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Neurological disease

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Abstract

Neurological disease may be caused by intracranial, spinal or neuromuscular pathology. Anaesthesia may be required for diagnostic investigation, surgical intervention or supportive management of neurological disease. This chapter discusses intracranial disease, spinal disease, neuropathies and neuromuscular disease and anaesthesia for neurological diagnostic procedures.

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/content/chapter/10.22233/9781910443231.chap28

Figures

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28.1 Schematic diagrams showing normal and raised ICP. (a) The normal intracranial compartment, consisting of the brain (80%), CSF (10%) and blood (10%) and their communication with the low-pressure systems. As the brain is displaced by either (b) a space-occupying lesion or (c) trauma and haematoma, the CSF volume is reduced. As ICP increases, it opposes the driving pressure from the mean arterial pressure (MAP), which remains at 70 mmHg, and cerebral perfusion pressure (CPP) falls. CPP = cerebral perfusion pressure; CSF = cerebro-spinal fluid; ICP = intracranial pressure; MAP = mean arterial pressure; SOL = space occupying lesion.
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28.2 Initially, compensatory mechanisms accommodate increases in intracranial volume, and ICP remains relatively stable (A). Once these mechanisms are exhausted, ICP rises dramatically with only small increases in intracranial volume (B). ICP = intracranial pressure.
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28.3 Autoregulation maintains a constant cerebral blood flow over a wide range of perfusion pressures (CPP or MAP) in the healthy brain. Outside this range, or in an injured brain where autoregulatory mechanisms are lost, CBF is directly related to the perfusion pressure. CBF = cerebral blood flow; CPP = cerebral perfusion pressure; MAP = mean arterial pressure.
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28.4 Cerebral blood flow is linearly related to CO except at extreme hypo- or hypercapnia, when maximum vasoconstriction or vasodilation occurs. Maintaining CO at the low end of the normal range is useful in reducing intracranial blood volume without the risk of excessive vasoconstriction and ischaemia. CBF = cerebral blood flow.
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28.5 MRI findings may be suggestive of increased ICP. Reduced ventricular size, loss of normal gyral architecture and midline shift are good indicators of increased ICP on (a) a transverse scan, while (b) a sagittal scan is important to rule out subtentorial (red arrow) or tonsillar (blue arrow) herniation. The degree of oedema may also be assessed as a guide for treatment before recovering the patient from anaesthesia.
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28.6 Invasive blood pressure monitoring showing the Cushing’s reflex during brain herniation following craniotomy. Arterial blood pressure (ABP) is severely elevated, while the heart rate has decreased. Invasive ABP monitoring is important in this situation, as non-invasive measurements may fail. Treatment should be instituted immediately.
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28.10 A peripherally inserted central catheter in a cat. Before placement, the catheter is measured to the correct length from the point of insertion in the medial saphenous vein to just caudal to the heart base. Central jugular catheters may also be used, but prolonged occlusion of the vein during placement may decrease venous return from the brain.
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28.11 A patient in intensive care with anaesthesia maintained using TIVA. Patients may be recovered in either sternal or lateral recumbency. Sternal recumbency may allow better spontaneous ventilatory function, although care must be taken in arthritic patients and jugular occlusion should be avoided. Extubation should be performed as soon as possible to prevent coughing.
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28.12 Patients may sustain head trauma as a result of road traffic accidents, falls, kicks or bites from dogs. Multiple other injuries may be sustained and so good assessment, fluid resuscitation and analgesia are vital.
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28.13 Positioning of a patient for caudal fossa surgery or suboccipital craniectomy involves flexion of the neck. An armoured endotracheal tube (ETT) avoids kinking of the tube and airway occlusion. If a normal ETT is used, it is important to monitor carefully for occlusion. ETT connections must be secure and elbow fittings can be useful. Capnography is very useful for early detection of kinking or disconnection from the breathing system. Jugular occlusion must also be prevented.
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28.14 Ketamine infusions may be continued postoperatively for 12–24 hours and appear to substantially reduce opioid requirements. Lidocaine infusions may also be used.
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28.17 Lidocaine patches may be placed alongside the surgical wound, covering the dermatomes involved. This will help to manage allodynia and hyperaesthesia in some patients.
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28.18 A patient requiring ventilatory support following ventral slot surgery at C2/C3. Respiratory function should be evaluated before extubation and, if possible, arterial catheters should be kept in place, as patients can deteriorate during the recovery period with ongoing inflammation affecting the phrenic nerve outflow.
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28.19 Abdominal pressure should be minimized in sternal recumbency by placing a support (sandbag or padding) underneath the pelvis to elevate it. The bladder should be expressed before surgery or a urinary catheter placed. Decreased intra-abdominal pressure will improve venous drainage from the vertebral canal, reducing the risk of haemorrhage during surgery.
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28.20 Patient positioning for ventral slot surgery usually involves extreme neck extension.
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28.21 Positioning for intubation is important if atlantoaxial subluxation or cervical spinal fracture is suspected. The head and neck should be kept in a horizontal plane and in a neutral position. Preoxygenation is worthwhile, and the use of a laryngoscope will greatly aid intubation.
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28.22 Oxygen supplementation is often required during recovery or before induction of anaesthesia in patients with a neck brace. If cyanosis develops, the brace should be loosened or reapplied. Before induction, the supporting bandage should be cut to allow rapid removal if difficulty arises at intubation.
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28.23 Patients with suspected megaoesophagus should be maintained in sternal recumbency with the head elevated for intubation to prevent aspiration. The cuff should be fully inflated before the head is lowered and suction should be available to clear pharyngeal fluid or other material.
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28.24 The pharynx should be raised above the level of the nose to allow fluid to drain from the oropharynx following extubation of patients with megaoesophagus or dysphagia.
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28.25 During CSF sampling, care must be taken to ensure that the endotracheal tube does not kink and that the patient does not move.

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