Small and rural hospitals can have a tough time keeping patients. Many will drive an hour or two to the nearest city for all but the most basic â" or most urgent â" care. And the sickest patients may have to be shipped out anyway, to reach the specialists that might save them. What if high-tech tools could bring the big-city expertise to their patients instead? Thatâs the pitch from Visicu Inc., a 10-year-old company acquired a few months ago by a unit of electronics giantPhilips. More than a