As the population of older adults increases, so too with the number of older adult patients that present for anesthesia and surgery. The development of delirium following surgery has some significant potential effects on patient outcomes; however, POD is often under diagnosed. Some studies reported that more than 50% of patients with delirium were undiagnosed by clinical teams. POD is associated with cognitive decline, increased hospital length of stay, discharge to institutional care, mortality and higher healthcare costs. POD contributes significantly to healthcare inefficiency; a diagnosis of POD is estimated by the Australian Commission on Quality and Safety in Healthcare to cost an additional $27,791 AUD. The incidence of POD reported in clinical trials depends on the risk profile of the study population, the frequency and duration of delirium assessments as well as the surgical procedure. Reported incidence may also vary due to the presence of high-risk pathways involving multi-specialty management and intervention. POD may present as either hyperactive or hypoactive subtypes, the latter being more difficult to detect.

There are few reports on the incidence of POD in New Zealand national level datasets, with single centre studies primarily looking at in-hospital delirium and demonstrating an incidence of 11.2 to 29% on mixed and/or medical wards. A review of elderly patients with neck-of-femur fractures found the incidences of POD to be as high as 39%. The current data suggests a significant level of morbidity due to POD in New Zealand hospitals, however there is lack of national level data in the surgical population; which is crucial for establishing demographic and regional need for effective intervention.

Eligible patients include those aged 18 years or over undergoing a surgical procedure in any of 71 public or private hospitals

Participant patients will have been assigned procedure codes for surgery and anaesthesia. Patients who had multiple procedures during an episode of care will have each procedure and relevant postoperative course analysed. Patients were excluded if the procedure was performed under local anaesthesia infiltration. Procedures performed under regional or neuraxial techniques will be included in the analysis.

As an observational study of encrypted data from the national data set there is no plan to provide individual participant data.