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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 stubby The 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 rapid A-aDO2 is larger: functio
4、nal airway closure Limits 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 VT A
5、irway resistance increasing: secretion, upper airway infection Diaphragmatic 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 na
6、sal breathers: 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 circulation Prolonged transitional circulation: prematurity, infection, acidosis, pulmonary disease resu
7、lting in 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 ventricles This developmental myocardial immaturity: sensitivity to volume loading, poor toler
8、ance of increased 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 mat
9、ure.,The 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 age dehydra
10、tion,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 breakdown,The Liver 2,A premature infants liver has minimal glycogen s
11、tores 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 is alkalotic; after
12、 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 24 to 36 hours of
13、birth. Upper -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 o
14、f brown fat). General anesthesia affects the metabolism of brown fat.-hypothermia Hypothermia: 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 nervo
15、us system Permeability of Blood brain barrier is great: opioiddecrement bilirubinkernicterus MAC,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-bra
16、in 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 larger initial
17、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 oxide Halotha
18、ne Enflurane Isoflurane Sevoflurane Desflurane,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, laryngospasm After anesthesia: seizure-lik
19、e activity,Isoflurane,Introduction of anesthesia and analepsia: rapid respiratory depression, coughing, laryngospasm After extubate: incidence of laryngospasm enflurane,Sevoflurane,induction is slightly more rapid anesthesia is steady respiratory tract irritation: small the production of toxic metab
20、olites as a result of interaction with the carbon dioxide absorbent must be considered . Introduction and short anesthesia: sevoflurane Prolonged anesthesia: elect other anesthetics,Desflurane,respiratory tract irritation: strong laryngospasm (50%) during the gaseous induction of anesthesia Concern
21、for the potential for carbon monoxide poisoning Hypertension and tachycardia,Intravenous anesthetics,Ketamine Thiopental Propofol Etomidate Benzodiazepines: diazepam, midazolam Opioids: morphine, fentanyl, alfentanil, sufentanil, remifentanil,Ketamine 1,Routes of administration: intravenous: 2 mg/kg
22、 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: increased production of secretions vomiting postoperative “dreaming“ hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressure
23、,Thiopental,Intravenous: 2.5% thiopental, 5 to 6 mg/kg Termination of effect occurs through redistribution of the drug into muscle and fat Thiopental 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 hig
24、hly lipophilic 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 used,Diazepam,0.
25、1-0.3 mg/kg, orally 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 intrav
26、enous administration. Administration: intravenous: 0.05 to 0.08 mg/kg, maximum of 0.8mg (weight10 kg) intramuscular: 0.1 to 0.15 mg/kg, maximum of 7.5 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: ra
27、pid onset; brief duration of 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 safety: the greater the administered dose, the greater the
28、 elimination. Clearance of alfentanil may be increased in children in comparison to adults,Sufentanil,use primarily for cardiac anesthesia Children are able to clear sufentanil more rapidly than adults do. Bradycardia and asystole: when a vagolytic drug was not administered simultaneously.,Remifenta
29、nil,Often use in pediatric anesthesia,Muscle Relaxants,Depolarizing Muscle Relaxant: succinylcholine Nondepolarizing Muscle Relaxants : Pancuronium, Vecuronium, Atracurium , Pipecuronium, Rocuronium,Succinylcholine,the dose required for intravenous administration in infants (2.0 mg/kg) is approximat
30、ely 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 procedures no histamine is released The disadvantage : tachycardia Administration: 0.1 mg/kg,Vecuronium,Vecuronium i
31、s useful for shorter procedures in infants and children no histamine is released Administration: 0.1mg/kg Duration : 20 30min,Atracurium,Useful for shorter procedures in infants and children Particularly useful in newborns and patients with liver or renal disease. Why? Administration:0.3 0.5 mg/kg D
32、uration : 30 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 more important than the choice of premedication ch
33、art 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 psychological makeup of the patient and family explain i
34、n 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 hours before anesthetic induction,Premedication (1)
35、,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 not normally necessary for the usual 6-month-old ch
36、ild 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 administered orally, intramuscularly, intravenously, r
37、ectally, 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 result in a sterile abscess Rectal : make the pat
38、ient 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 Higher doses of intramuscular ketamine (up to 10 m
39、g/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 determined by a number of factors: the medical condition
40、 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 of Anesthesia,Rectal administration of 10% metho
41、hexital 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 either markedly delayed or very rapid,Intramuscul
42、ar 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 anesthesia The main advantage : reliability the main disadvantage : painful,I
43、ntravenous 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 disadvantage : painful and threatening for the child,Th
44、e 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, asthma, intrathoracic foreign body inspiratory st
45、ridor : 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 area) and struggles to breathe against this obstru
46、ction, 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 anesthetic, an intravenous line is inserted If
47、 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
48、 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 laryngotracheobronchitis or epiglottitis usually requires an unc
49、uffed 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 1,Children with a full stomach 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 2,enrich the environment with a high flow of oxygen Additional equipment : two suction catheters , two appro