Cerebral disease: head trauma Flashcards
What is called the primary neurological injury
The primary neurological injury occurs at the time of trauma and is mechanical in nature
- the brain is subjected to laceration or shearing forces, resulting in bleeding or tearing of the neurovascular tissue
Primary injuries are not reversible
What is called the secondary neurological injury
Secondary neurological injury refers to the subsequent cascade of events that results in progressive neuronal damage
- it is due to local disruption of cerebral blood flow, cytotoxicity caused by increase excitatory neurotransmitter release and local inflammatory response
- these result in edema formation, ischemia and increased intracranial pressure
What is the modified glasgow coma scale
It is a tool that provides a quantitative measure that can be used to assess initial neurological status and to monitor any response to treatment
The scale incorporates three domains:
- level of consciousness (from comatose, unresponsive to repeated noxious stimuli to occasional periods of alertness and responsive to environment
- posture and limb motor function (from recumbent, depressed or absent spinal reflexes to normal gait with normal spinal reflexes) - brainstem reflexes (from bilateral, unresponsive mydriasis with reduced to absent ocullocephalic reflexes to normal PLR and oculocephalic reflexes)
A score of 1-6 is assigned to each domain
- the total score ranges from 3-18, with lower scores indicating more severe neurological deficits
How is the level of consciouness classified
The level of consciousness is classified, depending on the cat’s response to external stimuli,as:
- normal
- depressed
- obtunded
- stuporous
- comatous
Where is the lesion located when there is an altered states of consciouness
As a rule, altered states of consciouness relate either to a diffuse lesion or widespread multifocal lesions of both cerebral hemispheres or to a focal lesion affecting the ascending reticular activating system of the brainstem
It is important to be aware that extensive blood loss, moderate or severe hypothermia or hypoxemia can also severely alter the level of consciousness
What is a decerebrate posture? what is its prognosis value
Decerebrate posture is observed as a result of a rostral brainstem lesion and carries a guarded to poor prognosis
It is characterized by rigid extension of all limbs and opisthotonus, and is assoociated with a stuporous or comatose mental status
What is a decerebellate posture? What is its prognosis value
Decerebellate posture is often caused by an acute cerebellar lesion and can sometimes be episodic
It is characterized by opisthotonus with the forelimbs extended and hips flexed and is associated with a normal mentation
What is the basis for assessing the brainstem
Evaluation of pupil size/response and eye movements is the basis for assessing the brainstem category on the modified GCS
- miotic pupils indicate diffuse forebrain injury
- progression to mydriasis may indicate brain herniation and a progressive brainstem lesion necessitating immediate, aggressive therapy - bilateral mydriasis with no response to light is usually indicative of an irreversible midbrain lesion or brain herniation and carries a poor prognosis - fixed, unresponsive and mid-range pupils are usually seen with cerebellar herniation
Which brain imaging modality is best in evaluating head trauma
CT seems to be the most suitable for cats with head trauma because:
- it is faster
- it is less expensive
- it provides better resolution of bone details and acute hemorrhage than MRI
What is the most important consideration in the head-injured patient
The most important consideration in the head-injured patient is maintenance of cerebral perfusion and oxygenation
- hypovolemia and hypoxemia are strongly correlated with elevated ICP and increased mortality
What are the cornerstones of management of the animal with head trauma
Tier 1 therapy: extracranial stabilisation
- in the recumbent cat, the head should be kept slightly elevated above the horizontal to assist in lowering ICP by increasing venous return from the brain
- oxygen therapy and management of ventilation
- cerebral blood flow is tightly controlled by alterations in vasomotor tone regulated according to changes in arterial oxygen and carbon dioxide partial pressures, and systemic blood pressure
- fluid therapy
- if the cat is hypotensive, isotonic crystalloid boluses of 10-20 ml/kg should be given to effect until normal blood pressure is restored (SBP >=120 mmHg to preserve normal cerebral perfusion pressure)
- if the cat is euvolemic and not in shock, isotonic crystalloids should be administered at a maintenance fluid rate (2-3 ml/kg/h)
Tier 2 therapy: intracranial stabilisation
- hyperosmolar therapy
- mannitol:
- has been shown to reduce cerebral oedema, increase cerebral perfusion pressure and cerebral blood flow BUT it will exacerbate intracranial hemorrhage
- it should be avoided in hypovolemic patients
- Dose 0.25-1.0 g/kg IV over 10-20 min (no more than 2 doses per 6 hours)
- temporary hyperventilation
- it induces hypocapnic cerebral vasoconstriction
Tier 3 therapy: surgery
- elimination of any space-occupying mass within the cranial vault can help obtaining ICP reduction
- decompressive craniectomy is indicated within 12h in patients with severe head injury that are refractory to former treatment
induction of hypothermia
induction of barbiturate coma
- hypertonic saline:
- it can be used in hypovolemic patients
- dose 2-4 ml/kg IV
What are the ancillary treatment in head trauma
Analgesic and sedatives
- adequate analgesia is essential to prevent further elevation in ICP
- analgesia with opioids and then once hemodynamically stable NSAID to provide long term analgesia
- for cats showing severe agitation, sedation can be achieved using an IV infusion of dexmedetomidine at 0.1-1.0 µg/kg/h (this will also provide some analgesia)
Antiseizure treatment
- seizures should be initially treated with benzodiazepine (e.g., diazepam 0.5-2.0 mg/kg or CRI 0.5-2.0 mg/kg/h in 0.9% saline)
- intravenous levetiracetam can provide a viable alternative and can be administered as a 20 mg/kg IV bolus. The anticonvulsivant effect is rapid and is maintained for several hours
Should corticosteroids be used in head trauma
Given the lack of evidence for any beneficial effect after traumatic brain injury and strong evidence in human medicine showing a detrimental effect on neurological outcome, corticosteroids should not be administered to cats with head trauma
How is calculated the cerebral perfusion pressure
Cerebral perfusion pressure (CPP) = mean arterial pressure (MAP) - intracranial pressure (ICP)
- decreases in MAP and increases in ICP affect CPP and therefore cerebral blood flow (CBF) with subsequent ischemia and neuronal injury
