Intensive Care Unit in US hospitals

Dr. W. E. Dandy, a neurosurgeon at John Hopkins Hospital, Baltimore, Md started a 3 bed unit for post surgical neuro patients in 1923.
Barrow Neurological Institute site has a good historical narrative of the genesis of intensive care units as well as its own development.

Dedicated neuroscience units represented a relatively new concept to both St. Joseph's Hospital and the nursing profession at large. While Dr. W. E. Dandy is credited with opening a three-bed specialized care unit for postoperative neurosurgical patients in 1923 at the Johns Hopkins Hospital, the concept of such dedicated units was not widespread, nor did the concept of intensive care units (ICUs) take root for decades. ICUs were just beginning to appear in the late 1960s and early 1970s and typically were designated as postanesthesia care or coronary care units. In the nursing literature, a dedicated neuroscience ICU was first mentioned in 1975. At the time Barrow was founded, there were no dedicated neuroscience units in Arizona. Consistent with the national trend, the first ICU at St. Joseph's Hospital was the coronary care unit; the second ICU was the NICU. That first NICU housed a total of 6 beds. Four beds were clustered in a general ward setting, and there were two private rooms and one hyperbaric chamber. Despite the neurosurgical title of the NICU, nurses working there treated patients with disease processes other than those with a neurological dysfunction. The NICU included patients undergoing hyperbaric oxygen therapy and renal dialysis, patients requiring support by an iron lung, and burn patients. Ultimately, these services remained a part of the care provided at St. Joseph's Hospital, except for patients with burns. The latter were automatically transferred to Maricopa County Hospital when the burn unit opened there in the 1970s.
During these early years, scant assistive technology was available. Consequently, nursing care relied on close observation of patients and changes in their level of consciousness (LOC). As nurses and neurosurgeons recollect, the calls made to physicians from the ICU nurses were in response to changes in a patient's LOC. When reports of a decreased LOC were communicated to the physician, nurses were instructed to give patients a "pinch of mannitol." The LOC was the single most important assessment parameter. The NICU had no cardiac monitors. There was no invasive blood pressure monitoring. Temperatures were measured with mercury-filled thermometers, and blood pressure was measured with traditional sphygmomanometers. The only invasive lines were urinary catheters and nasogastric tubes.
In 1962, one registered nurse (RN) cared for one or two patients in the NICU. However, the staffing pattern was different on the general neurological-neurosurgical floor. Because specialized neurological units were new, it was difficult to establish staffing patterns and appropriate patient-to-nursing care ratios on the floor. At the time, the popular nursing model for patient care was referred to as Team Nursing. The Team consisted of an RN, a licensed practical nurse (LPN), and one nurse's aide to provide nursing care for 5 or 6 patients. The RNs were responsible for performing patient assessments, reviewing laboratory results, noting orders, and all communications with physicians. The LPNs administered all medications to the patients cared for by the team. The nurses' aide or orderly helped with the manual demands of patient care such as lifting, turning, and getting patients out of bed.
The physical component of neuroscience nursing was demanding. There were no specialized chairs to facilitate getting patients up or specially constructed slide boards to move patients from one horizontal surface to another. There were no special rinse free soaps for use during bathing. There were no electric beds. Hand cranks were used to raise or lower the head or knee position. The work was demanding, but as a former nurse who worked on the general neurosurgical ward for 20 years quipped "Of course it wasn't easy; if it was, any nurse could do it." The nurses who elected to work at Barrow and the physicians with whom they worked were committed to the ideal that every patient deserved a nurse who specialized in the care of the neurologically impaired.

My personal professional experience reflects above article. Most hospitals in the 60's, ICU started as coronary care units with cardiac monitors. Cardiologist train and certify nurses to read EKG and give appropriate treatment and meds in cardiac emergencies - defibrillation in V-fib, Lidocaine for V-tach, Atropine for bradycardia, Epinephrine for standstill among others. First and foremost, nurses observe, assess first before action!
My neurosurgical nursing experience started in early 80's. Observation and Assessment still first and foremost skill. Level of consciousness with coma scale and pupillary changes were important nursing observation and assessment skill.