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: 01 months Infants: 112 months Toddlers: 13 years small children: 412 years,DEVELOPMENTAL PHYSIOLOGY OF THE
2、INFANT,The pulmonary system 1,The 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 portion occurring at the cricoid cartilage:
3、uncuffed endotracheal tubes; patients younger 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 anesthesia is rapidA-aDO2 is larger: functiona
4、l 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 adults,The pulmonary system 3,Tidal volume(VT) is little; physiological dead space is 30% of VTAirwa
5、y 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 been described as obligate nasal br
6、eathers: 5 months of age.,The Cardiovascular System1,In uterus: foramen ovale, ductus arteriosus (rightleft)At birth: the fetal circulation becomes an adult-type circulation.- transitional circulationProlonged transitional circulation: prematurity, infection, acidosis, pulmonary disease resulting in
7、 hypercarbia or hypoxemia (aspiration of meconium), hypothermia, congenital heart 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 tolerance of i
8、ncreased afterload, heart rate-dependent cardiac output.,The Cardiovascular System3,Bradycardia and profound reductions in cardiac output : activation of the parasympathetic nervous system hypoxia anesthetic overdose The sympathetic nervous system and baroreceptor reflexes are not fully mature.,The
9、Kidneys,Renal 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 2 years of agedehydration,The L
10、iver 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 breakdown,The Liver 2,A premature infants liver has minimal glycogen stores and
11、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 is alkalotic; after birth the
12、 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 24 to 36 hours of birth. Upp
13、er -vomiting and regurgitation ; Lower -abdominal distention and failure to pass meconium.,Thermoregulation,Thin skin, low fat content, and a higher surface relative to weight allow greater heat loss to the environment in neonates. 保温Thermogenesis: shivering and nonshivering (metabolism of brown fat
14、). 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 system,More fat is in the central nervous systemPer
15、meability of Blood brain barrier is great: opioiddecrement bilirubinkernicterusMAC,Pharmacological Differences,The response to medications: body composition, protein binding, body temperature, distribution of cardiac output, functional maturity of the heart, maturation of the blood-brain barrier, th
16、e 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 larger initial dose (e.g., su
17、ccinylcholine); 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 oxideHalothaneEnfluraneIsof
18、luraneSevofluraneDesflurane,Nitrous oxide,lower dissolubility: 含气间隙的体积增大 neonate: pneumothorax, emphysema congenital diaphragmatic hernia or acromphalus necrotic enteritis,Enflurane,In the introduction of anesthesia: breathholding, cough, laryngospasmAfter anesthesia: seizure-like activity,Isofluran
19、e,Introduction of anesthesia and analepsia: rapidrespiratory depression, coughing, laryngospasmAfter extubate: incidence of laryngospasm enflurane,Sevoflurane,induction is slightly more rapid anesthesia is steadyrespiratory tract irritation: smallthe production of toxic metabolites as a result of in
20、teraction with the carbon dioxide absorbent must be considered .Introduction and short anesthesia: sevofluraneProlonged anesthesia: elect other anesthetics,Desflurane,respiratory tract irritation: strong laryngospasm (50%) during the gaseous induction of anesthesiaConcern for the potential for carbo
21、n monoxide poisoning Hypertension and tachycardia,Intravenous anesthetics,KetamineThiopental Propofol Etomidate Benzodiazepines: diazepam, midazolamOpioids: morphine, fentanyl, alfentanil, sufentanil, remifentanil,Ketamine 1,Routes of administration: intravenous: 2 mg/kg intramuscular: 5 to 10 mg/kg
22、 rectally: 10 mg/kg orally: 6 to 10 mg/kg intranasally: 3 to 6 mg/kg,Ketamine 2,Undesirable side effects: increased production of secretions vomiting postoperative dreaming hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressure,Thiopental,Intravenous: 2.5% t
23、hiopental, 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.,Propofol,Propofol is highly lipophilic and promptly dist
24、ributes 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 used,Diazepam,0.1-0.3 mg/kg, orally provides; may
25、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 administration. Administratio
26、n: 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 for surgery are
27、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 medical condition of the child, the needs of the planned surgical procedure, and the psycho
28、logical 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 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 ho
29、urs 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 premedication is no
30、t 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 may be admin
31、istered orally, intramuscularly, intravenously, rectally, sublingually, or nasally Although most of these 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
32、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 patient H
33、igher 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 determi
34、ned 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 Induction
35、 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: the child falls asleep in the parents arms, separates atraumatically from the parents. The main disadvantage : drug absorption can be
36、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 advantage
37、 : 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 induction by mask is contraindicated (e.g., in the presence of a full stomach) The main disadva
38、ntage : painful and threatening for the child,The Difficult Airway,Difficult 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, as
39、thma, 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 are
40、a) 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 local
41、 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 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 apart (A) and the airway open (B, broken lines),The Child with Stridor (3),
