Millers_Anesthesia_Pediatric_Chapter_76-77

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• Author: readwise.io
• Full Title: Millers_Anesthesia_Pediatric_Chapter_76-77
• Category: #articles
• Document Tags: ../../../Knowledge/Medicine/Paediatrics
• URL: https://readwise.io/reader/document_raw_content/38147938

Highlights

• Prenatal development is usually divided into
  three stages: (1) the germinal, (2) the embryonic, and
  (3) the fetal stage. (View Highlight)
• The germinal stage starts with con-
  ception and ends approximately 2 weeks later with the
  implantation of the embryo into the uterine wall. (View Highlight)
• The embryonic stage comprises the period
  between the third and eighth weeks of pregnancy and
  is characterized by intense cell proliferation, migration,
  and differentiation leading to the establishment of all
  major organs. Increased vulnerability to a wide variety
  of substrates, commonly called teratogens, during this
  period can induce major developmental defects, many
  of them incompatible with life (View Highlight)
• The fetal stage lasts
  from the ninth week of pregnancy to birth and is char-
  acterized by the growth and functional differentiation
  of organs formed during the embryonic period. Numer-
  ous exogenous factors, such as environmental toxins,
  ionizing radiation, and maternal infections as well as
  a multitude of drugs can interfere with the physiologi-
  cal patterns of organ development throughout the fetal
  period which, in turn, will result in organ dysfunction of
  variable severity (View Highlight)
• pregnancy is considered to reach full term between
  the completion of the 37th and the 42nd weeks of gestation (View Highlight)
• Apgar scores between 7 and 10 are considered reassuring,
  a score of 4 to 6 as moderately abnormal, while scores 3
  and below are usually indicative of poor outcome (View Highlight)
• fetuses reach an age of viability that may be considered,
  under tight medical support, as compatible with extrauter-
  ine life between the 22nd and 26th weeks after conception (View Highlight)
• Prematurity is stratified into mild preterm (32-37 weeks),
  very preterm (28-31 weeks) and extremely preterm (<28
  weeks) periods with increasing neonatal morbidity and
  mortality based on degree of prematurity (View Highlight)
• Infants
  weighing less than these norms can be classified as low
  birth weight (<2500 g), very low birth weight (<1500
  g), and extremely low birth weight (<1000 g) (View Highlight)
• During this critical period, the infant can readily revert
  from the adult type of circulation to a fetal type of circula-
  tion; this state is called transitional circulation (View Highlight)
• In neonates and infants, cardiac calcium stores
  are reduced because of the immaturity of the sarcoplasmic
  reticulum; consequently, these populations have a greater
  dependence on exogenous (blood-ionized) calcium and
  probably increased susceptibility to myocardial depression
  by volatile anesthetics that have calcium channel–block-
  ing activity. (View Highlight)
• The lung bud septates from the foregut during
  the first trimester and the gas exchanging portions of the
  airway are formed during the second trimester (View Highlight)
• In most cases, simple hyperventilation with resul-
  tant reduction in arterial partial pressure of carbon dioxide
  (PaCO2) will cause the pulmonary artery pressure to return
  to normal. (View Highlight)
• Alveo-
  lar ductal development starts at gestation week 24 while
  the septation of the air sacs begins around gestational
  week 36 (View Highlight)
• Alveoli then increase in number and size until
  a child is approximately 8 years old. Further growth is
  manifested as an increase in size of the alveoli and air-
  ways. (View Highlight)
• Risk factors increasing the likelihood of prolonged tran-
  sitional circulation include prematurity, infection, acidosis,
  pulmonary disease resulting in hypercapnia or hypoxemia
  (aspiration of meconium), hypothermia, and congenital
  heart disease. (View Highlight)
• The myocardial structure of the heart, particularly the
  volume of cellular mass devoted to contractility, is signifi-
  cantly less developed in neonates than in adults (View Highlight)
• Respiration is less efficient in infants than adults. The
  airway of infants is highly compliant and poorly sup-
  ported by the surrounding structures. The chest wall is
  also highly compliant; therefore the ribs provide little sup-
  port for the lungs; that is, negative intrathoracic pressure
  is poorly maintained (View Highlight)
• The small diameter of the airways
  increases resistance to airflow. Thus functional airway
  closure accompanies each breath. (View Highlight)
• Dead space ventila-
  tion is proportionally similar to that in adults; however,
  oxygen consumption is two to three times higher (View Highlight)
• developmental changes in contractile
  proteins, produce a leftward displacement of the cardiac
  function curve and less compliant ventricles. As a result
  of these differences, cardiac output is strongly dependent
  on heart rate; bradycardia is poorly tolerated because the
  infant cannot easily compensate for the decreased heart
  rate by increasing stroke volume to maintain normal car-
  diac output. (View Highlight)
• In pre-
  term infants, the work of breathing is approximately three
  times that of adults. This increased work of breathing can
  increase significantly by cold stress (i.e., increased meta-
  bolic demand for oxygen) or any degree of airway obstruc-
  tion. (View Highlight)
• The most frequently encountered arrhythmia in
  pediatric populations is hypoxia-induced bradycardia
  that can lead to asystole, if not appropriately handled.
  Ventricular fibrillation is extremely rare in infants and
  children. (View Highlight)
• Another important factor is the composition of the
  diaphragmatic and intercostal muscles. These muscles do
  not achieve the adult configuration of type I muscle fibers
  until the child is approximately 2 years old (View Highlight)
• Differences in airway anatomy explain the more likely
  potential for technical airway difficulties in infants than
  in teenagers or adults (View Highlight)
• Although neonates and infants are considered as obli-
  gate nasal breathers, they can also utilize the oral airway to
  maintain ventilation both spontaneously and in response to
  complete nasal obstruction.11 Even in preterm infants, the
  prevalence of spontaneous oral breathing has been reported
  to be as high as 50% during sleep, and oral breathing could
  be consistently initiated in this population upon nasal
  obstruction (View Highlight)
• Typically, the airway of infants dif-
  fers from adults in five ways7,8: (1) The relatively large
  size of the infant’s tongue, in relation to the oropharynx,
  suggests that the infant is more likely to sustain airway
  obstruction and technical difficulties during induction of
  anesthesia and laryngoscopy. Recently, however, mag-
  netic resonance imaging (MRI) studies have called this
  into question by showing that soft tissues surrounding the
  upper airway grow proportionally to the skeletal structures
  during childhood.9 (2) Other anatomic differences may
  account for some of the airway management challenges
  in children. The larynx is located higher (more cephalic)
  in the neck, thus making straight blades more useful than
  curved blades. (3) The epiglottis is shaped differently, being
  short, stubby, omega shaped, and angled over the laryngeal
  inlet. Control with the laryngoscope blade is therefore more
  difficult. (4) The vocal cords are angled; consequently, a
  blindly passed tracheal tube may easily lodge in the anterior
  commissure rather than slide into the trachea. (5) Finally,
  the infant larynx is funnel shaped, the narrowest portion
  occurring at the cricoid cartilage (View Highlight)
• While clas-
  sic teaching is that the adult larynx is cylindrical and the
  infant larynx is funnel shaped, it is now recognized that the
  narrowest portion of the airway in approximately 70% of
  adults is also in the same subglottic region at the level of the
  cricoid cartilage as it is in children. (View Highlight)
• The composition of the diaphragm and intercostal muscles
  significantly changes during the first 2 years of life. The number of type
  I muscle fibers is inversely related to age and may account, in part,
  for the ease of inducing respiratory fatigue as the work of breathing
  increases (View Highlight)
• The narrowest part of the adult larynx and the pediatric lar-
  ynx is at the level of the cricoid cartilage. Traditionally, the adult larynx
  was thought to be cylindrically shaped, but autopsy data suggest that
  the narrowing in adults (A) is not as pronounced as it is in infants (B).
  The narrowest part of the infant larynx occurs at the level of the cricoid
  cartilage; the normal adult configuration of the larynx is not achieved
  until the teenage years. This anatomic difference is one of the reasons
  uncuffed tracheal tubes have been traditionally preferred for children
  younger than 6 years of age (View Highlight)
• In general, since the epiglottis is more “U” shaped in
  young children and it may lie across the glottic opening,
  straight blades are routinely used in neonates and toddlers
  to directly elevate the epiglottis and visualize the vocal
  cords (View Highlight)
• mandibular protrusion, Mal-
  lampati’s classification, movement of atlantooccipital joint,
  reduced mandibular space, and increased tongue thickness
  have all been shown to be good predictors of airway prob-
  lems. (View Highlight)
• Historically, uncuffed endotracheal tubes were recom-
  mended in children less than 8 years of age, because it was
  thought that the narrowest part of the airway was the cri-
  coid ring and to minimize potential cuff-induced damage
  of the tracheal mucosa as well as to allow reduction of air
  flow resistance by inserting a larger size tube.192 Airway
  trauma can also occur when using an uncuffed tube with
  acceptable leak pressures. Moreover, a higher incidence
  of laryngospasm with the use of uncuffed tubes has also
  been reported, and there is no data of increased subglot-
  tic airway trauma when cuffed versus uncuffed tubes are
  used (View Highlight)
• Anesthetized
  children are particularly prone to upper airway collapse; it
  can be easily relieved by a combination of moderate head
  tilt, chin lift, jaw thrust, and the application of continuous
  positive airway pressure (View Highlight)
• A cuffed tube with no leak may also allow a more
  accurate estimate of end tidal carbon dioxide (CO2) con-
  centrations and avoid pollution of the operating room (View Highlight)
• the relatively frequent need for changing the
  endotracheal tubes due to significant leak associated with
  insertion of an uncuffed tube is also virtually eliminated by
  using cuffed tubes. Repeat laryngoscopy is avoided since
  inflating the cuff may allow insertion of a smaller tube and
  using the cuff to occlude the airway without the need for
  replacing the tube with a larger tube. (View Highlight)

New highlights added August 13, 2023 at 5:15 PM

• Routine requests for preoperative electrocardiograms (ECG) are not recommended for healthy children. There is, nevertheless, an ongoing controversy about the need for routine neonatal screening for long QT syndrome (LQTS) (View Highlight)
• Premedication with an
  aerosol of salbutamol has been shown to be effective in both
  the prevention and treatment of perioperative broncho-
  spasm in children with bronchial hyperreactivity (View Highlight)
• Since both perioperative stress and a number of anesthetics can lengthen QT interval, performing ECG in neonates and infants under 6 months of age may be an option. (View Highlight)
• Bronchial hyperreac-
  tivity, resulting primarily from the impact of the viral infec-
  tion on the autonomic nervous system, may persist for up to
  6 weeks or longer, well beyond the disappearance of clini-
  cal symptoms (View Highlight)
• Infants up to 9 months of age are less prone to separation anxiety, and will most probably accept parental surrogates (including soothing voices, gentle rocking, and being held) (View Highlight)
• Separation anxiety is the greatest problem in children between 1 and 3 years of age. (View Highlight)
• Most
  national guidelines recommend the “6-4-2 rule” meaning
  a minimum of 6-hour-long fasting for solid foods, 4-hour-
  long fasting for breast milk, and a 2-hour-long fasting for
  clear fluids. (View Highlight)
• the incidence of preoperative hypoglycemia is less than
  2.5% and is usually associated with fasting periods well
  exceeding currently recommended fasting guidelines (View Highlight)
• the use of 5% dextrose-containing fluid
  during surgery in pediatric patients has led to hypergly-
  cemia which, in turn, can also lead to increased morbid-
  ity and mortality (View Highlight)
• Neonates and infants
  also need dextrose supplementation during anesthesia sur-
  gery albeit at a lower rate than their normal maintenance
  requirements.228,229 The use of 1% to 2.5% dextrose-con-
  taining isotonic solutions for intraoperative maintenance
  in neonates and infants appears to be the best option while
  serial blood glucose measurements are needed to maintain
  blood glucose levels in the optimal range (View Highlight)
• Prevention of paradoxical air emboli is critical for the
  pediatric patient. A volume of air that is clinically unim-
  portant in an adult may prove catastrophic in an infant (View Highlight)
• Monitoring expired concentrations of carbon dioxide
  can be less accurate in small infants, but is still extremely
  useful for diagnosing changes over time and for issues (View Highlight)
• Propofol and inhaled anesthetics can result in profound
  cardiovascular depression in the neonate. In contrast,
  the synthetic opioids (e.g., fentanyl, sufentanil, alfentanil,
  remifentanil) are usually well tolerated, even in critically
  ill infants (View Highlight)
• During stable situations it is reasonable to aim for
  an oxygen saturation between 93% and 95% in preterm
  infants. However, because these infants have the highest
  oxygen consumption, oxygen saturation in the 93% to 95%
  range can change to severe hypoxemia within seconds. (View Highlight)
• When used, these potent opioids must be care-
  fully titrated to a defined response. Anesthesiologists must
  be particularly cautious about opioid-induced bradycardia
  and its consequences on cardiac output (View Highlight)
• The neonatal lung is fragile and particularly prone to
  injury from excessive tidal volumes. In contrast, careful
  attention to ventilation is required to maintain functional
  residual capacity and avoid atelectasis (View Highlight)
• Positive end expi-
  ratory pressures should be used. Even brief disconnection
  of the airway circuit or mechanical ventilator can lead to
  significant alveolar collapse and should thus be avoided if
  possible (View Highlight)
• The optimal blood pressure during neonatal anesthesia is
  unknown. Traditionally an acceptable mean arterial pres-
  sure in mm Hg was judged to be roughly the same as the
  postmenstrual age of the child in weeks; however there is
  little if any evidence to support this. (View Highlight)
• The major anesthesia concern around infant inguinal
  hernia repair is the risk of postoperative apnea. The major-
  ity of infants who develop postanesthesia apnea are former
  preterm infants (gestational age <37 weeks) and younger
  than 44 weeks postmenstrual age (PMA) (View Highlight)