What is the value of CT in emergency medicine?

In an emergency situation live-saving procedures have to be performed fast. This also involves rapid and targeted diagnostics for further therapy.

“Emergency-CT” rather implies the use of a CT in critical situations. The main purpose is enabling fast guided therapy and prognostic decisions or, alternatively, to make informed decisions when euthanasia may be necessary.
In veterinary emergency practice, ultrasound (Point-of-Care Ultrasound with A-FAST and T-FAST protocols) or radiographs are the preferred initial diagnostic measures. A CT as a more precise diagnostic tool is often not available. Also trained and licensed stuff is not available 24/7. Additionally, anaesthesia is mostly required, which increases the risk in critical situations. Cost restrictions and owner compliance limit the use of CT in emergency situations.

However, when performed routinely, emergency CT is fast, reliable, and easy to perform and can be the diagnostic method of choice for severely traumatized patients (e.g., traumatic brain injury). Due to the increasing availability of timely reporting from external teleradiology providers, the use of emergency CTs in veterinary facilities has therefore also increased.

Procedure and performance of an emergency CT scan

When critically ill patients, such as Öffnet externen Link in neuem Fenster polytraumatized or dyspneic patients, present to the practice or clinic, stabilization of cardiovascular and respiratory functions always has priority over further diagnostics. If potential life-threatening conditions, such as shock or hypoxemia are present, these should be treated first!
Imaging diagnostics should then be performed as early as possible, although the timing depends strongly on the patient's condition and stability.

Preparation of the patient

CT scans are usually performed under general anaesthesia or deep sedation. Therefore, also in the interest of optimal image quality and gentle performance of the CT, coordinated and proper planed examinations should be performed especially in the emergency patient.

Before induction of anaesthesia, the first step in stabilization is always to lower the ASA risk status. The methods used depend on the disease and can include oxygenation, thoracentesis, shock infusion, transfusion, diuretics and adequate analgesia.
Special care should be taken in pleural space disease, as thoracentesis must always be performed before anaesthesia if dyspnea is present. In cases of pneumothorax, mechanical ventilation should be avoided if possible, and thoracic drains should be placed before or at the beginning of anaesthesia, if necessary.
Since patients for emergency CT are usually very critical patients (e.g., shock, anemia, sepsis, respiratory distress), the risk of anaesthesia is also higher. If contrast medium is used, care must be taken to ensure that the patient is well volume loaded and hydrated. Otherwise, the risk of contrast induced of acute renal injury increases. Anaphylactic reactions, especially threatening in cardiovascular unstable patients, should also be kept in mind as a side effect of contrast application. In cases of congestive heart failure, the volume of contrast media or flushing solution also contributes to increased intravascular volume status and therefore may worsen congestion and dyspnea.

What are the differences between "awake CT" and "anaesthesia CT"?

The main advantage of the anaesthesia is that spontaneous movement of the patient is disabled and optimal positioning is possible.For thoracic or abdominal images, a provoked inspiratory breath hold (apnea images) is also possible.

The more severe the systemic deviations such as hypotension or dyspnea, general anaesthesia, contrast application and breath hold will put the patient at additional risk due to negative effect on blood pressure and oxygenation. This is why sometimes “awake” CT examinations without anaesthesia are performed, especially in emergency patients.

To perform awake CT examinations, especially small patients such as cats or small dogs, a cat basket with blankets or a plastic device the " Öffnet externen Link in neuem Fenster mouse trap" is used to place the animal on the CT table and minimize movement. Blankets and other padding material is used to wrap, immobilize and restrain the patient.

Indications for awake CT are:

Highly unstable patients who are dependent on further rapid diagnostics
Partly severely polytraumatized patients
Patient is comatose

However, anaesthesia is generally preferred, and preanesthetic stabilization as far as possible is a prerequisite.

Indications for an emergency CT

CT is superior to other imaging methods in many circumstances. Compared with radiographs, the CT achieves a more precise imaging of the body structures as well as a better overview compared to sonography. Ultrasound is more suitable for the assessment of internal organ structures.

There are clearly defined indications for an emergency CT. A computed tomography is the method of choice in:

Head trauma: intracranial pressure elevation or haemorrhage, aid in surgical planning, decision-making for or against decompression
The Koret CT Score (KCTS) is a prognostic CT-based scoring index for dogs and cats, based on abnormal findings on CT scans after traumatic brain injury. The KCTS can be used as an additional diagnostic tool for the prediction of survival. It should not be used alone to decide on euthanasia. The clinical course is more important than the score!
Polytrauma: which structures are involved? Partially performed as part of triage, as awake CT, as immediate assessment is essential
Pulmonary thromboembolism (CT as the only reliable method)
Pulmonary lobe torsion (CT as the only reliable method)
Spinal trauma
Impalement, bite injuries: Assessment of extent, recognition of involved structures and surgical planning
Foreign body search, e.g., stick injuries
Clarification of (unclear) respiratory distress - Oxygen supply is always necessary and the awake CT option is hardly suitable for respiratory distress because of breathing (movement) artefacts. Therefore, the option of mechanical ventilation or intensive oxygen therapy should be given during and after CT

Further indications for an emergency CT can be:

Neurological diseases

Paresis, paralysis (e.g. clarification of a discopathy)
Vertebral fractures: detection and assessment of the extent and planning of surgery
Seizure disorders (e.g. cluster seizures)
Meningitis

Although MRI is the gold standard for soft tissue changes in the brain, the use of CT is often preferred due to lack of equipment or time.

Abdomen

Metastasis screening in neoplasia patients (e.g. splenic or liver tumour)
Evaluation of septic patients, screening for source of sepsis and evaluation of the extent or delineation of significant alterations
Diagnostic workup of uroabdomen
Retroperitoneal processes

Retrobulbar foreign bodies

Assessment of deeper structures and extent is often more difficult on sonography, while foreign body screening is often easier on CT

Conclusions

Rely primarily on clinical examination and point-of-care-ultrasound and radiographs.
Do not go for a CT only because it is possible.
CT should answer specific questions and not be a "let's see what we find" approach. Scan the complete region of interest, but don't basically run full-body CTs. The point of an emergency CT is to stick to the basics and keep anaesthesia time as short as necessary.
Hasty anaesthesia without sufficient prior stabilization should be avoided, as this can cause severe complications and death of the patient
CT can provide more comprehensive information. It may also help reduce the risk of missed injuries.

Leading on from this, our follow-up article looks at the anaesthetic techniques in the critical patient. Stay tuned!

Our special thanks to Dr. ECVECC/ECVAA René Dörfelt for his scientific support in the preparation of this article!

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What is the value of CT in emergency medicine?

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