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Department of Anesthesiology and Pain Control Basic Principles of Anesthesiology Before the Advent of Anesthesia Patients felt like condemned criminals awaiting execution, and if they survived the experience, the memory of it haunted them for the rest of their lives Dire emergencies Repairing wounds, setting compound fractures, amputating limbs Mortality 30-50% Shock from pain, bleeding, infection Surgeons had the lowest prestige of all medical practitioners Before the Advent of Anesthesia “Suffering so great as I underwent cannot be expressed in words… The particular pangs are now forgotten; but the blank whirlwind of emotion, the horror of great darkness and the sense of desertion by God and man… I can never forget, however gladly I would do so.” Before the Advent of Anesthesia “I attended on two occasions the operating theatre and saw two very bad operations, one on a child, but I rushed away before they were completed. Nor did I ever attend again, for hardly any inducement would have been strong enough to make me do so.” Charles Darwin Speed was the most valued clinical skill Dexterity, next Little opportunity for careful dissection or improvements in technique Showmanship Amputation and lithotomy were done within 3 mins Hypnosis Opium Alcohol Exposure to cold Compression of peripheral nerves Constriction of carotid arteries Blow to the jaw Milestones March 30, 1842 Crawford Long Ether for excision of neck tumor Milestones 1844 Horace Wells Nitrous oxide for dental procedure Massachusetts General Hospital Turning Point October 16, 1846 William Morton Ether for excision of vascular neck mass Massachusetts General Hospital Father of Anesthesiology John Snow Devised a scholarly, scientific method to investigate the clinical properties and pharmacology of ether, chloroform, and other anesthetic agents Improved apparatus for administering ether, mastered clinical techniques of anesthetizing patients Brought anesthesia into public awareness First Anesthesiologists, UK John Snow, Joseph Clover, Sir Frederick Hewitt A physician dedicated specifically to the administration of anesthesia was appropriate and necessary Created a standard of excellence, fostered professionalism, formed anesthesia societies, and published papers on anesthesia First Anesthesiologists, US Arthur Guedel, John Lundy, Ralph Waters – Anesthesiology training program – Long Island Society of Anesthetists, 1905 – New York Society of Anesthetists, 1911 – American Society of Anesthetists, 1935 – American Society of Anesthesiologists, 1945 Overview Preoperative Evaluation Principles of General Anesthesia Complications of General Anesthesia Principles of Regional Anesthesia (separate lecture: preceptorial session) Recovery from Anesthesia Preoperative Evaluation Goals 1. 2. 3. 4. Obtain medical information to plan the anesthesia care Assess risk factors Obtain informed consent Provide preoperative education to patient and family (NPO and medication instructions) 5. 6. 7. Acquaint patient on the available anesthetic techniques; right to choose Provide px with clear expectations for anesthetic care and postoperative course Discuss pain control plans Review of Medical History Age, conceptual age in premature babies 2. Medications including herbal supplements 3. Allergies and their specific reaction 4. Cigarette, alcohol, and drug history 1. Past surgeries, anesthetic techniques, and complications encountered 6. History of surgical/ anesthetic complications in other family members 7. Birth and developmental hx in pediatric px 8. OB hx, LMP (reproductive age) 5. 9. Medical problems and degree of control 10. Exercise tolerance 11. Hx of airway problems: stridor, snoring, loose teeth, TMJ disease, previous hx of difficult airway Co-morbidities Ischemic Heart Disease: severity, progression, functional limitations, medications 1. • • • MI death in px w/o IHD = 1% MI death in px w/ IHD = 3% MI death for peripheral vascular surgery = 29% • Other risk factors: hypercholesterolemia, hyperlipidemia, smoking, DM, HPN, age, obesity, sedentary lifestyle Stress: during induction (intubation), intraop hemodynamic lability, extubation, postop pain Pulmonary disease: exacerbation of symptoms, medications 2. • • Higher morbidity: upper abdominal and thoracic surgeries Other considerations: Intubation - irritation of the airway; increased airway resistance Supine position - hypoxia High regional anesthesia - inadequate ventilation Hydration Renal disease 3. • • Acute tubular necrosis: most common cause of acute renal failure periop Exacerbation of pre-existing renal disease: Decreased cardiac output Altered autonomic nervous system activity Neuroendocrine changes Positive pressure ventilation Hyperventilation = shift of oxyhemoglobin curve Hypoventilation = acidosis = dangerous inc serum K Hepatobiliary disease 4. • Important: maintenance of adequate hepatic blood flow, choice of anesthetic drugs, adequate intravascular volume Metabolic and endocrine disease 5. • • • Thorough understanding of the pathophysiology of the endocrine problem Tailor the anesthetic technique and anesthetic drugs to minimize complications Readiness to manage each complication CNS disease 6. • • • Understanding of ICP, CBF, CMRO2 interrelationship Effects of anesthetic drugs, fluids, maneuvers, positioning with cerebral dynamics Control hemodynamics, smooth induction and emergence, pain control Review of Systems Systematic ROS to pick up signs or symptoms of other problems Physical Examination Verify: height & weight, BMI vital signs heart & lungs skin condition (turgor, jaundice, pallor) landmarks for regional technique neurologic function vascular access extremities airway evaluation Airway Evaluation Mallampati classification (ability to view posterior pharynx) Thyro-mental distance Mouth opening Patency of both nares Dentition Mask fit (facial anatomy, beard) Range of motion of the neck (BellhouseDore) Obesity Mallampati Classification The px is asked to open the mouth and protrude tongue maximally while in the sitting position Class 1 Faucial pillars, soft palate, uvula seen Class 2 Uvula masked by tongue base Only soft palate visualized Class 3 Class 4 Only hard palate Thyromental distance Bellhouse Dore maximal flexion and extension of the neck will identify limitations that might prevent optimal alignment of the OPL axes. *** Normal atlanto-occipital joint: 35 degrees of extension Other Methods of Airway Evaluation Combining the different airway evaluation increases the specificity and sensitivity of their predictive value 1. 2. 3. 5. Body habitus Mouth opening (interdental distance):>3 cm State of dentition, prominence of upper incisors, ability to protrude lower jaw beyond upper incisors Mandibular length: >9 cm normal ASA Classification & Mortality Rates Class 1: normal healthy patient Class 2: mild to moderate systemic disease Class 3: severe systemic that limits activity but not incapacitating Class 4: constant threat to life Class 5: moribund px not expected to survive 24 h with or without surgery Class 6: A brain dead patient whose organs are being harvested “E” refers to emergency situation; risks are doubled 0.06 %-0.1 % 0.27 %-0.4 % 1.8%-4.3% 7.8%-23% 9.4%-51% Informed Consent Include: Primary anesthetic plan Back up anesthetic plan Advantages and possible complications Death Preoperative Instructions 1. Fasting No solid food 8 h before scheduled surgery Adults & Children (>3 mos) clear liquids 3 h Infants (< 3mos) clear liquids 2 h **gastric emptying may vary in obese, pregnant, post-trauma or obstructed patients, or those with hiatal hernia, DM 2. Current medications may be continued up to the day of surgery 3. Preoperative medications Goals: a. allay anxiety: benzodiazepines b. reduce gastric acidity & residual volume: Acid pump inhibitor, H2 blocker, Metoclopramide c. antisialogogue: Atropine, Glycopyrrolate, Scopolamine d. minimize nausea & vomiting e. amnesia, sedation, analgesia f. reduce anesthetic requirement g. reduce vagal activity h. decrease histamine activity Anesthetic Techniques General Anesthesia Monitored anesthesia care Regional Anesthesia Centralneuraxis anethesia Spinal anesthesia Epidural Anesthesia Combined Epidural and Spinal Anesthesia Major peripheral nerve blocks Local infiltration blocks Principles of General Anesthesia Goals of GA Unconsciousness and amnesia Analgesia Muscle relaxation controlled state of depressed consciousness or unconsciousness produced by a pharmacologic method or nonpharmacologic method accompanied by: partial or complete loss of protective reflexes inability to maintain an airway inability respond to physical or verbal stimulus Indications 1. 2. 3. 4. Head and neck operations Thoracic operations Abdominal operations Limb operations where regional techniques are contraindicated Advantages of GA 1. 2. 3. 4. 5. Easily titratable Rapid onset Controlled duration of action Rapid recovery Secure airway Complications Drug-related cardiovascular depression 1. • • • • • • Hypotension Bradycardia Decreased organ perfusion Myocardial depression Cardiac arrythmias Cardiac arrest Drug-related respiratory depression 2. • • • Loss of protective reflexes Central depression of the respiratory center Respiratory muscle relaxation/ paralysis Drug-related gastrointestinal and urinary depression 3. • • • Ileus Loss of sphincteric tones Decrease sphlancnic blood supply if BP is low Drug-related neurologic depression 3. • • Inhalational anesthetics: decreased CMRO2, vasodilatation of cerebral blood vessels = +/- increase in ICP Intravenous drugs: CMRO2 and CBF 4. Complications associated with the technique: aspiration trauma during intubation laryngospasm difficult airway airway obstruction corneal abrasion nerve palsies Intravenous Agents Unconsciousness and Amnesia 1. Barbiturates (Thiopental, Thiamylal, Methohexital) 2. Rapid onset, short action Inhibit excitatory synaptic transmission thru GABA receptor effects Anticonvulsants, cerebral protectant Propofol GABA receptor effects Rapid recovery Benzodiazepines 3. • • • Anxiolytic, amnestic Diazepam, Lorazepam, Midazolam Inhibit synaptic transmission at the GABA receptor Etomidate 4. • • • Imidazole derivative Acts on the GABA receptor Produce the least cardiovascular depression Ketamine 5. • • • • Produce analgesia and amnesia Acts on the NMDA receptor; no action on GABA Dissociative anesthesia Delirium and hallucinations Analgesia Drugs 1. Opioid analgesics • • • • Morphine, Codeine, Meperidine, Fentanyl Act on - recetors in the brain and SC Side-effects: euphoria, sedation, constipation, respiratory depression Naloxone, Naltrexone: antagonists Non-opioid analgesics 2. • NSAIDs COX 1 & COX 2 non-selective Selective COX 2 inhibitors Neuromuscular Blocking Drugs Produce skeletal muscle paralysis thru blockade of the neuromuscular junction Ensure patient immobility intraop Should not be used alone (aware, in pain, unable to move) – Depolarizing muscle relaxants: bind to 2 alpha sub units of acetylcholine receptors causing depolarization then relaxation – Non-depolarizing muscle relaxants: bind to 1 alpha subunit of the receptor blocking Ach from binding Agent Duration Depolarizing NMB Succinylcholine 5-8 min Non-depolarizing Mivacurium Atracurium Vecuronium Rocuronium Pancurium < 1h(15-20m) < 1h(20-30m) <1h(30-40m) <1h > 1h Metabolism Pseudocholinesterase Plasma cholinesterase Hoffmann elimination Liver & kidneys Unchanged Kidneys Side-effects serum K, fasciculation aches, IOP & intragastric pressure Histamine release Intermediate onset Tachycardia large doses Tachycardia; long duration Inhalational Agents Provide unconsciousness & amnesia, analgesia, muscle relaxation – dose dependent which may likely cause unacceptable side-effects – use of adjuncts: opioids, NMB MAC: concentration of an inhaled anesthetic that prevents movement to a painful stimulus in 50% of patients Potency and speed of induction ≈ lipid solubility of the gas Agent MAC % Advantages Disadvantages N2O 105 Analgesia Expansion of air in closed space Halothane 0.75 Inexpensive; pleasant smell Arrhythmia; Hepatitis Enflurane 1.68 Muscle relaxation Odor; seizures Isoflurane 1.15 Same as enflurane Odor Desflurane 6 Rapid induction & recovery Expensive; Odor Sevoflurane 1.71 Mask induction; rapid onset & recovery Expensive Intraoperative Management Induction 1. • Preoxygenation IV drugs/ gas are administered = unconsciousness Mask ventilation Muscle relaxants = facilitate intubation Mask ventilation Rapid sequence induction: high risk for aspiration Same sequence except for mask ventilation in between Sellick’s maneuver: application of downward pressure on the cricoid cartilage to occlude the esophagus 2. Airway management Taken up during preceptorial QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. LMA / ILMA 3. Fluid therapy 1) Crystalloids: • Electrolyte containing with or without dextrose Normal saline 0.9% NaCl or D5 NSS PLR or D5 LR D5 0.3% NaCl D5 NM 2) Colloids: Contain dextrose or protein suspended in electrolyte solution High molecular weights HES Gelatin Albumin 3) Blood Recovery from Anesthesia PACU Continued intensive monitoring of px until they can safely be discharged Early recognition of complications that may necessitate re-operation Prompt recognition and management of medical disturbances Pain as the 5th Vital Sign “We need to train doctors and nurses to treat pain as a vital sign. Quality care means that pain is measured and treated” James Campbell, MD Presidential Address, American Pain Society November 11, 1996 ….as condition of licensure … include pain as an item to be assessed at the same time as vital signs are taken. … pain assessment shall be noted in the patient’s chart (Pain Assessment Bill) Pain as the 5th Vital Sign Modalities of Pain control 1. Round-the-clock parenteral drugs Opioids: Nalbuphine, Meperidine, Fentanyl, Morphine Tramadol NSAIDS 2. Patient controlled analgesia; continuous IV infusion 3. Continuous epidural analgesia 4. Regional blocks 5. Oral analgesics, rectal analgesics Visual Analogue Scale (VAS): 0 No pain 10 Worst imaginable pain Numeric Rating Scale 0 1 2 No pain 3 4 5 6 7 8 9 10 Worst pain The Whaley & Wong Faces Rating Scale Malignant Hyperthermia (MH) Life-threatening, genetic predisposition that develops during or after general anesthesia with exposure to trigger agents Triggering agents All volatile gas Succinylcholine Clinical presentation: hypermetabolic state (high temperature, tachycardia, high EtCO2, acidosis) muscle rigidity rhabdomyolysis, arrythmias, hyperkalemia, cardiac arrest Management of MH Supportive Dantrolene Report the case