Jordan, as a non-clinician I will fearlessly jump in and posit that a vital sign must be clearly defined, easily measurable, and actionable (meaning if it is out of normal bounds, there is something that may be done that is more likely than not to get it back within normal bounds without harming the patient). The addition of pain as a vital sign (c. 1990’s) — in retrospect — seems to have violated this framework. It yielded the opioid crisis. The AMA and the JC are now walking back the notion of pain as a vital sign. Pain can be managed (and some institutions have now adopted an opioid-free approach to pain management), but not everything we wish to manage needs to be considered a vital sign. Good diet and exercise have positive effects on vital signs, but are not themselves vital signs.
Is patient engagement important? Sure. If it is increased is the outcome likely to be improved? Yes. But I hesitate to add it as a vital sign because we do not yet have an agreed upon and quantifiable definition. The four vital signs may be measured and can be expressed in objective measurements (though of course, as you note, context is important in order to interpret those objective measures). Your post focuses on the increased engagement that may be achieved through human interaction. Digital health tools and platforms have demonstrated that other modalities may also be quite effective, as I expect you would agree …. But I’m not yet convinced that patient engagement is a vital sign.