Anesthesia Techniques & Risks PDF

An anesthetic technique is selected based on: 1-Pre-operative examination and clinical evaluation. 2-The type and extent of the surgical procedure. 3-The ability to perform various anesthetic techniques, based on experience and the ability of equipment and drugs. factors make anesthesia risker You...

An anesthetic technique is selected based on: 1-Pre-operative examination and clinical evaluation. 2-The type and extent of the surgical procedure. 3-The ability to perform various anesthetic techniques, based on experience and the ability of equipment and drugs. factors make anesthesia risker Your anesthesia risk might be higher if you have or have ever had any of the following conditions: 1-Allergies to anesthesia or a history of adverse reactions to anesthesia 2-Diabetes 3-Heart disease (angina, valve disease, heart failure, or a previous heart attack) 4-High blood pressure 5-Kidney problems 6-Lung conditions (asthma and chronic obstructive pulmonary disease, or COPD) 7-Obesity 8-obstructive sleep apnea 9-Stroke 10-Seizures or other neurological disorders 11-Smoking, or drinking some of the risks of anesthesia General anesthesia causes you to become unconscious. This type of anesthesia, while very safe, is the type most likely to cause side effects and to carry risks. Most side effects are minor and temporary, such as nausea, vomiting, chills, confusion for a few days, and a sore throat caused by a breathing tube. However, though rare, there are some more serious risks to be aware of: 1-Postoperative delirium or cognitive dysfunction – A condition called postoperative cognitive dysfunction can result in long-term memory and learning problems in certain patients. It’s more common in older people because an aging brain doesn’t recover from anesthesia as easily. In addition to the elderly, people who have conditions such as heart disease (especially congestive heart failure), Parkinson’s disease, or Alzheimer’s disease, or who have had a stroke before are also more at risk. It’s important to tell the physician anesthesiologist if you have any of these conditions. 2-Malignant hyperthermia – Some people inherit this serious, potentially deadly reaction to anesthesia that can occur during surgery, causing a quick fever and muscle contractions. If you or any family member has ever had heat stroke or suffered from malignant hyperthermia during a previous surgery, be sure to tell the physician anesthesiologist. 3-Breathing problems during and after surgery – Anesthesia can be more dangerous for patients who have obstructive sleep apnea, a condition that causes them to stop breathing while they sleep. In patients with this condition, anesthesia can cause the throat to close up during surgery and make it more difficult to regain consciousness and take a breath after surgery. risks associated with other types of anesthesia The safest type of anesthesia is local anesthesia, an injection of medication that numbs a small area of the body where the procedure is being performed. Rarely, a patient will experience pain or itching where the medication was injected. Regional anesthesia, which numbs a larger part of the body, such as from the waist down, is also safer than general anesthesia, but it does carry some risks. Patients sometimes experience headaches after having regional anesthesia. In rare cases, the injection can cause a collapsed lung if the needle is inserted in the chest area. Nerve damage from regional anesthesia also is a rare complication. Inhaled anesthetics Partial pressure or 'Tension" in inspired air is a measure of their concentration. The speed of induction of general anesthesia depend on; 1-inspired gas partial pressure (GA concentration). 2-ventelation rate. 3-GA solubility (less soluble GAs equilibrate more quickly with blood into tissue such as brain. Opioids (morphine,fentanyl,remifentanil) Remifentanil 1-GAs do not produce effective analgesia (except for ketamine) 2-Given before surgery to minimize hemodynamic changes produced by painful stimuli (this reduces GA requirements). 3-High doses can cause chest wall rigidity and post- operative respiratory depression. 4-Therapeutic doses will inhibit respiration (lead to increase CO2). 5-Used for post-operative analgesia. 6-Very potent but with a short t1\2(3-10mins) The duration of action of a drug is known as its half- life. This is the period of time required for the concentration or amount of drug in the body to be reduced by one-half. We usually consider the half- life of a drug in relation to the amount of the drug in plasma. A drug's plasma half-life depends on how quickly the drug is eliminated from the plasma. Classification of general anesthetics/ 1- Intravenous anesthetic agents; a-primary used for induction barbiturate (thiopental, methohexitone benzodiazepines; midazolam, lorazepam Midazolam (>Diazepam Lorazepam) 1--Used to produce anxiolytic amnesia and sedation prior to induction of GA with another agent 2-Sedative doses achieved with in 2 min, with 30 mins duration of action. etomidate propofol 1-produces anesthesia as rapidly as i.v. barb's &but recovery is more rapid than with barbs. 2-Recovery is not delayed after prolong infusion (due to more rapid clearness) 3-Antiemetic effect (patient with increase of nausea) 4-Can cause marked hypotension(>barb) 5-Commonly used as component of balanced anesthesia for maintenance of anesthesia following induction of anesthesia. Thiopental(pentothal) 1-Barbs are respiratory circulatory depressants Thiopental(pentothal) 1-Barbs are respiratory circulatory depressants (Contraindication; hypovolemia, cardiomyopathy, beta blockade, etc.) 2-Psychomotor impairment may last for days after use of single dose 3-Teste of garlic prior to anesthesia B- Total I.V. (maintenance) as propofol 2- Inhalational agents / primary used for maintains. A / inhalational gases as Nitrous oxide xenon N2O (laughing gas) Is clinically used as safe anesthetic (dentistry, ambulance, childbirth) and appreciated for its antianxiety effect The side effect Negative side effect may include nausea or vomiting, headaches increase sleepiness and\or excessive sweating or shivering Headaches can result if a patient dose not receive oxygen for at least five minutes after the nitrous has been turned off B /volatile agents Halothane, savoflurane, isoflurane, desoflurane Therapeutic Gases 1-Oxyygen a-Administered to prevent hypoxic injury. Causes of hypoxia during anesthesia? Hypoxia (problem with lung) Inadequate delivery to tissue Impaired utilization. b-Can have toxic effects due to free radical generation. 2-Inhaled Anesthetics a-Easily vaporized liquid halogenated hydrocarbons. b-Administration as gas Minimum Alveolar Concentration(M.A.C.) The minimum alveolar anesthetic concentration required to eliminate the response to painful stimulation in 50%of patients. 1-Ameasure of GA potency. 2-When several GAs are mixed, their MAC values are additive (e.g. nitrous oxide is commonly mixed with other anesthetics). MAC & Patient Condition 1-Pregnancy- decrease MAC (elevated progesterone) 2-Elderly-decrease MAC (less brain actively) 3-Chronic Alcoholics –increase MAC(cross-tolerance) 4-Acute alcoholic poisoning –decrease MAC(additive) Bispectrality index monitor; (EEG)is used to measure a patient's "Anesthetic depth" Elimination; Anesthesia is most commonly terminated by redistribution of drug from brain to the blood and out through the lung. Halothane and methoxyflurane undergo hepatic metabolism & can cause liver kidney toxicity respectively. Properties of inhaled anesthetics; Desflurane; Sevoflurane; 1-Very low blood; gas coefficient with relatively rapid onset of action recovery. 2-Widely used for outpatient surgery 3-non irritating to the airways. 4-usefull induction agent, particularly in children. Isoflurane; 1-medium onset of action & recovery. 2-used for induction maintenance of anesthesia. 3-Isoflurane "was "was the most commonly used inhalational. (has been largely replaced by desflurane) b-Halothane; 1-halothane undergoes>40%hepatic metabolism. 2-Rare cases of postoperative hepatitis occur. 3-Halothane can sensitize the heart to Epi(arrhythmias). b-Methoxy flurane F release during metabolism (70%)may cause renal insufficiency after prolonged exposure. c-Nitrous oxide Megoblastc anemia may occur after prolong exposure due to decrease in methionine synthase activity (Vit B 12 Deficiency) NMJ Blockers (Two types); 1-Depolarising Agent; Succinylcholine 2-Nondepolarising Agents; Curare type i.e.Atracurium a-relax skeletal muscle b-faciltate intubation c-insure immobility d-Reversed by neostigmine & glycopyrrolate during post-operative period. Nausea Vomiting General anesthetics effect the chemoreceptor trigger zone and brainstem vomiting center cause (nausea &vomiting). Why is neostigmine given with atropine? At the end of surgery, neostigmine has been given for the reversal of neuromuscular blocking agents with several adverse effects such as bradycardia and profuse secretion. Atropine has been used to prevent those side effects of neostigmine. Muscle relaxants are medicines that block the nerve impulses to the muscles. They sometimes are also referred toas neuromuscular blocking agents. These medicines are often used during general anesthesia, but they do not usually affect whetheryou are awake. why are muscle relaxants used in Anesthesia? Neuromuscular blocking agents, or muscle relaxants, are often used in surgery to prevent muscles from moving when a patient is unconscious. A recent study found that the use of neuromuscular blockers during general anesthesia is associated with an increased risk of postoperative pulmonary complications. Paralytics (Muscle Relaxants) Succinylcholine is a short acting paralytic that is often used for short procedures requiring intubation and in emergency situations. Vecuronium, rocuronium and (are longer-acting paralytics used to maintain paralysis during longer surgical procedure which general Anesthetic has poor muscle relaxant action? The following general anesthetic has good analgesic but poor muscle relaxant action: Halothane Maximum Safe Concentration (MSC) or Minimum Toxic Concentration (MTC): a depolarizing drug? Depolarizing agents Depolarizing agents produce their block by binding to and activating the ACh receptor, at first causing muscle contraction, then paralysis. They bind to the receptor and cause depolarization by opening channels just like acetylcholine does. what are the side effects of succinylcholine? Common side effects of succinylcholine include:  Jaw rigidity.  Low blood pressure (hypotension)  Muscle fasciculation may result in postoperative pain.  Muscle relaxation resulting in respiratory depression to the point of breathing cessation (apnea)  Respiratory depression.  Salivary gland enlargement. what are the side effects of neostigmine? Common side effects 1-excessive saliva production. 2- excessive sweating. 3- nausea. 4- vomiting. 5- diarrhea. 6- stomach cramps. Why does neostigmine cause bradycardia? The neostigmine-induced bradycardia is caused by its anticholinesterase effect which results in accumulation of acetylcholine and increased stimulation of the vagus receptors of the heart. The therapeutic index (TI) is the range of doses at which a medication is effective without unacceptable adverse events. Drugs with a narrow TI (NTIDs) have a narrow window between their effective doses and those at which they produce adverse toxic effects.