Q Is it possible for someone to be relatively immune to anesthesia? My character undergoes anesthesia for facial cosmetic surgery (scar removal), but the anesthetic doesn’t take and she freaks out. I imagine she’d be able to communicate this to the anesthesiologist, who’d then try a different form of anesthesia, but it would scare her in any case. A few years later could the same character be given a shot of morphine by the bad guy and again be relatively unaffected by it (maybe woozy but not out cold)? I figure he gives her what he thinks is enough to render her unconscious or even kill her, but she comes to eventually. I want the earlier operating room experience to give credence to the later morphine experience.
A Yes, this would work. Drugs of all types affect each of us in very different ways. Alcoholics can tolerate alcohol in quantities that would kill the normal person. Same for heroin in those addicted to that drug. Similarly, some people require a small dose of an anesthetic, while others take ten times as much. This is also true for morphine sulfate (MS in medical lingo). Just 2 or 3 milligrams might put one person out, while 20 might not sedate another. It’s extremely unpredictable.
In addition, some people have the exact opposite response to anesthetics and sedatives than what was intended. Rather than sedating or rendering them unconscious, the drug makes them hyperexcitable. They become disoriented, agitated, even combative. These are called idiosyncratic reactions. This is a general term for any reaction that is different from what is expected with a particular drug.
Your character could have a hyperexcitable reaction to the anesthetic, and the anesthesiologist would have to use a different one. Or she could simply not be affected by it as much as expected and still feel what was going on. Here a larger dose of the same anesthetic would finally put her out. She could then later have either of these reactions to the MS.
So, yes, your character could easily require more than the usual amount of either or both meds to be sedated. Or she could have an idiosyncratic reaction to either or both. She could even be resistant to one and hyper with the other. Anything is possible.