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The Patient with Altered Consciousness.
Ian Goulden - University of Leeds.*
*Basics Anatomy.Cerebellum. Co-ordination, skilful movement posture and balanceCerebrum.Interpretation of sensory data. Co-ordination of muscular movement. Intellectual and emotional processes.Meninges.Hypothalamus.Controls ANS.Emotion and behaviour.Temperature control.Circadian rhythmBrain Stem.
*Basics - The Reticular Activating SystemScattered throughout most of the length of the Brain Stem is a group of nuclei collectively called the Reticular Formation.
These receive axons from a large number of neurons and especially from nerves that innervate the face.
These axons play an important role in arousing and maintaining consciousness. The Reticular Formation and its connections constitute
- the Reticular Activating System (RAS)
It is involved with the Sleep / Wake Cycle.
*Basics - The Reticular Activating SystemVisual and acoustic stimuli and mental activities can stimulate the Reticular Activating System to maintain attention and alertness.
Conversely removal of visual or auditory stimuli may lead to drowsiness or sleep. Damage to cells of the Reticular Formation can result in coma.
The RAS is relatively sensitive to certain drugs - General anaesthetics function by suppressing this system.
Descending Fibres from the Reticular Formation constitute one of the most important motor pathways. Fibres from the Reticular Formation are critical in controlling respiratory and cardiac rhythms and other vital functions.
*Definitions.Consciousness is defined as a general awareness of oneself and the surrounding environment. (Hickey 1997) - capable of responding to sensory stimuli.
It is a dynamic state and can therefore, change. Eg. Waking from sleep.
In the same way Unconsciousness incapable of responding to sensory stimuli .
*Definitions.Consciousness is described as having two parts to it:
Arousal or wakefulness - a function of the reticular activating system (RAS) located in the brainstem.
Awareness or cognition - a function of the cerebral hemispheres.
*Underlying Mechanisms.Consciousness is dependent upon the cerebral hemispheres being intact and interacting with the ascending RAS.
It is maintained by a constant stream of impulses that are sent from the brain stem upwards into the two cerebral hemispheres.
Loss of consciousness therefore has two general mechanisms.
*Underlying Mechanisms.Cerebral Hemisphere Malfunction.
Brain Stem Malfunction.
*Underlying Mechanisms.Cerebral Hemisphere Malfunction.
Drug and alcohol intoxication.Hypoxic brain injury.Stroke.Metabolic disorders.Infection.Post seizure.
*Underlying Mechanisms.Brain Stem Damage.
Direct Damage.Brain Stem Infarct.
Indirect Damage (pressure from above).Cerebral Mass (clot, tumour, abscess)Cerebral Oedema (infarct, hypoxia, infection, injury)
Alterations in conscious level may be slow and progressive or may be acute.
Loss of consciousness may be brief or may be prolonged.
Accurate assessment of conscious level is one of the most important roles of the health care practitioner.
*Pathological Causes of Decreased Conscious Level. (after Shah 1999 and Gray and Toghill 2001)
Brain Injury / Irritation.Increase in Brain Volume.Increase in Cerebral Blood Volume.Increase in CSF Volume.
Metabolic Causes.Drugs and Poisoning.
*Pathological Causes of Decreased Conscious Level.Brain Injury / Irritation.
Cerebral infection - encephalitis / meningitis.
Increase in Brain Volume.
Cerebral oedema from head injury.
*Pathological Causes of Decreased Conscious Level.Increase in Cerebral Blood Volume.
Intracerebral haematoma. Increase in CSF Volume.
*Generalised metabolic or toxic disorders can depress brain function.
Major organ failure. (E.g liver or kidney failure)
Hypo / Hyperglycaemia. (blood sugar < 3 mmol/L = coma and possible fitting)
Electrolyte imbalance. (E.g disturbances of calcium, sodium and potassium.)
Pituitary, adrenal and thyroid disease. (E.g Hypothyroidism)
Cardiac Arrhythmias (E.g fast atrial fibrillation)
*Drugs / Poisoning.
Sedatives - barbiturates, opiates.
Amphetamines - tricyclic antidepressants.
Age: The incidence of altered consciousness increases with age.Cardiovascular status: Disorders that lower cardiac output, lower perfusion and precipitate arrhythmias.Pulmonary disorders: Disorders that cause hypoxia and hypoxaemia.Drug therapy: Sedation, analgesia, drug toxicity, drug interactions.Cerebral disorders: Including expanding lesions and brain injury.Surgical factors: Prolonged anesthesia time.Perceptual / sensory factors: Sleep deprivation, sensory overload, sensory deprivation.Metabolic factors: Changes in glucose level, hypermetabolism, hypometabolism.Fluid and electrolyte disturbances: Sodium and potassium imbalances, hypovolaemia.
Assessment and Management.
*Priorities.Establish exactly what happened.Immediate assessment (life threatening conditions).General assessment.Investigations.Working diagnosis.Management planContinue to monitor.
Where do you fit in?Blood and Urine.Drug screen, U and E, glucose, calcium, LFTs, ABGs, thyroid, cortisol levels, blood cultures etc.
CT / MRI Scanning.
*Assessment ?Consciousness cannot be measured directly and can only be assessed by observing a person's behaviour in response to different stimuli.
Assessment of consciousness is difficult because it can only be implied by an evaluation of the person's appearance and behaviour by another person. (Hickey 1997)
*Why Assess?3 reasons.Is the patients condition,
Level of consciousness.
*Vital Signs.Changes in respiration, in terms of rate and pattern of breathing, can give a good idea of the function of the brain stem.
Alterations in temperature may be due
to damage to the hypothalamus.
Rising blood pressure and falling heart rate may = increasing ICP. (Cushings sign)
Glasgow Coma Score. Teasdale and Jennett (1974) and (1976).
The most widely used scoring system for quantifying consciousness.
Allows standardisation of assessment.
*Glasgow Coma Score.Consists of three aspects of behavioural response, each evaluated independently.
Eye opening.Best verbal response.Best motor response.
It assesses the two aspects of consciousness: arousal and cognition.
*Glasgow Coma Score.Highest score = 15Lowest score = 3 (even patients who are brain stem dead score 3)
The phrase GCS of 10, 12 etc is largely meaningless and the figure should be broken down as E3V3M4, E3V4M4 etc.
A patient scoring of eight or less is considered to be in a deep coma.
Brief Aside.Applying Painful Stimuli.
*Painful Stimuli?When performing the GCS, you are trying to illicit a purposeful and specific response to painful stimuli (not just a response to the irritation).
As such stimuli that causes the patient to respond purposefully are favoured (across the midline and up) .
*Painful Stimuli?Trapezius pinch?Supraorbital ridge? (Not in facial #)Jaw margin? (Not in facial #)Lateral aspect of fingers?Sternal rub?Inflicting a painful stimulus may not always be needed, as the patient may find objects such as nasogastric tubes and oxygen masks irritating, and may localise spontaneously to such sources of irritation.
Back to the GCS
A patient with flaccid ocular muscles may have their eyes open at all times.
*Best Verbal Response.
*Best Motor Response.
Obeys command. 6- move your toes, lift up your arms, raise your eyebrows"Squeeze my fingers" - best not used as it may only stimulate a grasp reflex. (can do squeeze and release and repeat)Localises pain. 5Moves hand to remove a source of irritation. (with purpose)Eg. Supra-orbital ridge - patients hand must reach beyond the level of the chin, and must cross the midline. Flexion to pain. 4Normal response to pain as if touching a hot object, but no localising. (not purposeful, may be reflex) Abnormal flexion. 3Slower than above, characterised by adduction of the shoulder and flexion of the elbow, possibly with flexion of the wrist. Extension.2 Patient will straighten and internally rotate the elbow joint, adduct and internally rotate the shoulder and flex the wrist. NB: Posturing. None. 1No movement at all. NB: Spinal reflexes.
The upper extremities are flexed at the elbows and wrists. The legs may also be flexed.
Consider lesion in a mesencephalic (mid-brain) region of the brain.