Anesthesia Considerations for the Oral and Maxillofacial Surgeon

Matthew Mizukawa, Samuel J. McKenna, Luis G. Vega

• Publisher: Quintessence Publishing Co, Inc
• Year: 2019
• eBook ISBN: 9780867158847
• Topic: Medicine
• Subtopic: Dentistry

Although office-based anesthesia administration has been essential in the evolution of outpatient surgery, it is becoming more complex as people live longer and with more comorbid diseases. The purpose of this book is to strengthen the margin of safety of office-based anesthesia administration by helping practitioners determine whether the patients they treat are good candidates for office-based anesthesia. This book is organized into three sections. The first section provides a review of the principles of anesthesia, including the pharmacology of anesthetic agents, local anesthesia, patient monitoring, preoperative evaluation, the airway, and management of emergencies and complications. The major organ systems of the body are reviewed in section two, and the most common comorbid conditions that affect these systems are described in terms of their pathophysiology, diagnosis, management, and anesthesia-related considerations. Section three reviews patient groups that warrant special consideration in the administration of office-based anesthesia, such as geriatric, pediatric, pregnant, and obese patients. Spiral-bound and featuring tabs for quick and easy reference, this important book belongs on the shelf of every clinician who provides anesthesia in the office setting.

CHAPTER 14

The Central Nervous System

Normal Anatomy and Physiology

Metabolic Disorders

Neurodegenerative/Demyelinating Disorders

Cerebrovascular Accident

Structural

Psychiatric Disorders

The concepts of normal central nervous system (CNS) anatomy and physiology are integral to understanding the neuropharmacologic effects of anesthetic agents in patients with CNS conditions. This chapter focuses on the relevant pathophysiology, diagnosis, management, and anesthetic considerations of metabolic, neurodegenerative, cerebrovascular, structural, and psychiatric diseases of the CNS.

Normal Anatomy and Physiology

Anatomically, the CNS consists of the brain and the spinal cord. The brain is divided into the cerebrum, the brainstem, and the cerebellum. The cerebral cortex is the largest portion of the human brain and comprises two separate symmetric hemispheres joined caudally at their base by the corpus callosum. The cerebral cortex is responsible for higher functions of memory, motor function, sensory perception, and cognitive thought. Each hemisphere is divided by distinct fissures into four lobes (frontal, temporal, parietal, and occipital), each with a specific purpose and function. The hypothalamus and the thalamus lie beneath the cerebral cortex. The thalamus acts as a sensory relay station, connecting the peripheral nervous system to the cerebral hemispheres. It also participates in functions of wakefulness and consciousness. The hypothalamus is involved primarily in primitive perceptions and functions, such as hunger, thirst, sexual behavior, and sleep. It also contributes to the regulation of hormone secretion from the pituitary gland. The brainstem consists of the medulla, the pons, and the midbrain and is responsible for many primitive functions essential for survival. The medulla primarily regulates homeostatic functions, such as blood pressure, cardiac rhythm, and breathing. The pons is involved with coordinating eye and facial movements, facial sensation, hearing, and balance. The midbrain is an important locale for automatic ocular motion and other specific functions of the visual and auditory systems. The cerebellum maintains posture, balance, and muscular tone. It also is involved in the fine-tuning of motor activity and the ability to perform rapid, repetitive, and coordinated motor functions.¹

The spinal cord is an ovoid bundle of nervous tissue connecting the brain to the peripheral nervous system. It is approximately 43 to 45 cm in length in adults and extends from the caudal medulla at the level of the foramen magnum to the level of the L1-2 intervertebral space. Its primary functions are efferent motor transmission, afferent sensory conduction, and spinal reflex control.¹

The brain is contained within the bony cranium, whereas the spinal cord is protected by the vertebrae of the spinal column. Both the brain and the spinal cord are further protected by three layers of meninges, which, from the outermost to the innermost layer, are the dura mater, arachnoid mater, and pia mater. Between these layers are several clinically important anatomical spaces, including the epidural, subdural, and subarachnoid spaces. In particular, the subarachnoid space is notable because it contains cerebrospinal fluid (CSF), which is produced in the ventricular system of the brain and provides a cushion and basic immunologic protection to the brain and spinal cord. CSF is also important in the autoregulation of cerebral blood flow.¹

Anesthetic agents may have important effects on cerebral blood flow, metabolism, the properties of CSF, and intracranial pressure (ICP).

Cerebral blood flow

The adult human brain accounts for approximately 2% of total body weight but approximately 20% of total body oxygen utilization. Accordingly, the brain receives 12% to 15% of total cardiac output (750 mL/min in adults). Cerebral blood flow (CBF) varies from 10 to 300 mL/100 g per minute, depending on metabolic activity. The cerebral metabolic rate (CMR), a measure of cerebral oxygen consumption, increases with increased cerebral electrical activity. In the absence of substantial oxygen reserves and because of the high oxygen demands of the brain, unconsciousness occurs in seconds with any interruption in cerebral blood flow. If blood flow is not established within 3 to 8 minutes, irreversible cellular damage will occur.² Different regions of the brain are more or less sensitive to hypoxia.

An important concept in the discussion of CBF is cerebral perfusion pressure (CPP), which is defined as the difference between mean arterial pressure (MAP) and ICP. The association between CPP and ICP...

Table of contents

• Cover
• Halftitle Page
• Title Page
• Copyright Page
• Contents
• Dedications
• Preface
• Contributors
• Section I: Principles of Anesthesia Administration
• Section II: Anesthesia and Comorbid Disease
• Section III: Anesthesia in Special Patient Groups
• Appendices
• Index