哈爾濱醫(yī)科學(xué)臨床麻醉學(xué)小兒麻醉

1、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: 0–1 months Infants: 1–12 m

2、onths Toddlers: 1–3 years small children: 4–12 years,DEVELOPMENTAL PHYSIOLOGY OF THE INFANT,The pulmonary system 1,The relatively large size of the infant's tongue The larynx is located higher in the neck The e

3、piglottis is shaped differently, being short and stubbyThe vocal cords are angled The infant larynx is funnel shaped, the narrowest portion occurring at the cricoid cartilage: uncuffed endotracheal tubes; patients youn

4、ger than 6 years.,,The pulmonary system 2,Alveoli 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 anesth

5、esia 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

6、 of airway obstruction. RR: two times of adults,The pulmonary system 3,Tidal volume(VT) is little; physiological dead space is 30% of VTAirway resistance increasing: secretion, upper airway infectionDiaphragma

7、tic 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 been described as obl

8、igate nasal breathers: <5 months of age.,The Cardiovascular System1,In uterus: foramen ovale, ductus arteriosus (right→left)At birth: the fetal circulation becomes an adult-type circulation.-- transitional circulati

9、onProlonged transitional circulation: prematurity, infection, acidosis, pulmonary disease resulting in hypercarbia or hypoxemia (aspiration of meconium), hypothermia, congenital heart

10、 disease.,The Cardiovascular System2,The myocardial structure of the heart is less developed, produce less compliant ventriclesThis developmental myocardial immaturity: sensitivity to volume loading, poor tolera

11、nce of increased afterload, heart rate-dependent cardiac output.,The Cardiovascular System3,Bradycardia and profound reductions in cardiac output : activation of the parasympathetic nervous system

12、 hypoxia anesthetic overdose The sympathetic nervous system and baroreceptor reflexes are not fully mature.,The Kidneys,Renal function is markedly diminished in neonates and further diminished in preterm babi

13、es because of low perfusion pressure and immature glomerular and tubular function. Nearly complete maturation: approximately 20 weeks after birth Complete maturation :about 2 years of agedehydration,The Liver 1,The

14、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 br

15、eakdown,The Liver 2,A premature infant's liver has minimal glycogen stores and is unable to handle large protein loads: hypoglycemia acidemia failure to gain weight when the diet contains

16、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 is alkalotic; after birth the second day, pH is

17、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

18、system, symptoms will occur within 24 to 36 hours of birth. Upper --vomiting and regurgitation ; Lower --abdominal distention and failure to pass meconium.,Thermoregulation,Thin skin, low fat content, an

19、d a higher surface relative to weight allow greater heat loss to the environment in neonates. –保溫Thermogenesis: shivering and nonshivering (metabolism of brown fat). General anesthesia affects the metabolism of brown f

20、at.--hypothermiaHypothermia: delayed awakening from anesthesia, cardiac irritability, respiratory depression, increased pulmonary vascular resistance, and altered drug responses.,Central nervous system,More fat is in t

21、he central nervous systemPermeability of Blood brain barrier is great: opioid—decrement bilirubin—kernicterusMAC↑,Pharmacological Differences,The response to medications: body composition, protein

22、 binding, body temperature, distribution of cardiac output, functional maturity of the heart, maturation of the blood-brain barrier, the relative size (as well as functional maturit

23、y) 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

24、volume of distribution and larger 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 d

25、rug that redistributes into muscle: longer clinical effect (e.g., fentanyl); Others,Inhaled Anesthetics,Nitrous oxideHalothaneEnfluraneIsofluraneSevofluraneDesflurane,Nitrous oxide,lower dissolubility: 含氣間隙

26、的體積增大 neonate: pneumothorax, emphysema congenital diaphragmatic hernia or acromphalus necrotic enteritis,Enflurane,In the introduction of anesthesia: breathholding, cough, laryngospasmAfter anesthes

27、ia: seizure-like activity,Isoflurane,Introduction of anesthesia and analepsia: rapidrespiratory depression, coughing, laryngospasmAfter extubate: incidence of laryngospasm< enflurane,Sevoflurane,induction is s

28、lightly more rapid anesthesia is steadyrespiratory tract irritation: smallthe production of toxic metabolites as a result of interaction with the carbon dioxide absorbent must be considered .Introduction and short an

29、esthesia: sevofluraneProlonged anesthesia: elect other anesthetics,Desflurane,respiratory tract irritation: strong laryngospasm (?50%) during the gaseous induction of anesthesiaConcern for the potential for carbon

30、monoxide poisoning Hypertension and tachycardia,Intravenous anesthetics,KetamineThiopental Propofol Etomidate Benzodiazepines: diazepam, midazolamOpioids: morphine, fentanyl, alfentanil, sufentanil, remifentanil,K

31、etamine 1,Routes of administration: intravenous: 2 mg/kg intramuscular: 5 to 10 mg/kg rectally: 10 mg/kg orally: 6 to 10 mg/kg intranasally: 3 to 6 mg/kg,Ketamine 2,Undesirable side effects

32、: increased production of secretions vomiting postoperative "dreaming" hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pres

33、sure,Thiopental,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 h

34、ave low fat stores, such as neonates or malnourished infants.,Propofol,Propofol is highly lipophilic and promptly distributes into and out of vessel-rich organs.Short duration: rapid redistribution, hepatic glucuronidat

35、ion, and high renal clearance. Dose: 1-2 mg/kg; higher in infants younger than 2 years Pain: lidocaine, ketamine,Etomidate,Pain, bucking.No commonly used,Diazepam,0.1-0.3 mg/kg, orally provides; may als

36、o 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 solu

37、ble and therefore not usually painful on intravenous administration. Administration: intravenous: 0.05 to 0.08 mg/kg, maximum of 0.8mg (weight<10 kg) intramuscular: 0.1 to 0.15 mg/kg, maximum of 7.5

38、mg oral: 0.25 to 1.0 mg/kg, maximum of 20 mg rectal: 0.75 to 1.0 mg/kg, maximum of 20 mg nasal: 0.2 mg/kg sublingual: 0.2 mg/kg,Fentanyl,Fentanyl: rapid onset; brief duration of

39、 action Dosage: patient age, the surgical procedure, the health of the patient, and the use of anesthetic adjuvants.,Alfentanil,Eliminate: more rapidly than fentanyl Pharmacokinetics: independent of dose Margin of

40、safety: the greater the administered dose, the greater the elimination. Clearance of alfentanil may be increased in children in comparison to adults,Sufentanil,use primarily for cardiac anesthesia Children are able

41、to clear sufentanil more rapidly than adults do.Bradycardia and asystole: when a vagolytic drug was not administered simultaneously.,Remifentanil,Often use in pediatric anesthesia,Muscle Relaxants,Depolarizing Muscle

42、 Relaxant: succinylcholineNondepolarizing Muscle Relaxants : Pancuronium, Vecuronium, Atracurium , Pipecuronium, Rocuronium,Succinylcholine,the dose required for intravenous administration in infants (2.0 mg/kg)

43、is approximately twice that for older patients Intravenous administration of atropine before the first dose of succinylcholine may reduce the incidence of arrhythmias,Pancuronium,useful for longer proceduresno histamin

44、e is released The disadvantage : tachycardiaAdministration: 0.1 mg/kg,Vecuronium,Vecuronium is useful for shorter procedures in infants and childrenno histamine is released Administration: 0.1mg/kg Duration :

45、 20 – 30min,Atracurium,Useful for shorter procedures in infants and childrenParticularly useful in newborns and patients with liver or renal disease. Why? Administration:0.3 – 0.5 mg/kg Duration : >30 min,Rocuron

46、ium,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 for surge

47、ry are more important than the choice of premedication chart review, physical examination, and furnishing of information regarding the approximate time and length of surgery,Preoperative Preparation(2),evaluates the med

48、ical condition of the child, the needs of the planned surgical procedure, 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 ensur

49、e the utmost safety,Fasting,milk and solids: before 6 hours clear fluids up to 2-3 hours before induction Infants who are breast-fed may have their last breast milk 4 hours before anesthetic induction,Premedication (1)

50、,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,Premedit

51、ation (2),A premedication 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

52、premedication. An oral dose of 0.25 to 0.33 mg/kg (maximum, 20 mg),Premeditation (3),Premedications may be administered orally, intramuscularly, intravenously, rectally, sublingually, or nasally Although most of th

53、ese routes are effective and reliable, each has drawbacks,Merits and drawbacks,Oral or sublingual : not hurt but may have a slow onset or be spit out Intramuscular and Intravenous : painful and may result in a sterile

54、 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

55、midazolam (0.05 mg/kg) will result in a deeply sedated patient Higher doses of intramuscular ketamine (up to 10 mg/kg) combined with atropine and midazolam may be administered to patients with anticipated difficult veno

56、us access to provide better conditions for insertion of the intravenous line,Induction of Anesthesia,The method of inducing anesthesia is determined by a number of factors: ◆ the medical condition of the patient,

57、 ◆ 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 o

58、f a full stomach, and other factors,Rectal Induction of Anesthesia,Rectal administration of 10% methohexital reliably induces anesthesia within 8 to 10 minutes in 85% of young children and toddlers The main advantage:

59、 the child falls asleep in the parent‘s arms, separates atraumatically from the parents. The main disadvantage : drug absorption can be either markedly delayed or very rapid,Intramuscular Induction of Anesthesia

60、,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 adv

61、antage : reliability the main disadvantage : painful,Intravenous Induction of Anesthesia,Intravenous induction of anesthesia is the most reliable and rapid technique Intravenous induction may be preferable when induc

62、tion by mask is contraindicated (e.g., in the presence of a full stomach) The main disadvantage : painful and threatening for the child,The Difficult Airway,Difficult intubation: maintain spontaneous respirati

63、ons; placing a stylet in the endotracheal tube; fiberoptic brochoscope.,The Child with Stridor (1),expiratory stridor: intrathoracic airway obstruction ,. such as: bronchiolitis, asthma, intrathor

64、acic foreign body inspiratory stridor : extrathoracic upper airway obstruction , such as: epiglottitis, laryngotracheobronchitis, laryngeal foreign body,,,When a child has upper airway obstruction (as in ep

65、iglottitis, laryngotracheobronchitis, and extrathoracic foreign body) (shaded area) and struggles to breathe against this obstruction, dynamic collapse of the trachea increases,The Child with Stridor (2),maintaining spon

66、taneous respiration Induction of anesthesia with halothane or sevoflurane in oxygen by mask With the patient lightly anesthetized and after infiltration of local anesthetic, an intravenous line is inserted If stridor

67、 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)

68、or mechanical obstruction (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