Hospital Episode Statistics (HES) is a database containing details of all admissions, A and E attendances and outpatient appointments at NHS hospitals in England.

Adult Critical Care (ACC) is a subset of APC data. An Intensive Care Unit (ICU) or High Dependency Unit (HDU) ward in a hospital, known as a critical care unit, provides support, monitoring and treatment for critically ill patients requiring constant support and monitoring to maintain function in at least one organ, and often in multiple organs. Medical equipment is used to take the place of patients’ organs during their recovery.

Some critical care units are attached to condition-specific treatment units, such as heart, kidney, liver, breathing, circulation or nervous disorders. Others specialise in neonatal care (babies), paediatric care (children) or patients with severe injury or trauma.

Initially this data is collected during a patient's time at hospital as part of the Commissioning Data Set (CDS). This is submitted to NHS Digital for processing and is returned to healthcare providers as the Secondary Uses Service (SUS) data set and includes information relating to payment for activity undertaken. It allows hospitals to be paid for the care they deliver.

This same data can also be processed and used for non-clinical purposes, such as research and planning health services. Because these uses are not to do with direct patient care, they are called 'secondary uses'. This is the HES data set.

HES data covers all NHS Clinical Commissioning Groups (CCGs) in England, including:

private patients treated in NHS hospitals patients resident outside of England care delivered by treatment centres (including those in the independent sector) funded by the NHS Each HES record contains a wide range of information about an individual patient admitted to an NHS hospital, including:

clinical information about diagnoses and operations patient information, such as age group, gender and ethnicity administrative information, such as dates and methods of admission and discharge geographical information such as where patients are treated and the area where they live We apply a strict statistical disclosure control in accordance with the NHS Digital protocol, to all published HES data. This suppresses small numbers to stop people identifying themselves and others, to ensure that patient confidentiality is maintained.