On the pharmacology of ketamine: [Just for general information -- I'm aware that anyone with MD after their name is already aware of the following ]
* Ketamine itself is a negative inotrope.
* However, ketamine stimulates sympathetic discharge, so administering ketamine may increase CO / MAP, provided, the patient has a functional ability to increase their heart rate and constrict their peripheral vasculature. This may not always be the case, in which case ketamine may cause hypotension.
* It is not hemodynamically neutral. It just has less potential for hemodynamic compromise than benzodiazepines, and most opiates.
* Part of the hemodynamic effect of ketamine is to raise ICP. However it's also been trialed (unsuccessfully) as a neuroprotective. There is ongoing controvery as to its use in closed head injury.
* Ketmaine also has an intrinsic bronchodilator effect, making it beneficial in situations where bronchospasm is an issue, e.g. status asthmaticus.
Ketamine is beginning to find its way into prehospital care. For example this system -- which I don't work in, before anyone asks --- (http://www.albertahealthservices.ca/hp/if-hp-ems-mcp.pdf) allows ketamine for RSI or as a sole agent in the intubation of patients presenting with hypotension, airway burns, acute asthma or procedural sedation in hypotensive patients <80mmHg (e.g. pre-cardioversion, or for fracture realignment).
I think it's often finding use outside of the US in situations where US providers might opt to use etomidate.
As a medic, I'd happily come out to give pain control to anyone. I think it's one of the most tangible benefits of having an ALS response. It's something we actually know we're good at. Personally, I'd never have an issue with coming out to pain control someone. Or, in general, to back up BLS. I'd rather a BLS provider calls me, if they have a concern, and have it be a waste of time than have someone be too afraid to call, and have the patient suffer.
But this is going to depend on your system, and the availability of ALS resources.
I think that if you're close to the hospital, and can move the patient without undue pain, or you think that a critical life threat is present, then you probably shouldn't wait for ALS. In contrast, if you have someone with previously diagnosed renal colic, having symptoms suggestive of their prior renal colic, and they're a vomiting, diaphoretic mess on their bathroom floor, it might be better just to start an IV (if that's in your scope), and wait for someone who can give opiates.