NARD Diving MedicineDiving MD

Recompression

There are two basic classes of diving emergency requiring recompression, air embolism (arterial gas embolism) and the Bends (decompression sickness). Air embolism is the most dangerous diving accident, and is an extreme medical emergency requiring immediate recompression. When a diving accident takes place, and recompression is required, the victim should be transported to a chamber. Never undertake in-water recompression. The chance of increased harm to the diver vastly outweighs any anticipated benefit.

How DAN Works!

Rescue divers should grow familiar with all chambers in their area that accepts diving accidents on a 24 hour emergency basis. Heading to the closest recompression chamber is not always the best course of action. Not all chambers deal with divers. For this reason the Diving Accident Network (DAN) was formed in 1981, to aid in diving emergencies. They have an emergency network of on call physicians and regional coordinators. DAN does not furnish the location of a chamber. After receiving a call the operator pages the DAN physician on call. If he is not in the hospital, they will have him call you, or they will furnish you his number. The physician may counsel the caller, or refer him to a local diving physician. When required he will work with one of the regional coordinators. Each coordinator keeps up-to-date files on all chambers in his region, transportation to them, and other services. To reach DAN call (919) 684-8111 and tell the operator that this is a diving emergency and you must talk to the physician on call. It is best to call DAN from the Emergency Room, here the DAN physician can confer with the attending physician. When an accident occurs at sea call the Coast Guard by marine radio not DAN.

Most divers have no conception of how a recompression chamber functions. As a rescue diver understanding the operation of chambers can give you better awareness when dealing with patient needs, and chamber operators. Recompression is indicated in arterial gas embolism (air embolism), venous gas embolism (decompression sickness) and cases of omitted decompression. Chambers are also used for medical treatments of some diseases and injures, but we will only consider diving treatments. In order to render therapy, it must first be predetermined if the victim has arterial, or venous gas embolism.

The intention of recompression is to accomplish three primary goals:
  • To compress gas bubbles to a small diameter and volume thereby reviving blood flow.

  • Increase blood oxygen content and thereby oxygen circulation to the tissues.

  • To allow time for bubble resorption.

  • Most chambers therapy utilizes USN Oxygen Treatment Tables 6 and 6A.

Chambers are in two structural forms, Mono-Place and Multi-Place. The Multi-Place Chamber can best treat victims of air embolism. Multi-Place chambers have room for attendants, while Mono-Place do not. They can be pressurized with air, and supply the victim with oxygen via an oxygen delivery system separate from the surrounding pressure. This avoids oxygen toxicity. Mono-Placed chambers pressurize with oxygen. Multi-Place chambers have personnel locks so that additional personnel can enter as needed, Mono-Place have none. In the Multi-Place chambers extended treatment times can be used because they can add air breaks, or rest from breathing pure oxygen under pressure. Mono-Place chambers must have short treatment times, because they use only 100% oxygen. The greatest benefit of the Multi-Place chambers are they have a 6+ ATA limit. This is vital to the air embolism victim. Mono-Place chambers have a 3 ATA limit.

Multi vs Mono Placed Chambes
MULTI-PLACED CHAMBER MONO-PLACED CHAMBER
6 + ATA Limit 3 ATA Limit
Room for attendant No room for attendant
Large lock No personnel lock
Extended treatment Short treatments
Pressurized with air Pressurized with oxygen
Separate O2 delivery

Many people believe that by recompressing a victim to 33 feet or 2 ATA, they have diminished the size of any gas bubbles by one half. Because of this, some 2 ATM chambers are around. The bases of this thinking comes from Boyle's Law stating: For any gas at a constant temperature, the volume will vary directly with the absolute pressure. Put as the pressure increases, the volume decreases. This is true for volume relationships, but the victim needs diameter reduction, along with volume. It is the reduction in diameter that moves bubbles. For this reason all air embolism treatments descend the victim to 165 feet. While in decompression sickness, the bubbles are smaller, and only a drop to 60 feet is need for treatment.

PHYSICS OF GAS BUBBLES

FEET
fsw

Meters

ATA PSI BAR Relative
Volume
Relative
Diameter

0

0

1

14.7

0.99

100%

100.0%

33

10.0

2

29.4

1.97

50.0%

79.3%

66

20.1

3

44.1

2.96

33.3%

69.3%

99

30.2

4

58.8

3.95

25.0%

63.0%

132

40.2

5

73.5

4.93

20.0%

58.5%

165

50.3

6

88.2

5.92

16.7%

55.0%

297

75.4

10

147.0

9.86

10.0%

46.2%

It is easily seen from the chart that to decrease the size of a gas bubble by about one half, the depth needs to be at least 165 feet. For this reason air embolism victims are taken to 165 feet on initial treatment. If the victim only descends to 2 ATA the volume will be reduced by half, but the size of any bubbles will only decrease 20.7%.

Victims need to be treated promptly and adequately. Do not delay treatment unnecessarily. Remember that the effectiveness of chamber treatment decreases as the time between onset of symptoms and treatment increases. If the distinction between atrial gas embolism, and decompression sickness cannot be determined treat as air embolism. Disregarding minor symptoms can cause problems down the road. They can quickly become major. Follow the treatment table unless a hyperbaric physician recommends otherwise. If multiple symptoms occur, treat for the most serious. Air embolism is far more serious than Venous Gas Embolism.

For treating Decompression Sickness, USN treatment Table 6 is used. A complete neurological exam is done as treatment begins. While on the scene or en route to a medical facility the rescuer should start this exam. The sooner a first exam is done, the better one can determine progression of symptoms. At the chamber the victim is compressed to 60 feet and placed on pure oxygen. Descent rate is 25 ft/min. Time at 60 feet. begins on arrival there. After 20 minutes on oxygen, the victim goes on 5 minutes air. An alternation of 20 minutes oxygen, five minute air continues all the time while at 60 feet. After the first oxygen breathing period, the victim should be reexamined. After three cycles the victim ascends to 30 feet, with an ascent rate of 1 ft/min. on oxygen. While at 30 feet the cycle is 15 minutes air followed by 60 minutes oxygen, for two cycles. At the end of the last 60 minutes on oxygen the victim is surfaced, still breathing oxygen at 1 foot per minute. If the victim is suspected of having an air embolism he is treated with USN Table 6A. This takes the diver to 165 feet, to decrease the size of the bubbles. The rate of pressurization or descent is as fast as possible, or as fast as ears can be cleared. Attaining treatment depth is vital

When treating victims in the chamber they are kept awake while breathing oxygen below 30 feet. Blood pressure, respiration and pulse are monitored at set intervals, appropriate to condition. A tender is inside with the victim who is familiar with all treatment procedures, and signs and symptoms of all diving related disorders. While in the chamber, the tender ensures that the victim is lying down, and positioned to permit free blood flow to all extremities. The tender must watch the victim constantly for signs of relief. Drugs they may mask symptoms should not be given. Observation of signs and symptoms is the principal method of diagnosing conditions. Tenders also provide any first aid required, all communicating with outside personnel, attending to the victims needs, and administering oxygen.

During treatment, the victim is observed for any oxygen toxicity that may develop. At the first sign of toxicity the patient is removed from oxygen and allowed to breathe chamber air. After the initial treatment, the victim may require additional recompression. These treatments are indicated as long as a hyperbaric physician recommends them. When delay time between the initial treatment and the beginning of follow up treatment increases, the probability of benefit from additional treatments decreases. Once residual symptoms respond to additional recompression treatments such treatments should be continued until no further benefit is noted. Treatment is usually discontinued if no further improvement on two consecutive treatments are noted. After the diver has completed all recommended hyperbaric treatments he will need to know when he can return to diving. This will depend on the severity of the symptoms presented prior to treatment. Returning to diving can range from a few days to a few weeks, or not at all. When and if a diver can return to normal diving activity will rest with a hyperbaric or diving physician. Only when a diving physician clears a victim and advises that dive operations may be resumed, may the diver return to normal diving.

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