This video shows what it looks like from the inside when a needle thoracostomy is inserted into the chest. Note that it takes about a minute for the lung to expand, so be patient when you insert the needle. You can also get an idea of why the needle is only a temporary measure as the inflating lung begins to kink the catheter.
Don’t ask why there was a thoracoscope in the chest with a tension pneumo in the first place, though!
Source: The Trauma Professionals’s Blog