As with all activities we undertake, professionally or in our free time, safety is a key factor and prevention will always be more desirable than reaction with regards to possible injury or illness. Often, being aware of what not to do can be as important as knowing the correct way to proceed. 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.