Chapter 6

Basic Concept of General Anesthesia

Department of AnesthesiologyXiangya hospital

Central South University

General anesthesia is an altered physiologic state characterized by reversible loss of consciousness, analgesia of the entire body, amnesia and some degree of muscle relaxation.

Induction → Maintenance → Recovery

Definition of General Anesthesia

1.Induction of General Anesthesia

Definition

全麻诱导是指病人从清醒转为可以进行手术操作的麻醉状态的过程。

There are some complications or risks in this stage, e.g. reduction of blood pressure, arrhythmia, myocardial ischemia.

Induction of General Anesthesia-- -- Methods ① Rapid-sequence Intravenous Induction

tracheal intubation

muscle relaxants

mask ventilation for 5 minclose-fitting face mask100% oxygen delivery

unc ons ci ousnes s

sedat i ves , hypnot i c s orI nt r avenous anest het i cs agent s

Agent induction dose (mg/Kg)

Diazepam 0.2

Midazolam 0.1-0.2

Thiopental 3-5

Etomidate 0.3

ketamine 1-2

Propofol 1.5-2.5

Fentanyl 5-6 μg/kg

Intravenous induction agents

Muscle Relaxants

depolarizing nondepolarizing dose (mg/kg)

Succinycholine   1-2

  vecuronium 0.08-0.1

  atracurium 0.3-0.6

  pancuronium 0.08-0.1

  Rocuronium 0.6-1 

Induction of General Anesthesia Induction of General Anesthesia ① Rapid-sequence Intravenous Induction

-- Disadvantage and Complications ● Regurgitation and Vomitting ● Cardiovascular depression ● Respiratory depression● Histamine release ● Pain on injection

● Hiccup and muscle movements

Induction of General Anesthesia Induction of General Anesthesia ② Inhalational Induction-- Indications

● young children

● myasthenia gravies ● upper airway obstruction, e.g. Epiglottitis ● lower airway obstruction with foreign body

● bronchopleural fistula or empyema ● no accessible veins

Induction of General Anesthesia Induction of General Anesthesia Inhalational Induction-- Methods

Initially, nitrous oxide 70% in oxygen is used and anesthesia is deepened by gradual introduction of increments of a volatile agent, e.g. Halothane 1-3%, Enflurane 1.5-2.5%, Isoflurane 1-2% .

Induction of General Anesthesia Induction of General Anesthesia Inhalational Induction-- characteristics

● Spontaneous ventilation is to be maintained. ● the face mask is applied firmly as consciousness

is lost and the airway is supported manually. ● Insertion of an oropharyngeal airway , a laryngeal mask airway or a tracheal tube may be considered when anesthesia has been established.

Induction of General Anesthesia Induction of General Anesthesia Inhalational Induction

Disadvantage and Complications

● Slow induction of anesthesia

● Airway obstruction , bronchospasm ● Laryngeal spasm , hiccups ● Environmental pollution

Induction of General Anesthesia Induction of General Anesthesia ③ Induction with spontaneous ventilation -- Indications

● Airway obstruction

● anticipant difficult intubation

Induction of General Anesthesia Induction of General Anesthesia Induction With Spontaneous Ventilation

-- Characteristics

● Maintaining spontaneous ventilation

throughout the procedure

● Sufficient surface anesthesia

Induction of General Anesthesia Induction of General Anesthesia

④ Intravenous induction following conscious intubation -- Indications

● Patient with the risk of regurgitation

● Patient with postural hypotension

following anesthesia (e.g. paraplegia)

Induction of General Anesthesia Induction of General Anesthesia

⑤ Other induction methods

● intramuscular injection of ketamine ● take midazolam orally

● administration of fentanyl via mucosa

注意事项

• 保持呼吸道通畅 ---首要任务 • 保持一定麻醉深度，减轻插管应激反应• 静脉用药按 Kg体重计算、维持循环稳定• 诱导前，准备好麻醉机和插管用具，监测生命体征• 面罩加压给氧时， TV不宜过大，避免气体进入胃内→胃胀气、返流

⒉Maintenance of general anesthesia

镇静 sedation

镇痛 analgesia

肌松 muscle relaxation

⒉Maintenance of general anesthesia

Inhalational agents

Intravenous anesthetics

Opioids

Muscle relaxants

全麻维持与诱导紧密衔接了解手术进程，麻醉深度与手术刺激相适应做好呼吸管理，保持气道通畅，人工通气监 测 PETCO2 、 SPO2 及血气分析 :

颅脑手术 PaCO2 维持 30-35mmHg

冠心病病人 PaCO2 不宜太低，以免冠脉痉挛

注意事项

注意事项 ■ 使用肌松监测仪指导肌松剂的使用

■ 充分镇静、避免术中知晓■ 维持生命体征和内环境平稳，及时

处理术中失血性休克、过敏性休克、 心律失常等异常情况

⒊ Recovery

Antagonizing residual neuromuscular blockade

Extubation

Airway supporting

Recovery position is benefit to avoid airway obstruction

⒊ Recovery

• 严格掌握拔管指征，过早、过晚拔管均会造成严重后果

• 自然苏醒，必要时使用催醒药• MACawake: 肺泡气内吸入麻醉药浓度降至

0.4MAC （ 0.5 或 0.58MAC ）时， 95% 病人能按指令睁眼

4.Monitoring depth of anesthesia

Stages of anesthesia

麻醉深度监测技术

• 食道下端肌肉收缩波形和振幅的测定• 脑电双频谱指数（ Bispectral Index ， BI

S ） 清醒 : 80-100

外科麻醉期 : 40

• 体感诱发电位• 脑干听觉诱发电位