In January, in Japan, 25 hospitals refused to permit an ambulance to transport a man who was pronounced dead when he finally arrived at a hospital.
Were the patients already in the ED (Emergency Department) less stable than this patient?
Was this patient going to be the straw that breaks the camel’s back and result in the deaths of other patients already in the ED?
What kind of evidence do we have to justify diversion?
Paramedics rushed to his house but were told in turn by all 25 hospitals in the area that they could not accept the man because they did not have enough doctors or any free beds, a local city official said, adding some institutions were contacted more than once.
We do not know if he would still be alive if he had been transported to the first ED, or to the second, or to the third, . . . . We do not even know the cause of death. However, this is a good way to introduce the topic of diversion.
Diversion is not just a problem in Japan, but also in the US and other countries. It has become more convenient for many people to go to the ED than to wait to see a primary care physician. Until that problem is fixed (assuming that it ever is fixed), is diversion appropriate?
There have been a couple of studies in San Diego of what happens when diversion is minimized, or eliminated.
Even though volume went up, diversion dropped to almost zero.
The authors acknowledge that the main limitation of this study was the short time frame of the analysis, comparing one week to another.
In a longer study, diversion decreased and the need for transfers between hospitals dropped. There did not appear to be any negative consequences of minimizing diversion.
In summary, a community-wide effort to improve getting patients to requested EDs and decreasing ambulance diversion hours can be successful in a large community with an urban, suburban, rural, and remote population distribution. The success of such a process had the additional effect of decreasing the need for ED interfacility transfers for payer request reasons.
In this month’s Annals of Emergency Medicine is a study looking at what happened when Massachusetts banned diversion.
Figure 1. Changes in ED length of stay by hospital among A, admitted patients and B, discharged patients. C, Changes in ambulance turnaround time by hospital. D, Changes in total hospital volume before and after a ban on ambulance diversion by hospital.
It seems that the benefits of diversion are just another medical myth.
Research has led to the consensus that crowding is largely due to output factors, particularly the practice of boarding admitted patients in the ED2,7-10 because of lack of inpatient capacity. Ambulance diversion, in contrast, is an input factor, which has little effect on ED crowding.4 
Very few of the patients coming in to the ED are arriving by ambulance.
On July 3, 2008, the department released a policy directive ending the practice of ambulance diversion in the state, except in cases of internal hospital disaster.17 The policy took effect on January 1, 2009, allowing hospitals 6 months to prepare for the changes necessary for its implementation. This policy represented the first statewide ambulance diversion ban in the United States.
A lot of the bad things were supposed to occur when diversion was banned.
None of them happened.
Preliminary reports from hospitals suggest that the end of ambulance diversion has been a relative success because of operational changes made at individual hospitals in anticipation of the ban.24,28 Early reports from Boston Emergency Medical Services (EMS) suggest that there has not been an increase in ambulance turnaround time as feared, although this has not been formally studied.29 
At the Gathering of Eagles conference, this was one of the topics.
-It negatively impacts EMS operations and could jeopardize our ability to respond to the next critical patient.
-It often results in patients being transported to ED’s other than where their MD’s or medical records are.
-It negatively impacts patient satisfaction and provider morale.
-It does little if anything to reduce ED overcrowding.
In places that use diversion, when all of the hospitals are on divert, the dispatch center is supposed to notify the hospitals that dispatch will be making destination decisions until things improve. I have not seen any explanation for why that was not the case in Japan.
Diversion does not appear to provide any real benefit to anyone, except that it is consistent with the superstitions of many people, and medical people are as superstitious as gamblers.
 The effects of minimizing ambulance diversion hours on emergency departments.
Khaleghi M, Loh A, Vroman D, Chan TC, Vilke GM.
J Emerg Med. 2007 Aug;33(2):155-9. Epub 2007 Jun 18.
PMID: 17692767 [PubMed - indexed for MEDLINE]
 Community trial to decrease ambulance diversion hours: the San Diego county patient destination trial.
Vilke GM, Castillo EM, Metz MA, Ray LU, Murrin PA, Lev R, Chan TC.
Ann Emerg Med. 2004 Oct;44(4):295-303.
PMID: 15459611 [PubMed - indexed for MEDLINE]
 The effect of an ambulance diversion ban on emergency department length of stay and ambulance turnaround time.
Burke LG, Joyce N, Baker WE, Biddinger PD, Dyer KS, Friedman FD, Imperato J, King A, Maciejko TM, Pearlmutter MD, Sayah A, Zane RD, Epstein SK.
Ann Emerg Med. 2013 Mar;61(3):303-311.e1. doi: 10.1016/j.annemergmed.2012.09.009. Epub 2013 Jan 24.
PMID: 23352752 [PubMed - in process]
75-year-old Japanese Man Dies After Hospitals Reject Him 36 Times
By Yue Wang
March 06, 2013
Khaleghi, M., Loh, A., Vroman, D., Chan, T., & Vilke, G. (2007). The Effects of Minimizing Ambulance Diversion Hours on Emergency Departments The Journal of Emergency Medicine, 33 (2), 155-159 DOI: 10.1016/j.jemermed.2007.02.014
Vilke, G., Castillo, E., Metz, M., Upledger Ray, L., Murrin, P., Lev, R., & Chan, T. (2004). Community trial to decrease ambulance diversion hours: The San Diego county patient destination trial Annals of Emergency Medicine, 44 (4), 295-303 DOI: 10.1016/j.annemergmed.2004.05.002
Burke, L., Joyce, N., Baker, W., Biddinger, P., Dyer, K., Friedman, F., Imperato, J., King, A., Maciejko, T., Pearlmutter, M., Sayah, A., Zane, R., & Epstein, S. (2013). The Effect of an Ambulance Diversion Ban on Emergency Department Length of Stay and Ambulance Turnaround Time Annals of Emergency Medicine, 61 (3), 303-3110 DOI: 10.1016/j.annemergmed.2012.09.009