Storing Javascript value into PHP

Short note!
I'm programming a web app for a health clinic and I just had a problem to give a notification sound for the doctor if new patient registered.

I use SSE to update the list of the queuing patients. The number of the queuing patients will be reduced if one patient is served and added if a new patient registered. The notification sound should be ringed once when a new patient registered.

The question is, where should I put the update function since I save the header, the side menu and the body (content) separately.

If I put the update function in the body, the problem is I have to put the update function in every page. Well it is actually not a problem, it is just funny to put the same function in every page.

So I decide to put the function in the header, since every page uses the same header. The problem is wherever I browse through the web app, the notification sound just may only be ringed once!!!! That means, I have to store the current number of the queuing patients as a session variable. That is the solution, but the problem is how I can do that since the Javascript updating the number..???!!!!

For the record, Javascript is client side and php is server side. So it is imposible to save Javascript value into PHP, if I do it via Javascript. That is the second clue. I have to pass the Javascript value to PHP somehow and let the PHP stores the value to a session variable.

So this is how I do that:

1. Storing: Use AJAX to pass the Javascript value to PHP
2. Storing: Since I am using MVC, I make a function in Controller just for storing the value to a session variable.
3. Fetching: Make a Javascript function to fetch the value of the session variable and call it on loading windows. Storing PHP value into Javascript variable should not be a problem. 
4. Fetching: Put the AJAX function inside SSE and call it if the number of queuing patient is added.