Transcript Module I ANAESTHESIA

Module AE0001
Introduction to
Anesthesiology
D. John Doyle MD PhD FRCPC
[email protected]
51 slides Rev 1.0
ABOUT
ANESTHESIOLOGY
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Goals of Anesthesia
General Anesthesia
Regional Anesthesia
Perioperative Problems
Anesthesiology Involves ...
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Drugs and fluids
Lines and catheters
Monitors and equipment
Clinical knowledge and judgment
Technical and psychomotor skills
Team building and interpersonal relations
Crisis management and problem prevention
Dealing with patients and their fears
Anesthesia Techniques for Surgery
• General Anesthesia
 Spontaneous Breathing
 Machine Ventilation
 Cardiopulmonary Bypass
• Regional Anesthesia
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Epidural
Spinal
Plexus Block
Nerve Block
Anesthesia Techniques for Surgery
• Local Anesthesia (Infiltration)
• Other Methods
• Acupuncture
• Hypnosis
• Cold
What is General Anesthesia?
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Unconsciousness (no awareness)
Airway Management
Amnesia (no recall)
Analgesia (no pain)
Blunting of Reflexes
Physiological Homeostasis (stability)
Muscle Paralysis (sometimes)
General Anesthesia
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Assessment
Planning I: Monitors
Planning II: Drugs
Planning III: Fluids
Planning IV: Airway
Management
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Induction
Maintenance
Emergence
Postoperative
Goals and Issues in General Anesthesia
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Unconsciousness
Amnesia
Analgesia
Oxygenation
Ventilation
Homeostasis
Airway Management
Reflex Management
Muscle Relaxation
Monitoring
Airway Management Choices
• Intubation vs. LMA vs. “nothing special”
• Positive pressure ventilation vs.
spontaneous breathing
• Intubation awake vs. asleep
• Conservative vs. surgical airway
• Muscle relaxant vs. none
Airway Equipment
• Single Lumen Tracheal Tubes
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Regular
RAE
Armored
Nasal
Double Lumen Tubes
Laryngeal Mask Airway
Oropharyngeal Airways
Fiberoptic Intubation Cart
Difficult Intubation Kit
Surgical Airway Kit
Amnesia
• Generally sought, but not always desirable
• Lorazepam (Ativan) 2-4 mg sublingually
60 - 90 min preop
• Midazolam (Versed) 1 mg IV increments
• Scopolamine (old but still effective)
Analgesia
• Analgesia = no pain
• Anesthesiologists generally accept the
notion of “unconscious pain”
• Pain manifests under general anaesthesia
as increased sympathetic tone with
tachycardia, hypertension, diaphoresis etc.
• Pain Rx: fentanyl, morphine, epidural
analgesia
Reflexes
• Gag reflex
• Oculocardiac reflex
NOTE:
Epidural or spinal anaesthesia
sympathectomy effects may blunt the
tachycardia reflex response to hypovolemia
Homeostasis
• Fluid and electrolyte balance
• Adequate
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blood pressure
blood volume
hemoglobin concentration
urine output
temperature
Muscle Relaxation
• For intubation
• Where inadvertent patient movement might
be disastrous
• For abdominal muscle relaxation
• To facilitate positive pressure
ventilation
• Special purposes
– ECT therapy
– tetanus / lock jaw
Muscle Relaxants
• Succinylcholine
(very short effect; no reversal;
occasional nasty side-effects)
• Nondepolarizing Drugs
(require reversal eg, neostigmine+atropine)
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Curare
Pancuronuim
Vecuronium
Rocuronium etc.
Preoperative Assessment
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ASA Physical Status
Allergies
Medications
Identify Anaesthetic Considerations
Review Need for Consultations
Estimate Potential for Blood Loss
Postop Ventilation?
Need for ICU bed?
ASA Physical Status
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ASA - 1
ASA - 2
ASA - 3
ASA - 4
• ASA - 5
• ASA -6
HEALTHY
MILD DISEASE
SYSTEMIC DISEASE
CONSTANT
THREAT TO LIFE
MORIBUND
BRAIN DEAD
Identify Anesthetic Considerations
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Difficult Airway
COPD
Anemic
Hypertensive
Hypovolemic
Elderly
MH Susceptability
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Renal Failure
Poor LVF
Stridor
Obesity
TPN
Small Bowel Obstruction
and many other possibilities …
Regional Anesthesia
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Epidural Anesthesia
Spinal Anesthesia
Brachial Plexus Blocks
Other blocks
– intercostal blocks
– femoral nerve block
– ankle blocks
Pros and Cons
of Regional Anesthesia
Pros
Cons
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no airway problem
inexpensive
postop analgesia
easy cerebral
monitoring (by
talking to patient)
takes time
takes skills
high failure rate
uses needles
nerve injury
potential
Complications of
Regional Anesthesia
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Local anesthetic toxicity (CNS, CVS)
Nerve injury / irritation / radiculopathy
Hematoma
Infection
Technique failure
For epidurals
– high or total spinals
– wet taps and headaches
• For spinals
– headaches
– hypotension
Perioperative Problem Solving
… Start with the Differential Diagnosis
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Tachycardia
Bradycardia
Hypertension
Hypotension
High Airway
Pressures
• Hypercarbia
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Oliguria
Cyanosis
Restlessness
Hematuria
Hyperkalemia
Hypernatremia
Hypoxemia
Pneumothorax
Maximum Dose of Lidocaine
(Xylocaine)
• TOXICITY: Convulsions, CV Collapse
• 1% = 10 mg/ml 2%=20 mg/ml
• Toxic dose of lidocaine
– 5 mg/kg plain
– 7 mg/kg with added epinephrine
• EXAMPLE: 25 ml of 2% = 500 mg
(This is over 10 mg/kg if patient weighs only 100 lbs!)
Planning I: Monitors
BASIC
ADVANCED
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• CVP line
• PA line
EKG
BP
Temperature
Oxygen FIO2
Oxygen Line Pressure
Airway Pressure
Pulse Oximeter
Capnogram
Urine Output
Nerve Stimulator
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PA pressures
CVP
CO
SVR
• TEE
• ICP
• Evoked Potentials
Planning II: Drugs
• Induction
– IV vs Inhalation
• Maintenance
– IV vs Inhalation
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Muscle Relaxation
Narcotics
Hypnotics
Vasoactive / cardiac drugs
etc.
Planning III: Fluids
• Maintenance fluid requirements
• Preoperative fluid deficit
(from being NPO overnight)
• Third space losses
• Blood loss replacement
• Issues
– When to give colloid
– When to give blood products
– How to manage oliguria
Planning IV: Airways
• General Anesthesia vs.
Regional Anesthesia
• Spontaneous Ventilation vs.
Positive Pressure Ventilation
• Awake Intubation?
• Tracheostomy under local?
• Airway Equipment
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Oropharyngeal airway
Nasopharyngeal airway
Laryngeal Mask Airway (LMA)
Endotracheal tube
Planning V:
Postoperative Analgesia
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IM morphine e.g. 10 mg IM q3h prn
IV morphine e.g. 2-4 mg IV q10 min prn
PCA
Epidural Analgesia
Oral Analgesics
IV Induction Agents
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Thiopental
Propofol (Diprivan)
Etomidate
Ketamine
High-dose fentanyl (or other opiate)
High-dose midazolam
Potent Inhaled Anesthetics
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Ether (flammable)
Halothane (20% metabolized)
Enflurane (2% metabolized)
Isoflurane (0.2% metabolized)
Sevoflurane (newer, expensive, good
for inhalation inductions)
• Desflurane (newer, expensive, not good
for inhalation inductions)
• Even Xenon makes a passable agent!
Opiates in the OR
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Fentanyl (Sublimaze)
Sufentanil
Alfentanil
Remifentanil
Morphine
Meperidine (Demerol)
Hydromorphone (Dilaudid)
Anesthesiology Operating
Room Technology Issues
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Anesthesia Machines
Airway Gas Monitors
Physiological Monitoring Equipment
IV and Inhalational Drug Delivery
Technology
• Medical Ergonomics
• Safety Standards
About Anesthesiology
• MD degree, then 4-5 years more training
• Written and oral board exams
• Work in OR, ICU, pain service, even palliative
care
• Experts in resuscitation / reanimation
• Bring patients “to the brink of death” several times
a day
• Among most technically inclined MDs
Clinical Tools in Anesthesiology
Drugs
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intravenous
inhalational
epidural / spinal
oral / sublingual
Clinical Tools in Anesthesiology
Airway Management Tools
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Endotracheal tubes
Laryngoscopes
Oral and nasopharyngeal airways
Fiberoptic broncoscopes
Clinical Tools in Anesthesiology
Monitors
• Clinical observation
• Noninvasive techniques
• Invasive techniques
Anesthesia Machines
• Delivery of measured flows of gases:
oxygen, nitrous oxide, anesthetic gas
• Percent oxygen adjustable 25 to 100%
• Ventilator with adjustable rate and volume
• Lots of dials and gauges
• Lots of safety features
• Can be expensive and requires maintenance
Anaesthesia Machines:
Oxygen Safety Systems
• Electronic oxygen controller forbids oxygen
concentrations under 25%
• Pulse oximeter provides good clinical oxygenation
data (usually)
• Airway Gas Monitor warns about hypoxic gas
mixtures or about rebreathing of CO2
• Gauges display tank pressure, oxygen flow,
percent oxygen being delivered
• Oxygen tanks are green in US (white elsewhere)
and hook to yoke via PIN INDEX system
Anaesthesia Machines:
Ventilator Operations
ANESTHESIA VENTILATOR PARAMETERS
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Respiratory Rate (frequency)
Volume of each breath (tidal volume)
Ratio of expiration to inspiration (eg, 2 to 1)
Baseline lung distension (PEEP)
Percent (fraction) oxygen (FIO2)
Respiratory Monitoring
 Clinical: wheezing, crackles, equal air entry,
color, respiratory, pattern (rate, rhythm,
depth)
 Airway pressure
 Spirometry (measured tidal volume)
 Capnography (CO2 concentration vs. time)
 Oxygraphy (O2 concentration vs. time)
 Pulse oximetry
 OTHER : ETT cuff pressure, NIF, VC
BREATHING
• Spontaneous Breathing
– Specify percent (fraction) oxygen (FIO2)
– Clinically monitor airway, breathing
characteristics, and respiration rate
• Machine Ventilation
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Respiratory Rate (frequency)
Volume of each breath (tidal volume)
Baseline lung distension (PEEP)
Percent (fraction) oxygen (FIO2)
Respiratory Assessment
Clinical Assessment of Breathing
– Visual inspection: breathing pattern, rate,
depth, signs of airway obstruction
– Trend charting of respiratory rate
(increases in respiratory rate may herald
pulmonary edema; decreases in respiratory
rate may herald apnea)
Respiratory Assessment
Lab Respiratory Monitoring Methods
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Pulse Oximeter (art oxygen saturation )
Capnograph (expired CO2 conc signal)
Oxygram (expired O2 concentration sig)
Arterial Blood Gas Analysis
– arterial oxygen tension
– arterial carbon dioxide tension
– arterial pH
What is Monitoring?
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Keeping an “eye on the patient”
Patient defense strategy / algorithm
High-tech electronics
Old fashioned viligence
Preparing for future events
Keeping “quality” in the system, including
monitoring care providers
Standard Basic Monitoring
• Clinical means such as inspection, ascultation, attention
to movement, etc
• Blood pressure (usually by automatic cuff)
• Electrocardiogram (rate, rhythm, ST segment )
• Pulse Oximeter (arterial oxygen saturation)
• Capnogram (carbon dioxide conc signal at the airway)
• Anesthetic Agent Concentration Monitor
• Temperature (hypothermia is often undesirable)
• Neuromuscular Blockade (if needed)
• Tidal Volume (where available)
Patient Monitoring / Management
Involves:
things you measure (physiological measurement)
things you observe (clinical observation)
planning to avoid trouble (eg. induction planning)
inferring diagnoses (eg. big QT interval and
hypotension following massive transfusion: your best
guess is hypocalcemia)
planning to get out of trouble (eg. differential diagnosis
and response algorithm formulation)
Low Tech Monitoring
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BP cuff
Finger on the pulse and forehead
Monaural stethoscope
Eye on the rebreathing bag (SV)
Watching for desired or undesired movements
Looking at the patient’s face
 colour OK?
 diaphoresis present?
 pupils
Basic Monitoring
 Cardiac: Blood Pressure, Heart Rate, ECG
 ECG: Rate, ST Segment (ischemia), Rhythm
 Respiratory: AW Pressure, Capnogram, Pulse Oximeter
 Temperature [pharyngeal, axillary, PA (SGC)]
 Urine output (if catheter placed)
 Nerve stimulator [face, forearm](if NMB used)
 ETT cuff pressure (keep < 20 cm H2O)
 Auscultation (esophageal or precordial stethoscope)
 Visualization of some exposed portion of
the patient (clinical signs)
Special Monitoring
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Pulmonary artery lines (Swan Ganz)
Intracranial pressure (ICP)monitoring
Electrophysiological CNS monitoring
Renal function monitoring (indices)
Coagulation monitoring (eg ACT)
Acid-base monitoring (ABGs)
Monitoring depth of anaesthesia