20th Century

In the 1920s and 1930s, the complexity of surgical procedures increased, and several PACUs opened in the United States and abroad. For example, a three-bed neurosurgical unit was opened in 1923 at Johns Hopkins Hospital by Dandy and Firor.^{[4] [5]} It was not until World War II, however, that the number of PACUs increased quickly. The major reason for the increase was the shortage of nurses in the United States. PACUs were created so that an adequate level of nursing care could be provided for the immediate postsurgical patient.^[6] PACUs opened at the Mayo Clinic in 1942, at New York Hospital in 1944, and at the Ochsner Clinic in 1945.^[7]

Postoperative recovery care saved lives. In 1947, the Anesthesia Study Commission of the Philadelphia County Medical Society issued a report that further stimulated the growth of PACUs.^[8] The commission found that in an 11-year period, nearly half the deaths that occurred during the first 24 hours of surgery were preventable. They also found that at least a third of those deaths could have been prevented by improved postoperative nursing care.^{[5] [7]} After this report, many U.S. hospitals opened PACUs.^{[9] [10] [11]} In 1949, the Operating Room Committee for New York Hospital proclaimed^[12] : "Today it can be stated categorically that an adequate recovery room service is a necessity to any hospital undertaking modern surgical therapy."

During the 1950s and 1960s, PACUs and surgical intensive care units (ICUs) with postoperative respiratory support became more common. More complex surgical procedures were able to be performed on sicker patients. In many hospitals, the original ICUs proved too small to handle the large number of cases requiring intensive postoperative care. Many PACUs were therefore forced to serve as short-term ICUs for surgical patients. In the 1970s, PACUs were required to manage both routine patient recovery from anesthesia and critically ill postoperative patients with invasive monitoring.