I came across this April 2004 story in 24x7
on wireless planning for hospitals. Basically a FUD (fear uncertainty
and doubt) piece on the threat of radio frequency interference (RFI),
and lays out the basics of intentional and unintentional interference.
A good list of potential interference sources is provided.

The value proposition that's put forth in the article is the need for
frequency coordination. However, about the only radio still in use in
hospitals that is overly sensitive to interference is the channelized
telemetry system. Most wireless medical devices use digital technology
that adapts to interference by shifting frequency, greatly reducing the
incidence of interference.

Most wireless medical device or WLAN deployments simply need a good
site survey and network design to result in reliable performance.