Animal’Models’for’Intracranial’Pressure’ ·...

θωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµρτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµρτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµρτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµρτψυιοπασδφγηϕκλζξχϖβνµθ

Animal Models for Intracranial Pressure Monitoring in Traumatic Brain Injury

Submitted for Master of Surgery

Damian Amato

Animal Models for Intracranial Pressure Monitoring in Traumatic Brain Injury Dr. Damian P Amato

Thesis submitted for the degree of Master of Surgery, The University of

Adelaide

Discipline of Anatomy and Pathology

School of Medical Sciences

Faculty of Health Sciences

The University of Adelaide

Frome Road

South Australia, 5005.

June, 2010

ii

DECLARATION

I certify that, to the best of my knowledge, the material presented in this thesis is

my own original work except where due acknowledgement is made. This thesis or

any material contained within it has not been previously published for the award

of any degree in any university.

Damian Amato

June 2010

iii

PUBLICATION AND PRESENTATIONS

DP AMATO. Intracranial Pressure and Brain Tissue Oxygenation Monitoring in a

Sheep Model of Traumatic Brain Injury Presented at the Annual Scientific Meeting

of the Neurosurgical Society of Australasia, Alice Springs, Australia, September 17th

-‐19th, 2009.

Acknowledgement:

The Sheep Experiments described in sections 2.2 (Materials and Methods) and 3.1

(Results) were done in collaboration with Dr. Levon Gabrielian.

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ACKNOWLEDGEMENTS

I would like to thank and acknowledge my colleagues at the Hanson Centre for

Neurological Diseases in association with the University of Adelaide, School of

Medical Sciences, Discipline of Anatomy and Pathology. In particular, the generous

assistance offered to me by my supervisors Professor Robert Vink and Dr. Stephen

Helps. Professor Robert Vink was instrumental in the development of the project

from its initial stages and assistance with the production of this thesis. Dr. Stephen

Helps was indispensible. He was a constant source of ideas and advice from the

commencement of ethics proposals through to the development of methodology

for all animal models. In particular, his vast experience and assistance with the

experimentation was critical to the overall success of the project. In addition to his

practical guidance, I enjoyed our many discussions regarding the theory in this

text. Our combined ideas were developed through his enthusiasm for this work

and in particular this project. From both co-‐supervisors there was a wealth of

information regarding construction of this thesis, statistical analysis and

interpretation of the results. Considerable thanks to Dr. Emma Thornton for her

assistance with the statistical analysis and results section and Dr. Jenna Ziebell for

her advice, assistance with preparation of tissues for histology, as well as direction

with proofreading, layout and formatting of the thesis.

For the sheep experimentation component of this thesis I am grateful to Dr. Levon

Gabrielian with whom I worked closely to develop the sheep model for

measurement of intracranial pressure and brain tissue oxygenation in traumatic

v

brain injury. He was also of great assistance with advice regarding the technical

aspects of the experimental methods used in other parts of this project.

I also acknowledge the committed assistance of The IMVS Surgical Research

Facility staff, in particular Ms. Melissa Gourlay and Ms. Jess Imgraben who were of

invaluable assistance during the preparation and anaesthesia for the animals used

in these models. Further thanks go to Dr. Tim Kuchel for assistance and advice

regarding the anaesthesia for all animal models described in this thesis.

Finally, to all the staff and students of ‘The Vink Lab” I am grateful for the positive

atmosphere to which each of you have contributed. The youthful energy is

contagious.

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LIST OF ABBREVIATIONS

AAMI Association for the Advancement of Medical Instrumentation

AANS American Association of Neurological Surgeons

AEC Animal Ethics Committee

AIHW Australian Institute of Health and Welfare

ANOVA Analysis Of Variance

ARDS Adult Respiratory Distress Syndrome

ASDH Acute Subdural Haemorrhage

atm Atmospheres

BBB Blood-Brain Barrier

BTF Brain Trauma Foundation

CBF Cerebral Blood Flow

CDC Centers for Disease Control

CI Confidence Interval

CMRO2 Cerebral Metabolic Rate of Oxygen

CO Cardiac Output

CO2 Carbon Dioxide

CPP Cerebral Perfusion Pressure

CSF Cerebrospinal Fluid

CT Computed Tomography

vii

DAI Diffuse Axonal Injury

GCS Glasgow Coma Scale

ICP Intracranial Pressure

IM Intramuscular

IMVS Institute of Medical and Veterinary Sciences

IP Intraperitoneal

IV Intravenous

LFP Lateral Fluid Percussion

LN Notch Length

MAP Mean Arterial Blood Pressure

mg milligrams

µg micrograms

msec milliseconds

mmHg millimetres of mercury

MRI Magnetic Resonance Imaging

MVA Motor Vehicle Accident

NAT N-Acetyl Tryptophan

O2 Oxygen

PbtO2 Brain Tissue Oxygen Tension (partial pressure of oxygen in

brain tissue)

PCA Posterior Cerebral Artery

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SaO2 Arterial oxygen saturation (as measured by arterial blood gas

analysis)

S/C Subcutaneous

SpO2 Oxygen saturation (as measured by pulse oximetry)

TBI Traumatic Brain Injury

TPR Total Peripheral Resistance

WHO World Health Organization

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TABLE OF CONTENTS

DECLARATION................................................................................................................ II

PUBLICATION AND PRESENTATIONS .................................................................................... III

ACKNOWLEDGEMENTS .................................................................................................... IV

LIST OF ABBREVIATIONS .................................................................................................. VI

LIST OF TABLES.............................................................................................................XIII

LIST OF FIGURES .......................................................................................................... XIV

LIST OF EQUATIONS......................................................................................................XVII

LIST OF APPENDICES ....................................................................................................XVIII

ABSTRACT.....................................................................................................................1

CHAPTER 1. INTRODUCTION AND REVIEW OF LITERATURE ........................................................3

INTRODUCTION ......................................................................................................................................................3

REVIEW OF LITERATURE ...................................................................................................................................7

1.1 Epidemiology of Traumatic Brain Injury ..............................................................................................7

1.1.1 Definitions in Traumatic Brain Injury ................................................................................................8

1.1.2 Incidence of Traumatic Brain Injury...................................................................................................8

1.1.3 Causes of Traumatic Brain Injury.........................................................................................................9

1.1.4 Impact on Society of Traumatic Brain Injury............................................................................... 10

1.2. Mechanisms in Traumatic Brain Injury ............................................................................................. 11

1.2.1 Classification of Traumatic Brain Injury........................................................................................ 13

1.3 Primary Brain Injury................................................................................................................................... 13

1.4 Secondary Injury .......................................................................................................................................... 16

1.4.1 Brain Swelling and Cerebral Oedema.............................................................................................. 18

1.5 Intracranial Pressure (ICP) ...................................................................................................................... 19

x

The Monroe-Kellie Doctrine: ........................................................................................................................... 19

1.5.1 Intracranial Pressure Effects on Neurological Outcome for Patients with Severe

Traumatic Brain Injury. .................................................................................................................................... 20

1.5.2 Technological Aspects of Intracranial Pressure Monitoring ................................................. 21

1.5.3 Complications of ICP Monitoring Devices ...................................................................................... 21

1.5.4 Summary of Intracranial Pressure.................................................................................................... 22

1.6 Cerebral Perfusion, Brain Tissue Oxygenation and Ischaemia................................................. 22

1.6.1 Cerebral Perfusion Pressure................................................................................................................. 22

1.6.2 Cerebral Blood Flow ................................................................................................................................ 24

1.6.3 Pressure Autoregulation of Cerebral Blood Flow ....................................................................... 24

1.6.4 Metabolic Autoregulation of Cerebral Blood Flow .................................................................... 25

1.6.5 Cerebral ischaemia................................................................................................................................... 25

1.6.6 Brain Tissue Oxygenation...................................................................................................................... 26

1.7 The Tentorium Cerebelli and Brain Herniation Syndromes...................................................... 27

1.7.1 Definition of the Tentorium Cerebelli .............................................................................................. 27

1.7.2 Brain Herniation Syndromes ............................................................................................................... 29

1.8 Prevention of Secondary Brain Injury and Potential treatments............................................ 32

1.9 Animal Models in Traumatic Brain Injury ......................................................................................... 33

1.9.1 Impact Acceleration Models of TBI ................................................................................................... 34

1.9.2 Lateral Fluid Percussion Injury Models of TBI............................................................................. 35

1.10 Experiment Outline................................................................................................................................... 36

1.10.1 Sheep............................................................................................................................................................ 36

1.10.2 Guinea Pigs................................................................................................................................................ 36

1.11 Summary ....................................................................................................................................................... 37

xi

CHAPTER 2. MATERIALS AND METHODS ............................................................................38

2.1 Ethics approval.............................................................................................................................................. 38

2.2 Sheep Experiments ...................................................................................................................................... 38

2.2.1 Synopsis of Sheep Experiment Methodology................................................................................. 38

2.2.1 Anaesthesia and Handling of Sheep.................................................................................................. 39

2.2.2 Insertion of Femoral Arterial and Venous lines in the Sheep Model .................................. 42

2.2.3 Animal Positioning and Set-up for Sheep Model ......................................................................... 44

2.2.4 Preparation of Sheep Skull for Probe Insertion prior to Impact Acceleration Injury.44

2.2.5 Impact Acceleration Injury for Sheep Model of TBI................................................................... 46

2.2.6 Technique for Insertion of the Codman® ICP Microsensor probe in Sheep ..................... 47

2.2.7 Technique for Insertion of Licox® Brain Tissue Oxygenation Monitor in Sheep ........... 51

2.2.8 Animal Sacrifice and Perfuse Fixation............................................................................................. 51

2.2.9 Discarding of Animal Tissue Materials............................................................................................ 54

2.3 Guinea Pig Experiments ............................................................................................................................ 54

Guinea Pigs Anaesthesia and Handling ...................................................................................................... 55

2.3.1 Induction Anaesthesia ............................................................................................................................ 55

2.3.2 Maintenance Anaesthesia and Tracheostomy ............................................................................. 55

2.3.3 Change of Anaesthetic Protocol in the Guinea Pig Model ....................................................... 57

2.3.4 Insertion of femoral lines....................................................................................................................... 58

2.3.5 Animal Positioning and Craniotomy ................................................................................................ 59

2.3.6 Lateral Fluid Percussion Injury in the Guinea Pig...................................................................... 60

2.3.7 Codman ICP probe insertion ................................................................................................................ 62

2.3.8 Animal sacrifice with tissue perfusion and fixation................................................................... 63

xii

2.3.9 Discarding of Animal Tissue Materials............................................................................................ 63

2.4 Statistics ........................................................................................................................................................... 64

CHAPTER 3. RESULTS.....................................................................................................65

SHEEP MODEL....................................................................................................................................................... 65

3.1 Intracranial Pressure and Brain Tissue Oxygenation Monitoring in a Sheep Model of Traumatic Brain Injury...................................................................................................................................... 65

3.1.1 Sheep Arterial Blood Pressure ........................................................................................................ 65

3.1.2 Sheep Intracranial Pressure ............................................................................................................ 67

3.1.3 Sheep Cerebral Perfusion Pressure ............................................................................................... 67

3.1.4 Sheep Brain Tissue Oxygenation (PbtO2)..................................................................................... 69

3.2 GUINEA PIG MODEL.................................................................................................................................... 70

3.2.1 Anaesthesia, Sedation and Arterial Blood Pressure .................................................................. 70

3.2.2 Intracranial Pressure in Guinea Pigs ............................................................................................... 71

CHAPTER 4. DISCUSSION ................................................................................................73

4.1 Sheep Model of Intracranial Pressure and Brain Tissue Oxygenation Monitoring in Traumatic Brain Injury...................................................................................................................................... 74

4.2 Guinea Pig Model of Intracranial Pressure in Traumatic Brain Injury ................................. 74

4.3 The Contribution of the Tentorial Membrane to the Development of Intracranial Hypertension in TBI............................................................................................................................................ 75

CHAPTER 5. CONCLUSIONS..............................................................................................80

APPENDICES ................................................................................................................81

Appendix A Guinea Pig Experiment Diary ........................................................................................... 81

Appendix B Drugs Used in the Experiments. ....................................................................................... 86

Appendix C Monitoring and Data Collection for all Experiments............................................... 87

REFERENCES ................................................................................................................88

xiii

LIST OF TABLES

Table 1.1 Classification of Traumatic Brain Injury. Adapted from Finnie and Blumbergs (2002) .......... 14

Table 1.2 Extracranial and intracranial causes of secondary brain damage, adapted from Reilly and

Bullock “Head Injury: Pathophysiology and Management” second Ed............................................ 17

Table 4.1 The Comparative Anatomy of the Tentorium Cerebelli from Klintworth (1968). ....................... 78

xiv

LIST OF FIGURES

Figure 1.1 Non-contrast CT scan prior to surgery showing a large volume left acute subdural

haemorrhage. The maximal thickness of the clot was approximately 15mm with a

similar degree of midline shift. The Midline structures are clearly seen to have shifted

towards the patient’s right side. ...................................................................................................................5

Figure 1.2 Tentorium cerebelli from above showing the dural reflections that form some of the

venous sinuses of the posterior fossa. ...................................................................................................... 28

Figure 1.3 Cerebral herniation syndromes: subfalcine, transtentorial and cerebellar tonsillar

herniation. In subfalcine herniation it is the cingulate gyrus that is compressed beneath

the falx cerebri, picture from (Cotran et al., 2005). .......................................................................... 29

Figure 2.1 Ohmeda 7000 Ventilator used in sheep experiments, Ohmeda, USA. ........................................ 40

Figure 2.2 Criticare Anaesthetic monitor display. Model number: 602-1. Criticare Systems

Incorporated, USA. This monitor was used for end tidal CO2 and respiratory rate. ........... 41

Figure 2.3 A. Integra Neurosciences™ Camino® Licox CMP Tissue Oxygen Pressure Monitor. GMS

Advanced Tissue Monitoring Gesellschaft für Medizinische Sondentechnik D-42247 Kiel.

B. MacLab/2e with Bridge Amp Data acquisition system, ADInstruments Australia Pty

Ltd. .......................................................................................................................................................................... 43

Figure 2.4 Lateral view of sheep positioning set-up. Prone sphinx position with head supported by

custom made chin support. .......................................................................................................................... 45

Figure 2.5 Frontal view of Sheep experiment set-up, chin support and ventilator tubing shown. Note

ICP and Licox® probes in situ. ..................................................................................................................... 45

Figure 2.6 Humane Captive Bolt Stunner with Number 17 Red charges (Karl Schermer & Co.,

Germany). ............................................................................................................................................................ 47

Figure 2.7 Codman® Microsensor ICP probe............................................................................................................. 49

Figure 2.8 Codman® ICP Express Monitor: Model number: 82-6635, Codman and Shurtleff

Incorporated, Raynham, MA 02767-0350, USA. ................................................................................. 50

xv

Figure 2.9 Frontal view of sheep skull with scalp retracted. Left side of picture demonstrates the

Licox® probe within its guide cannula and sealed with wax. The right side of the picture

shows the ICP monitor in place. The coronal and sagittal sutures are also seen................. 50

Figure 2.10 Coronal section of sheep brain at the level of the coronal suture, viewed from in front.

The Licox® probe trajectory, lateral to the body of the right lateral ventricle and down to

the deep white matter is seen as a small haemorrhagic line. Also seen on the left side of

the brain (right side of photo) is a small haemorrhagic area at the cortex indicating the

position in the Codman® ICP microsensor............................................................................................. 53

Figure 2.11 Ventilator used for guinea pig experiments, Harvard Apparatus Inc., USA. ......................... 56

Figure 2.12 Microscope and heating mat used for guinea pig experiments. .................................................. 58

Figure 2.13 Fluid percussion device set-up on bench top. Horizontal cylinder of saline with outlet on

the left and swinging arm and piston on the right. Pressure transducer recording device

seen beneath swinging arm. ........................................................................................................................ 61

Figure 2.14 Anaesthetised guinea pig on foam block with secured cranial access bolt manually held

to outlet of fluid percussion device. The LFPI was given moments after this photograph

was taken. ............................................................................................................................................................ 62

Figure 3. 1 Arterial Blood Pressure readings over four hour post insertion of ICP and Licox®

monitors in sham sheep. Each point in this chart represents the mean value for all

animals’ ABP at the same time point. The error bars indicate the standard deviation, n=3

(sham), n=6 (TBI group). .............................................................................................................................. 66

Figure 3. 2 Comparison of Sheep Intracranial Pressure for TBI and Sham groups. Monitoring

commenced upon insertion of ICP probe and continued for 4 hours, recording at 15-

minure intervals. Error bars indicate standard deviation. The error bars indicate the

standard deviation, n=3 (sham), n=6 (TBI group). ........................................................................... 68

Figure 3. 3 Comparison of Cerebral Perfusion Pressure between TBI and sham sheep. The error bars

indicate the standard deviation, n=3 (sham), n=6 (TBI group)................................................... 68

Figure 3. 4 Brain Tissue Oxygenation (PbyO2). The error bars indicate the standard deviation, n=3

(sham), n=6 (TBI group). .............................................................................................................................. 69

Figure 3.5 Intracranial pressure for guinea pigs. The error bars indicate the standard deviation,

n=3 (sham), n=10 (TBI group). .................................................................................................................. 72

xvi

Figure 4.1 The schematic diagram summarises the tentoriual index in mammals possessing a

tentorial incisura. LN= Notch Length, PTL= Posterior Tentorial Length. From Klintworth,

1968........................................................................................................................................................................ 77

xvii

LIST OF EQUATIONS

Equation 1.1 Cerebral Perfusion Pressure,

CPP = MAP – ICP ........................................................................................................................................... 23

Equation 1.2 Mean Arterial Pressure,

MAP = (CO x SVR) + CVP............................................................................................................................ 23


MAP ≈ DBP + ⅓(SBP-DBP)....................................................................................................................... 23


MAP ≈ DBP +⅓PP......................................................................................................................................... 23

Equation 2.1 Sheep Tidal Volume,

Tidal Volume (mL) = Animal Mass (kg) x 10 (mL/kg)................................................................. 57

Equation 4.1 Klintworth Tentorial Index,

Posterior Tentorial Length (PTL)/Notch Length (LN) x 100 ................................................. 76

xviii

LIST OF APPENDICES

Appendix A “Guinea Pig Experiment Diary”

Appendix B Drugs Used in the Experiments

Appendix C Monitoring and Data Collection for all Experiments

Appendix D Raw Data

1

ABSTRACT

The aim of this study was to identify appropriate animal models of raised

intracranial pressure (ICP) and brain tissue oxygenation (PbtO2) following

traumatic brain injury (TBI) that would be suitable for the development of novel

therapies for secondary brain injury.

Monitoring of ICP and PbtO2 are important for understanding the effects of altered

cerebral perfusion pressure (CPP). Tissue oxygenation is determined by the

interaction of these variables and is important in the prevention of secondary

injury following TBI. Unfortunately, few animal models reproduce the ICP and

PbtO2 response that has been observed in the human condition. Previous studies at

the University of Adelaide have used an ovine model of TBI in which the

neuropathological response in these animals accurately mimics human TBI.

However functional studies using sheep, at present, are problematic. Development

of an alternative small animal model with scope for functional studies would assist

with development of clinical therapies.

Aside from rats, which do not exhibit profound increases in ICP without the

presence of a significant mass lesion, guinea pigs have been successfully used

previously in studies of TBI. We therefore compared the ICP and PbtO2 response in

guinea pigs with those of sheep. Compared to sheep, the guinea pig proved

unsuitable for the study of ICP. Their labile response to inhalational anaesthesia,

which included significant hypotension and bradycardia, was a confounding factor.

With careful review and alteration to the anaesthetic regime, this problem was

reduced, albeit that reproducible increases in ICP were never shown after TBI.

2

Although the reasons for a lack of ICP response in guinea pigs and rats are

unknown, we note that sheep have a higher tentorial index than both species, and

that the presence of an intact tentorium may restrict increases in pressure to a

single compartment, thus increasing ICP. We propose that species with higher

tentorial indexes may prove to be a more suitable than rodents for the study of ICP

and functional outcome after TBI.

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