The only reason that there aren't more is that not enough data are available on-line. I attended a talk by Chris Tsien here at the MIT Artificial Intelligence Laboratory. They are manufactured by companies such as Hewlett-Packard and SpaceLabs. Her team observed no cases in which something went wrong and a monitor did not beep. So now one nurse is potentially exposed to alerts from 100 monitors hooked up to 5 patients.
Monitors are signal-centric.
There is no attempt to make them patient-centric. For example, the pulse oximeter monitor doesn't look at the ECG signal or the state of the ECG monitor. It could integrate data from multiple sensors and only raise the alarm when a combination of signals suggested trouble. But a nurse-centric monitor would be even better. If there is only one nurse and she is busy resuscitating Patient A, whose heart is stopped, then there isn't much point in alerting her to the fact that Patient B is getting a little too much oxygen.