Import invoices. Status "Draft", but I want it to be "Sent"

Import invoices. Status "Draft", but I want it to be "Sent"

I have imported customers, no problem
I am now importing open, unpaid invoices.  In the import file I have set the status to "Sent", but they are still imported as "Draft". 
How can I import invoices and have the status set to Sent?  There have been no payment to these invoices. - What should I set in the Status filed of the import file?