All critical care nurses in the U.S. are registered nurses. Due to the unstable nature of the patient population the LPN/LVN's are rarely utilized in a primary care role in the intensive care unit.

Nurses in the US who wish to obtain certification in critical care nursing can do so through a national advisory board, known as the American Association of Critical Care Nurses. This advisory board sets and maintains standards for critical care nurses. The certification offered by this board is known as CCRN. This does not stand for 'Critical Care Registered Nurse' as is popularly believed, but is merely a certification as a critical care nurse for adult, pediatric and neonatal populations.

Registration is a regulatory term for the process that occurs between the individual nurse and the state in which the nurse practices. All nurses in the US are registered as nurses without a specialty. The CCRN is an example of a post registration specialty certification in critical care.
Critical care nursing is the field of nursing with a focus on the care of the critically ill or unstable patients. Critical care nurses can be found working in a wide variety of environments and specialties, such as emergency departments and the intensive care units.

There are also variants of critical care certification test that the AACN offers to allow nurses to certify in progressive care (PCCN), cardiac medicine (CMC) and cardiac surgery (CSC). In addition, Clinical Nurse Specialists can certify in adult, neonatal and pediatric acute and critical care (CCNS). In November, 2007, the AACN Certification Corporation launched the ACNPC, an advanced practice certification examination for Acute Care Nurse Practitioners. None of these certifications confer any additional practice privileges, as nursing practice is regulated by the individual's state board of nursing. These certifications are not required to work in an intensive care unit, but are encouraged by employers, as the tests for these certifications tend to be difficult to pass and require an extensive knowledge of both pathophysiology and critical care medical and nursing practices. The certification, while difficult to obtain, is looked upon by many in the field as demonstrating expertise in the field of critical care nursing, and demonstrating the individual's nurse's desire to advance their knowledge base and skill set, thereby allowing them to better care for their patients.

Intensive care nurses are also required to be comfortable with a wide variety of technology and its uses in the critical care setting. This technology includes such equipment as hemodynamic and cardiac monitoring systems, mechanical ventilator therapy, intra-aortic balloon pumps (IABP), ventricular assist devices (LVAD and RVAD), continuous renal replacement equipment (CRRT/CVVHDF), extracorporeal mechanical oxygenation circuits (ECMO) and many other advanced life support devices. The training for the use of this equipment is provided through a network of in-hospital inservices, manufacturer training, and many hours of education time with experienced operators. Annual continuing education is required by most states in the U.S. and by many employers to ensure that all skills are kept up to date. Many intensive care unit management teams will send their nurses to conferences to ensure that the staff is kept up to the current state of this rapidly changing technology.

Critical care nurses work in a variety of different areas, with a diverse patient population. There are many critical care nurses working in hospitals in intensive care units, post-operative care and high dependency units. They also work on medical evacuation and transport teams.

In August 2004, to demonstrate the work of critical care nurses Massachusetts General Hospital invited reporter Scott Allen and photographer Michelle McDonald from The Boston Globe to take part in an 'immersion experience' in the Surgical Intensive Care Unit (SICU). The Globe staffers spent eight months shadowing an experienced nurse and a trainee nurse to learn about nursing practice first hand. The result was a four part, front-page series that ran from October 23–-October 26, 2005, entitled Critical Care: The making of an ICU nurse.

Subspecialities of critical care nursing include such areas as Neonatal Intensive Care (also called Nursery ICU), Pediatric Intensive Care (or PICU), and Adult Intensive Care (or ICU). The patient population of these units is generally based on the age of the patient.

The Neonatal ICU has a patient population that primarily consists of newborn and premature infants. The NICU will care for patients up to about one month old, based on gestational age, at which point care will generally be assumed by the Pediatric Intensive Care unit.

The Pediatric Intensive Care unit will generally care for patients of about one month to eighteen years. After eighteen years, most patients will be admitted to an Adult Intensive care unit.

These are general guidelines, but all admissions to the intensive care unit are made on a case by case basis. For example, a newborn that was admitted from the Emergency Department will most likely be admitted to PICU, and not to the NICU. A seventeen year old, 235lb patient may be admitted to the Adult Intensive Care unit. Rarely, adult patients with congenital heart defects will be admitted to the PICU, as their physicians have been treating them since they were children and are familiar with their cardiac defects and treatment plan, however this depends on the skill mix and ability of critical care nurses

Further specialties of care can be found based on the disorder, disease or primary injury of the patient population. For example, a unit that is an Adult Intensive care unit, specialized in the care of trauma patients would be an Adult Trauma Intensive Care Unit. The focus of the unit is generally on either an adult or a pediatric/neonatal population, as the treatment methods differ for the age ranges.