1、Department of anesthesiologyCui Xiao Guang The provision of safe anesthesia for pediatric patients depends on a clear understanding of the physiologic, pharmacologic, and psychological differences between children and adults. Neonates: 01 months Infants: 112 months Toddlers: 13 years small children:
2、 412 yearsDEVELOPMENTAL PHYSIOLOGY OF THE INFANTThe pulmonary system 1The relatively large size of the infants tongue The larynx is located higher in the neck The epiglottis is shaped differently, being short and stubbyThe vocal cords are angled The infant larynx is funnel shaped, the narrowest port
3、ion occurring at the cricoid cartilage: uncuffed endotracheal tubes; patients younger than 6 years.The pulmonary system 2Alveoli increase in number and size until the child is approximately 8 years old. Functional residural capacity (FRC): the same with adult; induction and palinesthesia of anesthes
4、ia is rapidA-aDO2 is larger: functional airway closureLimits oxygen reserves: hypoxemia. The work of breathing: (In premature infants) three times of adults, increased by cold stress or some degree of airway obstruction. RR: two times of adultsThe pulmonary system 3Tidal volume(VT) is little; physio
5、logical dead space is 30% of VTAirway resistance increasing: secretion, upper airway infectionDiaphragmatic and intercostal muscles do not achieve the adult configuration of type I muscle fibers until the child 2 years old: apnea or carbon dioxide retention and respiratory failure.Infants have often
6、 been described as obligate nasal breathers: 5 months of age. The Cardiovascular System1In uterus: foramen ovale, ductus arteriosus (rightleft)At birth: the fetal circulation becomes an adult-type circulation.- transitional circulationProlonged transitional circulation: prematurity, infection, acido
7、sis, pulmonary disease resulting in hypercarbia or hypoxemia (aspiration of meconium), hypothermia, congenital heart disease. The Cardiovascular System2The myocardial structure of the heart is less developed, produce less compliant ventriclesThis developmental myocardial immaturity: sensitivity to v
8、olume loading, poor tolerance of increased afterload, heart rate-dependent cardiac output. The Cardiovascular System3Bradycardia and profound reductions in cardiac output : activation of the parasympathetic nervous system hypoxia anesthetic overdose The sympathetic nervous system and baroreceptor re
9、flexes are not fully mature. The KidneysRenal function is markedly diminished in neonates and further diminished in preterm babies because of low perfusion pressure and immature glomerular and tubular function. Nearly complete maturation: approximately 20 weeks after birth Complete maturation :about
10、 2 years of agedehydration The Liver 1 The functional maturity of the liver is somewhat incomplete. Most enzyme systems for drug metabolism are developed but not yet induced (stimulated) by the drugs that they metabolize. Jaundice: decreased bilirubin breakdownThe Liver 2A premature infants liver ha
11、s minimal glycogen stores and is unable to handle large protein loads: hypoglycemia acidemia failure to gain weight when the diet contains too much protein. The lower the albumin value, the less protein binding and the greater the levels of free drug.The Gastrointestinal System At birth, gastric pH
12、is alkalotic; after birth the second day, pH is in the normal The ability to coordinate swallowing with respiration does not fully mature until the infant is 4 to 5 months of age: gastroesophageal reflux If a developmental problem occurs within the gastrointestinal system, symptoms will occur within
13、 24 to 36 hours of birth. Upper -vomiting and regurgitation ; Lower -abdominal distention and failure to pass meconium. ThermoregulationThin skin, low fat content, and a higher surface relative to weight allow greater heat loss to the environment in neonates. 保温保温Thermogenesis: shivering and nonshiv
14、ering (metabolism of brown fat). General anesthesia affects the metabolism of brown fat.-hypothermiaHypothermia: delayed awakening from anesthesia, cardiac irritability, respiratory depression, increased pulmonary vascular resistance, and altered drug responses. Central nervous systemMore fat is in
15、the central nervous systemPermeability of Blood brain barrier is great: opioiddecrement bilirubinkernicterusMACPharmacological Differences The response to medications: body composition, protein binding, body temperature, distribution of cardiac output, functional maturity of the heart, maturation of
16、 the blood-brain barrier, the relative size (as well as functional maturity) of the liver and kidneys, the presence or absence of congenital malformations Alterations in body composition have several clinical implications for neonates a drug that is water soluble: larger volume of distribution and l
17、arger initial dose (e.g., succinylcholine); less fat: a drug that depends on redistribution into fat for termination of its action will have a longer clinical effect (e.g., thiopental); a drug that redistributes into muscle: longer clinical effect (e.g., fentanyl); Others Inhaled Anesthetics Nitrous
18、 oxideHalothaneEnfluraneIsofluraneSevofluraneDesflurane Nitrous oxidelower dissolubility: 含气间隙的体积增大 neonate: pneumothorax, emphysema congenital diaphragmatic hernia or acromphalus necrotic enteritisEnflurane In the introduction of anesthesia: breathholding, cough, laryngospasmAfter anesthesia: seizu
19、re-like activityIsoflurane Introduction of anesthesia and analepsia: rapidrespiratory depression, coughing, laryngospasmAfter extubate: incidence of laryngospasm enfluraneSevoflurane induction is slightly more rapid anesthesia is steadyrespiratory tract irritation: smallthe production of toxic metab
20、olites as a result of interaction with the carbon dioxide absorbent must be considered .Introduction and short anesthesia: sevofluraneProlonged anesthesia: elect other anestheticsDesflurane respiratory tract irritation: strong laryngospasm ( 50%) during the gaseous induction of anesthesiaConcern for
21、 the potential for carbon monoxide poisoning Hypertension and tachycardia Intravenous anestheticsKetamineThiopental Propofol Etomidate Benzodiazepines: diazepam, midazolamOpioids: morphine, fentanyl, alfentanil, sufentanil, remifentanilKetamine 1Routes of administration: intravenous: 2 mg/kg intramu
22、scular: 5 to 10 mg/kg rectally: 10 mg/kg orally: 6 to 10 mg/kg intranasally: 3 to 6 mg/kg Ketamine 2Undesirable side effects: increased production of secretions vomiting postoperative dreaming hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressureThiopental
23、Intravenous: 2.5% thiopental, 5 to 6 mg/kg Termination of effect occurs through redistribution of the drug into muscle and fatThiopental should be used in reduced doses (2 to 4 mg/kg) in children who have low fat stores, such as neonates or malnourished infants. PropofolPropofol is highly lipophilic
24、 and promptly distributes into and out of vessel-rich organs.Short duration: rapid redistribution, hepatic glucuronidation, and high renal clearance. Dose: 1-2 mg/kg; higher in infants younger than 2 years Pain: lidocaine, ketamine Etomidate Pain, bucking.No commonly usedDiazepam 0.1-0.3 mg/kg, oral
25、ly provides; may also be administered rectally has an extremely long half-life in neonates (80 hours)Contraindicat: until the infant is 6 months of age or until hepatic metabolic pathways have matured.Midazolam Midazolam is water soluble and therefore not usually painful on intravenous administratio
26、n. Administration: intravenous: 0.05 to 0.08 mg/kg, maximum of 0.8mg (weight30 min Rocuronium Rocuronium has a clinical profile similar to that of vecuronium and atracurium Advantage: can be administered intramuscularly Preoperative Preparation(1) The preoperative visit and preparation of the child
27、for surgery are more important than the choice of premedication chart review, physical examination, and furnishing of information regarding the approximate time and length of surgeryPreoperative Preparation(2)evaluates the medical condition of the child, the needs of the planned surgical procedure,
28、and the psychological makeup of the patient and familyexplain in great detail what the child and family can expect and what will be done to ensure the utmost safetyFasting milk and solids: before 6 hours clear fluids up to 2-3 hours before induction Infants who are breast-fed may have their last bre
29、ast milk 4 hours before anesthetic induction Premedication (1)The need for premedication must be individualized according to the underlying medical conditions, the length of surgery, the desired induction of anesthesia, and the psychological makeup of the child and family Premeditation (2)A premedic
30、ation is not normally necessary for the usual 6-month-old child but is warranted for a 10- to 12-month-old who is afraid to be separated from parents Oral midazolam is the most commonly administered premedication. An oral dose of 0.25 to 0.33 mg/kg (maximum, 20 mg) Premeditation (3)Premedications ma
31、y be administered orally, intramuscularly, intravenously, rectally, sublingually, or nasally Although most of these routes are effective and reliable, each has drawbacks Merits and drawbacksOral or sublingual : not hurt but may have a slow onset or be spit out Intramuscular and Intravenous : painful
32、 and may result in a sterile abscess Rectal : make the patient feel uncomfortable Nasal : irritating, although absorption is rapid Premeditation (4)Midrange doses of intramuscular ketamine (3 to 5 mg/kg) combined with atropine (0.02 mg/kg) and midazolam (0.05 mg/kg) will result in a deeply sedated p
33、atient Higher doses of intramuscular ketamine (up to 10 mg/kg) combined with atropine and midazolam may be administered to patients with anticipated difficult venous access to provide better conditions for insertion of the intravenous line Induction of Anesthesia The method of inducing anesthesia is
34、 determined by a number of factors: the medical condition of the patient, the surgical procedure, the level of anxiety of the child, the ability to cooperate and communicate (because of age, developmental delay, language barrier), the presence or absence of a full stomach, and other factors Rectal I
35、nduction of AnesthesiaRectal administration of 10% methohexital reliably induces anesthesia within 8 to 10 minutes in 85% of young children and toddlers The main advantage: the child falls asleep in the parents arms, separates atraumatically from the parents. The main disadvantage : drug absorption
36、can be either markedly delayed or very rapid Intramuscular Induction of Anesthesia Many medications, such as ketamine (2 to 10 mg/kg combined with atropine and midazolam), or midazolam alone (0.15 to 0.2 mg/kg), are administered intramuscularly for premedication or induction of anesthesiaThe main ad
37、vantage : reliability the main disadvantage : painful Intravenous Induction of AnesthesiaIntravenous induction of anesthesia is the most reliable and rapid technique Intravenous induction may be preferable when induction by mask is contraindicated (e.g., in the presence of a full stomach) The main d
38、isadvantage : painful and threatening for the child The Difficult AirwayDifficult intubation: maintain spontaneous respirations; placing a stylet in the endotracheal tube; fiberoptic brochoscope. The Child with Stridor (1)expiratory stridor: intrathoracic airway obstruction ,. such as: bronchiolitis
39、, asthma, intrathoracic foreign body inspiratory stridor : extrathoracic upper airway obstruction , such as: epiglottitis, laryngotracheobronchitis, laryngeal foreign body When a child has upper airway obstruction (as in epiglottitis, laryngotracheobronchitis, and extrathoracic foreign body) (shaded
40、 area) and struggles to breathe against this obstruction, dynamic collapse of the trachea increases The Child with Stridor (2)maintaining spontaneous respiration Induction of anesthesia with halothane or sevoflurane in oxygen by mask With the patient lightly anesthetized and after infiltration of lo
41、cal anesthetic, an intravenous line is inserted If stridor worsens or mild laryngospasm occurs, the pop-off valve is closed sufficiently to develop 10 to 15 cm H2 O of positive end-expiratory airway pressure. When a child has upper airway obstruction caused by laryngospasm (A) or mechanical obstruct
42、ion (B), the application of approximately 10 cm H2 O of positive end-expiratory pressure (PEEP) during spontaneous breathing often relieves the obstruction. That is, PEEP helps keep the vocal cords apart (A) and the airway open (B, broken lines) The Child with Stridor (3)A child with laryngotracheob
43、ronchitis or epiglottitis usually requires an uncuffed endotracheal tube that is 0.5 to 1.0 mm (internal diameter) smaller than normal total airway obstruction occur and mask ventilation or endotracheal intubation not be possible - tracheotomy The Child with a Full Stomach 1Children with a full stom
44、ach must be treated the same as adults with a full stomach child may be uncooperative and refuse to breathe oxygen before induction of anesthesia The Child with a Full Stomach 2enrich the environment with a high flow of oxygen Additional equipment : two suction catheters , two appropriately sized la
45、ryngoscopesWhile the child is breathing oxygen, atropine (0.02 mg/kg, up to 0.6 mg) may be administered intravenously cricoid cartilageEndotracheal TubesFor most children, the proper-size endotracheal tube and the proper distance of insertion relative to the alveolar ridge of the mandible or maxilla
46、 are moderately constant. Tube diameter (in mm) = age/4+4Infant 3 months to 1 year: 10 cm Child 1 year: 11 cm Child 2 year: 12 cm Length of tube (in cm) = age/2+12 the tip of the endotracheal tube should pass only 12 cm beyond an infants glottis. The Dedicated Pediatric EquipmentRendell-Baker-Soucek
47、 maskAyres T tubeJackson Rees improved type of Ayres T tube: have reservoir bag; airflow: 1000 ml+ 100 mlBW(kg) /min ( weight15 kg Plain tetracaine (1%) Dose (mg/kg) 0.5 0.4 0.3 Volume (mL/kg) 0.05 0.04 0.03 Duration (min) 75 80 85 Tetracaine (1%) with epinephrine Dose (mg/kg) 0.5 0.4 0.3 Volume (mL
48、/kg) 0.05 0.04 0.03 Duration (min) 120 120 125 Bupivacaine (0.5%) Dose (mg/kg) 0.5 0.4 0.3 Volume (mL/kg) 0.1 0.08 0.06 Duration (min) 6575 7080 7585 Axillary approaches Axillary approaches to the brachial plexus: classic approach (A) and transcoracobrachialis approach (B), indicating the pectoralis
49、 major muscle (1), axillary artery (2), and coracobrachialis muscle (3).Dose - Volumes for Single-Shot Procedures by Weight Block 210 kg (mL/kg) 15 kg (mL) 20 kg (mL) 25 kg (mL) 30 kg (mL) 40 kg (mL) 50 kg (mL) 60 kg (mL) 70 kg (mL) Para scalene 1 12.5 15 17.5 20 22.5 25 27.5 30 Interscalene 1 12.5
50、15 17.5 20 22.5 25 27.5 30 Peri -subclavian 1 12.5 15 17.5 20 22.5 25 27.5 30 Axillary 0.5 7.5 10 10 12.5 15 17.5 20 25 Coracoid 0.5 7.5 10 10 12.5 15 17.5 20 25 Lumbar plexus * 1 15 17.5 20 20 20 20 20 20 Femoral 0.7 8 12 15 15 17.5 20 22.5 25 Fascia iliaca 1 12.5 15 17.5 20 22.5 25 27.5 30 Proxima
