Pediatric Anesthesia

1. Pediatric Anesthesia Department of anesthesiology Cui Xiao Guang

2. The provision of safe anesthesia for pediatric patients depends on a clear understanding of the physiologic, pharmacologic, and psychological differences between children and adults.

3. Neonates: 0–1 months • Infants: 1–12 months • Toddlers: 1–3 years • small children: 4–12 years

4. DEVELOPMENTAL PHYSIOLOGY OF THE INFANT

5. The pulmonary system 1 • The relatively large size of the infant's 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: uncuffed endotracheal tubes; patients younger than 6 years.

7. 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: functional 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

8. The pulmonary system 3 • Tidal volume(VT) is little; physiological dead space is 30% of VT • Airway 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 nasal breathers: <5 months of age.

9. The Cardiovascular System1 • In uterus: foramen ovale, ductus arteriosus (right→left) • At birth: the fetal circulation becomes an adult-type circulation.-- transitional circulation • Prolonged transitional circulation: prematurity, infection, acidosis, pulmonary disease resulting in hypercarbia or hypoxemia (aspiration of meconium), hypothermia, congenital heart disease.

10. 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 tolerance of increased afterload, heart rate-dependent cardiac output.

11. 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.

12. 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 • dehydration

13. 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

14. 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 too much protein. • The lower the albumin value, the less protein binding and the greater the levels of free drug.

15. The Gastrointestinal System • At birth, gastric pH is alkalotic; after 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 birth. Upper --vomiting and regurgitation ; Lower --abdominal distention and failure to pass meconium.

16. 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.--hypothermia • Hypothermia: delayed awakening from anesthesia, cardiac irritability, respiratory depression, increased pulmonary vascular resistance, and altered drug responses.

17. Central nervous system • More fat is in the central nervous system • Permeability of Blood brain barrier is great: opioid—decrement bilirubin—kernicterus • MAC↑

18. 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 absence of congenital malformations

19. 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 action will have a longer clinical effect (e.g., thiopental); • a drug that redistributes into muscle: longer clinical effect (e.g., fentanyl); • Others

20. Inhaled Anesthetics • Nitrous oxide • Halothane • Enflurane • Isoflurane • Sevoflurane • Desflurane

21. Nitrous oxide • lower dissolubility: 含气间隙的体积增大 neonate: pneumothorax, emphysema congenital diaphragmatic hernia or acromphalus necrotic enteritis

22. Enflurane • In the introduction of anesthesia: breathholding, cough, laryngospasm • After anesthesia: seizure-like activity

23. Isoflurane • Introduction of anesthesia and analepsia: rapid • respiratory depression, coughing, laryngospasm • After extubate: incidence of laryngospasm< enflurane

24. Sevoflurane • induction is slightly more rapid • anesthesia is steady • respiratory tract irritation: small • the production of toxic metabolites as a result of interaction with the carbon dioxide absorbent must be considered . • Introduction and short anesthesia: sevoflurane • Prolonged anesthesia: elect other anesthetics

25. Desflurane • respiratory tract irritation: strong laryngospasm (≅50%) during the gaseous induction of anesthesia • Concern for the potential for carbon monoxide poisoning • Hypertension and tachycardia

26. Intravenous anesthetics • Ketamine • Thiopental • Propofol • Etomidate • Benzodiazepines: diazepam, midazolam • Opioids: morphine, fentanyl, alfentanil, sufentanil, remifentanil

27. 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

28. Ketamine 2 • Undesirable side effects: increased production of secretions vomiting postoperative "dreaming" hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressure

29. 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.

30. 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/kg; higher in infants younger than 2 years • Pain: lidocaine, ketamine

31. Etomidate • Pain, bucking. • No commonly used

32. 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 metabolic pathways have matured.

33. 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 (weight<10 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

34. 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.

35. Alfentanil • Eliminate: more rapidly than fentanyl • Pharmacokinetics: 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

36. 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.

37. Remifentanil • Often use in pediatric anesthesia

38. Muscle Relaxants • Depolarizing Muscle Relaxant: succinylcholine • Nondepolarizing Muscle Relaxants : Pancuronium, Vecuronium, Atracurium , Pipecuronium, Rocuronium

39. Succinylcholine • the dose 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

40. Pancuronium • useful for longer procedures • no histamine is released • The disadvantage : tachycardia • Administration: 0.1 mg/kg

41. Vecuronium • Vecuronium is useful for shorter procedures in infants and children • no histamine is released • Administration: 0.1mg/kg • Duration : 20 – 30min

42. 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 • Duration : >30 min

43. Rocuronium • Rocuronium has a clinical profile similar to that of vecuronium and atracurium • Advantage: can be administered intramuscularly

44. 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 approximate time and length of surgery

45. 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 in great detail what the child and family can expect and what will be done to ensure the utmost safety

46. 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

47. 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

48. 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 midazolam is the most commonly administered premedication. An oral dose of 0.25 to 0.33 mg/kg (maximum, 20 mg)

49. 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

50. 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 patient feel uncomfortable • Nasal : irritating, although absorption is rapid