Diving Medicine

Decompression Sickness

A SIMPLIFIED GUID TO CHAMBER RECOMPRESSION THERAPIE

Decompression Sickness

Decompression sickness (DCS) is a syndrome that follows the reduction in environmental pressure massively or rapidly enough to cause the formation of bubbles from gases already dissolved within body tissues. It represents one of the many man made illnesses though; its exact nature is still not fully understood.

In compressed gas diving, DCS happens if :

1-The elimination of the inert gas(es) dissolved within body tissues during exposure can not adequately parallel the rate of reduction of external pressure (as in case of fast ascents).

2-The amount of residual inert gas at the end of a particular dive (dives) (Supersaturation) is high enough to create a gradient between the gas tension in the body and the gas atmospheric partial pressure enough to enhance bubble formation (as in case of overriding dive tables limits).

3-Accumulation of the inert gas in the body due to repeated diving for a few days (inert gas load) despite normal profiles and ascent rates. (always triggered by individual susceptibility).

After the initial bubbles form, other gases naturally dissolved in the tissues as O2 & CO2 get forced into the bubbles by tension gradient causing bubble growth and aggravation of symptoms.

*The inert gas that initiates bubble formation in DCS is different with different breathing mixtures e.g. Nitrogen in diving on Air or Nitrox. Helium in diving on Heliox Nitrogen or Helium or both in diving on Trimix.

*Decompression Sickness due to bubbles forming inside blood vessels (intravascular bubbles) is currently called Venous Gas Embolism (VGE) as the bubbles mainly erupt in the venous side of circulation where the blood pressure is far lower than that of the arterial side.

*Decompression Sickness was reported in deep breath-hold diving when:
1- Done repeatedly as in pearl divers, OR
2- Done shortly after compressed air diving in which the nitrogen load was relatively high.

*Decompression Sickness can occur without being preceded by diving when flying up relatively fast to altitudes starting from 23,000 feet above sea level in a non pressurized air craft.

Concepts
1-Decompression must have taken place.
2-The victim must have been exposed to gas (es) under pressure.
3-The rate or ratio of pressure change must have exceeded a critical point.

Synonyms of DCS

1. Caisson’s Disease
The first clinical cases were described in tunnel workers doing caisson sinking (non-divers).

2. Dysbarism
This is a very broad description that could as well include conditions such as barotrauma of the ascent.

3. Bends
A very commonly used term which refers to the posture of a diver suffering from the pain of one type of DCS mainly affecting one or more joints originally called the Grecian Bend.

4. Chokes
Refers to the clinical syndrome of respiratory distress as a result of pulmonary vascular obstruction by numerous bubbles forming in the venous circulation following decompression.

5. Staggers
This describes the gait of a victim suffering from inner ear decompression sickness causing balance disturbance (Menier’s Decompression). Always encountered in surface demand or technical SCUBA mixed gas diving as a result of substituting an inert gas of a low diffusion coefficient at depth by another that has a higher coefficient as in (the condition known as isobaric counter-diffusion). E.g. replacing Air or Nitrox by Helium without any increase in pressure (depth). Staggers can also be the result of cerebral (brain), cerebellar (brain stem) or upper spinal DCS.

Clinically

DCS is differentiated into 3 types:
TypeI DCS and can be presented in the form of:
1- Extreme fatigue.
2- Skin bends
In the form of blotching on the skin (mottled rash) frequently called Cutis Marmorata the condition that might be also itchy.
3- Joint pain (limb bend or Musculoskeletal pain-only symptoms)
Which is severe pain in one or more joints and might be preceded by numbness or throbbing on the affected part.
*Relief of pain when applying distal pressure is diagnostic.
*The most commonly affected joints in recreational divers are shoulder and elbow joints while knee joint “bend” is more commonly
seen in caisson workers, aviators and deep saturation divers.
*Usually when two joints are affected, they are adjoining ones (shoulder & elbow OR Hip & knee)
4- Lymphatic Symptoms
Where localized swelling and pain occurs in involved lymph glands.
*Recently, US Navy manual added to the definition of Type I DCS that it: 1-should be accompanied with a normal neurological examination before treatment & 2-resolution of symptoms must take place within first oxygen breathing period on a standard oxygen treatment table (see tables).
TypeII DCS
Where the nervous system (central or peripheral), the inner ear or cardio-pulmonary systems are involved producing serious signs
and symptoms.
TypeIII DCS
Has been newly postulated as another, more serious, manifestation when the already supersaturated diver develops DCS as a complication of arterial gas embolism resulting from pulmonary barotrauma. (A combination between AGE & VGE which is now well recognized, but fortunately not very common).

Since bubbles can form inside cells (intracellular), outside cells (extra- cellular) or even inside blood vessels (intravascular), DCS can present in a variety of symptoms and signs, which pose a diagnostic problem for the non-experienced officer. Amongst these symptoms:

- Skin rash
- Back pain
- Dizziness
- Girdle pain
- Hearing problems as ringing in the ears
- Tingling or strange sensations
- Consciousness disturbance
- Memory changes
- Extreme fatigue
- Balance problems
- Shortness of breath
-Joint pain
-Itching
- Chest pain
-Paralysis
- Urination difficulty
-Nausea, vomiting
-Visual disturbances
-Speech problems
-Disorientation

As a general rule, any symptoms developing after a dive which can not be explained should be regarded as Decompression Sickness until proved otherwise.

It is important however to establish whether symptoms are diving related, and a. good procedure is to:
1. Refer back to the dive profiles of the last few dives (depth and exposure times) and consider any unusual events happening during these dives like: emergency or fast ascents, omitted stops, YOYO like profiles, reversed profile(s), multiple ascents, a very cold or strenuous exposure etc.
2. Overview the individual factors involved such as overweight, over 40 years of age, or dehydration.(see below)
3. Pay attention to Inert gas load (in case of repeated diving days).

Factors and Conditions leading to the occurrence of DCS

I-Inadequacies of published diving tables:
Most diving tables carry a risk of DCS because:
-They are square dive profile dependant, the practice which is more or less never practiced by sport divers.
-They were developed for a specific group of divers ( e.g. very fit, young navy divers)

*A table with an incidence of DCS of less than 3% is regarded a safe table. *The majority (86%) of USA recreational divers who develop DCS have (apparently) complied with the decompression tables and the BSAC would suggest a figure of 40%.

II-Failure of a diver to observe or fulfill accepted safe decompression tables due to:
1. Ignorance of correct tables.
2. Altitude or repetitive diving without table adjustment.
3. Omission of a decompression stop
*Dive computers: Can make diving practice easier and allow divers to spend more time under water than conventional tables as they compute dive and depth input against the tables and calculate inert gas absorption and elimination in a number of theoretical body tissues continuously to credit the diver for multi-level dives. But amongst disadvantages of dive computers are:
-They do not take all factors into consideration like: water temperature, age, body figure, dehydration or exertion.
-They have a high incidence of faults or failure during underwater exposure.
-It is practically possible to override these computers without being aware of it.

In fact diving computers are responsible for a good number of DCS cases in sport diving.

III-Rate of Ascent
A rapid rate of ascent is one of the most powerful physical stimuli for bubble formation and growth. Until recently, most researchers advocated rates of ascent in the order of 18-20 meters (60feet) per minute, now many published tables and computers will advise a rate of ascent as slow as 10 meters per minute.

IV-Individual factors

1. Dehydration: is one of the major predisposing factors in the occurrence of DCS as dehydration renders the blood more viscous the condition, which reduces perfusion of tissues and thus the elimination of inert gas. Dehydration can happen as a result of
1. inadequate fluid intake.
2. Drinking dehydrating agents like all kinds of alcohol and strong coffee.
3. Dehydrating conditions as diarrhea and vomiting.
(Note that, during diving there is a continuos fluid loss due to perspiration, dry gas breathing and immersion).

2. Age: altered blood flow due to atherosclerosis associated with age increases the risk of DCS.

3. Sex: some literature reported a 3-fold incidence in females, but recent studies seem to contradict this statement.

4.Obesity: is a point of controversy:
Some authors accuse fat tissue of being a contributing factor (having a great affinity to nitrogen thus increasing the nitrogen load in case of repeated diving days) whilst others believe in its action as a good reservoir for nitrogen in cases of short deep exposures.

5. High serum Cholesterol levels can enhance bubble formation by rendering the blood more viscous.

6. Improper training of equipment usage (mainly the BCD).

7. Overconfident attitude in a poorly educated or a well trained diver.

8. Any underlying condition that hampers the anatomy of the body can form a bubble trap due to scarring and alteration in local tissue perfusion and gas elimination yielding to the occurrence of DCS. E.g. a previous joint, spine or brain injury or affection, also any previous episode of DCI.

9. Increased carbon dioxide pressures due to exertion or increased breathing resistance because of faulty equipment, which increase nitrogen loading.

Onset of Symtomps

Although the highest gradient for bubble formation exists when the diver surfaces, it takes though some time for the bubbles to form and then produce their effects.(A Coca-Cola bottle takes considerable time to go flat after opening) Mainly most cases of DCS are presented between 10 minutes and 2 hours after surfacing.

A stastisical study showed that DCS onset of symptoms is as follows :
50% within 30 minutes after surfacing.
80% within 60 minutes after surfacing.
95% within 3 hours after surfacing.
100% within 24 hours after surfacing.

It is important to differentiate between onset of symptoms and time of presentation, which could be influenced by some factors. Delayed onset does not disqualify the diagnosis of DCS or alter its management.

However, DCS is more likely to develop rapidly under the following conditions:
-Deep dives, due to rapid load and release of gas from fast tissues.
-Rapid ascents, due to increased gradient.
-Repetitive dives, where bubbles are already existing from previous dives.
-Omitted Decompression stops.
-Existence of one or more of mentioned predisposing factors.
Slower (delayed) onset is observed with:
-More shallow dives.
-Pushing tables limits.
-Slower ascents.

*One example, when symptoms appear within a few minutes after surfacing is a case of blown up decompression where the dive is relatively deep ending with an extremely fast rate of ascent due to faulty equipment or unexpectedly out of air situation. In 92% of these cases, the bubbles form inside the tissues of the spinal cord (Spinal decompression) and the main presentation is Paraplegia (paralysis of the lower half of the body together with disturbed sensory & urinary functions).

*Bubbles can form after a relatively deep dive due to enhancement of the circulation, as in cases of strenuous exercise, hot showers or alcohol drinking shortly after this dive.

*Some authors denoted that divers & tunnel workers can develop some kind of tolerance (adaptation) to DCS which increases with daily diving & decreases after a few days layoff. It appears as if, with regular diving, a slight degree of resistance to DCS can develop for that diving depth. As a matter of fact, the incidence of DCS in cassion workers is halved in the second week and again in the third week. This acclimatization might result from either increased body tolerance to bubbles (physiological adaptation), or more probably from decreased number & volume of bubbles and gas nuclei (physical adaptation).

First aid in Decompression Sickness

I-MAINTAIN LIFE

II- OXYGEN(O2)
100% oxygen breathing should be started as soon in any suspected case of DCS. Oxygen provides the following benefits to the diver :
1. Adds no more inert gas.
2. Washes out dissolved inert gas by minimizing its partial pressure in the lungs.
3. Washes the inert gas out of bubbles by maintaining a tension gradient in the tissues reducing the bubble size.
4. Improves blood and tissue oxygenation.
5. Helps reduce respiratory distress.
6. May reduce shock and cerebral oedema.

So, Oxygen breathing might improve existing symptoms and prevent other symptoms from occurring.

Oxygen delivery systems commonly used in diving first aid in Egypt

A) Demand System
The easiest and most effective way to achieve near 100% O2 in case of a spontaneously breathing victim is the demand valve delivery system, it also reduces the waste of O2 especially in the newly introduced O2 Rebreathing Delivery System.

B) Constant flow system

I) Simple face mask
It is the most commonly used O2 mask, though having the following disadvantages:
1.Often seals poorly.
2.Large ventilation holes allow O2 to be further diluted with ambient air.
So this simple mask delivers O2 at concentrations as low as 35-50%.

II) Partial rebreather mask
Fitted with a reservoir bag, which helps to elevate O2 concentrations up to 55- 65%.

Some authors recommend O2 breathing to be intermittent, which means that you should allow 5 minutes air break every 15-20 minutes on O2 to reduce the harmful effect of O2 on lung tissues. On the other hand, most facilities are not concerned with air breaks during transport since the inspired O2 concentration is unfortunately far lower than 100% due to the type of delivery system used or the poor mask seal. In addition, even when reaching a relatively high O2 concentration, the harmful effect expected on the lungs can be neglected compared to benefits of oxygen in case of diving emergency.

*Periods of O2 breathing should be recorded and the diver’s response to O2 should be observed and relayed to the treating Hyperbaric physician.

*Industrial oxygen must never be used as a substitute to medical oxygen.

III- POSITIONING
If DCS is suspected, the injured diver should be positioned horizontally without the head or legs elevated.
- If the diver feels faint, has a thready pulse or low blood pressure, elevation of the legs may improve the case. However, if the diver’s condition appears to deteriorate as a result, the legs should be lowered.
- Unconscious or nauseated divers should be placed on one side with the neck extended (recovery position).
- Any diver requiring resuscitation should be placed supine.
- Some injured divers, such as those suffering from heart problems, may find it easier to breathe while sitting or semi-reclined.

Trendlenberg position (victim lying on left side with his feet raised up 30 degrees) was thought to reduce the incidence of bubbles transportation to the brain and heart against gravity. But recent studies proved this to be incorrect. Doppler studies showed that bubbles readily traveled against gravity due to heart pumping action in the circulatory closed system, no matter what the position was.

On the other hand, raising the feet up while putting the head down will produce the following undesirable effects
1. Increase the intracranial tension aggravating any existing cerebral oedema.
2. Interfere with normal respiratory movements because of pressure on the diaphragm by stomach contents.
3. Enhance vomiting with the risk of aspiration.
4. Convert a case of Venous Gas Embolism (VGE) into a case of Arterial Gas Embolism (AGE) in victims having an underlying septal defect e.g. patent foramen ovale (PFO).

IV- FLUIDS In any suspected case of DCS, fluid administration is extremely important as dehydration is one of the major contributing factors. Encourage the conscious victim to drink +300 ml of water per hour. If the tender has medical training background, an intravenous line of saline or Ringers is recommended especially for an unconscious diver.

V- DRUGS
Amongst drugs that have a role in providing successful first aid to a diver suffering from DCS are:
1. Aspirin
High doses might kill pain, which could mask disease progress, so recommended dose is 1 tablet of 300 mg, which helps reduce platelet aggregation thus hindering clotting mechanisms of blood. Aspegic is an injectable form available on the market. Aspirin is contraindicated in cases of Inner ear decompression ( menier’s form) so don’t give the patient Aspirin if he shows any dizziness, vertigo, hearing or balance problems.
2.Cortisone
Works as an anti/inflammatory and helps to reduce cerebral oedema. Dexamethazone 8 mg is the recommended injectable form. Giving 2 ampoules IM is highly beneficial only in cases where CNS is involved.
3.Valium ( diazepam)
This helps in
-Sedation
-Decreasing muscle activity and spasm.
-Antagonizing the effect of cortisone which increases the effect of O2 toxicity on the central nervous system.
Valium is also a specific treatment for vestibular DCS. The dose is 1 tablet 5 mg.

Aminophylline may be contraindicated in decompression incidents as it results in dilatation of the lung vessels with marked release of trapped bubbles into the systemic circulation.

VI-TREAT ASSOCIATED PROBLEMS e.g. Shock, Hypothermia, Near drowning, Injuries etc.

*The first and most significant aid is to plan for safe dives including accident management and plans for evacuation to the nearest recompression facility.

*Dive leaders should co-operate with chamber personnel by doing what is asked of them, being honest in all of their answers to questions and having understanding and appreciation for chamber personnel and consultants, as these people are trying to be helpful and they have stress and tasks associated with their function during the course of treatment itself.

Gas Embolism (GE)

Gas embolism (GE) or Arterial Gas Embolism (AGE) is a dangerous condition which is the result of gas passing into the circulation causing temporary vascular occlusion and infarction.
In compressed gas diving, AGE may result from either: I-Over-expansion of the lungs or part of the lungs due to failure of the expanding gas to escape while the ambient pressure is falling markedly (referred to as barotrauma of the ascent) and is encountered in one of the following conditions:
1.Spasm of the wind pipe or holding breath during ascent, where the capillaries and small vessels are stretched and may tear along with other tissues. Since these vessels are small and are often compressed by distended gas sacs, embolism does not result until over-distension is relieved by exhalation usually upon surfacing, then inspired atmospheric air will pass into pulmonary circulation then to the heart and systemic circulation and symptoms will appear very shortly after surfacing. (Air is always the causative gas no matter what the breathing gas is).
2.Partial lung obstruction during ascent, as in case of mucous plugging in heavy smokers, the case in which the breathing gas passes into the pulmonary circulation then to the heart leading to gas embolism with serious symptoms those can appear even before surfacing.
3.Underlying lung disorder as in Emphysema and bronchial asthma.
*In bronchial asthma patients, gas embolism always happens if the rate of ascent is relatively fast, as the narrowed respiratory passages will not allow the rapidly expanding gas to escape adequately leading to over-expansion and gas embolism though the patient is exhaling normally during ascent.
II- As a complication of DCS when (rarely) intravascular bubbles form in the arterial side of the circulation, OR when intravascular venous bubbles pass to systemic circulation (right to left shunt) due to the presence of a cardiac septal defect as Patent (persistent) Foramen Ovale (PFO).
*Only a small volume of gas in the systemic circulation is capable of producing severe disturbances. Serious effects and even death may result from blockage of cerebral or coronary vessels by bubbles. Other tissues affected may include the spinal cord, spleen, liver, kidneys or limbs.

Amongst the symptoms of AGE
Dizziness-weakness-paralysis-collapse-balance problems-consciousness disturbance-convulsions-visual and hearing disturbances-urine retention-nausea and vomiting-speech problems.

Prevention of air embolism

1. Diagnosis of any existing pulmonary illness should be the first priority in examined candidates for diving practice.
2. Whilst using compressed gas, trapping might happen while ascending from depth at a rapid rate even in a healthy individual (especially smokers due to mucous plugging) so, any diver should not only keep breathing all the time, but should also consider ascending slowly from any dive.
3. Good training including good planning and gas source monitoring all the time as well as proper handling of emergency and stressful situations.

First aid in gas embolism

1.Maintain Life
2.Oxygen
3.Positioning
4.Treat associated problems.

Refer back to First Aid of DCS.

Pneumothorax

Is the result of air escaping between the lung and the inner wall of the chest cavity (Plueral cavity). As the air continues to expand, there is partial or total collapse of the lung. In serious cases the heart may be displaced. Pneumothorax can be spontaneous, and can result from trauma to the chest cage or as complication of any underlying lung pathology. And is probably the only absolute contra-indication for chamber treatment so, it has to be ruled out before accepting candidates for Hyperbaric Oxygen treatment. (See section of Hyperbaric chambers)

In compressed gas diving, pneumothorax is encountered as one of the three consequences of lung over-expansion injury: (Gas Embolism – Mediastinal or Subcutaneous Emphysema and Pneumothorax) And is always presented by: sudden onset of couch, sharp pain in the chest usually made worse by breathing, shortness of breath which is always rapid and shallow and sometimes cyanosis (blueness of skin and lips). If Gas Embolism is not suspected, recompression of a case of pneumothorax is not recommended. If breathing is impaired seriously and no physician is available to surgically vent that cavity, recompression to the point of relief might be recommended. A surgeon must then be locked into the chamber to insert a chest tube before decompression is possible.

*Off shore chambers may be very infective, so care must be taken to adequately sterilize the chamber before performing any penetrative procedure under pressure as inserting a chest tube.

*Air embolism is more commonly encountered in cases presented with emphysema than in cases of pneumothorax.

Chambers

A Chamber is a vessel (usually cylindrical in shape with hemispherical ends) which is capable of being pressurized or depressurized and held at a pressure which is different from the surrounding ambient pressure.

Different terminology are used interchangeably to denote different chambers regarding usage including: Compression, Decompression, Recompression, Hyperbaric and Hypobaric (altitude) chambers. Some of the chamber characteristics are also used to describe these chambers such as:
1. Diameter measurements ( in inches or cm).
2. Rated working pressure (W.P) usually in ATA.
3. Number of compartments and locks which they possess which provides a list of different terms including: Single-lock, Double-lock, Multi-lock, Mono-place, Multi-place, etc.
4. Number of patients that the chamber can accommodate in a single compression e.g. One man, Two man, 12 persons etc.
5. Number of penetrators ( sealed holes)

Generally speaking A chamber should be equipped at least with the following:
1. Pressurization and Exhaust systems.
2. Depth control gauges and control panels.
3. View ports.
4. Safe or external lighting system.
5. 2 way communication systems.
6. A fire extinguishing system.
7. Stop watches for time control.

Hyperbaric chambers

Basically used for Hyperbaric oxygenation (HBO), which means providing pure medical oxygen to breathe under pressure higher than atmospheric pressure. The list of diseases that are handled using HBO include:
- Follow up treatment of DCI.
- CO poisoning.
- Soft tissue infections including gangrene.
- Wound healing problems.
- Diabetic foot.
- Bone infection.
- Sudden deafness and tinnitus.
- Bone necrosis due to radiation therapy.
- Vascular insufficiency.

Chambers used for HBO are either:
- Air pressurized chambers where the candidates breathe oxygen through demand valves and exhaust it over-board. Those Chambers are relatively big and adapt many persons together carrying out HBO treatment tables.
- Pure Oxygen pressurized chambers, they are mostly small chambers made of steel, aluminium or acrylic and can take only one person (one man chamber) and are not used in any case where an emergency needing hands-on attendance is likely to happen.

Are used in industry and research to decrease pressure around subjects and objects to less than the atmospheric pressure. Usually found in aviation medicine centers.

Compression Chambers

Used mainly for research and experimental work as:
- Studying the effect of breathing different gases under pressure on different body systems.
- Also used in setting new dive tables.
- One basic use of compression chambers is testing pressure, oxygen and nitrogen tolerance.
Some governmental agencies require their divers or dive candidates to pass pressure or oxygen tolerance tests before they are eligible for diver training or annual recertification.

The purpose of testing oxygen tolerance is to prohibit those individuals who are susceptible to O2 intoxication from diving or at least from pure oxygen and technical diving usually carried out by Navy, technical and commercial divers.

Decompression Chambers: (also called Deck Decompression Chambers DDC)

These are chambers used mainly for surface decompression for navy and commercial divers, which is a technique used for carrying out all or part of the diver’s decompression requirements in a chamber at the surface. This technique reduces the time the diver must spend in water and reduces total decompression time when an O2 surface decompression table is applied. Surface decompression offers many safety advantages for divers including:
1.Less exposure to the cold water.
2.Exposure to constant pressure during decompression which is unaffected by changing sea conditions.
3.Constant surveillance by technical and medical personnel.

The maximum allowable time from leaving last deco stop in water to reach first stop in chamber is 5 minutes.(remember the Coca-Cola bottle)

*The above technique of surface decompression is frequently called Planned Omitted Decompression. In case of unplanned (accidental) omitted decompression, if a chamber is not available, an omitted decompression case should reduce activity, drink plenty of fluids and breathe pure O2 while transported to the nearest chamber. Special care should be taken to detect any signs of DCS. Do not recompress a diver with omitted decompression in water.

Recompression Chambers

These are Hyperbaric chambers used to deal with decompression caused illness (DCI) where recompression is the only technique known that can deal adequately with such problems. Special extra features that should exist in a chamber used for recompression treatment include:
1. A working pressure of at least 6 ATA.
2. Containing demand oxygen breathing apparatus preferably a built in breathing system (BIBS) which has overboard discharge oxygen breathing masks, and O2 analyzing system.
3. Be a double lock chamber that has 2 compartments capable of being pressurized independently allowing medical personnel and tenders to enter and leave the chamber without having to subject the patient to any change in pressure.
4. A relatively fast compression rate to fulfill demands of different recompression treatment tables.

*A double lock chamber is not designed to carry out 2 different treatment tables at the same time. However, a skillful operator and a well-trained tender under certain circumstances can do this.

What a chamber experience is like! If you have the opportunity to take a chamber ride, do so. There is nothing more impressive for a diver than being inside a chamber during pressurization, venting and ascent. Although chambers differ, there are some elements, which most experiences will have in common. One of these is noise, gases rush in through small orifices during pressurization and venting and unless muffled, the noise can be too loud to talk over. In addition voices become weird and sometimes difficult to understand due to increased gas density with increasing pressure. Another obvious sensation is the rapid change in temperature and humidity during pressure change. During depressurization, the chamber gets cool and clouds of humidity can form.

A chamber ride is not a treatment, but it will yield an idea of what one would be like.

Operating a Recompression Chamber

I- Pre-dive check
A pre-dive check should be conducted before each operation (after making sure that all pressure gauges were calibrated within 12 month). The check should, as a minimum , require that the chamber:
- Be clean.
- Be free of unnecessary & combustible equipment.
- Be free of noxious odour.
- Doors and seals are undamaged.
- Seals are lubricated.
- Drain valves are closed.
- Stopwatches are working.
- All tables available.
- Medical kit is complete and at hand.
- Logging papers and pens are there.

Checking Gas Supply (line ups)
1.Air Supply:
Air storage should be sufficient to pressurize the chamber 2 times to 50 meters sea water (6ATA) and ventilate throughout the treatment. To calculate that, you should know:
- the litric capacity of the chamber
- the litric capacity and the working pressure of the supplying air bank OR the flow rate of supplying low pressure breathing air compressor. *Make sure that compressors are serviced and lubricated properly, their intake is clean and not picking up exhaust from toxic sources. *Before activating the air supply check that both pressure and exhaust valves of the chamber are closed.
2.Oxygen Supply:
O2 System should be inspected and carefully examined as follows:
- Cylinders are full and labeled (medical O2) & Valves are open.
- Back-up cylinders are at hand.
- Regulators (Reducers) are set at the required intermediate pressure.
- Oxygen masks are installed and functioning.
- Oxygen supply valves to the chamber and discharge valves are open only when Oxygen is in usage.

*Smoking in the vicinity of the chamber is strictly prohibited.

*Analyzing each single O2 tank for % is a recommended procedure especially if the O2 area provider is dealing in supplying other gases.

Checking electrical system:
Whenever possible it is better to keep all electricity outside the chamber. When it is inside, only low voltage wiring is allowed and control switches should be kept outside. Light system check include:
- Lights are all working.
- Wiring has been recently inspected.

Lights inside the chamber must never be covered with clothing, blankets or other articles that might heat up and ignite.

Checking communication systems:
Must be checked to insure that the system and the backup system (usually low voltage intercom) are operational.

II-Chamber Ventilation
Ventilating chambers with fresh air is necessary to maintain safe levels of CO2 (less than 1.5%) and O2 (less than 25%) in chamber atmosphere, to eliminate excess moisture forming inside and to reduce temperature build up due to compression and activity of personnel inside. The amount and rate at which air must be circulated in the chamber depends upon chamber volume, temperature, number of personnel inside, their level of activity, breathing gas and breathing apparatus being used.

*The amount and flow of air ventilated through the chamber is controlled by regulating the intake valve together with the exhaust valve while maintaining a constant chamber pressure. (Hurricane vent) *Practically the exact amount of air passing through valves is not easy to establish unless a flow meter is used (normally fixed next to exhaust valve), so as a general rule ventilate a chamber regularly, increase frequency when number of people is higher, or when personnel increase their activity, also ventilation should be increased when oxygen is being breathed in the chamber, especially when (dump in) systems are used (always monitor with the O2 analyzer). Increased humidity in the chamber atmosphere indicated by fogging, is also a good reason for ventilation, also ventilate in case of temperature build up indicated by thermometer (if available) or reported by tender inside, and in case of defective or deficient CO2 scrubber.

III-Fire Prevention:
The key of fire prevention in a hyperbaric environment is:
1. Remove any material that might ignite.
2. Remove any material that may cause a spark.
3. Keep oxygen concentration in the chamber atmosphere always well below 25% Indicated by the oxygen analyzer.
4. All equipment should be pressure tested and spark proof.
5. All equipment , wiring and circuits included must be fire proof, and explosion proof.
6. If no specific Hyperbaric fire extinguisher is installed, a water or sand bucket should be placed inside the chamber.

IV- Post-dive check
-Remove unnecessary materials as body waste, disposed medical supplies, used cloths, sheets, etc. and replace what needs replacement whenever possible.
- Clean the inside of the chamber and properly ventilate if necessary.
- Disinfect breathing masks.
- Shut all air and O2 valves and bleed off all intermediate pressure valves.
- Secure and bleed off pressure of fire Suppression System (if existing).
- Turn off all electrical supplies ( to internal light and communication systems).
- Make sure stopwatches are stopped.

Personnel requirement for operating a recompression chamber:
The minimum team that is required for conducting any recompression operation should consist of:
1. An operation supervisor.
2. An inside tender.
3. An outside tender.
4. A diving physician in certain circumstance.

1. The Operation Supervisor
Is in complete charge of the whole operation and must be familiar with all phases of treatment and operation procedures. He must ensure that communications, logging and all phases of treatment are carried out according to prescribed procedures.

2.The Inside Tender
Must be familiar with all signs and symptoms of diving related injuries, capable of conducting thorough neurological examination, familiar with signs of relief of patient’s symptoms. Must be qualified to insert IV canulas or lines as well as giving IV/IM injections when instructed to do so. (Preferably be a paramedic) He should also be familiar with early signs of O2 toxicity and be well trained to deal adequately with a convulsive patient inside the chamber. He should be able to monitor and take good care of the patient during all stages of treatment inside the chamber. Other responsibilities include
- Communication with outside personnel.
- Providing normal assistance including equalization procedures as required.
- Effective O2 administration to the patient.
- Ensure ear protection during compression and ventilation. ( In case of relatively noisy chambers)
- Maintain a clean chamber and transfer of body waste as required.
Signs of O2 toxicity
Most easily remembered using the acronym (VENTID)
V. Visual disturbance, usually in the form of tubular vision.
E. Ear, auditory hallucinations are usually encountered.
N. Nausea, sometimes vomiting.
T. Twitching starts in the lips and ends up as generalized convulsions (seizure) which can sometimes set without any signs of warning. *In case of a convulsing patient, the inside tender should:
1. Discontinue O2 breathing at once.
2. Report immediately to the operator to halt any ascent.
3. Protect the convulsive from injuring him/herself without opposing the convulsive movements.
4. Protect the tongue with a padded mouth gag.
5. Ensure an open airway during and after the convulsive state subsides, as the patient may remain unconscious up to 30 minutes afterwards.
I. Irritability.
D.Dizziness.
Other symptoms include difficulty in breathing, impaired consciousness and lack of co-ordination.

3.The Outside Tender
Responsibilities:
- Maintaining and controlling air supply.
- Maintaining and controlling supply of O2 and other breathing gases.
- Keeping times in all phases of treatment.
- Communication with inside personnel.
- Decompressing any inside tending personnel leaving chamber in the outer lock.
- Pressurization, ventilation and exhaust of the chamber and conducting accurate ascent and descent rates.
- Operating the medical lock.
- Careful logging of all tables.
- Marking used oxygen cylinders and making sure they will be sent away for refilling right after finishing with treatment and making sure that the air storage is being promptly recharged for standing by.

4.The Diving Physician
Though it might not be possible to have a diving physician present during all treatment, it is essential that the supervisor be able to consult a diving medicine specialist by telephone or radio.

*If the patient has symptoms of serious decompression sickness or air embolism, the team will require additional personnel.

*If the treatment is prolonged, a second team may have to relieve the first.

*Patient with serious decompression sickness or air embolism should be accompanied by a qualified tender inside the chamber, but treatment should not be delayed to comply with this requirement.

Neurological Examination include:

- Orientation
For time, place and persons.
- Memory
Immediate, recent and remote.
- Mentation (Smarts)
Serial of 7 test.
- Level of consciousness
- Cranial nerves
Smell, sight, eye movement, chewing, hearing, talking, shoulder muscles, sticking the tongue out.
- Deep reflexes
Knee & elbow tendon reflexes.
- Superficial reflexes
Abdominal & planter (look for Babinski sign).
- Speech problems
- Gait & balance
Check walking & Rhomberg test for balance.
- Sensory nerves
Check touch, pain, pressure and temperature sensations and determine any level of impairment or loss.
- Motor power
Check muscle strength and bilateral equality.
- Muscle tone
Spastic or flaccid.
- Co-ordination
Finger to nose test.

All neurological findings should be recorded for reporting and prognosis follow-up purpose.

Chamber Recompression Therapy

“No-one who has seen the victim of compressed air illness, gravely ill or unconscious, put back into a chamber and brought back to life by the application of air pressure, will forget the extraordinary efficiency of recompression, or will be backward in applying it to a subsequent case of illness.” (Robert Davis, 1935)

Diving accidents requiring recompressing divers in a Recompression Chamber (namely Decompression Sickness (DCS) and Gas Embolism (GE)) are put together under the term Decompression Illness (DCI). The goal of recompression therapy is to prevent further as well as permanent injuries caused by DCI. Proper application of recompression therapy can abort the mechanisms by which this illness can cause permanent tissue deformation and in many cases complete resolution of symptoms can be achieved.

Frequently, it is very difficult to diagnose accurately the exact nature or seriousness of a diving accident so if any manifestations of DCS or GE are observed, it is of much greater importance to initiate treatment immediately than to delay treatment for a more accurate diagnosis and when differentiation between a serious case of DCS and GE can not be made, the treatment of AGE should be conducted.

An initial evaluation, which helps to decide the urgency of a DCI case, is categorized by the following:
1- Onset of symptoms. (the longer the surface interval prior to symptoms, the less likely they are to worsen)
2- Severity of symptoms. (severe symptoms include: disorders of gait, consciousness, mental ability, limb movement, respiration & circulation)
3- The organ systems affected. (musculoskletal- CNS- inner ear- circulatory- respiratory systems)
4- The change of symptoms with time. (evolution)
pay attention to following expressions:
- static symptoms.
- Progressive symptoms.
- Spontaneous improvement.
- Relapsing.
Based on onset & severity of symptom, organ systems involved & time course, three degrees (categories) of urgency are defined:
-Category A (Emergent) in which all available resources should be mobilized to ensure that recompression treatment will be obtained as fast as possible (do not waste time for examination or proper diagnosis).
-Category B (Urgent) in which the patient will need treatment (recompression) as soon as it can be arranged (not an extreme emergency).
-Category C (Timely) in which symptoms are not obvious without detailed examination & the hyperbaric physician can make the decision to delay or abort the treatment of a patient in this category.

*In water recompression should never be attempted (even if the victim is fully conscious and equipped with an Oxygen rebreather having a full face mask) because of the following reasons:
1. The signs and symptoms of DCI are unpredictable as usually bubbles take time to develop and other serious manifestations can happen under water that can lead to serious complications.
2. Lack of proper medical attendance under water.
3. Recompression tables require a huge stock of different breathing gases and take long periods of time which can never be satisfactorily and safely achieved under water.

*In a case of assumed limb bend (pain-only), if the diagnosis is uncertain, a test recompression at 2.8 ATA (18 meters) for 20-40 minutes on O2 with 5-10 minutes Air break in-between is indicated:
-If the pain remains unchanged, it is safe to assume that it is not a diving related incident.
-If the pain is reduced or aggravated, this indicates DCS & treatment should be continued.
Aggravation of pain might be due to redistribution of the gases involved in bubble formation or might indicate a bone bubble.

*Isolated inner ear DCS encountered in Helium & Hydrogen diving is much less documented in SCUBA air diving and has to be differentiated from inner ear barotrauma leading to round window membrane rupture that produces similar symptoms as: dizziness, vertigo, vomiting, tinnitus, hearing loss or orientation problems. Recompression will usually provide no relief in case of a membrane rupture and is thought to increase the flow (leakage) of the perilymph to the middle ear, which might aggravate the case. An inner ear barotrauma is always associated with equalization difficulty and is encountered during descent, ascent or after diving while inner ear DCS might be associated with other forms of DCS and is encountered at depth or during ascent (in helium exposures) or after diving in air dives. If differentiation is not possible, recompression therapy should be instituted taking the following in-chamber precautions into consideration:
1- The diver should not be exposed to a high pressure gradient when using the BIBS mask. (to avoid further barotrauma).
2- The diver should be kept in an upright sitting position during the course of treatment.
3- The diver should be discouraged to increase CSF pressure as by performing Valsalva to equalize the pressure in the chamber.

The approach to a diving casualty that needs chamber recompression has 3 views:
1. Recompress to a pressure (depth) similar to the depth of the original dive and decompress according to the time of exposure of that dive (old French technique).
2. Recompress to depths that produce a clinically acceptable result and then decompress according to special tables (Australian technique). The above 2 methods are not satisfactory because the choice of treatment tables will depend upon a lot of variables, which makes it confusing even for a skilful supervisor since a different table for each individual case should be worked out.
*These tables though, might be very effective for some cases when prompt recompression takes place.

3. Recompress to a predetermined fixed depth, i.e. according to standard recompression treatment tables.
These tables are scientifically developed taking in consideration bubble physics as well as the effect of gases under pressure. A lot of gases were utilized in the development of such tables including Air, Oxygen, Heliox ( Helium + Oxygen), Nitrox ( Air + Oxygen) and Trimix ( Helium + Nitrogen + Oxygen )
The privileges of using these tables are:
1. They have a relatively high cure rate ( up to 90% when the elapsed time before recompression is relatively short).
2. They enable the average operator to easily decide which tables to use according to the severity of symptoms, prognosis and recurrence during the different stages of treatment.
3. They require a chamber of a maximum working pressure of 6 ATA, which is relatively low, compared to other chambers required to carry out other suggested treatment tables. (except for table 8 USN)

The tables, which are chosen for recompression treatment in The Red Sea territory, are the U.S. Navy Recompression
Treatment Tables & Comex Treatment Tables using air, oxygen and Nitrox as breathing media.
*Tables 1A, 2A, 3 and 4 will not be published here because they are only used in absence of Oxygen and are not recognized by us any more.
*Table 5 is Oxygen treatment of Pain-only DCS.
*Table 6 is Oxygen treatment of serious DCS.
*Table 6A is Air & Oxygen treatment of Gas Embolism.
*Table 7 is Oxygen treatment of unresolved or life threatening DCI after failure of the initial treatment on table 6A or 4, the table starts upon arrival at 60 feet with a minimum duration of 12 hours of Oxygen at that depth followed by a very prolonged Oxygen decompression schedule.
*Table 8 can be used for recompression treatment up to 225 feet or to extend holds at depth between 165 & 60 feet in other tables.
*Comex Cx12 table is a shallow oxygen table suitable for treatment of mild and delayed cases.
*Comex 30A table is a 30 meters 50% Nitrox table for treatment of serious DCS with minimal nitrogen load seen in other deep air tables.

Which tables to choose?
This will depend entirely on:
*The diagnosis. (Is it TypeI DCS, TypeII DCS, TypeIII DCS or AGE?)
*The initial evaluation.(severity & urgency)
*How much time already elapsed before getting into the chamber.
*Any change of clinical picture on normobaric Oxygen breathing.
*Response of the patient to chamber treatment stages. (recompression,O2 breathing & decompression) symptoms can improve, remain stable,progress or even deteriorate. You could see a relief or a relapse!

A flow chart is given to provide a systematic method for selection, activation and extension of each individual table. (See Appendix)

Recent studies however encourage avoiding recompression to 50 meters (6ATA) when Air is the only gas available to breathe unless extremely unavoidable as the therapeutic potential of O2 at 2.8 ATA are much higher than those of Air at 6 ATA the fact that explains itself as follows:
1. O2 breathing will increase oxygenation of tissues and keep the partial pressure of the inert gas in the lungs as low as possible to enhance its elimination from the body minimizing any further contribution, while absorption of excess nitrogen (N2) during recompression on deep Air tables may aggravate the case.
2. Studies indicated that the lifetime of a bubble should not vary markedly with pressure in excess of 3 ATA.
3. Bubble reduction in an O2 breathing patient at 3 ATA is 4 -5 times greater than with Air breathing at the same pressure.
4. With O2 breathing the gas tension gradient from bubble to tissue is maintained optimal throughout the treatment preventing bubble growth.
5. Hyperbaric O2 breathing ensures prevention of oedema caused by hypoxia of the CNS.
6. It has been proven that O2 breathing at 3 ATA is a specific treatment for cerebral oedema.
7. Research studies showed that intra-vascular bubbles will have a length /diameter ratio varying from 1/1 to 30/1 which makes mechanical reduction of bubble size to 1/6 under 6 ATA only applicable to extra-vascular or spherical bubbles. In other words, recompression on deeper tables is beneficial only in certain incidents.
8. Other difficulties with air tables may include: aggravation of symptoms during ascent, prolonged decompression, nitrogen narcosis and DCS for attendants and respiratory distress due to increased air density under pressure especially in patients already having respiratory affection.
However in a serious case of DCI following air dives, presenting within a relatively short period (max. of 2 hours), where the gas bubbles are suspected to be still the major tissue insult, as in cases of spinal (blown up) decompression or AGE, the mechanical pressure (bubble squeeze) of 6 ATA tables might be accepted in spite of the massive nitrogen load caused by breathing Air at such depth.

A good escape is to use Nitrox 50 at 5 ATA (40 meters) to:
1. Mechanically crush the bubbles.
2. Reduce loading of excess nitrogen.
3. Benefit from the higher Oxygen partial pressure.

Another solution is to use 50/50 Heliox at 4 ATA (30 meters), which has the advantage of adding no more nitrogen to the body

*Some authors showed the possibility of using a Heliox rebreather inside the chamber in case the Hyperbaric facility has no access to utilizing different treatment gases through the chamber panel.

* O2 or Heliox mixtures should be used in the treatment of DCS developing after Heliox diving while Heliox tables are believed to be far better than standard Air tables in treating DCS developing after diving on Trimix, as well, Heliox usually succeeds when air tables fail in treating serious DCS cases following air dives.

Once the treatment table has been chosen, treatment is conducted by carrying out recompression and decompression procedures specified in this chosen table.

If complications (recurrence) develop during or after treatment, procedures are given in a specific flow chart.(See Appendix).

The inside tender(s) who enter and leave the chamber whilst carrying out the treatment tables for the victim should be decompressed on Air or Oxygen in the outer lock of the chamber all the way back to the surface using the U.S Navy Standard Air Decompression tables or Surface Decompression tables using Oxygen putting into consideration calculating their residual nitrogen from previous in-water or in-chamber exposures (dives).

Follow-up HBO treatment

Some cases of serious DCI will require further treatment in the chamber in the form of Hyperbaric Oxygen (HBO) sessions. CNS O2 toxicity in HBO treatment is rare because all treatments are carried out at pressure below 2.8 ATA and the duration of a single treatment seldom exceeds 2 hours. Pulmonary O2 toxicity (more often seen as a result of prolonged normobaric O2 exposure) should as well be put in consideration despite that most clinical findings reported no remarkable impairment of lung functions after prolonged HBO treatment. The concept of unit pulmonary toxic dose (UPTD) is used to express the HBO pulmonary toxic dose in terms of an equivalent exposure to O2 at normal atmospheric pressure. In situations where prolonged exposure to HBO is required, the benefits of treatment versus the risks of Oxygen toxicity effect on the lung tissues of the patient should be carefully weighed.

*After recompression treatment is successfully achieved, returning to atmospheric pressure together with starting air breathing might lead to recurrence of symptoms due to nitrogen access to the tissues and permitting the existing small bubbles to regrow. The administration of oxygen after recompression therapy reduces the incidence of recurrence and hence the need for further chamber treatment. A recommended practice is to institute a 30 minutes air / 30 minutes oxygen regime for 6-8 hours right after recompression treatment is completed to prevent deterioration of the patient’s clinical state.

Diving fitness after a decompression accident:
It has been shown by researchers that changes in blood composition following decompression takes at least 10 days before returning to normal picture. It thus seems wise to prohibit diving during this period.

Following DCS, unless changes are made to the exposure, the past is likely to be repeated – but with greater severity.

If any neurological residue persists after 3 months, some authors will permit diving for short periods to a maximum of 9 meters provided that the diver’s psychological and physical fitness is not impaired. But I personally think that the diver should be advised to stop diving altogether due to increased susceptibility to future damage by already hampered nervous system.

Flying after diving and chamber treatment

- Cabin pressure of most air crafts is adjusted to 2500 meters (8000 feet which equals 0.74 ATA), the reduction of pressure that might be sufficient to push residual inert gas(es) dissolved in diver’s tissues to come out of solution forming bubbles (Decompression sickness).
- So flying within 12 hours after diving (super-saturation period) is a recognized hazard that should be avoided
- A victim suffering from DCS, should be evacuated by helicopter or air craft at very low altitude or in a pressurized air craft at cabin pressure not less than 250 meters (800 feet), the patient should be breathing O2 until arrival at a recompression facility.

-Flying after chamber treatment has always been a point of controversy!
As a matter of fact, bubbles may persist without evidence after DCS or hyperbaric treatment, as well; hypoxia (altitude effect) might cause recurrence of symptoms in patients treated for neurological DCS. So, it is recommended to wait at least 4 days after the DCS patient appears cured or 7 days after he has reached a plateau in responding to daily HBO treatment before flying. If the patient has to be transferred earlier, this should be carried out in:
1-An air craft pressurized to ground level, OR
2-A normal air craft pressurized to 8000 feet while breathing 100% oxygen and after 2-4 hours oxygen breathing at ground level, OR
3-An 800 feet pressurized aircraft while breathing 100% oxygen all through the time of the flight.

*Tenders on tables 5,6 or 6A should wait at least 12 hours before flying while tenders on tables 4 or 7 should not fly before 48 hours.
*Patients receiving HBO sessions for non-diving related maladies can fly shortly after any chamber treatment provided that the tables used did not employ any air periods.

Summary of rules for Recompression treatment

- Follow the treatment tables accurately unless modified by a specialized diving physician.
- Maintain accurate ascent and descent rates.
- A qualified tender must accompany the casualty in the chamber during treatment.
- Examine the patient thoroughly before admission, at the treatment depth., before and after arrival at each step, and during long stops.
- Treat an unconscious patient for gas embolism or serious DCS unless this possibility can be ruled out without question.
- Be alert to O2 toxicity when O2 is used.
- In the event of O2 convulsions, remove oxygen, halt ascent and restrain the patient from hurting him/herself.
- Maintain O2 use within the time and depth limitations.
- Observe the patient for at least 6 hours after the treatment for recurrence of symptoms.
- Keep the patient near the chamber for the following 24 hours after treatment.
- Maintain a well stocked medical kit at hand.
- Carefully log all stages of treatment and keep to use as record when needed.
References

1. U.S. navy diving manual
2. NOAA diving manual
3. Text book of Hyperbaric medicine (K.K Jain)
4. Hand book of HBO therapy (B. Fischer / K.K Jain)
5. Under-water medicine (Stanley Miles)
6. Under-water medicine of South African navy
7. Advanced Diving Technology and Techniques (NAUI)
8. Oxygen first aid for divers (John Lippman)
9. Diving & Subaquatic Medicine (Carl Edmonds)