Anesthesia By dr .abeer mansour

or state of being unaware and unresponsive to painful stimuli Definition of Anesthesia: is a reversible state of central nervous system (CNS) depression, resulting in loss of response to and perception of external stimuli. or state of being unaware and unresponsive to painful stimuli

Concomitant use of drugs Multiple adjunct agents: surgical patients receive one or more of the following preanesthetic medications: H2 blockers, such as famotidine or ranitidine to reduce gastric acidity; benzodiazepines, such as midazolam or diazepam to allay anxiety and facilitate amnesia; opioids such as fentanyl for analgesia; antihistamines such as diphenhydramine for prevention of allergic reactions; antiemetics such as ondansetron to prevent nausea and the possible aspiration of stomach contents; and/or anticholinergics such as glycopyrrolate to prevent bradycardia and secretion of fluids into the respiratory tract .These agents facilitate smooth induction of anesthesia and, when administered concurrently, also lower the dose of anesthetic required to maintain the desired level of surgical anesthesia. However, such coadministration can also enhance undesirable anesthetic effects (for example, hypoventilation), and may produce negative effects that are not observed when each drug is given individually

STAGES AND DEPTH OF ANESTHESIA

General anesthesia can be divided into three stages: induction, maintenance, and recovery. Induction is defined as the period of time from the onset of administration of the potent anesthetic to the development of effective surgical anesthesia in the patient. Maintenance provides a sustained surgical anesthesia. Recovery is the time from discontinuation ofadministration of anesthesia until consciousness and protective physiologic reflexes are regained. .

Depth of anesthesia 1. Stage I—Analgesia: Loss of pain sensation results from interference with sensory transmission in the spinothalamic tract. The patient progresses from conscious and conversational to drowsy. Amnesia and reduced awareness of pain occur as Stage II is approached. 2. Stage II—Excitement: The patient experiences delirium and possibly combative behavior. There is a rise and irregularity in blood pressure and respiration as well as a risk of laryngospasm. To shorten or eliminate this stage of anesthesia, a rapid acting agent, such as propofol, is given intravenously before inhalation anesthesia is administered. 3. Stage III—Surgical anesthesia: There is gradual loss of muscle tone and reflexes as the CNS is further depressed. Regular respiration and relaxation of skeletal muscles with eventual loss of spontaneous movement occur in this stage. This is the ideal stage of anesthesia for surgery. Continuous careful monitoring is required to prevent undesired progression into Stage IV. 4. Stage IV—Medullary paralysis: Severe depression of the respiratoryand vasomotor centers occur during this stage. Death can rapidly ensue unless measures are taken to maintain circulation and respiration

Types of anesthetics I. Inhalation anesthetics II. Intravenous anesthetics III. Local anesthetics

Block Na+ channels Action Disrupt membrane lipids Inhalation anesthetics Mechanisms of action : Activate K+ channels Block Na+ channels Action Disrupt membrane lipids In general, all general anesthetics increase the cellular threshold for firing, thus decreasing neuronal activity.

I. Inhalation anesthetics Nitrous Oxide Rapid onset Good analgesia Used for short procedures and in combination with other anesthetics Supplied in blue cylinders Enflurane (Ethrane) Similar to Halothane Less toxicities Halothane (Fluothane) Volatile liquid Narrow margin of safety Less analgesia and muscle relaxation Hepatotoxic Reduced cardiac output leads to decrease in mean arterial pressure Increased sensitization of myocardium to catecholamines Isoflurane (Forane) Volatile liquid Decrease mean arterial pressure resulting from a decrease in systemic vascular resistance

Inhalation anesthetics(Pharmacokinetics) The concentration of a gas in a mixture of gases is proportional to the partial pressure Inverse relationship between blood: gas solubility and rate of induction

Inhalation anesthetics Side Effects Reduce metabolic rate of the brain Decrease cerebral vascular resistance thus increasing cerebral blood flow = increase in intracranial pressure Malignant Hyperthermia Rare, genetically susceptible Tachycardia, hypertension, hyperkalemia, muscle rigidity, and hyperthermia Due to massive release of Ca++ Treat with dantrolene (Dantrium), lower elevated temperature, and restore electrolyte imbalance

II. Intravenous anesthetics Ketamine (Ketaject, Ketalar) Block glutamate receptors Dissociative anesthesia: Catatonia, analgesia, and amnesia without loss of consciousness disorientation, sensory and perceptual illusions, vivid dreams Cardiac stimulant Propofol :works by increasing GABA-mediated inhibitory tone in the CNS. Propofol decreases the rate of dissociation of the GABA from the receptor, thereby increasing the duration of the GABA-activated opening of the chloride channel with resulting hyperpolarization of cell membranes. At supra clinical concentrations, it may directly activate the receptor’s chloride channel. Rapid onset and recovery Mild hypotension Antiemetic activity

Local anesthetics Blockade of sensory transmission to brain from a localized area Blockade of voltage-sensitive Na+ channels Use-dependent block Administer to site of action Decrease spread and metabolism by co-administering with adrenergic receptor agonist (exception….cocaine) local anesthetic is a drug that causes reversible local anesthesia and a loss of nociception. When it is used on specific nerve pathways (nerve block),

Local anesthetics Local anesthetics - esters or amides a lipophilic aromatic group to a hydrophilic, ionizable amine. Most are weak bases

Mechanism of action

Local anesthesia The most widely used of the local anesthetic compounds are bupivacaine lidocaine mepivacaine procaine ropivacaine and tetracaine . Of these, lidocaineis probably the most commonly used. Bupivacaine is noted for its cardiotoxicity. Mepivacaine should not be used in obstetric anesthesia due to its increased toxicity to the neonate. Local anesthesia

Add to LA vasoconstrictors Epinephrine/Phenylephr ine/ Levonordefrin Prolong duration Minimize effect of LA vasodilatation  toxicity  intensity of block  bleeding Add to LA vasoconstrictors

New Zealand white rabbit , clinically healthy, Were used, the animal study protocol was approved by the ethics committee for animal experiments in the faculty of dentistry, Mosul University. The animals were housed in wire mesh cages with standered condition food and water were provided at libitum, Rabbits were anesthetized with injection of 50mg/kg ketamine hydrochloride (Ketamine, Hameln, Germany)and xylazine 5 mg /kg (Xyla,Interchemie, Holland) respectively, and atropine sulfate injection (50) microgram / kg intra muscularly in femur was routinely asepsis and montair the stages of anesthesia Practical procedure