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