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Ottawa CT Head Rule

For adults with minor head injury (GCS 13–15 + LOC, amnesia, or confusion). Any criterion positive = CT required.

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Qué es Ottawa CT Head Rule?

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The Ottawa CT Head Rule is a validated clinical decision rule designed to identify which patients with minor head injury require computed tomography (CT) imaging of the brain to exclude clinically important brain injury. It was developed by Ian Stiell and colleagues at the University of Ottawa in Canada and published in The Lancet in 2001. The rule applies to patients presenting to the emergency department with blunt head trauma resulting in loss of consciousness, amnesia, or confusion (a GCS score of 13-15 at assessment). It defines seven high-risk factors for brain injury: GCS score below 15 at 2 hours after injury, suspected open or depressed skull fracture on examination, any sign of basal skull fracture (haemotympanum, 'panda eyes' periorbital ecchymosis, cerebrospinal fluid otorrhoea or rhinorrhoea, Battle's sign behind the ear), vomiting two or more episodes, age 65 years or older, amnesia for events 30 or more minutes before impact, and dangerous mechanism of injury (pedestrian struck by motor vehicle, occupant ejected from vehicle, or fall from height greater than 3 feet or 5 stairs). If any of these factors is present, CT head is indicated. The Ottawa CT Head Rule was derived with a sensitivity approaching 100% for clinically important brain injury and for injuries requiring neurosurgical intervention. Importantly, the rule is only applicable to patients with minor head injury — it should not be used for patients with GCS below 13, patients on anticoagulants, patients with known seizure disorders, or pregnant women.

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Fórmula

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Ottawa CT Head Rule: CT required if ANY of: GCS <15 at 2 hours after injury; Suspected open or depressed skull fracture; Any sign of basal skull fracture; Vomiting ≥2 episodes; Age ≥65 years; Amnesia before impact ≥30 minutes; Dangerous mechanism (pedestrian vs vehicle, ejection, fall >3ft/5 stairs); Sensitivity ~100% for neurosurgically important injury

Leyenda de variables

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Símbolo	Nombre	Unidad	Descripción
GCS	Glasgow Coma Scale at 2 hours	3-15	GCS <15 at 2 hours post-injury is a high-risk criterion
RA	Retrograde Amnesia	minutes	Duration of amnesia for events before impact; ≥30 minutes is a criterion
DM	Dangerous Mechanism	yes/no	Pedestrian vs vehicle, ejection from vehicle, fall >3ft or 5 stairs

Cómo Ottawa CT Head Rule

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1Confirm applicability: patient must have minor head injury (GCS 13-15) with loss of consciousness, amnesia, or confusion. Exclude GCS <13, anticoagulants, known seizure disorder, pregnancy.
2Assess GCS at 2 hours post-injury: if still below 15 at this time point, CT is indicated (not at initial presentation).
3Examine for signs of skull fracture: check for Battle's sign (bruising behind the ear over the mastoid), haemotympanum (blood behind eardrum), periorbital ecchymosis (raccoon eyes), CSF from ear or nose.
4Ask about vomiting — two or more episodes of vomiting after the injury indicate CT.
5Document the patient's age — 65 years or older is a criterion for CT regardless of other findings.
6Determine amnesia duration for events before the impact: if 30 minutes or more of pre-impact amnesia, CT is required.
7Identify dangerous mechanism: pedestrian struck by motor vehicle, ejection from vehicle, fall from more than 3 feet or 5 stairs — any dangerous mechanism requires CT.

Ejemplos resueltos

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Ejemplo 1CT Required — Elderly with Vomiting

Dado:72-year-old who fell and hit head, brief loss of consciousness, GCS 15 at 2 hours, vomited twice, no neurological deficit

Resultado:CT Head REQUIRED — 2 criteria met (age ≥65, vomiting ≥2)

Proceed to CT head despite normal GCS; elderly patients have higher risk of subdural haematoma

Age ≥65 alone is sufficient to trigger CT under this rule. Elderly patients are at significantly increased risk of intracranial haemorrhage even after seemingly minor head trauma due to brain atrophy and anticoagulant use.

Ejemplo 2CT Required — Dangerous Mechanism

Dado:35-year-old ejected from car in RTA, GCS 15 at 2 hours, no vomiting, amnesia for 15 minutes

Resultado:CT Head REQUIRED — Dangerous mechanism (ejection from vehicle)

Vehicle ejection is a high-energy mechanism even with minimal neurological symptoms

Ejection from a vehicle subjects the unrestrained occupant to severe deceleration forces. Despite a GCS of 15, this mechanism mandates CT to exclude intracranial injury.

Ejemplo 3CT Not Required

Dado:28-year-old knocked out briefly during football, GCS 15 at 2 hours, single episode of nausea, amnesia for 10 minutes, no dangerous mechanism

Resultado:CT Head NOT required by Ottawa criteria

Observe with head injury advice; return precautions provided

No Ottawa criteria present. This patient can be discharged with written head injury advice after a period of observation. Concussion protocol and sports return-to-play guidance apply.

Ejemplo 4Basal Skull Fracture Signs

Dado:45-year-old after head injury in assault, Battle's sign (post-auricular bruising) and haemotympanum on examination

Resultado:CT Head REQUIRED — Basal skull fracture signs + GCS <15 at 2h

Urgent CT; consider neurosurgery referral if fracture confirmed

Clinical signs of basal skull fracture indicate a high-energy impact. Battle's sign typically develops 12-24 hours after injury, so it may not be present at initial assessment.

Aplicaciones prácticas

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Emergency department triage to decide which head-injured patients need CT imaging, reducing radiation exposure and healthcare costs., representing an important application area for the Ottawa Head Ct in professional and analytical contexts where accurate ottawa head ct calculations directly support informed decision-making, strategic planning, and performance optimization

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Emergency medicine training as a paradigm example of a well-validated clinical decision rule applicable to high-volume emergency conditions., representing an important application area for the Ottawa Head Ct in professional and analytical contexts where accurate ottawa head ct calculations directly support informed decision-making, strategic planning, and performance optimization

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Quality improvement auditing of CT brain utilisation in emergency departments — comparing rates to Ottawa Rule-predicted necessity., representing an important application area for the Ottawa Head Ct in professional and analytical contexts where accurate ottawa head ct calculations directly support informed decision-making, strategic planning, and performance optimization

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Medicolegal documentation to demonstrate a structured clinical decision-making process was used in head injury assessment., representing an important application area for the Ottawa Head Ct in professional and analytical contexts where accurate ottawa head ct calculations directly support informed decision-making, strategic planning, and performance optimization

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Telemedicine consultations where a remote clinician can assess Ottawa criteria from a standardised clinical assessment performed by the treating clinician., representing an important application area for the Ottawa Head Ct in professional and analytical contexts where accurate ottawa head ct calculations directly support informed decision-making, strategic planning, and performance optimization

Casos especiales

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Anticoagulant Use

In the Ottawa Head Ct, this scenario requires additional caution when interpreting ottawa head ct results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when ottawa head ct calculations fall into non-standard territory.

Paediatric Head Injury

Witnessed vs Unwitnessed LOC

Repeated Head Injury (Second Impact Syndrome Risk)

{'title': 'Repeated Head Injury (Second Impact Syndrome Risk)', 'body': 'Athletes with recent prior concussion who sustain another head injury require lower CT thresholds even when Ottawa criteria are not met, due to the risk of second impact syndrome — a potentially catastrophic rapid cerebral swelling triggered by a second concussive event before full recovery.'}

Ottawa CT Head Rule — Criteria Summary

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Criterion	Category	Comment
GCS <15 at 2 hours post-injury	High risk	Not at initial presentation — at 2 hours
Suspected open or depressed skull fracture	High risk	Clinical examination finding
Any sign of basal skull fracture	High risk	Battle's sign, haemotympanum, raccoon eyes, CSF leak
Vomiting ≥2 episodes	High risk	Repeated vomiting, not isolated nausea
Age ≥65 years	High risk	Applies regardless of other findings
Amnesia before impact ≥30 min	Medium risk	Retrograde amnesia duration
Dangerous mechanism	Medium risk	Pedestrian vs vehicle, ejection, fall >3ft/5 stairs

Preguntas frecuentes

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What is the Canadian CT Head Rule and how does it differ?

The Canadian CT Head Rule is a similar but slightly different tool from the same research group, developed for patients with GCS 13-15 after witnessed LOC or amnesia. It has two tiers of criteria — high-risk (neurosurgical intervention) and medium-risk (any brain injury on CT). The Ottawa CT Head Rule slightly predates and overlaps with it.

Is the 2-hour GCS window clinically important?

Yes. The GCS criterion specifically refers to GCS below 15 at 2 hours post-injury, not at initial assessment. A patient may arrive with GCS 14 that improves to 15 quickly — it is the GCS at 2 hours that determines the criterion, allowing transient changes to be distinguished from persistent impairment.

What are the specific criteria that indicate a head CT scan is required under the Ottawa CT Head Rule?

The Ottawa CT Head Rule mandates a CT scan if any of these high-risk factors are present: GCS score <15 at 2 hours post-injury, suspected open or depressed skull fracture, any sign of basal skull fracture, two or more episodes of vomiting, or age ≥65 years. Additionally, a CT is recommended for patients with a GCS of 15 if any medium-risk factors are present, such as amnesia to events ≥30 minutes prior to impact or a dangerous mechanism of injury.

How effective is the Ottawa CT Head Rule in detecting clinically significant brain injuries?

The Ottawa CT Head Rule demonstrates high sensitivity for detecting clinically important brain injuries, typically reported at 98-100%. This means it is very effective at identifying nearly all patients who actually have an injury requiring intervention. Its specificity is lower, around 10-15%, which helps reduce unnecessary CT scans while maintaining patient safety.

What are the key inclusion and exclusion criteria for applying the Ottawa CT Head Rule?

The rule is designed for alert adult patients (GCS 15) aged 16 years and older with minor head injury (loss of consciousness, amnesia, or disorientation) within 24 hours of injury. It excludes patients on anticoagulants or with bleeding disorders, those with a pre-existing brain tumor or aneurysm, pregnant women, and patients with obvious penetrating trauma or severe facial trauma.

Errores comunes a evitar

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!Applying the rule to patients with GCS <13, anticoagulants, or coagulopathies — these exclusion criteria are essential for safe use.
!Measuring GCS at initial presentation instead of at 2 hours post-injury — the criterion specifically uses the 2-hour value.
!Counting a single episode of nausea or one vomit as positive — the criterion requires two or more vomiting episodes.
!Assuming a negative rule result means no imaging is ever needed — the rule reduces unnecessary CT use; it does not eliminate clinical judgement.
!Not examining for signs of basal skull fracture (Battle's sign, haemotympanum) in all minor head injury patients — these signs change management immediately.
!Using Ottawa CT Head Rule without providing clear written head injury discharge advice and return precautions to patients who do not meet CT criteria.

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Consejo Pro

Document GCS explicitly at 2 hours post-injury as a separate value from the admission GCS — many emergency records fail to capture the 2-hour GCS, making the Ottawa criterion unverifiable. A simple timestamp on the nursing observation chart at 2 hours ensures this critical data point is not missed.

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¿Sabías que?

The Ottawa CT Head Rule was developed as part of the Ottawa Rules project, which also produced the Ottawa Ankle Rules (one of the most successfully implemented clinical decision rules in history, reducing unnecessary ankle X-rays by 40%). The head injury version went through rigorous derivation and validation across multiple Canadian emergency departments before publication in The Lancet in 2001.

Referencias

📖Dificultad:Principiante

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Ottawa CT Head Rule

Ottawa CT Head Rule

Qué es Ottawa CT Head Rule?

Fórmula

Leyenda de variables

Cómo Ottawa CT Head Rule

Ejemplos resueltos

Aplicaciones prácticas

Casos especiales

Anticoagulant Use

Paediatric Head Injury

Witnessed vs Unwitnessed LOC

Repeated Head Injury (Second Impact Syndrome Risk)

Ottawa CT Head Rule — Criteria Summary

Preguntas frecuentes

What is the Canadian CT Head Rule and how does it differ?

Is the 2-hour GCS window clinically important?

What are the specific criteria that indicate a head CT scan is required under the Ottawa CT Head Rule?

How effective is the Ottawa CT Head Rule in detecting clinically significant brain injuries?

What are the key inclusion and exclusion criteria for applying the Ottawa CT Head Rule?

Errores comunes a evitar

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