Question
How long can nerves/tissues in the spinal cord survive without oxygen before they become damaged. i.e if the nerves are pressured or trapped by a nitrogen bubble in spinal cord area after sub aqua diving. The casualty needs to be treated in a recompression chamber but what is the time limit before damage is caused ?  

Answer
Gary:
If the nitrogen bubble is trapped in the spine around the nerves, the time for decompression before a nerve damage occurs will depend on the size of the bubble. If the bubble is small, then the pressure exerted on the nerves may allow survival of the nerves for a long time. This kind of compression is very rare.
Nitrogen more often gets trapped inside the blood vessels. The bubble virtually blocks all flow of blood to the tissue where the blood was transported. This is called ischemia. All oxygen and nutrients transported in the blood are blocked from reaching the area supplied by that blood vessel. The spinal cord and brain cannot tolerate complete lack of blood flow for more than 3 minutes without damage. However many times there is only a partial block. The time critical for survival of the tissue can vary greatly depending on how partial the block is. Typically, this partial blocks can allow survival of the spinal cord or brain for 15 min to few hours. Probably less that 4 hours or so.
FCM