Basic Principles of Anesthesiology
Department of Anesthesiology and Pain ControlDepartment of Anesthesiology and Pain Control
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 emergenciesRepairing 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. Obtain medical information to plan the anesthesia care
2. Assess risk factors3. Obtain informed consent4. Provide preoperative education to
patient and family (NPO and medication instructions)
5. Acquaint patient on the available anesthetic techniques; right to choose
6. Provide px with clear expectations for anesthetic care and postoperative course
7. Discuss pain control plans
Review of Medical History
1. Age, conceptual age in premature babies
2. Medications including herbal supplements
3. Allergies and their specific reaction4. Cigarette, alcohol, and drug history
5. 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)
9. Medical problems and degree of control
10. Exercise tolerance11. Hx of airway problems: stridor,
snoring, loose teeth, TMJ disease, previous hx of difficult airway
Co-morbidities
1. Ischemic Heart Disease: severity, progression, functional limitations, medications
• 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
2. Pulmonary disease: exacerbation of symptoms, medications
• 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
3. Renal disease• 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
4. Hepatobiliary disease• Important: maintenance of adequate
hepatic blood flow, choice of anesthetic drugs, adequate intravascular volume
5. Metabolic and endocrine disease• Thorough understanding of the
pathophysiology of the endocrine problem
• Tailor the anesthetic technique and anesthetic drugs to minimize complications
• Readiness to manage each complication
6. CNS disease• 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 (Bellhouse-
Dore) Obesity
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
Class 3 Only soft palate visualized
Class 4 Only hard palate
Mallampati Classification
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. Body habitus2. Mouth opening
(interdental distance):>3 cm>3 cm
3. State of dentition, prominence of upper incisors, ability to protrude lower jaw beyond upper incisors
5. Mandibular length: >9 >9 cm normalcm normal
ASA Classification & Mortality Rates
Class 1: normal healthy patientClass 2: mild to moderate systemic diseaseClass 3: severe systemic that limits activity but
not incapacitatingClass 4: constant threat to lifeClass 5: moribund px not expected to survive
24 h with or without surgeryClass 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. FastingNo solid food 8 h before scheduled surgeryAdults & Children (>3 mos) clear liquids 3 hInfants (< 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: benzodiazepinesb. reduce gastric acidity & residual volume:
Acid pump inhibitor, H2 blocker, Metoclopramide
c. antisialogogue: Atropine, Glycopyrrolate,
Scopolamined. minimize nausea & vomitinge. amnesia, sedation, analgesiaf. reduce anesthetic requirementg. reduce vagal activityh. 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 non- pharmacologic method
accompanied by:partial or complete loss of protective reflexesinability to maintain an airwayinability respond to physical or verbal stimulus
Indications
1. Head and neck operations2. Thoracic operations3. Abdominal operations4. Limb operations where regional
techniques are contraindicated
Advantages of GA
1. Easily titratable2. Rapid onset3. Controlled duration of action4. Rapid recovery5. Secure airway
Complications
1. Drug-related cardiovascular depression
• Hypotension• Bradycardia• Decreased organ perfusion • Myocardial depression• Cardiac arrythmias• Cardiac arrest
2. Drug-related respiratory depression• Loss of protective reflexes• Central depression of the respiratory center• Respiratory muscle relaxation/ paralysis
3. Drug-related gastrointestinal and urinary depression
• Ileus• Loss of sphincteric tones• Decrease sphlancnic blood supply if BP is
low
3. Drug-related neurologic depression
• 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 Amnesia1. Barbiturates (Thiopental, Thiamylal,
Methohexital) Rapid onset, short action Inhibit excitatory synaptic transmission thru GABA
receptor effects Anticonvulsants, cerebral protectant
2. Propofol GABA receptor effects Rapid recovery
3. Benzodiazepines• Anxiolytic, amnestic• Diazepam, Lorazepam, Midazolam• Inhibit synaptic transmission at the GABA
receptor
4. Etomidate• Imidazole derivative• Acts on the GABA receptor• Produce the least cardiovascular depression
5. Ketamine• Produce analgesia and amnesia • Acts on the NMDA receptor; no action on GABA• Dissociative anesthesia• Delirium and hallucinations
Analgesia Drugs1. Opioid analgesics
• Morphine, Codeine, Meperidine, Fentanyl• Act on - recetors in the brain and SC• Side-effects: euphoria, sedation,
constipation, respiratory depression• Naloxone, Naltrexone: antagonists
2. Non-opioid analgesics• 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 Metabolism Side-effects
Depolarizing NMB Succinylcholine 5-8 min Pseudocholinesterase
serum K, fasciculation aches, IOP & intragastric pressure
Non-depolarizing Mivacurium Atracurium Vecuronium Rocuronium Pancurium
< 1h(15-20m)
< 1h(20-30m)
<1h(30-40m)
<1h > 1h
Plasma cholinesteraseHoffmann eliminationLiver & kidneysUnchangedKidneys
Histamine releaseIntermediate onsetTachycardia large dosesTachycardia; 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
1. Induction 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 aTIFF (Uncompressed) decompressor
are needed to see this picture.
LMA / ILMA
3. Fluid therapy1) 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 control1. Round-the-clock parenteral drugs
Opioids: Nalbuphine, Meperidine, Fentanyl, Morphine
Tramadol NSAIDS
2. Patient controlled analgesia; continuous IV infusion
3. Continuous epidural analgesia4. Regional blocks5. Oral analgesics, rectal analgesics
Visual Analogue Scale (VAS):
0 10 No pain Worst imaginable
pain
Numeric Rating Scale
0 1 2 3 4 5 6 7 8 9 10No pain 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 agentsTriggering 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
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