Dr. Alvin Rajkomar was doing rounds with his team at the University of California, San Francisco Medical Center when he came upon a puzzling case: a frail, elderly patient with a dangerously low sodium level.

As a third-year resident in internal medicine, Dr. Rajkomar was the senior member of the team, and the others looked to him for guidance. An infusion of saline was the answer, but the tricky part lay in the details. Concentration? Volume? Improper treatment could lead to brain swelling, seizures or even death.

Dr. Rajkomar had been on call for 24 hours and was exhausted, but the clinical uncertainty was “like a shot of adrenaline,” he said. He reached into a deep pocket of his white coat and produced not a well-thumbed handbook but his iPhone.

With a tap on an app called MedCalc, he had enough answers within a minute to start the saline at precisely the right rate.

The history of medicine is defined by advances born of bioscience. But never before has it been driven to this degree by digital technology.

The proliferation of gadgets, apps and Web-based information has given clinicians — especially young ones like Dr. Rajkomar, who is 28 — a black bag of new tools: new ways to diagnose symptoms and treat patients, to obtain and share information, to think about what it means to be both a doctor and a patient.

And it has created something of a generational divide. Older doctors admire, even envy, their young colleagues’ ease with new technology. But they worry that the human connections that lie at the core of medical practice are at risk of being lost.

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