Chapter 011 - pharm notes PDF

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11 General and Local Anesthetics KEY POINTS Anatomy, Physiology, and Pathophysiology Overview • Anesthetics are drugs that reduce or eliminate pain by depressing nerve function in the central nervous system (CNS) and/or the peripheral nervous system. This state of reduced neurologic function is called anesthesia. Anesthesia is the loss of the ability to feel pain resulting from the administration of an anesthetic drug. • General anesthesia is a drug-induced state in which the nerve impulses of the CNS are altered to reduce pain and other sensations throughout the entire body. General anesthesia involves complete loss of consciousness, loss of body reflexes, elimination of pain and other sensations throughout the entire body, and skeletal and smooth muscle paralysis, including paralysis of respiratory muscles. This loss of normal respiratory function requires mechanical or manual ventilatory support to avoid brain damage and suffocation (death from respiratory arrest). • Local anesthesia does not involve paralysis of respiratory function but does involve elimination of pain sensation in the tissues innervated by anesthetized nerves. Functions of the autonomic nervous system, which is a branch of the parasympathetic nervous system, may also be affected. Pharmacology Overview General Anesthetics • General anesthetics are drugs that induce general anesthesia and are most commonly used to induce anesthesia during surgical procedures, including the administration of specific parenteral anesthetics. Inhalational anesthetic drugs are also general anesthetics and include volatile liquids or gases. Adjunct anesthetics or simply adjuncts can be thought of as “helper drugs” when their use complements the use of any other drug(s). They are used simultaneously with general anesthetics for anesthesia initiation (induction), sedation, reduction of anxiety, and amnesia and include neuromuscular blocking drugs (NMBDs), sedative-hypnotics, and/or anxiolytics and antiemetics. Nondepolarizing NMBDs are used as an adjunct to general anesthesia to provide skeletal muscle relaxation during surgery and/or mechanical ventilation. • The overall effect of general anesthetics is a progressive reduction of sensory and motor CNS functions. The degree and speed of this process varies with the anesthetics and adjuncts used along with their dosages and routes of administration. • Adverse effects of general anesthetics are dose dependent and vary with the individual drug. The heart, peripheral Copyright © 2017, Elsevier Inc. All rights reserved.

circulation, liver, kidneys, and respiratory tract are the sites primarily affected. • Malignant hyperthermia is an uncommon, but potentially fatal, genetically linked adverse metabolic reaction to general anesthesia. It is classically associated with the use of volatile inhalational anesthetics as well as NMBDs. • In large doses, anesthetics are potentially life threatening, with cardiac and respiratory arrest as the ultimate causes of death. However, these drugs are almost exclusively administered in a very controlled environment by personnel trained in advanced cardiac life support. Drugs for Moderate Sedation • Moderate sedation, conscious sedation, and procedural sedation are synonymous terms for anesthesia that does not cause complete loss of consciousness and respiratory arrest. Moderate sedation allows the patient to relax and have markedly reduced or no anxiety, yet still maintain his or her own open airway and response to verbal commands. • The most commonly used drugs for moderate sedation include a benzodiazepine, usually midazolam, with an opioid, usually fentanyl or morphine. Local Anesthetics • Local anesthetics are the second major class of anesthetics. They reduce pain sensations at the level of peripheral nerves, although this can involve intraspinal anesthesia. They are also called regional anesthetics because they render a specific part of the body insensitive to pain. • They are commonly used in clinical settings in which loss of consciousness is undesirable or unnecessary, such as childbirth and other situations in which spinal anesthesia is desired, dental procedures, suturing of skin lacerations, and diagnostic procedures. • Local anesthesia of specific peripheral nerves is accomplished by nerve block anesthesia or infiltration anesthesia. Nerve block anesthesia involves relatively deep injections of drugs into locations adjacent to major nerve trunks or ganglia. • The systemic adverse effects depend on where and how the drug is administered. • Local anesthetics have little opportunity to cause toxicity under most circumstances. Systemic reactions are possible if sufficiently large quantities are absorbed into the systemic circulation. To prevent this from occurring, a vasoconstrictor such as epinephrine is often co-administered with the local anesthetic to maintain localized drug activity.

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CHAPTER 11 General and Local Anesthetics

Neuromuscular Blocking Drugs • NMBDs prevent nerve transmission in skeletal and smooth muscles, leading to paralysis. • The main therapeutic use of NMBDs is for maintaining skeletal muscle paralysis to facilitate controlled ventilation during surgical procedures. • The muscle paralysis induced by depolarizing NMBDs (e.g., succinylcholine) is sometimes preceded by muscle spasms, which may damage muscles. • The primary concern when NMBDs are overdosed is prolonged paralysis requiring prolonged mechanical ventilation. Nursing Process • It is important to note that anesthetics are not drugs that are typically given by the registered nurse unless the nurse is a licensed nurse anesthetist. Exceptions to this statement are orders for topical forms, such as oral swish-and-swallow solutions that may be used during chemotherapy and lidocaine patches for pain relief. • For any form of anesthesia and during any phase of anesthesia, the major parameters to assess are airway, breathing, and circulation (ABCs). • Include in your assessment questions regarding allergies and use of prescription as well as over-the-counter drugs, herbals, supplements, and social and/or illegal drugs. • The patient’s use of alcohol and nicotine must be assessed. A history of alcohol abuse may result in the development of withdrawal symptoms during recovery from anesthesia and/ or surgery. • Neurologic assessment includes a thorough survey of the patient’s mental status. Determine and document the level of consciousness, alertness, and orientation to person, place, and time prior to the anesthesia. • The therapeutic effects of any general or local anesthesia include the following: loss of consciousness and reflexes during general anesthesia and loss of sensation to a particular area during local anesthesia (e.g., loss of sensation to the eye during corneal transplantation). • For patients undergoing general anesthesia, assessing the patient’s temperature is especially important because of the risk of malignant hyperthermia, and close monitoring is required if malignant hyperthermia occurred during the anesthesia process. The tendency is inherited, so questions about related signs and symptoms in the family’s and patient’s medical histories are important to document and report. Malignant hyperthermia may be fatal if not promptly recognized and aggressively treated. Signs and symptoms include rapid rise in body temperature, increased pulse rate (tachycardia)/respiratory rate (tachypnea), muscle rigidity, and unstable blood pressure. The patient who has undergone general anesthesia should be constantly monitored for the occurrence of adverse effects of the anesthesia. These may include myocardial depression, convulsions, respiratory depression, allergic rhinitis, and decreased renal or liver function. • For patients about to undergo anesthesia with NMBDs, perform a complete head-to-toe assessment with a thorough medical and medication history.

• With the use of conscious or moderate sedation, as with any anesthesia technique, assessment for allergies, cautions, contraindications, and drug interactions is important. • Moderate sedation provides the therapeutic effect of a decreased sensorium but without the complications of general anesthesia; however, there are CNS depressant effects associated with the drugs used. • Use of spinal anesthesia requires thorough assessment with an emphasis on the ABCs, respiratory function, and vital signs, specifically blood pressure. • With spinal anesthesia, nursing interventions should include constant monitoring for a return of sensation and motor activity below the anesthetic insertion site. Because of the risk that the anesthetic drug may move upward in the spinal cord and breathing may be affected, continually monitor respiratory and breathing status. • The use of epidural anesthesia (also called regional anesthesia in some textbooks) does not pose the same risk of respiratory complications, but monitoring is still needed to confirm overall homeostasis, such as measurement of vital signs and pulse oximetry to determine oxygen saturation levels. • For those receiving spinal anesthesia, therapeutic effects include loss of sensation below the area of administration, and adverse effects include hypotension, hypoventilation, urinary retention, the possibility of a prolonged period of decreased sensation or motor ability, and infection at the site. • With epidural anesthesia, therapeutic effects are similar to those seen with intrathecal anesthesia; however, adverse effects include possible spinal headache (often severe) and/ or loss of motor function or sensation below the area of administration. • For local anesthesia, review the patient’s medical history to assess for any pre-existing illnesses, such as vascular disease, aneurysms, or hypertension, because these may be contraindications to the use of the vasoconstrictor with the anesthetic. In addition, with these local anesthetics, assess for allergies to the drug as well as baseline vital signs. • If an anesthetic ointment or cream is used, the nurse will thoroughly cleanse and dry the area to be anesthetized before applying the drug. If a topical or local anesthetic is being used in the nose or throat, remember that it may cause paralysis and/or numbness of the structures of the upper respiratory tract, which can lead to aspiration. • Regardless of the type of anesthesia used, one of the most important nursing considerations during the preanesthesia, intraanesthesia, and postanesthesia periods is close and frequent observation of all body systems. Begin with a focus on the ABCs of nursing care, vital signs, and oxygen saturation levels as measured by pulse oximetry as well as by the clinical presentation of the patient. • Should the patient require pain management once the anesthesia has been terminated, remember that the anesthetic and any adjuvant drugs used continue to have an effect on the patient until the period of the drugs’ action has passed. Therefore, administer sedative-hypnotics, opioids, nonopioids, and other CNS depressants for pain relief cautiously and only with close monitoring of vital signs. Copyright © 2017, Elsevier Inc. All rights reserved....