Something

     public static void Update(int iVatID, decimal dVat, bool isActive)
        {
            ISession objSession = Pcms.Classes.Base.NHibernateHelper.SessionFactory.OpenSession();
            ITransaction objTransaction = null;
            try
            {
                objTransaction = objSession.BeginTransaction();
                Pcms.Classes.Vat objVat = new Pcms.Classes.Vat();
                objVat.VatID = iVatID;
                objVat.Percentage = dVat;
                objVat.isActive = isActive;
                objSession.Update(objVat);
                objTransaction.Commit();
            }
            catch (HibernateException objException)
            {
                objTransaction.Rollback();
                throw objException.InnerException;
            }
            finally
            {
                objSession.Close();
            }
        }