Neuromonitoring Techniques

Quick Guide for Clinicians and Residents

Hemanshu Prabhakar

• Publisher: Academic Press
• Year: 2017
• eBook ISBN:
  9780128099162
• Topic: Medicine
• Subtopic: Anesthesiology & Pain Management

Neuromonitoring Techniques: Quick Guide for Clinicians and Residents provides a quick and easy guide to understanding various neuromonitoring equipment. Chapters include intracranial pressure monitoring, EEG-based monitors, evoked potentials and transcranial doppler. This book is written for trainees, clinicians and researchers in the fields of neurosurgery, neurocritical care, neuroradiology, neuroanesthesia and neurology. As specialized neuromonitoring is now routinely done in neurosurgical cases, it provides an important resource for neurologists, neurophysiologists, anesthesiologists and residents who are expected to have theoretical and practical knowledge on different systems. Each monitoring system is discussed separately, with examples, images, reference values and their interpretations. - Provides a quick and easy guide to understanding various neuromonitoring techniques - Presents information on each monitoring system, with examples, images, reference values and their interpretation - Useful for trainees, clinicians and researchers in the fields of neurosurgery, neurocritical care, neuroradiology, neuroanasthesia and neurology

Chapter 1

Intracranial Pressure Monitoring

Chiara Robba Addenbrooke's Hospital, Cambridge, United Kingdom

Abstract

Despite recent research that has been equivocal, intracranial pressure (ICP) monitoring is invaluable in the management of neurocritical care patients, including head injury, poor grade subarachnoid hemorrhage, stroke, intracerebral hematoma, meningitis, acute liver failure, hydrocephalus, benign intracranial hypertension, etc. Monitoring of ICP requires an invasive transducer, and an intraventricular drain connected to an external pressure transducer is still considered to be the ‘‘gold standard’’ method.

However, some attempts have been made to measure ICP noninvasively, with promising results.

Information can be derived from ICP and its waveforms, including cerebral perfusion pressure, brain compensatory reserve, regulation of cerebral blood flow and volume, and content of vasogenic events. There are many possible conditions that can lead to elevated intracranial pressure, for acute, chronic, and both intracranial or extracranial causes. Since increased intracranial pressure is associated with increased morbidity and mortality, it should be promptly detected, and treatment must be immediately started with appropriate intensive care.

Keywords

Cerebral perfusion pressure; Intracranial pressure; Microtransducer; Neuromonitoring

Contents

Introduction

Pathophysiology

Invasive ICP

External Ventricular Drainage

Microtransducer Devices

Epidural and Subdural Devices

Intraparenchymal Microtransducers

Noninvasive ICP

Invasive Readings and Interpretation

Waveform Analysis

Index of Pressure–Volume Compensatory Reserve (RAP)

Effect of Anesthetics on Intracranial Pressure

Propofol

Barbiturates

Etomidate

Benzodiazepines

Opioids

Ketamine

Dexmedetomidine

Current Evidence, Applications, and Discussion

Suggested Readings

References

Introduction

Increased intracranial pressure (ICP) is an important cause of secondary brain injury, and it is associated with poor outcome.¹ Several conditions are associated with intracranial hypertension (ICH), including extracranial (fever, increased abdominal and intrathoracic pressure, hypercarbia, hypoxia) and intracranial causes (cerebral edema, hematoma, contusion, cerebrospinal fluid (CSF) disturbance).² In this setting, ICP monitoring is crucial in the management of neurocritical care patients, as clinical signs of ICH are tardive and poor predictors of elevated ICP.³

Invasive monitoring through an intraventricular or intraparenchymal catheter is indicated in all severe traumatic brain injured (TBI) patients with positive brain computed tomography (CT) findings, or normal brain CT if the patient is older than 40 years or in the presence of systolic blood pressure below 90 mm Hg or in the case of abnormal flexion or extension in response to pain⁴; however, invasive techniques are associated with certain risks, including infections and hemorrhage (Fig. 1.1).⁵

Pathophysiology

Pathologic ICH is defined when ICP raises persistently above 20 mm Hg. The intracranial volume, consisting of brain parenchyma, blood, and CSF, is enveloped by the rigid skull bone.^6,7 Under physiological conditions the total intracranial volume remains constant because of compensatory mechanisms, which operate to maintain a constant and adequate cerebral blood flow (CBF), and ICP. According to the Monro-Kellie doctrine,^6,7 ICP is the result of the volume and compliance of each intracranial component (brain parenchyma, arterious blood, venous blood, CSF) within the intracranial compartment. The relationship between ICP variations and the volume of intracranial contents defines the compliance characteristics of the intracranial compartment. The intracranial compliance can be defined as the change in volume over the change in pressure (dV/dP).

Figure 1.1 Examples of hemorrhagic complication associated with invasive ICP monitoring. (A) Brain CT showing an extradural hemorrhage after ICP bolt insertion, which required surgical evacuation. (B) Follow-up brain MRI in a patient previously monitored with an intraparenchymal device, showing a contusion on its trajectory.

In the presence of an intracranial mass (e.g., brain swelling, hydrocephalus, hematomas, or abscesses), compensatory mechanisms operate to maintain ICP and CBF constant by displacing CSF into the thecal sac and by compressing the cerebral venous compartment via venoconstriction and extracranial drainage.

The relationship between ICP and volume is not linear. Initially, pressure increases only slightly with increasing volume. There, compensatory mechanisms allow ICP to elevate only slightly with increase of volume. When these compensatory mechanisms have been ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Contributors
• Foreword
• Preface
• Acknowledgment
• Introduction to Monitoring Techniques
• Chapter 1. Intracranial Pressure Monitoring
• Chapter 2. Cerebral Blood Flow Monitoring
• Chapter 3. Jugular Venous Oximetry
• Chapter 4. Electroencephalography-Based Monitors
• Chapter 5. Transcranial Doppler Ultrasonography
• Chapter 6. Evoked Response Monitoring
• Chapter 7. Near-Infrared Spectroscopy
• Chapter 8. Brain Microdialysis
• Chapter 9. Brain Tissue Oxygenation
• Chapter 10. Cognitive Function Monitoring
• Chapter 11. Functional MR Imaging
• Index