The CEO of the biggest health care system in the state fiercely defended the practice of a single surgeon performing two operations at the same time in a talk this morning, saying the practice likely saved lives during the Boston Marathon bombing. Dr. David Torchiana, CEO and president of Partners HealthCare and former chairman and CEO of the Massachusetts General Physicans Organization, was asked about the practice toward the end of an executive forum of the Boston Chamber of Commerce. The largest hospital in Partners' chain, Massachusetts General, was featured prominently in a piece in the Boston Globe recently that was largely critical of the practice of doctors performing two surgeries at once.