Your Medical Expenses are a Non Refundable Tax Credit that are used to reduce your tax payable. If you do not need to use them this year, you should not include them on your tax return at all. What you do is hang on to them and then you can claim them in the following year by using a "one year block". 

How this works is you choose an optimal time period that ends in the tax year you are filing. For example: If you began incurring high Medical Expenses in March 2018, your one year block would be March 1st, 2018 to February 28th, 2019.