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what do you see in the picture?
• An anesthesia machine• A beautiful and smart anesthetist
Administration of General Anesthesia
Xiao Ying (肖颖)The First Affiliated Hospital of
Sun Yat-sen UniversityMar 2010
Overview
• What is general anesthesia?• Preoperative preparation• Induction: going off to sleep• Maintenance: keeping pt asleep • Emergence: waking up • Transport
What is general anesthesia
• Primary goals
Safety is top priority Amnesia: no memory of the event Hypnosis: unconcious Analgesia: free of pain Block certain autonomic reflexes Optimal surgical conditions:
immobolity
What is general anesthesia
• Secondary goals Medical condition Surgical procedures
Surgical settings
Examples for secondary goals • Patients with CAD: Oxygen supply-
demand balance • Neurosugery: ICP control, brain
relaxation and CPP maintenance• Obstetrics: anesthetics and fetal
depression, difficult airway• Day surgery vs Inpatient: which kind of
analgesic you should choose to minimize postoperative pain and decrease PONV?
Preoperative preparation
• Preoperative evaluations Airway examination Interim changes in pt’s condition Medications Laboratory data Consultant notes Last oral intake
Preoperative preparation• Intravascular volume Dehydration: adequately hydrate the pt before
induction• Intravenous access• Preoperative medicationsAnxiety Benzodiazepine: Midazolam Opioid: Morphine or FentanylNeutralize gastric acid and decrease gastric
volume
Which kind of pt is at increased risk of aspiration of gastric content?
• Recent meal• Trauma • Bowel obstruction• Pregnancy• History of gastric surgery• Increased intra-abdominal pressure• History of active reflux
Monitoring
Standard monitoring for GA
ECG
NBP
Pulse oximetry
Capnography
Oxygen analyzer
Induction
Let the pt go off to sleepPreoxygenation
8L~10L/min
IV or Inhalational
induction
Airway management
Induction techniques
• Intravenous: the most common method
• Inhalation: for special pt (pt with difficult airway, pediatric pt)
• Intramuscular :rarely used,only used in uncooperative pts and young children
Airway management• ASA Closed Claims Study(美国麻醉学会已结案的诉讼)
35 % of claims are RESPIRATORY events
90 % resulted in brain damage or death
90% resulted from Difficulty in INTUBATION or EXTUBATION
Airway management
• Airway patency is critically important
Oral airway
Nasophryngeal airway
Laryngeal mask airway
Intubation
Maintenance
Increasing depth of anesthesia
stageⅠ
Amnesia
Loss of
consciousness
Stage Ⅱ
Delirium
Injurious responses
to noxious stimuli
Stage Ⅲ
Surgical anesthesia
Painful stimulation does
not elicit somatic reflexes
or deleterious autonomic
responses
Stage Ⅳ
Overdosage
Circulatory
failure
Maintenance
Maintain homeotasisVital signsAcid-base balanceTemperatureCoagulationVolume status
Maintenance
• Lack of awareness and no memory of the event
Incidence of awareness High risk surgical population High risk pt High risk anesthesia method
How to avoid awareness
• To recognize the high risk pt• Monitor the depth of anesthesia• Somatic and autonomic response
are nonspecific and unreliable• Bis monitor for high risk pt
Depth of anesthesia • Intensity of surgical stimulation• Response suggesting inadequate
anesthetic depth:• Somatic: movement, coughing, changes
of respiratory pattern• Autonomic: tachycardia, hypertension,
mydriasis, sweating, tearing• Unreliable and nonspecific• Sympathetic activation may be caused
by other reasons
Maintenance methods
• Volatile (Isoflurane, Desflurane or sevoflurane combined with nitrous oxide)
• Nitrous oxide-opioid relaxant technique
• IV anesthesia• Combinations• General anesthesia combined with
regional anesthesia
Ventilation
Ventilation1. Spontaneous or assisted ventilation2. Controlled ventilation Tidal volume: 10-12ml/kg
Respiratory rate: 8-10 breaths/min
3. Assessment of ventilation Capnography
Pulse oximeter Airway pressure Reservoir breathing bag Ventilator bellow
VentilationPeak inspiratory pressureHigh airway pressure >25~30cmH2O
Breathing circuit problem ETT obstruction or movement Altered lung compliance Change in muscle relaxation Surgical compression
IV Fluids• Intraoperative IV fluids
requirements
1. Maintenance fluid requirements
2. Third space losses and insensible losses
3. Blood losses
IV Fluids1. Crystalloid sollutions: maintenance
fluid requirement, evaporative losses, and third space losses
2. Colloid sollutions: replace blood loss or restore intravascular volume
3. Blood transfusion
Intravascular volume assessment
• Trends of heart rate, blood pressure, and urine output
• Central venous pressure, pulmonary artery occlusion pressure, right and left end-diastolic volumes(using TEE) and cardiac output
• Hemotocrit, platelet count, fibrinogen concentration, prothrombin time, thromboplastin time
Emergence from GA
Goals:
awake Responsive Full muscle strength Adequate pain
control
Extubation
• Awake extubation• Indications Risk of aspiration Difficult airways Tracheal or maxillofacial surgery
Extubation• Awake extubation• Criteria Awake Hemodynamically stable Full muscle strength Able to follow simple verbal
commands Breathing spontaneously with
adequate ventilation
Extubation
• Awake extubation• Special technique: removal of
ETT over a flexible stylette Indication: patency of the
airway is uncertain or reintubation may be difficult
Extubation
• Deep extubation• Indications Severely asthmatic patients Middle-ear surgery Open-eye surgery Inguinal herniorrhaphy
Extubation
• Deep extubation• Criteria Sufficient anesthetic depth to
avoid response to airway stimulation
Spontaneous breathing with adequate ventilation
Agitation
• Causes Pain Hypoxia Hypercarbia Airway obstruction Full bladder
Transport
Questions