Has there been any new developments in technology that may help us high injection rates in patients who can not tolerate an 18g needle (or at times even a 20g)?

The answer is yes. This past year the Nexiva Diffusics catheter got FDA approval for use. 

This allow us to use smaller needles and still get high injection rates. The 20g Diffusics can inject up to 10 cc/sec and the 22g up to 6.5 cc/sec. This is a major step forward.

IV Catheter Safety

• Most IV catheters are pressure rated and usually the safety on the injector is for a pressure of 300 psi or less. Exceeding this can result in product leakage and or damage to the catheter and potentially injury to the patient
• Some of the newer generation IV catheters like the BD Nexiva Diffusics can be used to a psi of 325
• Please be certain that you are aware of what catheter you use and in practice it is ideal to use one brand only to prevent errors in setting the psi values in routine practice.