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Neurological Disease and Anaesthesia (view source)

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==Introduction==
 
==Introduction==
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Respiratory disease is one of the most common problems in veterinary medicine and can be classed in many different ways, including obstructive and restrictive. The respiratory tract is a route of entry for many infectious agents as well as there being anatomical problems, for example ''brachycephalic obstructive airway syndrome'' seen in brachycephalic breeds. Respiratory disease poses many issues for an anaesthestist from intubation issues in cases of upper airway obstructive disease to ventilation perfusion mismatch and respiratory depression caused by some of the agents used.
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Neurological disease can be '''intracranial, spinal''' or '''neuromuscular'''. Their presentations can be variable, ranging from a patient who appears otherwise healthy and normal, to one that is in a coma. These patients may require a general anaesthetic for diagnostic procedures, surgery or supportive therapy.  
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==Upper Airway Obstruction==
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There are a number of different syndomes in patients that cause upper airway obstruction. This include:-
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*Brachycephaic obstructive airway syndrome
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*Collapsing trachea
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*Pharyngeal and retropharyngeal masses (e.g. absecesses, cysts and neoplasia)
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*Laryngospasm
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''Clinical signs'' seen in these patients can include stridor, dyspnoea, and increased effort, but in some patients, depending on the severity and disease present, no clinical signs may be seen.
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Upper airway obstruction can sometimes lead to problems intubating a patient, and in some cases it is impossible to intubate a patient meaning that placement of a tracheostomy tube is required. These patients will often require preoxygenation before induction and a calm environment as to not over stress and exacerbate any breathing problems that may be present, for example, hyperventilation can promote collapse of the upper airway.  
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===Laryngeal Paralysis===
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==Intracranial==
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In dogs, diagnosis of laryngeal paralysis is performed by examination of the larynx under a light plane of anaesthesia. This is often performed at the same time as corrective surgery, if a diagnosis of laryngeal paralysis is highly suspcious. Anaesthetic agents should be selected carefully, to prevent any effects to laryngeal function which may complicate diagnosis, e.g. high doses of opioids should be avoided if possible. If the patient undergoes surgery, swelling may present as a problem post operatively, which can usually be managed with anti inflammatories, e.g. non steroidal anti inflammatories are often sufficient.
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Intracranial neurological disease can include such conditions as head trama, epilepsy and neoplasia.
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===Intracranial Pressure===
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One of the biggest concerns with intracranial conditions is an increase in intracranial pressure (ICP). Clinical signs of increased ICP include depression, changes in pupils, and cardiovascular and respiratory changes. These increases in ICP can be avoided by using such agents as diuretics, positioning the patient to prevent jugular occulsion which may lead to an increase in central venous pressure which in itself should be avoided as can increase ICP and finally the use of IPPV to allow for normocapnia.  
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Preanaesthetic considerations in patients with elevated ICP include the use of diuretics and correction of any underlying electrolyte disturbances. The premedication choices are patient dependent as some patients may require no premedication. However, drugs which induce vomiting as these can exacerbate the increase in ICP. The patient should be preoxygenated and then at induction the patient should be sufficiently anaesthetised to avoid the patient coughing at intubation. As with any patient, extensive monitoring should be used throughout the procedure. The patient should ideally be kept anaesthestised until they are normothermic and good hydration status. Multimodal analgesia should be used and on recovery, sedation may be required to allow for a calm recovery. As with any neurological patient, they should be monitored for any seizure activity.  
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===Brachycephalic Obstructive Airway Disease===
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===Epilepsy===
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This syndrome is a combination of conditions including ''stenotic nares'', ''elongated soft palate'', ''everted laryngeal saccules'',  and ''laryngeal collapse''. Care of these patients is similar to that of those with laryngeal paralysis, however, greater care is required in selection of any sedation and anaesthetic agent used as to not exacerbate breathing problems that may already be present. Once any agent has been given to these patients, including premedication, they should not be left without supervision and intubation equipment and oxygen should be readily available in case of an emergency.  
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It is important for antiepileptic therapy to continue for any epileptic patient undergoing a general anaesthetic. It is important to have IV access in these patients to allow for quick administration of anti-epileptic drugs if required. Ideally, masked induction should be avoided in these patients as it may induce seizure activity.
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In status epilepticus, total intravenous anaethesia can be used to stop seizures until the patient can be stabilised via other means.  
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==Lower Airway Disease==
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==Spinal==
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Lower airway disease rarely presents as an emergency in terms of anaesthesia and so time can be taken in preparing for the procedure, unlike upper airway disease. As in any patient, a full physical examination should be performed to identify the underlying condition, and further testing such as concious thoracic radiographs, ultrasound and thoracocentesis should be performed when necessary.  
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As in any disease, severity ranges between patients. Spinal disease can affect any part of the spine, and each requires specific positioning. Analgesia should always be given as part of the premedication, and multimodal analgesia should be used. Fluid replacement is important in cases where haemorrhage is suspected. Post operatively, the patients should be restricted and so may require sedation to prevent too much movement. Animals that are recumbant require turning to prevent sores developing and many spinal patients need a urinary catheter placed.  
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===Ventilation Perfusion Mismatch===
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==Neuromuscular==
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Many conditions of the lower airway cause a ventilation perfusion mismatch. These include such conditions as:-
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Preoperatively, radiographs should be taken in patients suspected of having a neuromuscular disease to rule in/out megaoesophagus. Patients should be preoxygenated and rapid intravenous induction should be performed. Patients should be kept in sternal recumbancy to prevent aspiration of any regurgitation that may occur prior to intubation, and if available, suction should be used when necessary. Throughout the anaesthetic, patients should be closely monitored as IPPV may be necessary. Post operatively, a PEG tube may be required to feed patients with megaoesophagus and tracheostomy performed in those patients that may have ventilation difficulties.
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*Bronchitis
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*Pneumonia
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*Emphysema
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*Contusions
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*Emboli
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*Pulmonary oedema
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*Feline Asthma
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In many of these cases, agents which ''clear'' the airway should be selected to try and optimise function of the diseased pulmonary tissue. Agents known to cause severe respiratory depression should also be avoided. Severe cases may require preoxygenation before induction and intubation and if possible, local anaesthetic and sedative techniques should be be used, to avoid risks associated with general anaesthesia in these patients.
         
[[Category:Diseases and Anaesthesia]]
 
[[Category:Diseases and Anaesthesia]]
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