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Monitoring Ventilation

Overview Until the early twentieth century, animal life was defined by the presence of spontaneous ventilation. Absence of breathing implied death or impending death, although experiments with resuscitation and artificial ventilation had occurred since the eighteenth century. The defining characteristics of spontaneous ventilation , depth and frequency, were early indicators of anesthetic action, with profound depression of respiration indicating the deepest plane of ether narcosis. The…

Respiratory Gas Monitoring

Overview The gases of interest to the anesthesia caregiver include oxygen (O 2 ), carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and the potent volatile inhaled anesthetic agents of which desflurane, sevoflurane, and isoflurane are in common use. Other gases that may be relevant in certain situations are nitrogen (N 2 ), helium (He), nitric oxide (NO), and xenon (Xe). Although gas monitors…

Humidification and Filtration

Overview Under normal physiologic conditions, the upper airway adds heat and moisture to inspired air to prevent drying of lower airway secretions, plugging, and mucosal injury. When dry medical gases bypass the upper airway via an endotracheal tube, the normal heat and moisture exchange function of the upper airway is compromised. This function of the upper airway may be replaced in two ways. First, heat and…

Anesthesia Ventilators

Overview Since the 1960s, the use of intermittent positive-pressure ventilation (IPPV) has become widespread during surgical and diagnostic procedures that require anesthesia. Today’s observer might wrongly conclude that the research, development, and methods for mechanical ventilation in the operating room (OR) had occurred only recently. However, much of the necessary experimentation and design took place much earlier. Anesthesia ventilators are commonly compared with mechanical ventilators used…

Waste Anesthetic Gases and Scavenging Systems

Trace Concentrations of Anesthetic Gases Concern over trace concentrations of anesthetic gases dates back to 1967, when Vaĭsman reported findings of a survey of 354 anesthesiologists in Russia. All worked in poorly ventilated operating rooms (ORs) and used nitrous oxide (N 2 O), halothane, and ether. Of the total, 303 responded to the survey; and of these, 110 were female. Female responders reported 31 pregnancies, 18…

Breathing Circuits

Introduction The anesthesia machine serves to create a desired mixture of anesthetic gases, vapors, oxygen, and air (as well as other gases such as helium and carbon dioxide, albeit less frequently). The patient is the recipient of these prepared gas mixtures of known composition, and the breathing circuit is the interface between the anesthesia machine and the patient. This circuit delivers the gas mixture from the…

Anesthesia Vaporizers

General Principles The term vapor describes the gaseous phase of a substance at a temperature at which the same substance can also exist in a liquid (or solid) state, below the critical temperature of that substance. Critical temperature is defined as the temperature above which a gas cannot be liquefied by pressure alone. If the vapor is in contact with a liquid phase, the two phases…

The Anesthesia Machine and Workstation

Anesthesia Gas Delivery System The Anesthesia Machine as a Component of an Anesthesia Workstation The modern anesthesia gas delivery system is composed of the anesthesia machine (see the following section), anesthesia vaporizer(s) (see Chapter 3 ), breathing system (see Chapter 4 ), ventilator (see Chapter 6 ), and waste gas scavenging system (see Chapter 5 ). The basic arrangement of these elements is the same in…

Medical Gases: Storage and Supply

Overview Anesthesia providers were once expected to know a great deal about the storage and supply of medical gases. In both large and small institutions, anesthesiologists often had to rely on their own knowledge and skill in this area to manage the many aspects of medical gases, from purchasing to troubleshooting. Changes in technology and institutional organization have relieved the anesthesiologist of most of these responsibilities.…

The Pediatric Patient

Key Points ▪ Survival of the neonate depends on pulmonary vascular resistance transitioning from a high to a low state. PVR is increased by hypoxemia acidosis, hypothermia, and stress; inability to lower PVR in fetal circulation will not allow extrauterine neonatal survival. ▪ Congenital laryngeal webs are glottic, extending to subglottic area, with vocal cord dysfunction from mild hoarseness to aphonia. Treatment of anterior webs includes…

The Geriatric Patient

Key points ▪ Patients with Huntington's disease are at higher risk of pulmonary aspiration, altered anesthetic pharmacology, and worsening generalized tonic spasms. Rapid-sequence induction with cricoid pressure is recommended for general anesthesia. ▪ Autonomic dysfunction from amyloidosis has dramatic perioperative ramifications. Administering anesthetics to patients with amyloidotic polyneuropathy risks significant hypotension; depolarizing muscle relaxants are controversial. ▪ In patients with idiopathic pulmonary fibrosis, anesthetic evaluation focuses…

Pregnancy and Obstetric Complications

Key points ▪ Airway changes throughout pregnancy worsen during labor and delivery as a result of mucosal edema. ▪ Anesthetic agents are not teratogenic; however, inhalation anesthetics and many intravenous agents may trigger developmental apoptosis and other neurologic insults that could impact cognitive development. ▪ Amniotic fluid embolism is associated with coagulation abnormalities as well as hypoxia and cardiovascular collapse. ▪ HELLP (hemolysis, elevated liver enzymes,…

Burns

Key points ▪ The morbidity and mortality associated with burns vary with total area burned, depth of burn, presence of inhalation injury, and coexisting diseases. ▪ Adequate fluid resuscitation, appropriate analgesia, and early excision of wounds are vital to improve the outcome in burn patients. ▪ Understanding the pathophysiologic changes associated with major thermal injury, particularly the hypermetabolic response, is essential for perioperative care of burn…

Trauma and Acute Care

Key points ▪ Trauma is the 10th leading cause of death globally (16,000 people daily). Motor vehicle crashes, firearms, poisoning, falls, and suffocation account for 81% of all trauma deaths. ▪ Every anesthesiologist will likely care for injured patients acutely or for follow-up surgery. ▪ Trauma deaths occur in a trimodal distribution: at the scene, hours after injury, and days to months after injury. ▪ The…

Mineral, Vitamin, and Herbal Supplements

Key points ▪ With use of alternative medicines such as minerals, vitamins, and herbals increasing worldwide, the medical community needs a more comprehensive understanding of these agents. ▪ Anesthesiologists need to recognize the potential for bleeding, drug interactions, and end-organ damage in surgical patients taking supplements (e.g., kava linked to liver failure; St. John's wort and meperidine causing serotonergic crisis; “G” herbals causing dose-dependent anticoagulant effects).…

Psychiatric and Behavioral Disorders

Key points ▪ An estimated 26.2% of Americans age 18 and older have a diagnosable mental disorder in a given year (58 million people). ▪ Mental disorders and their associated use of psychotropic medications, including antidepressants, anxiolytics, major tranquilizers, anticonvulsants, and mood stabilizers, introduce neurochemical, behavioral, cognitive, and emotional factors that complicate medical or surgical tasks. ▪ Anesthesiologists face unique challenges assessing patients with psychiatric disease,…

Mitochondrial Disease

Key points ▪ Oxidative phosphorylation is critical to aerobic cellular energy production. ▪ Five enzyme complexes make up the electron transport chain, encoded by nuclear DNA (nDNA) and mitochondrial DNA (mtDNA). Mutations in mtDNA or nDNA can result in defective oxidative phosphorylation and underlie inherited mitochondrial myopathies, encephalomyopathies, and cytopathies. ▪ Most volatile and intravenous anesthetic agents inhibit complex I of the electron transport chain. ▪…

Diseases of the Endocrine System

Key points ▪ Anesthetic management of endocrine surgical patients should consider not only the organ of interest but also the end-organ consequences of the endocrine dysfunction and possible rare syndromes. ▪ Severe symptomatic hypercalcemia (especially > 14 mg/dL) constitutes a medical emergency, often mandating treatment before completing the diagnosis. ▪ If rapid parathyroid hormone assay is contemplated intraoperatively (to determine effectiveness of resection), propofol use is…

Infectious Diseases and Biologic Weapons

Key Points ▪ Patients with severe sepsis are at particular risk for hepatic and renal injuries. ▪ The major cardiovascular events in sepsis are vasoplegia, reduced stroke volume, and microcirculatory failure. ▪ Patients with multiorgan dysfunction syndrome (MODS) become confused, delirious, and ultimately stuporous and comatose. ▪ The four main pillars in the management of the patient with severe sepsis are immediate resuscitation, empiric therapy, source…

Hematologic Diseases

Key points ▪ Preoperative recognition of anemia is essential to provide a systems approach to treatment. ▪ The decision to transfuse a patient with blood products should be based on the entire clinical picture and not the absolute laboratory value. ▪ Coexisting diseases of leukocytes can alter anesthetic care. Careful preoperative evaluation helps avoid complications from obstructive tumor and radiation and chemotherapy side effects. ▪ Thrombocytopenia…