1、Pediatric Anesthesia 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
2、small children: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 na
3、rrowest portion 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 an
4、esthesia 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;physiologi
5、cal 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 been de
6、scribed 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,acidosis,pulmonary dise
7、ase 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 volume loading,poor tolera
8、nce 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 reflexes are not fully mature.Th
9、e 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 2 years of agedehydration The Liv
10、er 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 has minimal glycogen stores and is unable
11、 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 second day,pH
12、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.Upper-vomiting and reg
13、urgitation;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 nonshivering(metabolism of brown fat).General anesthesia affects
14、 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 the central nervous systemPermeability of Blood brain barrier is
15、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 the blood-brain barrier,the relative size(as well as functional maturit
16、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 volume of distribution and larger initial dose(e.g.,succinylcholine);less fat:a drug that depends on redi
17、stribution 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 oxideHalothaneEnfluraneIsofluraneSevofluraneDesflurane Nitrous oxidelower dissolubility
18、: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:seizure-like activityIsoflurane Introduction of anesthesia and analepsia:rapidrespiratory depression
19、,coughing,laryngospasmAfter extubate:incidence of laryngospasm enfluraneSevoflurane 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
20、and short anesthesia:sevofluraneProlonged anesthesia:elect other anestheticsDesflurane respiratory tract irritation:strong laryngospasm(50%)during the gaseous induction of anesthesiaConcern for the potential for carbon monoxide poisoning Hypertension and tachycardia Intravenous anestheticsKetamineTh
21、iopental Propofol Etomidate Benzodiazepines:diazepam,midazolamOpioids:morphine,fentanyl,alfentanil,sufentanil,remifentanilKetamine 1Routes 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 2Undesirable side eff
22、ects:increased production of secretions vomiting postoperative dreaming hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressureThiopental Intravenous:2.5%thiopental,5 to 6 mg/kg Termination of effect occurs through redistribution of the drug into muscle and f
23、atThiopental 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 and promptly distributes into and out of vessel-rich organs.Short duration:rapid redistribution,hepatic glucuronidation,and hig
24、h 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,orally provides;may also be administered rectally has an extremely long half-life in neonates(80 hours)Contraindicat:until the infant is 6 mon
25、ths of age or until hepatic metabolic 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(weight30 min Rocuronium Rocuronium has a clinical profile similar to that of
26、 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 chart review,physical examination,and furnishing of information regarding the approx
27、imate time and length of surgeryPreoperative Preparation(2)evaluates the medical 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 ensure the u
28、tmost 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 breast milk 4 hours before anesthetic induction Premedication(1)The need for premedication must be individualized according to the underlying medical condit
29、ions,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 child but is warranted for a 10-to 12-month-old who is afraid to be separated from parents Oral mida
30、zolam 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,rectally,sublingually,or nasally Although most of these routes are effective and reliable,each has drawbacks
31、Merits and drawbacksOral 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 patient feel uncomfortable Nasal:irritating,although absorption is rapid Premeditation(4)Midrange doses of intramuscular
32、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 mg/kg)combined with atropine and midazolam may be administered to patients with anticipated difficult venous access to provide bett
33、er 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,the surgical procedure,the level of anxiety of the child,the ability to cooperate and communicate (because of age,de
34、velopmental delay,language barrier),the presence or absence of a full stomach,and other factors Rectal Induction 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
35、the parents arms,separates atraumatically from the parents.The main disadvantage:drug absorption 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/
36、kg),are administered intramuscularly for premedication or induction of anesthesiaThe main advantage: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 i
37、nduction by mask is contraindicated(e.g.,in the presence of a full stomach)The main disadvantage: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)
38、expiratory stridor:intrathoracic airway obstruction,.such as:bronchiolitis,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,la
39、ryngotracheobronchitis,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 spontaneous respiration Induction of anesthesia with halothane or sevoflurane in oxygen by mask With the
40、 patient lightly anesthetized and after infiltration of local 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 obstru
41、ction 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 wi
42、th Stridor(3)A child with laryngotracheobronchitis 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 Fu
43、ll Stomach 1Children 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 2enrich the environment with a high flow of oxygen Additional equipment:two suction cat
44、heters,two appropriately sized laryngoscopesWhile 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 ridg
45、e 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 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 EquipmentRen
46、dell-Baker-Soucek 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/k
47、g)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 major muscle(1),a
48、xillary 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 15 17.5 20 22.5 25 27.5 30 Peri-subclavian
49、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 Proximal sciatic 1 15 17.5 20 22.5 25 27.5 30 3235 Po
50、pliteal fossa 0.3 4 5 6 7.5 10 10 10 10 MonitoringThe complexity of monitoring applied to pediatric patients must be consistent with the severity of the underlying medical condition and the planned surgical procedure.Routine Monitoring precordial stethoscope,esophageal stethoscope,blood pressure cuf
