Administration of general anesthesia

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