Lowering tightly-coupled dependencies when waiting for client message

I'm currently designing a server-client game and would like to lower the amount of tightly-coupled dependencies within the game. Basically, I would like the client to change its state when receiving a message from the server. The pseudocode would look something like this:

    switch(inputThread.getMessage()){
    case "dead":
        die();
        break;
    case "heal":
        heal();
        break;
    }

The problem is that changing what gets sent on the server end requires me to also change the client end, which could be problematic if I want to send a large variety of messages. What design pattern could I use to separate the client and server?