To the extent that you have joint legal custody this dispute may well need to be resolved by the Court. If the Court finds that your ex-husband is acting unreasonably one potential remedy is to grant you sole legal custody, at least with respect to medical decision.
If you already have sole legal custody, inform the care providers of this and proceed without your ex-husband's consent.
To the extent that you feel that you may need additional information or to change any existing custody and visitation orders you should consult with an experienced family law attorney in your community.
Any substantive or procedural information contained in this response is for informational purposes only. The provision of this information does not constitute legal advice nor does it create an attorney-client relationship. To obtain legal advice relevant to your situation you should contact a local family law attorney. The Law Office of Matthew J. Rudy is happy to provide a free one-hour consultation to individuals located in the greater San Francisco Bay Area.