Signs and Symptoms of Decompression Illness

 

What is DCI ?

Decompression Illness(DCI) is a term used to describe both Decompression Sickness (DCS) and Cerebral Arterial Gas Embolism (CAGE). It is caused by the expansion of inert gas bubbles (Nitrogen) into tissues on decreasing pressure. The tissues affected tend to be those tissues with a poorer blood supply, as the nitrogen is less readily removed. Three gas laws are of particular importance with regard to DCI;

Boyle’s Law states “for any gas at a constant temperature, the volume of a gas will vary inversely with the absolute pressure”.


Dalton’s Law states “the total pressure exerted by a mixture of gases is equal to the sum of the pressures of each of the different gases making up the mixture, with each gas acting as if it alone was present and occupied the total volume”.

Henry’s Law states “the amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of that gas in contact with the liquid and the solubility coefficient of the gas in the particular liquid”.

As can be seen from the above at deeper depths more nitrogen will be dissolved in tissues, on ascent the nitrogen will come out of solution forming bubbles which if they cannot be removed will cause the symptoms of DCI.

It is the bubble size rather than the fact that they are nitrogen that causes the problems.

Risk Factors for DCI
The following are examples of factors that can increase the chance of DCI and is not meant as an all-inclusive list.

Depth of dive
Dives deeper than 40m are an independent risk factor for DCI

Inadequate decompression
Remember most computers are based on theoretical data
Tables are often based on fit young men (e.g. USN tables based on Navy divers), most recreational divers do not fall into this category!
It is always safer to do slightly longer decompression than is the minimal requirement according to the computer/tables.


Repeated dives
Following a dive the body will have a residual nitrogen load, this needs to be taken into account when planning the following dive(s).


Patent Foramen Ovale (PFO)
This is a communication between the right and left side of the heart through the wall between the two upper chambers (atria).
Due to pressure changes at birth, in the majority of the population it closes and seals.
If it remains open blood can be shunted from the right (deoxygenated) side to the left (oxygenated) side of the heart bypassing the lungs, any nitrogen bubbles in the blood will not be filtered out by the lungs and will be able to pass into the arterial circulation and to the brain.
25% of the general population have a PFO but up to 75% of those with unexplained DCI have a PFO
A test involving an ultrasound scan of the heart (echocardiogram) and injecting a saline solution that has been vigorously mixed with blood can be performed in divers with unexplained DCI to determine whether they have a PFO.


Equipment failure
Not always avoidable but check kit thoroughly before diving and ensure you know how to use any new kit and have checked it at shallow depth.


Alcohol
A frequent contributing factor for DCI, consumption the night prior to a dive causes a degree of dehydration which will increase the chance of DCI.


Smoking
Causes blood vessels to vasoconstrict which will reduce tissue perfusion. Increases amount of CO (carbon monoxide) in the blood which reduces the bodies oxygen carrying capacity.


Temperature
Cold water increases the oxygen demand on the body.


Obesity
Fat is five times more soluble to nitrogen than muscle, so there is an increased nitrogen load.


Gender
There is some evidence to suggest that there is an increased chance of DCI for women mid-menstrual cycle. Men are more likely to have an episode of DCI than women due to risk taking behaviour.


Flying
At altitude there is a lower partial pressure of each gas
According to Boyle’s Law the volume of a gas will therefore increase. If nitrogen bubbles are present their volume will increase, worsening any symptoms of DCI.In view of this it is recommended that flying be avoided until 12-24 hours after a dive.

Symptoms and Signs
The following are some of the symptoms of DCI.

 

General

Anorexia
Excessive fatigue
Malaise
Headache
Vomiting
Pain
Joint pains
Ear pain
Chest pain
Skin
Itching
Redness
Marbling
Level of conscious
Speech and thoughts
Orientated in time and place
Personality change
Dysphasia (difficulty speaking)
Hearing and vision
Hearing loss
Vertigo
Tinnitus
Visual impairment
Strength
Weakness of limbs
Sensation
Paraesthesia (pins and needles)
Numbness
Co-ordination
Gait
Poor balance
Bladder and bowels
incontinence
Pulmonary
Cough
Shortness of breath
Voice changes
Haemoptysis (coughing up blood)

Treatment


Hyperbaric oxygen therapy is required, until a hyperbaric facility is reached, oxygen via a mask with a reservoir bag and re-hydration should be commenced.

Hyperbaric oxygen causes a reduction in the size of the bubbles by increasing the pressure (Boyle’s Law) and an increase in the rate of removal of the nitrogen by increasing the concentration gradient (Henry’s Law).

Different facilities will use different recompression tables at London Hyperbaric Medicine we use the COMEX 30 table, and US Navy Tables 5 and 6 for the treatment of DCI.

Divers with DCI require multiple treatments depending on there degree of symptoms. Divers are generally treated until all symptoms have resolved or until further treatments do not produce any further improvements in symptoms.