In the United States, anesthesia can be administered by physician anesthesiologists, an anesthesiologist assistant, or nurse anesthetist. Anesthesia providers Anesthesiologists Anesthesiologists are physicians (MD/DO) specializing in the practice of anesthesiology. The training of a physician anesthesiologist typically consists of 4 years of college, 4 years of medical school, 1 year of internship, and 3 years of residency optionally followed by a one-year fellowship in a sub-specialty. It is the highest training level for all practitioners delivering anesthesia in the United States. While most physicians practicing anesthesiology in the United States pass a comprehensive board exam, board certification is not required in order to practice anesthesiology. Physicians who have successfully completed training in an ACGME accredited program become board eligible at the time of graduation and may practice anesthesiology until board certification is attained, commonly within one year post graduation. According to an American Society of Anesthesiologists (ASA) press release Anesthesiologists provide or participate in more than 90 percent of the 40 million anesthetics delivered annually. Other specialties within medicine are closely affiliated to anesthesiology. These include intensive care medicine and pain medicine. Specialists in these disciplines have completed training in anesthesia including a three-year residency in anesthesia with an additional year in an accredited fellowship in a sub specialty of anesthesia (e.g. Pain, Critical Care Medicine, Obstetric Anesthesia, Pediatric Anesthesia). Anesthesiology is not limited to the operating room. Physician anesthesiologists are termed "peri-operative physicians", and are involved in optimizing the patient's health before surgery, performing the anesthetic and associated procedures (e.g. neuraxial anesthesia, specialized intravascular access), following up the patient in the post-anesthesia care unit and post-operative wards, and ensuring optimal analgesia throughout. Some sub-specialty physician anesthesiologists are an integral member of the critical care team in Surgical Intensive Care Units (SICU) and manage complex surgical patients throughout their hospitalization. Certified Registered Nurse Anesthetists (CRNA) Certified Registered Nurse Anesthetists are advanced anesthesia providers advanced practice registered nurses specializing in the provision of anesthesia are Certified Registered Nurse Anesthetists (CRNAs). As of 2018, CRNAs represent more than 50% of the anesthesia workforce in the United States, with 52,000 providers, according to the American Association of Nurse Anesthetists, and administer more than 40 million anesthetics each year. Thirty-four percent of nurse anesthetists practice in communities of less than 50,000 due to the rural pass-through program where "eligible hospitals may use reasonable-costs based Part A payments in lieu of the conventional Part B