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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 INFANT
2、,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:uncuffed
3、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:functional airway closur
4、eLimits 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 VTAirway resistance increasing:s
5、ecretion,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 breathers:5 months of age.,The
6、 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 hypercarbia or hypoxemia(aspiration o
7、f 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 increased afterload,heart rate-dependent card
8、iac 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 Kidneys,Renal function is markedly diminished i
9、n 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 Liver 1,The functional maturity of the liver is som
10、ewhat 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 is unable to handle large protein loads:hypoglycemia ac
11、idemia 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 second day,pH is in the normal The ability to coordinate sw
12、allowing 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.Upper-vomiting and regurgitation;Lower-abdominal distention and fai
13、lure 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).General anesthesia affects the metabolism of brown fat.-hypothermiaHypo
14、thermia: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 systemPermeability of Blood brain barrier is great:opioiddecrement bilirubinkernicterusM
15、AC,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,the relative size(as well as functional maturity)of the liver and kidneys,the presence or
16、 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.,succinylcholine);less fat:a drug that depends on redistribution into fat for termination of its
17、 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 oxideHalothaneEnfluraneIsofluraneSevofluraneDesflurane,Nitrous oxide,lower dissolubility:含气间隙的体积增大 neonate:pneumothorax,emphysema
18、 congenital diaphragmatic hernia or acromphalus necrotic enteritis,Enflurane,In the introduction of anesthesia:breathholding,cough,laryngospasmAfter anesthesia:seizure-like activity,Isoflurane,Introduction of anesthesia and analepsia:rapidrespiratory depression,coughing,laryngospasmAfter extubate:in
19、cidence of laryngospasm enflurane,Sevoflurane,induction is slightly 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 anesthesia:sevofluraneProlon
20、ged anesthesia:elect other anesthetics,Desflurane,respiratory tract irritation:strong laryngospasm(50%)during the gaseous induction of anesthesiaConcern for the potential for carbon monoxide poisoning Hypertension and tachycardia,Intravenous anesthetics,KetamineThiopental Propofol Etomidate Benzodia
21、zepines:diazepam,midazolamOpioids:morphine,fentanyl,alfentanil,sufentanil,remifentanil,Ketamine 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:increased production of secr
22、etions vomiting postoperative dreaming hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressure,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 r
23、educed 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 distributes into and out of vessel-rich organs.Short duration:rapid redistribution,hepatic glucuronidation,and high renal clearance.Dose:1-2 mg/
24、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 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 m
25、etabolic pathways have matured.,Midazolam,Midazolam is water soluble and therefore not usually painful on intravenous 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 re
26、ctal: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 action Dosage:patient age,the surgical procedure,the health of the patient,and the use of anesthetic adjuvants.,Alfentanil,Eliminate:more rapidly than fentanyl Pharmacokinetic
27、s:independent of dose Margin of 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 to clear sufentanil more rapidly than adults do.Bradycar
28、dia and asystole:when a vagolytic drug was not administered simultaneously.,Remifentanil,Often use in pediatric anesthesia,Muscle Relaxants,Depolarizing Muscle Relaxant:succinylcholineNondepolarizing Muscle Relaxants:Pancuronium,Vecuronium,Atracurium,Pipecuronium,Rocuronium,Succinylcholine,the dose
29、required for intravenous administration in infants(2.0 mg/kg)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 histamine is released The dis
30、advantage:tachycardiaAdministration:0.1 mg/kg,Vecuronium,Vecuronium is useful for shorter procedures in infants and childrenno histamine is released Administration:0.1mg/kg Duration:20 30min,Atracurium,Useful for shorter procedures in infants and childrenParticularly useful in newborns and patients
31、with liver or renal disease.Why?Administration:0.3 0.5 mg/kg Duration: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 sur
32、gery 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 medical condition of the child,the needs of the planned surgical procedure,and the p
33、sychological 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
34、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 premedication is not
35、 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 administere
36、d 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 result in a ster
37、ile 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 Higher doses of intramuscular
38、 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 determined by a number of factors:the
39、 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 of Anesthesia,Rectal administration of
40、 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 either markedly delayed or very rapid,Intramus
41、cular 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:reliability the main disadvantage:painful,Intraven
42、ous 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,The Difficult
43、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 stridor:extrathoracic upp
44、er 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 obstruction,dynamic collapse of the trach
45、ea 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 stridor worsens or mild laryngospasm
46、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
47、)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 uncuffed endotracheal tube that is 0.5 to 1.0 mm(intern
48、al 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 brea
49、the 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 appropriately sized laryngoscopesWhile the child is breathing oxygen,atropine(0.02 mg/kg,up to 0.6 mg)may be administered intrave
50、nously cricoid cartilage,Endotracheal Tubes,For most children,the proper-size endotracheal tube and the proper distance of insertion relative to the alveolar ridge of the mandible or maxilla are moderately constant.,Tube diameter(in mm)=age/4+4Infant 3 months to 1 year:10 cm Child 1 year:11 cm Child
