1 / 89

ANESTHESIA FOR PEDIATRICS

Dr Masood EntezariAsl. ANESTHESIA FOR PEDIATRICS. INTRODUCTION. the incidence of anesthesia-related mortality and morbidity remains higher in infants than in adults and higher in younger than older children .

fay-christian
Download Presentation

ANESTHESIA FOR PEDIATRICS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Dr Masood EntezariAsl ANESTHESIA FORPEDIATRICS

  2. INTRODUCTION • the incidence of anesthesia-related mortality and morbidity remains higher in infants than in adults and higher in younger than older children. • In the post anesthesia care unit(PACU), problems primarily or secondarily related to airway complications are more likely to develop in the youngest infants. • The incidence of critical events (most often respiratory) is higher in infants younger than 1 year than in children older than 1 year, especially in infants weighing less than 2 kg • the frequency of anesthetic cardiac arrest in infants is less when care is delivered by pediatric-trained/experienced practitioners

  3. FLUIDS AND ELECTROLYTES • Considerations that influence fluid homeostasis include: (1) anatomic factors related to the distribution of body fluids (2) physiologic factors such as basal requirements and abnormal metabolic rate (3) functional immaturityof the kidneys andliver (4) pathologic factors secondary to the special setting of illness, anesthesia, and surgery

  4. Maintenance Requirements

  5. Replacement of Ongoing Losses

  6. Normal Distribution of Water • Total-body water consists of extracellular fluid (ECF) and intracellular fluid (ICF) • ECFincludes plasma volume and interstitial fluid volume • In the early stages of fetaldevelopment, water constitutes approximately 94% of body weight • As gestation continues, total-body water decreases so that at 32 weeks' gestation, 80% of body weight is water and, at term, total-body water is 78%of body weight • Adult proportions of fluid to body weight are reachedbetween the age of 9 months and 2 years • Adult femaleshave approximately 55% of their body weight as total-body water, with males averaging 60%

  7. RELATIONSHIP OF BODY FLUID COMPARTMENTS • The relationship of ECF and ICF also changes during fetal growth • ECF decreases from 60% of body weight at the fifth month to approximately 45% at term • ICFincreases from 25% in the fifth month of fetal life to 33% at birth • In adult males, the ICF and ECF compartments approximate 40% and 20% of body weight, respectively • The plasma volume component of ECF remains constant at about 5% of body weight throughout life • Interstitial water is greater in infants (40%) and declines to 15% and 10% of body weight in men and women, respectively

  8. ELECTROLYTECOMPOSITION OF BODY FLUIDS • The electrolyte composition of the body fluids of infants is also different from that in adults • Higher plasma chloride and lower bicarbonate and pH imply a mild metabolic acidosis with reduced buffering power (Tables) • In the first 10 days of postnatal life (term infants), serum potassium levels may be as high as 6.0 to 6.5 mEqlL • In term infants, serum potassium ranges from 3.5 to 5.5 mEqlL after the first 2 to 3 weeks of life • Another unique feature of newborns is the reduced protein concentration, which results in lower intravascular oncotic pressure

  9. Laboratory Values in Children

  10. Developmental Changes in Blood Gas Values in children

  11. Over the first week of life, water exchange is often negative because of ongoing losses through the skin, lungs, and urine in the setting of limited intake • A 7-kg infant with a 21OO-mL ECF volume takes in and excretes approximately 700 to 1000 mL of fluid daily, which represents a 33% turnover in ECF • By comparison, a 70-kg adult with a 14,000-mL ECF volume excretes approximately 2000 mL of fluid daily for a 14% turnover • This high rate of fluid exchange may expose infants to more rapid development of both dehydration and over hydration

  12. PEDIATRIC AIRWAY • Preoperatively, the anesthesiologist must meticulously assessall aspects of the airway to develop detailed and flexible plansfor (1) intubating the trachea, (2) intraoperative airway management (3) postoperative recovery (Table( • The anesthetic plan for management of the child's airway may be influenced by the site of surgery • Maintaining upper airway patency is an active process that is depressed during general anesthesia • During spontaneous ventilation, the upper airwayis exposed to potentially collapsingnegative pressure during inspiration • The pharynx is prone to collapse because negative pressure pulls the tongue against the pharynx • General anesthesia depresses activity of the upper airway and thereby predisposes to oropharyngeal obstruction

  13. Endotracheal Tube Sizes

  14. The contribution of the tongue to airway obstruction is exaggerated in infants because the tongue is large relative to the total volume of the mouth • Infants or children with small upper airways secondary to craniofacial anomalies, weakness as a result of neuromuscular or central nervous system disorders, impingement on the airway secondary to tumors or hemangiomas, or dysfunction of the tracheobronchial tree because of an upper respiratory infection (URI) are especially prone to pharyngeal obstruction by the tongue

  15. Head position is important in maintaining upper airway patency during anesthesia • Flexing an infant's head may cause the upper airway to collapse more readily • In addition, the small, soft airways of neonates (especially premature neonates) are more compressible if the neck is flexed • Extending or keeping the neck in a neutral position while applying positive airway pressure during ventilation with a bag and facemask is important, particularly during induction of general anesthesia

  16. Unique Anatomic Features • The larynx of infants is higher in the neck (C3-4) thanin adults(C4-5) • An infant's epiglottis is large, but it is narrow and short • A straight laryngoscope blade may allow the larynx of a normal infant to be visualized more easily • When laryngeal anatomy is distorted by craniofacial anomalies (micrognathia or midface hypoplasia), direct visualization of the larynx may be impossible, and alternative methods of securing the airway should be available • An infant's vocal cords are slanted such that the posterior commissure is more cephalad than the anterior commissure

  17. This arrangement may predispose the anterior sublaryngeal airway to trauma from an endotracheal tube • The subglottic area is prone to traumatic injury from an endotracheal tube because the narrowest portion of an infant's larynx is at the cricoid cartilage • In adults, the narrowest portion is the glottic rim • Thus, an endotracheal tube that easily passes through the vocal cords of an infant or child may fit snugly in the subglottis and cause subglottic edema and symptoms of increased airway resistance after tracheal extubation • This increased resistance is usually reversible, but subglottic stenosis may develop after prolonged tracheal intubation with an oversizedendotrachealtube

  18. Airway Assessment • Difficult tracheal intubation generally occurs when facial or oral pathology prevents visualization of the larynxor when the larynx is easily visualized by direct laryngoscopy but a lesion in the supraglottic, glottic, or subglottic region interfereswith insertion of the endotracheal tube • Whenthe past medical history documents previous difficult airway management and tracheal intubation, it is recommendedthat a physician experienced in performing pediatric bronchoscopy be presentduring initial airway management • Fiberopticairway endoscopy with or without the aid of a laryngeal mask airway (LMA) may be indicated for securing a difficult airway • In some circumstances, it may be prudent to have available a surgeon skilled in performing cricothyrotomy or tracheostomy (or both) • In somesituations, performing a controlled tracheostomy may be less traumatic than persisting with multiple attempts at direct laryngoscopy

  19. DEVELOPMENTAL PHYSIOLOGY

  20. DEVELOPMENTAL PHYSIOLOGY • Respiratory System • Circulatory System • Renal Function • Hematology

  21. Respiratory System (Table)Lung Development • Alveoli develop mainly after birth and increase from 20 million terminal air sacs in a newborn to approximately 300 million alveoli at 18 months of age • In general, extra uterine viability is first likely after 26 weeks when the respiratory saccules have developed and vascularization by capillaries has occurred • Supportive care of a premature infant commonly includes oxygen and positive pressure ventilation, and infections are inevitable

  22. Comparison of Pulmonary Variables

  23. RIB CAGE • The compliantrib cage of a newborn produces a mechanical disadvantage to effective ventilation • The negative intrapleural pressure produced by normal inspiratory effort tends to collapse the cartilaginous, compliant chest of an infant (especially a premature newborn), which causesparadoxical chest wall motion and limits airflow during inspiration • The circular configuration of the rib cage (ellipsoid in adults) and the horizontal angle of insertion of the diaphragm (oblique in adults) cause distortion of a newborn's rib cage and inefficient diaphragmatic contraction.

  24. DIAPHRAGM • An adult diaphragm contains 55% type I fibers (fatigue resistant, slow-twitching, highly oxidative fibers), whereas the diaphragm of a full-term infant has 25% and that of a preterm infant has 10% • A lower proportion of type I fibers predisposes these primary respiratory muscles to fatigue • The intercostal muscles show a similar developmental pattern

  25. PULMONARY SURFACTANT • Pulmonary surfactant effects dramatic changes in lung mechanics, including distensibility and end-expiratory volume stability • The development of respiratory distress syndrome of the newborn correlates with insufficient (premature infants) or delayed (infants of diabetic mothers) synthesis of surfactant • The most significant decrease in infant mortality observed in 20 years in the United States occurred in 1990, the year that surfactant was released commercially • However, chronic lung disease persists as a common problem in approximately 20% of premature infants as a result of the complex interplay of many factors in addition to surfactant during normal growth and development of the lungs

  26. Circulatory System

  27. FETAL CIRCULATION • The fetal circulation is characterized by: (1) increased pulmonary vascular resistance (2) decreased pulmonary blood flow (3) decreased systemic vascular resistance (4) right-to-left blood flow through the patent ductus arteriosus and foramen ovale • At birth, the onset of spontaneous ventilation and elimination of the placental circulation decrease pulmonary vascular resistance and increase pulmonary blood flow • Simultaneously, systemic vascular resistance increases, left atrial pressure increases, the foramen ovale closes functionally, and the right-to left shunting ceases • Whenanatomic closure is achieved and cardiac anatomy is normal shunting through the ductus arteriosus is eliminated

  28. Arterial hypoxemia or acidosis in a newborn can precipitate return to a fetal pattern of circulation (pulmonary arterial vasoconstriction, pulmonary hypertension, reduced pulmonary blood flow) • This combination leads to right atrial pressure increasing above left atrial pressure and thereby results in right-to-left shunting through the foramen ovale and ductus arteriosus • This return to a fetal circulatory pattern, termedpersistent fetal circulation or persistent pulmonary hypertension of the newborn, further exacerbates the arterial hypoxemia and acidosis

  29. MYOCARDIAL FUNCTION • The relative noncompliance of the neonatal heart implies a limited capacity to handle a volume load or to increase stroke volume for augmentation of cardiac output (or both) • Thus, the "Frank-Starling" responses considered to play a limited role, whereas the heart rate is critical for maintaining cardiac output in a newborn • Over the first months of life, myocardial contractility gradually increases, which allows cardiac output to be maintained over a wide range of preload and after load

  30. EVALUATIONOF CARDIOPULMONARY FUNCTION • The initial step in evaluating the cardiopulmonary system of a newborn begins with the physical examination • Skin color, capillary filling time, trends in blood pressure, heart rate, intensity of peripheral pulses, presence of a murmur or S3 or S4 heart sounds, respiratory rate, effort, and breath sounds, as well as decreased urine output or metabolic acidosis, should be assessed • Interpretation of the electrocardiogram, chest radiograph, and echocardiogram will allow rational planning for intraoperative monitoring, selection of anesthetic drugs, delivery of intravenous fluids, postoperative recovery, and the extent of the proposed surgical procedure (total correction or staged procedure)

  31. Comparison of Cardiovascular Variables

  32. Renal Function

  33. Renal Function • Urine production increases from about 5 ml/hr at 20 weeks, to about 18 ml/hr at 30 weeks, to about 50 ml/hr at 40 weeks of gestation • Although the kidneys are not essential for maintaining normal fluid and electrolyte balance in a fetus, urine production contributes to normal amniotic fluid volume and is critical for normal pulmonary and urinary tract development

  34. GLOMERULAR FILTRATION RATE • The renal function of a newborn versus an adult is characterized by a decreased glomerular filtration rate (GFR), decreasedexcretion of solid materials, and decreased urine concentrating ability • The GFR increases with gestational age, and by 34 to 36 weeks of gestation, values are similar to those reported for full-term infants • Over the first3 months of life, the GFR increases twofold to threefold • A slower rise is noted until adult values are reached by 12 to 24 months of life

  35. RENAL TUBULAR FUNCTION • Limited renal tubular reabsorptive function is the basis for the loss of bicarbonate and the "normal" acidosis that occur in a newborn, particularly premature newborns (sometimes called renal tubular acidosis type 4) • Similarly, proximal renal tubular reabsorption of sodium increases with gestational age • Of note, arterial hypoxemia, respiratory distress, and hyper bilirubinemia can increase fractional sodium excretion • The limited distal renal tubular function also impairs the ability of the kidneys to excrete a sodium load. In addition, tubular immaturity affects the conservation of amino acids, nucleosides, glucose, and other essential substrates

  36. Hematology

  37. Hematology • At birth, a full-term newborn normally has a hemoglobin concentration of 18 to 20 g/dl • a preterm infant usually has a lower hemoglobin concentration ranging between 13 and 15 g/dl (Tables) • Approximately 70% to 80% of the hemoglobin at birth is fetal hemoglobin (HgF), but the concentration of HgF decreases to physiologically insignificant levels by 3 to 6 months of age • The high affinity of HgF for oxygen shifts the oxyhemoglobin dissociation curve to the left so that P 50(normally 18 to 20 mm Hg) is less than the adult value (27 mm Hg) • Although high oxygen affinity improves the fetus's ability to uptake oxygen from the mother at the placental interface, after birth this same high affinity decreases the amount of oxygen released at tissue levels. • In a normal newborn, higher hemoglobin levels, greater blood volume, and increased cardiac output (per unit weight) compensate adequately for HgF • Such normal, term infants tolerate the gradual decrease in hematocrit (and HgF) over the first few months of life, with the nadir reaching values as low as 9 to 10 g/dl • By comparison, the concentration of hemoglobin in a very-Iow-birth-weight (VLBW, 1 500 g) or extremely-low-birth-weight (ELBW, <1000 g) infant at birth normally ranges between 13 and 15 g/dl

  38. Of note, the nadir of a premature (<30 weeks' gestation) infant's hemoglobin may be as low as 6 to 7 g/dl by 3 to 4 months of age • Erythropoietin is now routinely administered to infants in the neonatal intensive care unit, thereby avoiding such profound anemia • Newborns with cardiovascular or respiratory instability often benefit from a hematocrit higher than 40% to 45% to facilitate adequate oxygen delivery • Blood loss exceeding 10% to 15% of blood volume (or even less in some patients) may not be tolerated by newborns, especially VLBW infants • Cross-matched blood should be available for surgery in a newborn, especially when blood loss is anticipated • Assessment of clotting function should be considered before major surgery in a newborn because the synthesis of prothrombin and factors II, VII, and X is limited in an immature liver • Perinatal asphyxia and septicemia affect the function and concentration of both clotting factors and platelet count and thereby result in coagulopathies • Before surgical intervention, the availability of fresh frozen plasma, fibrinogen, and platelets must be considered

  39. Hematologic Values in Children

  40. Developmental Changes in Blood Volume

  41. MEDICAL AND SURGICAL DISEASES THAT AFFECT THE NEWBORN

  42. Necrotizing Enterocolitis • Necrotizing enterocolitis (NEC) is a gastrointestinal emergency that primarily affects premature infants younger than 32 weeks' gestational age • NEC is a systemic process primarily related to the sepsis that accompanies intestinal necrosis and increased mucosal permeability • The most common anatomic site is the ileocolic region, but NEC is frequently discontinuous and involves both the small and large intestine (Fig) • The primary pathologic finding in NEC is coagulative or ischemic necrosis, but inflammation is also prominent

  43. CLINICAL MANIFESTATIONS • Typically, a preterm baby in whom NEC develops has a history of perinatal asphyxia or postnatal cardiorespiratory instability and manifests gastrointestinal signs between the 1st and 10th days of life (abdominal distention, retained gastric secretions that may be bile tinged, vomiting, bloody or mucoid diarrhea, and occult blood loss in stools) • Bowel necrosis and perforation may develop and be accompanied by sepsis with thermal instability, lethargy, metabolic acidosis, hypotension, hypoxia, jaundice, disseminated intravascular coagulation(DIC), and generalized bleeding • Most infants with NEC have a decreased platelet count (50,000 to 75,OOO/mm3) and prolongedprothrombin(PT) and partial thromboplastin times(PTT) • Abdominal radiographs may reveal dilated, fixed (adynamic ileus) loops of bowel, gas in the portal venous system, and pneumoperitoneum

  44. TREATMENT • Unless there is evidence of intestinal necrosis or perforation, the initial treatment of NEC is nonoperative and includes: - decompression of the stomach - cessation of feeding - broad-spectrum antibiotics - fluid and electrolyte therapy - parenteral nutrition - correction of hematologic abnormalities • Inotropic drugs may be needed to maintain hemodynamic stability • Bowel perforation is the most important indication for surgery

  45. Other events that increase the likelihood for surgical intervention include: - peritonitis - air in the portal system - bowel wall edema - ascites -progressively deteriorating hemodynamic status

More Related