Head trauma

5 Head trauma




INITIAL PRESENTATION


Obtunded, stupor, coma.



INTRODUCTION


Being hit by a car, human, large animal, falling tree or furniture, being shot at or in a dog fight are all reported causes of head trauma in small animals. The dog that knocks its head against a door frame and carries on walking will not have sustained clinically significant head trauma.



SIGNALMENT


A 6-year-old male crossbred dog.



CASE PRESENTING SIGNS


Presented in a mentally unresponsive state.



CASE HISTORY


A sudden onset of stupor or coma (Table 5.1) should not automatically be blamed on external trauma, unless, of course, the event is witnessed or has produced other physical evidence. The owner must always be questioned, however briefly, on the animal’s recent health status.


Table 5.1 Causes of stupor and coma







































Brainstem Bilateral cerebrum
Trauma Metabolic encephalopathies
Hypoglycaemia
Hyperosmolar (DKA; hypernatraemia)
Hypo-osmolar (water intoxication)
Uraemia
Acidosis
Anoxia
Portosystemic shunt
Hyperkalaemia
hypocalcaemia
Tumour Toxicity
Inflammation Post-ictal
Vascular Hydrocephalus
Hydrocephalus Herniation with secondary compression of brainstem

In this case, the dog had been exercising off the lead and out of view. A train was heard to pass nearby. The dog was called but failed to return. The animal was found soon after, in lateral recumbancy in an unresponsive mental state. The owners presented the dog, saying it had been hit by a train.



CLINICAL EXAMINATION


Initial assessment of a traumatized animal is done quickly and is repeated at frequent intervals. Mental state, pupil size and pupil light reflex (PLR), eye movement (resting position, spontaneous movement, and vestibulo-ocular reflex, VOR) should be noted. Approximately 10% of traumatic brain-injured humans also have a cervical spine injury. Avoid rotating or hyperextending the neck.


The Glasgow Coma Scale was modified by Dr Andy Shores for use in small animals and this helps monitor progression of signs (Table 5.2). One study found that there was a 50% probability of survival during the first 48 hours after head trauma in dogs with a score of 8. Contrary to humans, the age of the animal did not predict survival. The study was not able to suggest a long-term prognosis based on either survival or functional capacity.


Table 5.2 The modified Glasgow Coma Scale for small animals





































































Small animal coma scale Score
Motor activity  
Normal gait, normal spinal reflexes 6
Hemiparesis, tetraparesis, or decerebrate activity 5
Recumbent, intermittent extensor rigidity 4
Recumbent, constant extensor rigidity 3
Recumbent, constant extensor rigidity with opisthotonus 2
Recumbent, hypotonia of muscles, depressed or absent spinal reflexes 1
Brainstem reflexes  
Normal pupillary light reflexes and oculocephalic reflexes 6
Slow pupillary light reflexes and normal to reduced oculocephalic reflexes 5
Bilateral unresponsive miosis with normal to reduced oculocephalic reflexes 4
Pinpoint pupils with reduced to absent oculocephalic reflexes 3
Unilateral, unresponsive mydriasis with reduced to absent oculocephalic reflexes 2
Bilateral unresponsive mydriasis with reduced to absent oculocephalic reflexes 1
Level of consciousness  
Occasional periods of alertness and responsive to environment 6
Depression or delirium, capable of responding but response may be inappropriate 5
Semicomatose, responsive to visual stimuli 4
Semicomatose, responsive to auditory stimuli 3
Semicomatose, responsive only to repeated noxious stimuli 2
Comatose, unresponsive to repeated noxious stimuli 1

Note: Asymmetrical abnormalities (e.g. pupil size) are assigned the lower score of the two possible. Score before medication and supportive care administered. Oculocephalic reflex, VOR; Semicomatose-stuporous.


Examination in this case revealed:


• Coma

• Lateral recumbency

• Bilaterally symmetrical pinpoint pupils

• VOR was present

• Regular respiration with good thoracic excursions

• Absence of external signs of trauma

• Heart rate and pulse rate were 126 bpm

• Temperature was 37.7°C.


Neuroanatomic localization


The lesion was localized to the cerebrum or brainstem ARAS based on the coma.



Differential diagnosis


It seemed highly unlikely that a dog could be hit by a train and not be visibly damaged by the experience. Head trauma from a blunt projectile may have occurred. Increased intracranial pressure from neoplasia, cerebral haemorrhage, or inflammation would be expected to have shown some earlier signs of mentation or behaviour change or have a less-acute onset but this is not always the case. Metabolic encephalopathy can alter mentation acutely and for extended periods of time (hours).



CASE WORK-UP



1. Assessing oxygenation
• Pulmonary contusions are common post-trauma. Auscultation detects increased lung sounds distributed unevenly over the thorax, or decreased lung sounds with consolidation. There is no specific therapy. Treatment is supportive.

• Neurogenic pulmonary oedema is rare but most often associated with severe head trauma. It progresses within hours or days to resolution or death. Improvement, if it is to occur, is usually seen within 48 hours. It results from a central sympathetic discharge from an increase in ICP. Treatment is aimed at reducing ICP, oxygenation, and diuretics.

• Respiration patterns are often altered in coma. A lack of increased effort does not imply adequate oxygenation/ventilation.

2. Assessing ventilation
• Hypoventilation results from brain injury, thoracic trauma and pain, weakness secondary to spinal cord or brainstem injury. In addition, ventilation-perfusion mismatch can follow head trauma without evidence of pulmonary disease on the radiographs.

• Short, shallow respiration with intermittent attempts at deep respiration accompanies pleural space disease (pleural effusions, pneumothorax).

• Respiratory acidosis is a warning that respiratory failure will occur.

3. Assessing systemic perfusion
• Hypoperfusion manifests as a faster heart rate (dog), weaker pulse, paler mucous membrane colour, slower capillary refill time, and lower rectal temperature. Hypovolaemic animals have a depressed mentation which improves with treatment. The mortality rate in humans with severe traumatic brain injury is doubled with a systolic blood pressure of <90 mmHg.


CLINICAL TIP


Systemic hypotension does not result from lesions rostral to the lower brainstem.


4. Assessing intracranial pressure (Table 5.3)
• The closed skull gives the traumatized, swelling brain little room for accommodation. Increasing ICP forces blood and CSF out of the brain. As ICP equals or exceeds the systemic arterial pressure, the systemic blood pressure increases and a reflex bradycardia follows. These reflex changes are called the Cushing’s reflex and are more common in end-stage disease.

• Increases in ICP are monitored by neurological examination in veterinary patients. Papilloedema is rarely seen after acute head injury in humans.

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Head trauma
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