In my world, a subdissociative (pain) dose of ketamine is .1-.3 mg/kg (or around 10-25 mg), and I have certainly had people complain of unpleasant dysphoria toward the upper end of that range, particularly when pushed. Full dissociation is closer to 1 mg/kg -- and I haven't found much use for in-between doses. Doesn't seem like partial dissociation would help much with anxiety.
Well -- that's not true. In reality, I've used doses around 50 mg for procedural-type sedation in the ICU setting -- in fact I've rarely gone much higher. But that's in shocky, ill patients, and I think it's acting like a much higher dose.
I've certainly seen patients starting to experience significant alterations in sensorium even at only 0.2 mg/kg including hallucinations, alteration in the perception of time, complaints of "fractals"/narrowing perception of vision/objects "jumping" in their field of vision; which has resulted in significant anxiety. These seem to be especially prevalent when administered quickly, including infusions times as long as five minutes on IVPB or syringe pump.
I actually cared for a patient who ended up with a stress/demand inducted STEMI when she had been given ketamine at 0.2 mcg/kg and shortly afterwards informed that she could not have narcotics due to being on a narcotic medication stewardship plan (and a complaint of exacerbation of chronic pain).
I think that this is pretty patient specific because I've also given 0.5 mg/kg ketamine doses as a slow push (1-2 minutes) to patients with severe intractable pain not responsive to high dose IV narcotics who had good pain relief and minimal alteration in sensorium. This has been in adults and peds, and most of these patients were either opioid naive or with relatively little prior exposure including splenic infacts, multi-system trauma, ischemic bowel, compartment syndrome, and so on.
We have used ketamine as a partial dissociate for conscious intubations, with other adjudicative medications such as a lido neb, with pretty good success. Every time we have used this method though it has been from patients with prior intubations/ICU management for whom the intubation itself was not as frightening as their disease process (to the patient anyway); typically on COPD, CHF, Asthma/RAD, and HAE patients. We've always intubated with the patient in a seated position and used either a glidescope or bronch so I doubt there is a lot of use in the field, let alone outside of the critical care setting.
For patients with relatively poor tolerance but can be coached I think that precedex is a great drug, a small dose of ativan or valium might be helpful but can potentially cause worsening respiratory status. I would think most of the patients who would probably be able to tolerate/benefit ketamine could probably be coached for a period of time anyway; with the exclusion of asthma/RAD. In my experience patients who are in distress and truly fight the BiPAP (excluding pediatrics) typically get tubed shortly anyway.
