The feedback theory

The cerebrum regulates incoming information by a positive feedback mechanism (Guyton & Hall 2000). A second feedback cycle that stimulates proprioceptors in skeletal muscles is also shown in Figure 28.2.

Figure 28.2 The feedback mechanism, showing two feedback cycles passing through the RAS. In cycle A, the RAS excites the cerebral cortex and the cortex in turn re-excites the RAS. This initiates a cycle that causes continued intense excitation of both regions. In cycle B, impulses are sent down the spinal cord to activate skeletal muscles. Activation of the muscle stimulates proprioceptors to transmit sensory impulses upward to re-excite the RAS. Consciousness results when the RAS, in turn, stimulates the cerebral cortex.

After a prolonged period of wakefulness, the synapses in the feedback loops become increasingly fatigued, reducing the level of stimulation and activity directed to the reticular activating system and thereby inducing a state of lethargy, drowsiness and eventually sleep (Guyton & Hall 2000). Figure 28.2 illustrates a number of activating pathways passing from the mesencephalon upwards.

Reduced awareness

Reduction in awareness reflects generalised brain dysfunction, as seen in systemic and metabolic disorders (see Figure 28.3). These disorders interfere with the integrity of the RAS, affecting the patient’s arousal response.

In the early stage, subtle changes may occur in the patient’s behaviour. They may exhibit signs of hyper-excitability and irritability, alternating with drowsiness, progressing to confusion and increased levels of disorientation. Minor disturbance such as irritability can easily go undetected and comments from a relative such as ‘she does not seem to recognise me today’ may denote a subtle change in behaviour that requires further investigation. Martin (1994) suggests that nurses who are expert in the care of head-injured patients can identify cues which indicate behavioural, cognitive, motor and sensory changes even in mild brain dysfunction.

Any new or acute change from the patient’s normal baseline behaviour must be reported and documented. The patient’s nursing care plan will also need to be re-evaluated and new goals for care set.

Cognitive disabilities, e.g. poor concentration or short-term memory problems, may only become apparent when a patient returns home. These can cause emotional distress for both the patient and family, particularly if they go unheeded and help is not provided. The primary care team plays a major role in supporting patients following acquired brain injury, facilitating referral to specialist agencies (see www.bann.org.uk).

Delirium

Delirium is a fluctuating mental state characterised by confusion, disorientation, fear and irritability. The patient may be talkative, loud, offensive, suspicious or extremely agitated. This behaviour reflects generalised brain dysfunction due to interference with the RAS, affecting the arousal mechanism (Siddiqi et al 2007). Patients will present with a range of symptoms including:

Delirium is very distressing for the patient and their relatives who may witness their altered behaviour. Early diagnosis and treatment with medication, and environmental changes such as reducing noise or sensory input may help to alleviate some of the symptoms.

Stupor

The term stupor describes a state whereby the patient is quiet and tends not to move, except in response to vigorous and repeated noxious stimuli (Hickey 2003).

Coma

Coma is an impaired state where the patient is totally unaware of themselves and their environment. It may vary in degree but in its worse stage, no reaction of any kind is obtainable from the patient. Always assume that an unconscious patient is able to hear and understand what you say, particularly if you need to discuss sensitive issues with their relatives. Hearing can often be the last sense to be lost and the first one to come back before they are able to respond.

Dementia

This condition is caused by a generalised and progressive loss of cortical tissue in the brain. Mental functions progressively decline with global deterioration of memory, thought processes, motor performance, emotional responsiveness and social behaviour.

As the condition develops, speech and communication becomes difficult and behaviour becomes increasingly inappropriate until control of basic and vital processes is completely disorganised. Alzheimer’s disease is the most prevalent type of progressive dementia but there are numerous other causes.

Although dementia is an irreversible condition, new drug therapies such as donepezil (Aricept®) are being used successfully to delay onset of the disease. Patients with normal pressure hydrocephalus may be helped by insertion of a ventricular shunt (Wilson & Islam 2004, Dalvi 2010; see also Life NPH in Useful websites, p. 756).

Vegetative state

Vegetative state (VS) is a term used to describe a condition that may occur following a severe brain injury, where there is extensive damage to the cerebral cortex. Although the patient has sleep/waking cycles, the higher centres of the brain are destroyed. Physiologically, the brain stem is functioning but the cerebral cortex is not, and patients can survive for several years requiring full-time nursing care. The British Medical Association (1996) recommends ‘that the diagnosis of irreversible Permanent Vegetative State (PVS) should not be considered or confirmed (and therefore treatment not be withdrawn) until the patient has been insentient for 12 months’. Some neuro-rehabilitation units use a structured technique for assessing various sensory aspects of communication, movement awareness and wakefulness, known as SMART (sensory modality assessment and rehabilitation technique – www.smart-therapy.org.uk/), to enable clinicians to make a more accurate diagnosis of patients they suspect may be in PVS.

There is ongoing debate, both in the UK and other countries, about the moral, ethical and legal issues surrounding the care and treatment of these individuals and the dilemma posed by some patients to ‘the right to die’ and withdrawal of treatment has received considerable professional, public and political attention over recent years (Porter 2005) (see www.ethics-network.org.uk).

Locked-in syndrome

This occurs when there is damage to the pons in the brain stem, resulting from cerebral vascular disease or trauma, paralysing voluntary muscles without interfering with consciousness and cognitive functions. The patient is unable to speak and is sometimes unable to breathe spontaneously, the latter requiring mechanical ventilation and respiratory support. However, the patient is able to control vertical eye movements and blinking and may be able to use these movements to develop a simple communication system. It is important to remember that the patient is cognitively aware, even if they appear to be mentally and physically inert. For further information about PVS and locked-in syndrome, see Randall (1997), Smith (1997) and Royal College of Physicians (2003).

Eye opening

This assesses the integrity of the RAS in the brain stem and is observed and recorded using the following categories.

Spontaneously = scores 4. The patient opens their eyes when first approached, which implies that the arousal response is active.

To speech = scores 3. The nurse should speak to the patient by calling their name and asking them to open their eyes. It may be necessary to increase the level of the verbal stimulation to gain a reaction.

To pain = scores 2. A gentle shake of the patient’s shoulder may be sufficient to elicit a response. If the patient still fails to open their eyes, a painful stimulus must be used. Pressure is applied to the lateral inner aspect of the second or third finger using a pen or pencil, for a maximum of 15 seconds (Figure 28.5). Nail bed pressure is contraindicated as it will cause excessive bruising.

Figure 28.5 Applying a peripheral painful stimulus: fingertip stimulation.

None =scores 1 . If the painful stimulus does not elicit any response from the patient this indicates a deep depression of the arousal system and the patient is recorded as having no eye opening.

Verbal response

This assesses the area of the brain associated with receptive and expressive speech.

Orientated = scores 5. Patients are assessed as orientated in person, place and time if they can state their name, where they are and what the year and month are. Avoid asking them to state the day or the date as they are not easily remembered, especially after a period of time in hospital.

Confused = scores 4. The patient is able to produce phrases or sentences but the conversation is rambling and inappropriate to the questions being asked.

Inappropriate words = scores 3. The patient offers monosyllabic words, usually in response to physical stimulation. The words and phrases make little or no sense and may express obscenities.

Incomprehensible sounds = scores 2. The patient will moan or groan in response to painful stimulation. The verbal response may contain indistinct mumbling but no intelligible words.

None = scores 1. The patient is unable to produce any verbal response despite prolonged and repeated stimulation.

Motor response

This assesses the patient’s best motor response. Only the best response from the arms is recorded as leg responses to pain are less consistent and may be confused with a simple spinal reflex. The responses described below are shown in Figure 28.6.

Figure 28.6 Motor responses. A. Obeys commands (‘lift up your arms’). B. Localising to pain. C. Flexing to pain. D. Abnormal flexion. E. Extending to pain.

Obeys commands. Score = 6. The patient has the ability to follow instructions, for example, ‘put out your tongue’, ‘lift up your arms’, ‘show me your thumb’.

Localises to pain. Score = 5. If the patient does not obey commands, an external stimulus must be applied. In the absence of any facial, orbital or skull fractures, pressure is applied with the flat of the nurse’s thumb over the cranial nerve underlying the supraorbital ridge under the eyebrow (Figure 28.7a). Pressure is gradually increased for a maximum of 15 seconds. Providing the patient has not sustained a cervical fracture, the ‘trapezius pinch’ (Figure 28.7b) is a useful alternative; the trapezius muscle (the large triangular muscle of the neck and thorax) is squeezed between the nurse’s fingers and thumb. The response is recorded as ‘localising to pain’ if the patient moves their arm across the midline, to the level of the chin, in an attempt to locate the source of the pain (Figure 28.6b). During the course of the day, the patient may display a localising response to other sources of irritation, e.g. suctioning, nasogastric tube or urinary catheter.

Figure 28.7 Applying a central painful stimulus. A. Supraorbital ridge pressure. B. Trapezius pinch.

Flexion to pain. Score = 4. Following the application of a central painful stimulus, either the trapezius squeeze or supraorbital ridge pressure, the patient responds by flexing their arm normally by bending their elbow and weakly withdrawing their hand; no attempt to localise towards the source of the pain is made.

Abnormal flexion. Score = 3. In response to a painful stimulus, the patient bends their elbow with adduction of the upper arms and abnormal posturing of the wrist and fingers, otherwise known as decorticate posturing. This indicates more severe dysfunction of the brain and is a poor prognostic sign.

Extension to pain. Score = 2. Following painful stimulation, the patient responds by rigid extension, i.e. straightening the elbows and hyperpronation of the forearms, otherwise known as decerebrate posturing. The response usually includes spastic hand and wrist movements, with an inward rotation of the shoulders and forearms. The legs are generally straight, with the feet pointing outwards.

None. Score = 1. This response is only recorded when sufficient painful stimulus has been applied to provoke a response and no detectable movement has been observed.

Vital signs

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