Neurological Emergencies - part 1 ppsx

Causes of coma Consciousness depends upon an intact ascending reticularactivating substance ARAS in the brain stem acting as thealerting or awakening element of consciousness, together w

Neurological Emergencies

Four th edition

Emergencies Four th edition

Edited by

RAC Hughes

Head, Depar tment of Clinical Neurosciences, Guy’s, King’s and St Thomas’ School of Medicine,London, UK

© BMJ Publishing Group 2003 BMJ Books is an imprint of the BMJ Publishing Group All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise, without the prior written permission of the publishers.

First published in 1994

by BMJ Books, BMA House, Tavistock Square,

London WC1H 9JR www.bmjbooks.com First edition 1994 Second edition 1997 Third edition 2000 Fourth edition 2003

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0 7279 1774 9

Typeset by SIVA Math Setters, Chennai, India

Printed and bound in Spain by GraphyCems, Ltd

Simon Shorvon, Matthew Walker

JD Pickard, M Czosnyka, LA Steiner

8 Management of subarachnoid haemorrhage 247

Thomas A Kopitnik, Carol Croft, Shawn Moore,

11 Acute neuromuscular respiratory paralysis 377

RAC Hughes, A McLuckie

12 Acute visual loss 408

Shirley H Wray

13 Criteria for diagnosing brain stem death 437

MD O’Brien

Peter JD Andrews

Reader in Anaesthesia, Critical Care and Pain Medicine,University of Edinburgh, Clinical and Surgical Sciences(Anaesthetics) and Western General Hospital, Edinburgh, UK

RA Johnston

Consultant Neurosurgeon, Institute of Neurosurgical Sciences,Queen Elizabeth National Spinal Injuries Unit, SouthernGeneral Hospital, Glasgow, UK

Thomas A Kopitnik

Professor of Neurological Surgery, Director of CerebrovascularSurgery, University of Texas Southwestern Medical Center,Dallas, Texas, USA

Consultant Intensive Care Physician, Intensive Care Unit,

St Thomas’ Hospital, London, UK

Shirley H Wray

Professor of Neurology, Department of Neurology, HarvardMedical School and Director, Unit for Neurovisual Disorders,Massachusetts Hospital, Boston, Massachusetts, USA

This popular book is designed for every doctor who deals withneurological emergencies Each chapter reviews currentmanagement and the evidence for its efficacy, and concludeswith a brief summary of recommendations that should be a

useful aide-mémoire in an emergency

The fourth edition of the book, which was first published

as a series in 1993 in the Journal of Neurology, Neurosurgery

and Psychiatry, has been thoroughly revised and based on the

latest evidence The first-time reader will find succinct reviews

of the pathogenesis and especially management of all thecommon neurological emergencies “Neurological” is used inthe broadest sense to include neurosurgery (head injury,compression, subarachnoid haemorrhage, raised intracranialpressure), psychiatry (delirium, acute behaviour disturbances),neuro-ophthalmology (acute visual failure), infectious disease(cerebral infections), and intensive care (acute neuromuscularrespiratory paralysis) Old lags can quickly bring themselves

up to date because each chapter has taken advantage of theincreasing collection of relevant Cochrane reviews to providethe best evidence on which to base practice Are you confidentthat you know the latest guidelines for head injury, raisedintracranial pressure and acute spinal cord compression, thebest antibiotics for meningitis, and the best antiepileptic drugregimen for status epilepticus?

Although a book like this is inevitably targeted at the doctor

in training, especially residents in internal medicine, accidentand emergency medicine, and neurology (includingneurosurgery and psychiatry), we are all perpetual students ofmedicine We hope therefore that this work will help thewhole profession improve the care of neurological patientswhen they most need it, in an emergency

We regret to report the death of Dr Martin Wood shortlyafter submitting the fine chapter on cerebral infections, ofwhich he was co-author

RAC HUGHES

and reversible causes are corrected Delay in institutingtreatment for a patient with raised intracranial pressuremay have obvious consequences in terms of pressure coningbut, similarly, the unnecessary investigation by imagingtechniques of patients in metabolic coma may delay theinitiation of appropriate therapy It is therefore essential forthe physician in charge to adopt a systematic approach,initially to ensure resuscitation then to direct further teststowards producing the most rapid diagnosis and the mostappropriate therapy The development of such a systematicapproach demands an understanding of the pathophysiology

of consciousness and the ways in which it may be deranged

Causes of coma

Consciousness depends upon an intact ascending reticularactivating substance (ARAS) in the brain stem acting as thealerting or awakening element of consciousness, together with

a functioning cerebral cortex of both hemispheres whichdetermines the content of that consciousness The ARAS is acontinuous isodendritic core, extending from the medullathrough the pons to the midbrain which is continuouscaudally with the reticular intermediate grey lamina of thespinal cord and rostrally with the subthalamus, thehypothalamus, and the thalamus (Figure 1.1).3 The functionsand interconnections of the ARAS are considerable and its rolegreater than that of a simple cortical arousal system There arenamed nuclei throughout the reticular formation Although itwas originally considered that cortical arousal depended uponprojections from the reticular formation via the midlinethalamic nuclei to the thalamic reticular nucleus and cortex,

it now seems unlikely that the thalamic reticular nucleus is thefinal relay The specific role of the various links from thereticular formation to the thalamus has yet to be identified Similarly the neurotransmitters involved in this arousalsystem are not fully determined though it seems likely that, inaddition to cholinergic and monoaminergic systems, gammaaminobutyric acid (GABA) may be important in controllingconsciousness.4–6

It follows from the anatomy and pharmacology of theARAS that structural damage to this pathway or chemical

derangement of the neurotransmitters involved aremechanisms whereby consciousness may be impaired Suchconditions will occur with focal lesions in the brain stem,mass lesions in the posterior fossa impinging directly on thebrain stem, or mass lesions involving the cerebral hemispherescausing tentorial pressure coning and consequentlycompromising the ARAS either by direct pressure or byischaemia (Figure 1.2) In addition toxins, including mostcommonly ingested drugs, may have a significant depressanteffect upon the brain stem ARAS and thereby result in loss ofconsciousness.

The content of consciousness resides in the cerebral cortex

of both hemispheres Unlike those discrete cortical functionssuch as language or vision which are focally located within thecortex, the content of consciousness can best be regarded asthe amalgam of all cognitive functions Coma arising fromdisruption of cortical activity requires a diffuse pathology such

as generalised anoxia or ischaemia, commonly seen aftercardiac arrest or anaesthetic accidents, or cortical vasospasmseen in infective meningitis, or subarachnoid haemorrhage,where generalised cortical ischaemia is believed to be thecause of disruption of function

The physician attempting to diagnose the cause of comashould consider the following

1 Supratentorial or infratentorial mass lesions Typically these

will provide evidence of raised intracranial pressure andcommonly produce focal signs Processes such asneoplasm or haematoma, infarction with cerebral oedema,abscess, focal encephalitis, and venous sinus thrombosismust all be considered

2 Subtentorial destructive lesions or the local effect of toxin.

These processes will directly damage the ARAS in brainstem infarction, rhombencephalitis, brain stemdemyelination, and the more common effects of self-poisoning with sedative drugs

3 Diffuse damage to the cerebral cortex Bilateral cortical injury

is most commonly seen following hypoxia and ischaemia

(c)

Diencephalic herniation

Uncal herniation causing third nerve palsy

Figure 1.2 Causes of coma (a) Focal brain stem lesions; (b) mass lesions; (c) diffuse cor tical pathology

but may be mimicked by hypoglycaemia, ketoacidosis,electrolyte abnormalities, bacterial meningitis, viralencephalitis, and diffuse postinfective encephalomyelitis.

It is also the likely pathology of coma followingsubarachnoid haemorrhage

Definitions

There is a continuum from the individual in fullconsciousness to the patient in deep coma The terminologywhich is most usually employed derives from the BrainInjuries Committee of the Medical Research Council (MRC).7

1 Confusion “Disturbance of consciousness characterised

by impaired capacity to think clearly and to perceive,respond to and remember current stimuli; there isalso disorientation.” Confusion involves a generaliseddisturbance of cortical cerebral function which is usuallyassociated with considerable electroencephalographic(EEG) abnormality Some authors describe an interveningstate between normal consciousness and confusion, that

of “clouding of consciousness”.2

2 Delirium “A state of much disturbed consciousness with

motor restlessness, transient hallucinations, disorientationand delusions.”

3 Obtundation “A disturbance of alertness associated with

psychomotor retardation.”

4 Stupor “A state in which the patient, though not

unconscious, exhibits little or no spontaneous activity.”Although the individual appears to be asleep he or she willawaken to vigorous stimulation but show limited motoractivities and usually fail to speak

5 Coma “A state of unrousable psychologic unresponsiveness

in which the subject lies with eyes closed and shows nopsychologically understandable response to externalstimulus or inner need.” This may be shortened to “a state

of unrousable unresponsiveness” which implies both thedefect in arousal and in awareness of self or environmentmanifest as an inability to respond A more usefulassessment of coma is that derived from the hierarchicalGlasgow Coma Scale.8 Patients who fail to show eye

opening in response to voice, perform no better than weakflexion in response to pain, and make, at best, onlyunrecognisable grunting noises in response to pain, areregarded as being in coma This allows the patient to have

an eye opening response of two or fewer, a motor response

of four or fewer, and a verbal response of two or fewer Thesum Glasgow Score of eight should not be regarded asbeing definitive of coma since the total score can beachieved in several different ways (see below)

6 Vegetative state “A clinical condition of unawareness of

self and environment in which the patient breathesspontaneously, has a stable circulation and shows cycles ofeye closure and eye opening which may simulate sleepand waking This may be a transient stage in the recoveryfrom coma or it may persist until death.”9 When thecortex of the cerebral hemispheres of the brain recoversmore slowly than the brain stem or when the cortex isirreversibly damaged there will arise a situation in whichthe patient enters a vegetative state without cognitivefunction This may be a transient phase through whichpatients in coma pass as they recover or deteriorate but,commonly after anoxic injuries to the brain, a statedevelops in which the brain stem recovers function butthe cerebral hemispheres are not capable of recovery This

is the “persistent vegetative state” described by Jennettand Plum.10Such patients may survive for long periods, onoccasion for decades, but never recover outwardmanifestations of higher mental activity and thecondition, which is comparatively newly recognised,relates to the development of modern resuscitativetechniques Other terms have, in the past, been used toidentify similar conditions including coma vigile, theapallic syndrome, cerebral death, neocortical death, andtotal dementia

7 Akinetic mutism This term has been used to define a

similar condition of unresponsiveness but apparentalertness together with reactive alpha and theta EEGrhythms in response to stimuli The major difference fromthe vegetative state, in which there is tone in the musclesand extensor or flexor responses, is that patients withakinetic mutism have flaccid tone and are unresponsive toperipheral pain It is thought that this state is due to

bilateral frontal lobe lesions, diffuse cortical lesions, orlesions of the deep grey matter.11

8 The locked-in syndrome Feldman12 described a efferented state caused by a bilateral ventral pontine lesioninvolving damage to the cortico-spinal, cortico-pontine,and cortico-bulbar tracts The patient has total paralysisbelow the level of the third nerve nuclei and, althoughable to open, elevate and depress the eyes, has nohorizontal eye movements and no other voluntarymovements The diagnosis depends upon the clinicianbeing able to recognise that the patient can open the eyesvoluntarily and allow them to close and can signal assent

de-or dissent, responding numerically by allowing the eyelids

to fall Similar states are occasionally seen in patients withsevere polyneuropathy, myasthenia gravis, and after theuse of neuromuscular blocking agents

9 Pseudo-coma Rarely, patients who appear in coma without

structural, metabolic, toxic, or psychiatric disorder beingapparent can be shown by tests of brain stem function tohave intact brain stem activity and corticopontineprojections and not to be in coma

Resuscitation

Although resuscitation is commonly performed by thecasualty officer or the anaesthetist in the intensive care unitrather than by the neurologist, it is appropriate that theneurologist remembers that in patients who are unconscious,protection of the airway, respiration, support of the circulation,and provision of an adequate supply of glucose are allimportant in stabilising the patient It is frequently necessary tointubate the trachea in a patient in coma, not only to ensure

an adequate airway but also to prevent the aspiration of vomit

It is also important to note the respiratory rate and patternbefore intubation and certainly before instituting mechanicalventilation; because depressed respiration may be a clue to drugoverdose or metabolic disturbance, increasing respiration tohypoxia, hypercapnia, or acidosis and fluctuating respiration to

a brain stem lesion The possibility that respiratory failure is thecause of a coma should always be considered in a patient withdisordered respiration

Once adequate oxygenation and circulation are ensured andmonitored, blood should be withdrawn for the determination

of blood glucose, biochemical estimations, and toxicology It

is reasonable to give a bolus of 25–50 g of dextrose despite thepresent controversy about the use of intravenous glucose inpatients with ischaemic or anoxic brain damage It could beargued that extra glucose in this situation might augmentlocal lactic acid production by anaerobic glycolysis andeventually worsen ischaemic or anoxic damage In practice,with ischaemic or anoxic brain damage and even in thepresence of a diabetic ketoacidosis the administration of such

a quantity of glucose will not be immediately harmful and

in the hypoglycaemic patient it may well be life saving Areasonable compromise would be to obtain an earlyassessment of the level of blood glucose by Dextrostix testing,but these are not sufficiently accurate to preclude the need forformal laboratory assessment When glucose is given in thissituation an argument can be made for giving a bolus ofthiamine at the same time to prevent the precipitation ofWernicke’s encephalopathy.13

An essential part of resuscitation includes the establishment

of baseline blood pressure, pulse, temperature, the insertion of

an intravenous line, and the stabilisation of the neck, togetherwith an examination for meningitis It may be difficult in thosepatients who sustain some degree of trauma in their collapse

to assess the stability of the neck, but the establishment of

an adequate airway certainly takes precedence and theidentification of meningism in a febrile patient probably takesprecedence over the stabilisation of neck movements In acomatose, febrile patient with meningism seen outside thehospital environment, the intramuscular injection of penicillinbefore transfer is now recognised to carry a significant advantage

History

Once the patient is stable it is important to obtain as muchinformation as possible from those who accompanied thepatient to hospital or who watched the onset of coma Thecircumstances in which consciousness is lost are of vitalimportance in helping to identify the diagnosis Generally,coma is likely to present in one of three ways: as the

predictable progression of an underlying illness; as anunpredictable event in a patient with a previously knowndisease; or as a totally unexpected event Distinctions betweenthese presentations are often achieved by the history of thecircumstances in which consciousness was lost In the firstcategory are patients following focal brain stem infarctionwho deteriorate or those with known intracranial mass lesionswho show similar deterioration In the second category arepatients with recognised cardiac arrhythmia or the known riskfactor of sepsis from an intravenous line In the final category

it is important to determine whether there has been a previoushistory of seizures, trauma, febrile illness, or focal neurologicaldisturbances The history of a sudden collapse in the midst of

a busy street or office indicates the need for differentinvestigations from those necessary for the patient discovered

at home in bed surrounded by empty bottles which previouslycontained sedative tablets

Examination and monitoring

The third phase of the management of the patient in comainvolves a rapid but systemic examination to identify possiblecauses of coma

Temperature

Fever usually indicates infection and, rarely, a brain stem ordiencephalic lesion affecting the temperature centres.14 Mostcommonly the combination of fever and coma indicatessystemic infection such as pneumonia or septicaemia, or acerebral cause such as meningitis, encephalitis, or abscess.When seizures occur together with fever, the possibility ofencephalitis or cerebral abscess is greatly increased Heat strokemay present as febrile coma when the clue to the diagnosis is

in the environment Hypothermia is most commonly seen as acomplication of an accident or cerebrovascular disease when

an elderly patient is discovered, having lain for hours or days

in an underheated room This may also be seen followingintoxication with alcohol or barbiturates, with peripheralcirculatory failure and, rarely, with profound myxoedema

Heart rate

A tachyarrhythmia or bradyarrhythmia may be significant

in identifying the cause of cerebral hypoperfusion Irregularity

of the pulse always raises the question of atrial fibrillation andassociated embolic disease

Blood pressure

Hypotension might indicate shock, myocardial infarction,septicaemia, or intoxication It may also indicate diabetesmellitus or Addison’s disease Hypertension is of less help inthe diagnosis of coma as it may be the cause, as in cerebralhaemorrhage or hypertensive encephalopathy, or the result ofthe cerebral lesion

Respiration

For those reasons already given assessment of respirationmay be compromised by the need to give sedation but,generally, slow and shallow breathing raises the question ofdrug intoxication Deep rapid respiration suggests pneumonia

or acidosis but may also occur in brain stem lesions causingcentral neurogenic hyperventilation

Integument

The appearance of the skin and mucous membranes mayidentify anaemia, jaundice, cyanosis, or carbon monoxidepoisoning Bruising over the scalp or mastoids, or the presence

of blood in the external auditory meatus or nostrils, raises thepossibility of basal skull fracture, and bruising elsewhere in thebody raises the question of trauma An exanthem may indicatethe presence of a viral infection causing meningoencephalitis

or of meningococcal septicaemia, or raise the question ofhaemorrhagic disease Hyperpigmentation raises the possibility

of Addison’s disease Bullous skin lesions are frequently seen inbarbiturate intoxication Kaposi’s sarcoma, anogenital herpeticlesions, or oral candidiasis would raise the question of theacquired immune deficiency syndrome (AIDS) with aconsequent plethora of possible central nervous systemdisease

The odour of the breath of an unconscious patient mayindicate intoxication with alcohol, raise the question ofdiabetes, or suggest uraemic or hepatic coma

Cardiovascular

Auscultation and examination of the heart may indicatevalvular disease and raise the possibility of endocarditis Bruitsover the carotid vessels may indicate the presence ofcerebrovascular disease, and splinter haemorrhages seen in thenail beds raise the possibility of subacute bacterial endocarditis

or collagen vascular diseases

Abdomen

Examination of the abdomen may reveal signs of trauma orrupture of viscera; hepatomegaly or splenomegaly raises thepossibility of a portocaval shunt, and the finding of polycystickidneys raises the possibility of subarachnoid haemorrhage

Meningism

Examination of the skull and spine is important and thephysician should always look for neck stiffness Kernig’s test inwhich the resistance to flexion of the thigh with the legextended is examined, or Brudzinski’s test in which the flexion

of one thigh is noted to cause flexion of the other, should beperformed to help in differentiating neck stiffness due tomeningeal irritation from that due to a developing tonsillarpressure cone Positive Kernig’s and Brudzinski’s tests togetherwith neck stiffness imply inflammation in the lumbar thecaand suggest a diffuse meningitic process If these tests arenegative, however, then the neck stiffness alone is moresuggestive of a foraminal pressure cone.15

Fundal examination

The presence of papilloedema or fundal haemorrhage oremboli, together with the findings of hypertensive vascular or