor trauma are, of course, extremely large. The exami­nation of many millions, or even billions, of cases of minor injury would in all likelihood not find a single death from such a cause and so such a mecha­nism may be readily discounted by those who argue from epidemiological and statistical data . . . In fact, it is the only argument open to those who discount a link between trauma and the development of multiple areas of sclerosis.

Convulsions in the Water: Dive Accident Management and Emergency Procedures

A convulsion in itself rarely causes injury, but the secondary consequences for a scuba diver can be disastrous. First, the intense muscle contraction of the neck and jaw can cause the diver to spit out the mouthpiece, which is difficult to reinsert. Consequently, the diver is likely to drown unless rescued quickly. There is a risk of pulmonary barotrauma leading to AGE (arterial gas embolism) if a diver ascends too rapidly or out of control; however, the threat of drowning outweighs that of AGE.

Stroke symptoms

The symptoms typical of a stroke are not always associated with block­age of a major blood vessel in the brain; symptoms indistinguishable from stroke may affect patients labelled as having multiple sclerosis—only the age of the patient and a history of other symptoms allow it to be distinguished from a stroke. A condition that must be considered in patients with a stroke has already been referred to in relation to multiple sclerosis; it is the dis­ease associated with thrombosis known as the anti-phospholipid syndrome, discovered by Dr. Graham Hughes in the 1980s, often referred to as the Hughes syndrome.¹⁸ When it affects the nervous system it mimics multiple sclerosis and so provides yet more confirmation that the disease underlying the formation of the areas of sclerosis starts in the blood vessels. A hundred years before the anti-phospholipid syndrome was discovered, Harald Rib­bert, a German pathologist, had suggested that multiple sclerosis was associ­ated with thrombosis, after he had seen that the earliest damage surrounded veins. Hughes syndrome is one cause of venous thrombosis, although it may also cause arterial thrombosis and embolism. Optic neuritis and paraplegia from damage to the spinal cord may also occur in Hughes syndrome, just as they do in multiple sclerosis, almost certainly from tiny emboli break­ing off from an area of thrombosis. It is most important for the diagno­sis of Hughes syndrome to be made, because the condition can be treated with aspirin and other drugs to prevent further attacks. However, it is also clear from the localised brain swelling seen on MRI in patients with the anti-phospholipid syndrome, that the attacks are likely to respond to hyperbaric oxygen treatment.

"When we have a stroke, our brain is starved of oxygen, causing the catastrophic death of nerve cells and leaving us paralysed and unable to speak." - Colin Blakemore, neuroscientist quoted in the Daily Telegraph, March 2010.

The danger from sharks to humans is a combination of size, aggression, and dentition. Any shark over 3 ft (0.9 m) long should be regarded cautiously, and if over 8 ft (2.4 m) long, should be avoided even if this requires that the diver leave the water. For example, grey reef sharks (Carcharhinus amblyrhynchos) that range between 3–7 ft (0.9–2.1 m) in length are numerous in shallow tropical waters, and diving operations often cannot be performed unless the presence of sharks in the area is tolerated. When such sharks are in the vicinity, divers should avoid making sudden or erratic movements. Common sense dictates that no injured or distressed animals should be in the water because these are known to precipitate shark attacks. When operations are conducted in the presence of sharks, each group of divers should include one diver who keeps the sharks in view and is alert for changes in their behavior. The chances of trouble are minimal as long as the sharks swim slowly and move naturally. The situation may become dangerous, however, if the sharks assume agitated postures, such as pointing their pectoral fins downward, arching their backs, or elevating their heads. If feeding in a group, sharks may become highly agitated and bite at anything and everything, including each other. Most victims are attacked violently and without warning by single sharks. The first contact may be a “bumping” or an attempt by the shark to wound the victim prior to the definitive strike. Severe skin abrasions and lacerations can be caused in this manner due to the abrasiveness of shark skin, which is covered with denticles, small tooth-like projections which are modified placoid scales.

We would like to share a compelling testimonial that we just received from Dr. Calderone, CEO of Olympia Medical Center in Los Angeles, CA, regarding his hospital's use of the just released Hyperbaric Patient Safety Instructions. Since implementing the use of the brochures at their hyperbaric clinic, the Olympia Medical Center has had a consistent patient satisfaction score in the 90th percentile. Read Dr. Calderone's testimonial below.

Divers have used air as a breathing gas since the beginning of diving. Its principal advantages are that it is readily available and inexpensive to compress into cylinders or use directly from compressors with surface-supplied diving equipment. Air is not the “ideal” breathing mixture for diving because of the decompression liability it imposes. Since decompression obligation is dependent on exposure to inspired PN2 (nitrogen partial pressure), this obligation can be reduced by replacing a portion of the nitrogen content of the diver’s breathing gas with oxygen, which is metabolized by the body. This is the fundamental benefit of enriched air nitrox (Nx) diving (Wells 1989). Historically, the two most commonly used nitrox mixtures in NOAA have been 32% and 36% oxygen. Once called NOAA Nitrox 32 (NN32) and NOAA Nitrox 36 (NN36), such mixtures are now identified using a more general nomenclature as Nx32 and Nx36. The remaining gas in nitrox mixes is considered to be nitrogen, even though it may contain other inert gases like argon. “Nitrox” is a generic term that can be used for any gaseous mixture of nitrogen and oxygen, but in the context of this chapter, the implication is that nitrox is a mixture with a higher concentration of oxygen than that of air. Using such oxygen enhanced mixtures can significantly increase the amount of time a diver can spend at depth without incurring additional decompression when compared to air diving.

Performing repetitive dives requires a the use of a dive plan. The diver must know what the no-stop dive time limits will be for the dives prior to descending so as not to incur additional decompression obligations. A planned dive schedule will work assuming the diver adheres to the maximum depth and time parameters defined before descending; however, this does not always occur. There are many reasons why divers may find themselves deeper than planned. Some of these might include: higher than normal tides while working on a specific site, down-welling currents, the need to descend deeper to pick up tools or experimental apparatus that may have been dropped, the unexpected need to provide assistance to divers who are working at deeper depths (either on a routine or emergency basis), or perhaps just plain inattention of the divers.

Thermal Stress Irrespective of Ambient Temperature
Hypothermia is not a problem exclusive to frigid environments—it can occur irrespective of ambient temperature. Similarly, divers may also suffer extremes of hot and cold thermal stress simultaneously during the same dive. There have been documented cases of severe heat exhaustion in arctic waters by commercial divers as a result of wearing thick, occlusive drysuits, aggravated by dehydration from breathing dry compressed gas and perspiring from prolonged underwater swimming or heavy underwater work. Perspiration from excessive or from pre-dive overheating can also cause the diver’s drysuit underwear to lose insulation, thus predisposing him to hypothermia.

In this podcast and article by Roque Wicker, MBA, author of HBOTechBlog.com, and creator of the Hyperbaric Oxygen Therapy Patient Safety Instructions we explore the relationship between effective patient education on hyperbaric compliance, patient satisfaction, and reimbursement. 

When you prepare for a dive trip, there are things you pack that are on the "must have" list, such as mask, fins, BCD, and regulator. Then there are the things that you "should have" such as wetsuit, defog, and sunscreen. All of the other items typically fall onto the "it would be nice to have" list, such as snacks, sunglasses, and a camera. The question we have for you today is, onto which list do your dive rescue and dive accident management skills fall?