Pain and Anesthesia I

Astute medical students sometimes ask: why does the anesthetized patient need pain medications? After all, under general anesthesia, patients aren't conscious, they aren't aware, they shouldn't be feeling any pain, they shouldn't remember the surgery. It's an interesting question, and I'm not sure I have a fully satisfactory answer. Most of our anesthetics don't provide analgesia; that is, they don't quell that unpleasant sensation of hurt we feel when we are cut. They simply make it so patients aren't aware of what they're feeling, if that makes any sense.

And patients under anesthesia do respond to noxious stimuli (our euphemism for pain). An unconscious patient may breathe faster, increase their blood pressure, and have a higher heart rate on incision. Although the brain is blissfully unaware, the rest of the body reacts, and stress hormones pour out, perhaps at higher quantities since the patient cannot react. We often use these measures as indicators of how much pain a patient experiences and how much analgesia they may need. Working in pain medications protects the other organs by alleviating the stress response of surgery and allows for a smoother wake-up at the end of the case as we know how much the patient needs.

All of this is fascinating to me; it seems to suggest that pain is not solely a subjective experience because even if you take away that experiential aspect, we think patients have pain. Are there objective ways to measure it? Why is our understanding of this phenomenon so limited?