How do I calm my nerves before rare high-stakes procedures?

You are competent at the everyday procedures, and that competence is proof you can learn hard things. The rare ones rattle you because you do them seldom, so your hands have less memory of them. That anxiety is about reps, not ability. Nerves before a high-stakes, uncommon procedure are not a warning that you will fail. They are your mind taking it seriously, which is exactly what you want in that moment. The steadiest clinicians still feel it. They have just learned to act alongside the feeling instead of waiting for it to pass. Before the next rare one, rehearse it in your head start to finish, and review the steps even if you know them. Mental practice narrows the gap that low reps leave. The anxiety may still show up. Let it. You can be nervous and precise at the same time.