Hi, in day to day life docs face these type of problems. When some comes in collapse stage, we can't find vein , over use of vein for intravenous injections is the second reason for these type of vein. If persons are obese
and extra fat is over his body location of veins are very difficult. In some cases vein become a thin thread like . Regular excercises are the best way as this makes vein very patent but it take regularity and long time. Some times an expert can find vein but careless fellow don't find.