PowerShell Terminal Services/Citrix

Hi I am trying to use Powershell 2.0 to carry out the following task on Citrix XenApp 6.5

I am using the following command

Send-XASessionMessage -ServerName

I would like to send a message to all sessions on a particular server

However when I try it asks me for a specific sessionId

From the -sessionID parameter is there a way to select all sessions?

Thanks

Dean