Pharmacology:Chapter 18 , 19 , 20
Name Two classes of general anesthetics by their routes of drug administration and describe the physiological effects associated with their use.
*Induction of General Anesthesia- is the time acquired to take a patient from consciousness to Stage 3. * Maintenance of general anesthesia is the ability to keep safely in Stage 3. *Notes* - The depth of anesthesia is continually monitoring may continually monitored by vital signs, body temperature, ECG,EEG, and general observation of the patient. * The ideal general anesthetic would produce rapid induction and slow maintenance without entering Stage 4 anesthesia. In addition, recovery from the ideal general anesthesia would occur rapidly without side effects. There are three major categories of anesthesia: Local anesthesia, Monitored Anesthesia Care (MAC), and general anesthesia. *Local anesthesia inhibits sensation in a specific area of the body. The individual remains conscious; sensory nerve condition is inhibited, but motor neurons are not affected; and sensory nerve function returns to normal (reversible) within minutes to hours of administration. * Monitored anesthesia care refers to intravenous sedation with midazolam, followed by propofol and or fentanyl. These drugs rapidly induce a sleepy state where the patient is calm and less responsive to pain before or during a procedure. * The critical word in this type of anesthesia is monitored. The intravenous anesthetics used in this ambulatory setting have special instructions to alert medical personnel to the need for specific observation, evaluation, and electronic monitoring of the patient through the recovery period. General anesthesia produces a loss of consciousness in which the patient is totally unaware of pain and does not remember (amnesic) the surgical events or diagnostic produces on awakening. Another commonly used term to describe anesthesia is balanced anesthesia.
Explain what an adjunct to anesthesia is and cite two examples of drug adjuncts used with general anesthetics.
Anesthetic adjuncts are used to augment specific components of anesthesia, permitting lower doses of general anesthetics with fewer side effects. * Hydromorphone *Fentanyl
Explain how anesthetic modulate CNS neuronal conduction.
Eventually, general anesthetics are carried to the CNS, where lipid solubility permits access across membranes so that the primary pharmacological effect can be produced. The degree of CNS depression resulting in anesthesia is related to the concentration of the anesthetic in the brain. Page 254 - Central Nervous System - The primary nonancsthetic effects of general anesthetics on the CNS involve regulation of cerebral blood flow, change in intracranial pressure, and seizure induction.
Identify the various stages of general anesthesia with the physical responses as the central nervous system (CNS) is depressed and define balanced anesthesia and monitored anesthesia care.
General Anesthesia: Deep State of unconsciousness in which there is no response to stimuli, including painful stimuli. Stage 1: Analgesia * During Stage 1, the cerebral cortex is gradually inhibited. This stage is characterized by a decreased response to pain (Analgesia), a feeling of euphoria (well-being or elation), and a loss of consciousness (sleep). * Once the cerebral cortex is fully depressed, Stage 2 is achieved and they hypothalamus assumes control of the body function. Stage 2: is known as the "excitement phase" because there is an overall increase in sympathetic tone. Blood pressure, heart rate, respiration, and muscle tone increase during this stage. * During stage 2 cardiac arrhythmias may occur. Eventually, respiration becomes more regular as excitation is inhibited. The change in respiratory pattern is an indication that patients are in Stage 3. Stage 3: is usually referred to as surgical anesthesia because surgery is most efficiently performed at this level of general anesthesia. * Stage 3 is divided into four planes (1-4) that reflect the progressive depth of CNS depression. During this stage, cardiovascular and respiratory functions return to normal, spinal reflexes are inhibited, and skeletal muscles are relaxed. Surgical incisions can be made throughout Stage 3 without producing pain or skeletal muscle contraction. Stage 4: is the phase of medullary paralysis. This stage represents an overdose of general anesthetic, in which cardiovascular and respiratory centers in the medulla are inhibited and death occurs. The clinical signs associated with each stage of general anesthesia vary with the general anesthetic being used. Some anesthetics produce excellent analgesia at stage 1, while others do not produce any analgesia until stage 3. However, most anesthetics used today are capable of producing Stages 3 and 4 anesthesia as just described. An anesthetic that produces all stages of general anesthesia ( 1, 2,3,and 4). is a complete anesthetic. * To be clear, Stage 4 is not a therapeutic objective. To keep the patient in Stage 3 and not Stage 4 reflects the skill and experience of the anesthesiology team.
Explain why more than one anesthetic may be administered to provide muscle relaxation without totally depressing the brain.
Page 261 * Most general anesthetics that take patients into Stage 3, Plane 3 anesthesia produce skeletal muscle relaxation. However, it may be advantageous in certain operations (abdominal and thoracic) to have skeletal muscle relaxation for a long time with minimal CNS depression. For this purpose, neuromuscular blocking drugs, also called paralytics, such as succinylcholine, may be administered during surgery. These drugs produce adequate skeletal muscle relaxation by interfering with acetylcholine-modulated nerve conduction at the synaptic site while patients are maintained in early Stage 3 anesthesia. The neuromuscular blocking drug succinylcholine is a standard for rapid sequence induction (RSI) used briefly at the beginning of some procedures to facilitate endotracheal intubation. Succinylcholine is the only depolarizing ages used for RSI. Because of its rapid onset, ultrashort duration of action and safety, it is the paralytic of choice in almost all cases of RSI in adults.
Describe how volatile liquid anesthetics are excreted from the body and how this differs from the way local anesthetics are excreted.
The liquids (halogenated hydrocarbons) are vaporized for inhalation. Those routinely used as general anesthetics include enflurane (ethane), desflurane (Soprano), halothane (fluothane), isoflurane (Forane), and sevoflurane (Ultane). These anesthetics are inhaled through the nose and mouth by means of face mask. Air (Oxygen) must be included in the anesthetic mixture and rate of delivery of throughout the surgical procedure. Inhalation anesthetics are delivered to the alveoli and then to the blood for distribution to the tissues. * These drugs have solubility characteristics where some drugs are more soluble in the blood and like staying there (Volatile Liquids), or they are nor very soluble in the blood and can't wait to move out of the blood (Nitrous oxide, desflurane, sevofluarane).
