1. CDC 2009 http://www.cdc.gov/media/pressrel/2009/r090128.htm
2. Roan S Anesthesia’s effect may linger after patient goes home 2005 http://healthpolicy.stanford.edu/news/gaba_discusses_longterm_risks_of_anesthesia_surgery_in_la_times_article_20050708/
3. Acute pain management: programs in US hospitals and experiences and attitudes among US adults;Warfield;Anesthesiology.,1995
4. Optimising postoperative pain management in the ambulatory setting;Shang;Drugs.,2003
5. WHO WHO’s pain ladder 1986 http://www.who.int/cancer/palliative/painladder/en/