Thanks a lot!
It is working after a few changes.
ppExtComLines.SaveToStream(ppLob);
ppDS.DeclareVariable('p_ext_notes',otBLOB);
ppDS.SetComplexVariable('p_ext_notes',ppLob);
ppDS.SQL.Text:='begin gdp.gdp_edit.ip_clear_and_init_comments(:p_id); gdp.gdp_edit.pp_temp_blob:=:p_ext_notes; end;';
ppDS.Execute;