Two things you could do I think...
Here's how you could do either:
$pinfo = New-Object System.Diagnostics.ProcessStartInfo
$pinfo.FileName = "notepad.exe"
$pinfo.RedirectStandardError = $true
$pinfo.RedirectStandardOutput = $true
$pinfo.UseShellExecute = $false
$pinfo.Arguments = ""
$p = New-Object System.Diagnostics.Process
$p.StartInfo = $pinfo
$p.Start() | Out-Null
#Do Other Stuff Here....
$p.WaitForExit()
$p.ExitCode
OR
Start-Job -Name DoSomething -ScriptBlock {
& ping.exe somehost
Write-Output $LASTEXITCODE
}
#Do other stuff here
Get-Job -Name DoSomething | Wait-Job | Receive-Job