An intensivist is a physician (M.D. or D.O.) who specializes in the care of critically ill patients, most often in the intensive care unit (ICU). Intensivists can be internists (pulmonologists, emergency medicine physicians, or other sub-specialist), anesthesiologists, pediatricians (including neonatologists), or surgeons who have completed a fellowship in critical care medicine. The intensivist must be competent not only in a broad spectrum of conditions common among critically ill patients but also with the technical procedures and devices (i.e. mechanical ventilators) used in the intensive care setting.