Does the use of the Canadian CT Head rule (CCHR) definition of minor head injury in a regional NSW emergency department safely lead to lower utilisation of computer tomography (CT) imaging in patients over 65 when compared to the NSW Closed Head Injury guidelines definition?

The study will combine both a retrospective and prospective arm assessing patients over 65 who present to the Port Macquarie Base Hospital emergency department (PMBH ED) after a blunt head trauma. The retrospective arm will involve a chart review of patients who presented due to head trauma from January-Decemeber 2019 and received a computerised tomography (CT) scan. Each patient electronic medical record (EMR) will be retrospectively assessed for the following features: 1. The presence of Canadian CT Head Rule (CCHR) inclusion criteria: Glasgow Coma Scale (GCS) of 13-15 with one of the following: witnessed loss of consciousness, definite amnesia or witnessed disorientation post blunt head trauma 2. The presence of CCHR exclusion criteria: anticoagulation, dementia, intoxication, bleeding disorder, penetrating skull injury, depressed skull fracture, acute focal neurological deficit that can’t be ascribed to an extracerebral cause, no history of trauma as the primary event eg. syncope, post-traumatic seizure, unstable vitals due to trauma or reassessment of the same head injury 3. CT results and patient outcome 4. Length time from ordering to reporting of imaging within 24 hours 5. Miscellaneous: antiplatelet medication It will then be determined whether the patient should have undergone a CT brain according to the CCHR definition of minor head injury (MHI). Within the prospective arm of the study, all patients over 65 that present to PMBH ED from 13th July- 31st August 2020 post blunt head injury will be prospectively enrolled. Clinicians ordering a CT Brain in this population will be asked to answer questions via a pop up link in EMR that will auto-populate. This data will be cross-checked with the patients electronic medical record and additionally assessed for the above features. After the data is collected it will then be analysed to see if applying the more restrictive CCHR definition of minor head injury can safely decrease the utilisation of CT Brains in this population without missing a clinically significant brain injury. Clinically significant brain injury is defined according to the CCHR as any acute brain finding on CT which would normally require admission to hospital and neurological follow-up unless the patient is neurologically intact and has one of the following lesions: solitary contusion less than 5 mm in diameter; localised subarachnoid blood less than 1mm thick; smear subdural haematoma less than 4 mm thick; isolated pneumocephaly, or closed depressed skull fracture not through the inner table.