小儿麻醉2

nullPediatric Anesthesia Pediatric Anesthesia Department of anesthesiology Cui Xiao Guangnull The provision of safe anesthesia for pediatric patients depends on a clear understanding of the physiologic, pharmacologic, and psychological differences between children and adults. nullNeonates: 0–1 months Infants: 1–12 months Toddlers: 1–3 years small children: 4–12 yearsDEVELOPMENTAL PHYSIOLOGY OF THE INFANTDEVELOPMENTAL PHYSIOLOGY OF THE INFANTThe pulmonary system 1The pulmonary system 1The 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.nullThe pulmonary system 2The 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 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 adultsThe pulmonary system 3The pulmonary system 3Tidal 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. The Cardiovascular System1The Cardiovascular System1In 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. The Cardiovascular System2The Cardiovascular System2The 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. The Cardiovascular System3The 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. The KidneysThe 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 age dehydration The Liver 1 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 breakdownThe Liver 2The Liver 2A 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.The Gastrointestinal System 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. ThermoregulationThermoregulationThin 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. Central nervous systemCentral nervous systemMore fat is in the central nervous system Permeability of Blood brain barrier is great: opioid—decrement bilirubin—kernicterus MAC↑Pharmacological Differences 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 Alterations in body composition have several clinical implications for neonates 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 Inhaled Anesthetics Inhaled Anesthetics Nitrous oxide Halothane Enflurane Isoflurane Sevoflurane Desflurane Nitrous oxideNitrous oxidelower dissolubility: 含气间隙的体积增大 neonate: pneumothorax, emphysema congenital diaphragmatic hernia or acromphalus necrotic enteritisEnflurane Enflurane In the introduction of anesthesia: breathholding, cough, laryngospasm After anesthesia: seizure-like activityIsoflurane Isoflurane Introduction of anesthesia and analepsia: rapid respiratory depression, coughing, laryngospasm After extubate: incidence of laryngospasm< enfluraneSevoflurane 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 anestheticsDesflurane Desflurane respiratory tract irritation: strong laryngospasm (≅50%) during the gaseous induction of anesthesia Concern for the potential for carbon monoxide poisoning Hypertension and tachycardia Intravenous anestheticsIntravenous anestheticsKetamine Thiopental Propofol Etomidate Benzodiazepines: diazepam, midazolam Opioids: morphine, fentanyl, alfentanil, sufentanil, remifentanilKetamine 1Ketamine 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 2Ketamine 2Undesirable side effects: increased production of secretions vomiting postoperative "dreaming" hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressure Thiopental 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. PropofolPropofolPropofol 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 Etomidate Etomidate Pain, bucking. No commonly usedDiazepam 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. Midazolam 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/kgFentanyl 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 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 Sufentanil 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.RemifentanilRemifentanilOften use in pediatric anesthesia Muscle Relaxants Muscle Relaxants Depolarizing Muscle Relaxant: succinylcholine Nondepolarizing Muscle Relaxants : Pancuronium, Vecuronium, Atracurium , Pipecuronium, Rocuronium SuccinylcholineSuccinylcholinethe 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 Pancuronium Pancuronium useful for longer procedures no histamine is released The disadvantage : tachycardia Administration: 0.1 mg/kgVecuroniumVecuroniumVecuronium is useful for shorter procedures in infants and children no histamine is released Administration: 0.1mg/kg Duration : 20 – 30min AtracuriumAtracuriumUseful 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 Rocuronium Rocuronium Rocuronium has a clinical profile similar to that of vecuronium and atracurium Advantage: can be administered intramuscularly Preoperative Preparation(1) 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 Preoperative Preparation(2)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 Fasting 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)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)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) Premeditation (3)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 Merits and drawbacksMerits 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)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 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 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, developmental delay, language barrier), ◆ the presence or absence of a full stomach, and other factors Rectal Induction of AnesthesiaRectal 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 the parent‘s arms, separates atraumatically from the parents. The main disadvantage : drug absorption can be either markedly delayed or very rapid Intramuscular Induction of Anesthesia 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 anesthesia The main advantage : reliability the main disadvantage : painful Intravenous Induction of AnesthesiaIntravenous Induction of AnesthesiaIntravenous 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 AirwayThe Difficult AirwayDifficult intubation: maintain spontaneous respirations; placing a stylet in the endotracheal tube; fiberoptic brochoscope. The Child with Stridor (1)The Child with Stridor (1)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 null 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 trachea increases The Child with Stridor (2)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 occurs, the pop-off valve is closed sufficiently to develop 10 to 15 cm H2 O of positive end-expiratory airway pressure. null 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)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 (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 1The Child with a Full 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 2The Child with a Full Stomach 2enrich the environment with a high flow of oxygen Additional equipment : two suction catheters , two appropriately sized laryngoscopes While the child is breathing oxygen, atropine (0.02 mg/kg, up to 0.6 mg) may be administered intravenously cricoid cartilage Endotracheal TubesEndotracheal TubesFor 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. nullnullTube diameter (in mm) = age/4+4 Infant 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 1–2 cm beyond an infant's glottis. The Dedicated Pediatric EquipmentThe Dedicated Pediatric EquipmentRendell-Baker-Soucek mask Ayres T tube Jackson Rees improved type of Ayres T tube: have reservoir bag; airflow: [1000 ml+ 100 ml×BW(kg)] /min ( weight<10kg) Laryngeal mask Epidural anesthesiaEpidural anesthesia Epidural block procedures: sacral intervertebral approach (1), lumbar approach (i.e., midline route) (2), and thoracic approach (i.e., midline route) (3).Local Anesthetics Local Anesthetics 0.8%～1.5% lidocaine 0.1%～0.2% tetracaine 0.25%～0.5% bupivacaine 0.25%～0.5% ropivacaineCaudal anesthesiaCaudal anesthesiaCaudal block procedure. A, Insertion of the needle at right angles to the skin in relation to the coccyx (1) and the sacrococcygeal membrane (2). B, Cephalad redirection of the needle after piercing the sacrococcygeal membrane. Spinal anesthesiaSpinal anesthesiaAxillary approaches Axillary approaches Axillary approaches to the brachial plexus: classic approach (A) and transcoracobrachialis approach (B), indicating the pectoralis major muscle (1), axillary artery (2), and coracobrachialis muscle (3).nullDose Dose MonitoringMonitoringThe 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 Routine Monitoring precordial stethoscope, ↘ esophageal stethoscope, blood pressure cuff, electrocardiogram, temperature probe, pulse oximeter, end-tidal carbon dioxide monitor Invasive Monitoring Invasive Monitoring Arterial catheter Central venous catheterIntravenous FluidIntravenous Fluidthe high metabolic demands the high ratio of body surface area to weight. The basis for calculating The basis for calculating Other Other Fluid deficits, Third-space losses, Modifications because of hypothermia or hyperthermia, Requirements caused by unusual metabolic demands null50% of the resulting deficit is replaced in the first hour and 25% in each of the next 2 hours. Loss with the surgical procedure: from 1 mL/kg/hr for a minor surgical procedure to as much as 15 mL/kg/hr for major abdominal procedures. The composition of the intravenous fluid The composition of the intravenous fluid Child with greater hypoxic brain damage : high blood glucose levels, recommend not using glucose-containing solutions routinely, especially for brief operative procedures All deficits and third-space losses: A balanced salt solution (e.g., lactated Ringer's solution)