If a variable is at class level (ie, `private MyDataAccessClass _dataAccess;`, can it be used as part of a using statement within the methods of that class to dispose of it correctly?

Is it wise to use this method, or is it better to always declare a new variable with a `using` statement (ie, `using (MyDataAccessClass dataAccess = new MyDataAccessClass())` instead of `using (_dataAccess = new MyDataAccessClass())`)?