Pediatric & Neonatal anesthesia pathophysiology Part 1 Flashcards
Prematurity is considered to be
birth before 37 weeks gestation
Low-birth weight is
<2500 g
Very low birth weight is
<1500 g
Extremely low birth weight is
<1000g
Deaths from prematurity could be prevented from
warmth
breastfeeding
basic care for infections
safe O2 use for breathing difficulties
The major differences that exist between the pediatric and adult airway include:
tongue position of the larynx epiglottis vocal cords subglottis
The older child will have airway features that represent
a transition between neonate and adult
Describe how the infants tongue differs from that of an adult.
infant’s tongue is relatively large in proportion to the rest of the oral cavity
contributes to easy obstruction of the infant’s airway
oral airway helps to relieve the obstruction
Describe the nasal passages of the pediatric airway.
relatively narrow
Describe the tonsils and adenoids in the infant airway
pronounced salivary secretions
large tonsils and adenoids
Describe the larynx in the infant.
the position of the larynx is higher (more cephalad) for neonates to 2 years of age
larynx seems more anterior
infant’s C3-C4 (adult is C4-C5)
a straight laryngoscope blade more effectively lifts the tongue from the field of view
Describe the difference in the epiglottis of the infant.
adult’s epiglottis is flat & broad with an axis parallel to the trachea
infant’s epiglottis is narrower, omega shaped and angled away for the axis of the trachea
often obstructs the view of the vocal cords and is more difficult to lift
Describe the difference in the vocal cords of the infant.
infant’s vocal cords have a lower (caudad) attachment anteriorly than posteriorly, whereas in the adult the axis of the vocal cords is perpendicular to the trachea
can lead to difficult intubation with the tip of the ETT help up at the anterior portion of the folds
Describe the trachea in infants.
Shorter than adults (infant 4-5 cm- adult 10-12 cm)
insertion is 3x size of tube
Describe the sublgottic in infants.
traditionally thought it was the narrowest portion of a child’s larynx and that it is funnel shaped BUT recent studies say that it is oblong shaped (football shaped) and may be more narrow and cylindrical in the AP dimension but wider in the transverse
Small airways are predisposed to
obstruction & difficulty with ventilation
Resistance to airflow is
inversely proportional to the 4th power of the radius (Pousielle’s Law)
Partial occlusion of the ETT due to kinking or secretions greatly
increases the work of breathing of the premature infant
A tight-fitting ETT that compresses tracheal mucosa may
cause edema= reduced luminal diameter (and to a greater degree in children)
Diseases that narrow the pediatric airway include.
subglottic stenosis
tracheal stenosis
tracheobronchomalacia
Describe subglottic stenosis.
90% of acquired subglottic stenosis are the result of ETT and prolonged intubation
often requires placement of a smaller ETT
Describe tracheal stenosis.
often occurs at carina and creates added resistance distal to the ETT
Describe tracheobronchomalacia.
the intrathoracic airway collapses during exhalation
PEEP & CPAP are helpful to stent open the airway
Production surfactant begins between
23 to 24 weeks gestation ****
-concentration of surfactant is often inadequate until 36 weeks post conception
The structure and function of immature lungs predisposes the infant to
alveolar collapse & hypoxia
-these factors lead to reduced lung volumes and lung compliance, increased intrapulmonary shunting, and V/Q mismatch
Prenatally, alveoli are thick-walled,
fluid-filled saccular spaces that are surfactant deficient and require greater pressures to initially expand
There are low numbers of ______ in the intercostal & diaphragmatic muscles in infants.
type 1 muscle fibers**
marathon muscles, slow twitch muscles, used for prolonged activity
-do not develop adequate type 1 fibers until >6-8 months (adult 55%)
The chest wall is more
horizontal & pliable***** in pediatrics
minimal vertical movement= decreased room for lung expansion & diaphragmatic ventilation
Decreased type 1 muscle fibers and differential chest wall shape results in
early fatigue & propensity for apnea
_______ respirations begin in utero
episodic
The passage of the fetus through birth canal forces
much of the fluid from the lungs through the nose and mouth
- during birth approx. 90 mLs of fluid is forced via the “vaginal squeeze”
- delivery- compression is relieved and air is sucked into lungs
- infants delivered by C-section may have more residual fluid in the lungs
The respiratory rate is _____ in infants and small children
increased
Oxygen consumption is
2-3x’s higher in babies
also have immature hypoxic and hypercapnic drives
**Vt/kg is
constant throughout development
Infants have ______ FRC & closing capacity compared to adults.
decreased FRC & increased CC
Premature infants possess a ___________ response to hypoxia
biphasic ventilatory response
initially ventilation increases in response to hypoxia, but after several minutes ventilation decreases and bradycardia* & apnea* may occur
- the ventilatory response to hypothermia* and carbon dioxide* is also decreased
The combination of anesthetic effects, an immature respiratory control system and immature intercostal and diaphragmatic muscles increases the risk of
hypoxia, hypercapnia, and apnea in the postoperative period
Respiratory distress syndrome is a
breathing disorder that affects newborns; common in premature infants born >6 weeks early
Respiratory distress syndrome develops secondary to a
lack of surfactant production and results in airway collapse with hypoxia
Treatment of RDS may lead to
bronchopulmonary dysplasia
Anesthetic concerns with respiratory distress syndrome include:
anemia
history of apnea, residual chronic respiratory disease, impaired gas exchange
history of prolonged ventilation, residual subglottic stenosis
Bronchopulmonary dysplasia is a form of
chronic lung disease that occurs in patients who have survived severe neonatal lung disease (kind of like emphysema in adults)
The cause of bronchopulmonary dysplasia is uncertain, but may be related to
increased end-inspiratory lung volumes and frequent collapse and reopening of alveoli
- oxygen toxicity, barotrauma of positive-pressure ventilation, inflammation, and ETT intubation on immature lungs have also been suggested as causative factors
Infants with bronchopulmonary disease may require supplemental oxygen and may develop
lower airway obstruction and air trapping, CO2 retention, atelectasis, bronchiolitis, and bronchopneumonia
The ventilation strategies for patients with bronchopulmonary dysplasia includes
using small tidal volumes (4-6 mL/kg), greater respiratory rates, PEEP, and minimize inspired oxygen concentration
Apnea in the premature infant is inversely related to
preconceptual age**
- the sum of the conceptional age and the postnatal age
Apneic episodes in the premature infant include both
failure to breath (central apnea) and failure to maintain a patent airway (obstructive apnea)
Apnea may also be accompanied by
bradycardia & desaturations
Additional risk factors for apnea in the premature infant include
low birth weight, anemia, hypothermia, sepsis, neurological abnormalities, and type of surgical procedure
Describe the risk of apnea for neonates <2500 grams and less than 1000 grams
<2500 grams= 25% risk for apnea
<1000 grams= 85% risk for apnea
reduction of 50% occurs after 44 weeks PCA
_______ occurs commonly after anesthesia and surgery in preterm infants
apnea
can continue to occur up to 48 hours postoperatively
True or false: apnea can still occur with regional anesthesia
TRUE
Describe management of the preterm infant with apnea
plan for in-house admission for all premature infants <60 weeks postconceptual age with continuous apnea and bradycardia monitoring for 24-48 hours deferment of elective surgery until >44-50 weeks PCA IV caffeine (5-10 mg/kg) Nasal CPAP or tracheal intubation with ventilation
The premature infant is at a greater risk of _________ during anesthesia and surgery
cardiovascular collapse
Cardiovascular collapse is more common in anesthesia & surgery in the neonate because of
fetal heart has more connective tissue, less organized contractile elements & has an increased dependence on extracellular calcium
- less compliant tissue and less sensitive to catecholamines
- small circulating blood volumes- relatively small surgical blood loss can cause result in hypovolemia & hypoperfusion
- autoregulation is not well-developed and heart rate may not increase with hypovolemia resulting in decreased blood flow and oxygen delivery to brain and organs with relatively little blood loss
Describe the neonatal myocardium
general immaturity & decreased number of myofibrils- reduced contractility (inotropy) & reduced relaxation (lusitropy)
- afterload increases are poorly tolerated
- preload reductions are poorly tolerated
- reliant on serum level of ionized calcium
- decreased response to volume loads
- right & left ventricles are equal
- PSNS is well developed (more so than SNS)
Failure of the ductus arteriosus to close in the micropremie further increases the risk of
cardiovascular collapse during major surgery
-as high as 20-30% of infant born before 34 weeks
A PDA promotes
pulmonary hypertension
congestive heart failure
Changes in __________ alter the direction of flow through the PDA
systemic or pulmonary vascular resistance
Right to left shunting through the PDA occurs with
increased PVR and results in hypoxia, hypercarbia, and acidosis
Left to right shunting through PDA occurs with
hypotension and pulmonary volume overload (all blood is not going forward, it is coming backwards
The fetal heart contains
the ductus venosus, ductus arteriosus, and foramen ovale
_______ originates from the fetal internal iliac arteries and delivers fetal blood to placenta where it is oxygenated
two umbilical arteries**
One umbilical vein carries
oxygenated blood from the placenta to the fetus
The majority of the umbilical vein blood bypasses the liver via the _________ and empties into the _________ where it mixes with less oxygenated blood from the lower half of the body.
ductus venosus****
inferior vena cava****
IVC blood enters the right atrium and is directed by the Eustachian valve across the
foramen ovale & into the left atrium
the left ventricle pumps this blood to the upper body through the great vessels of the aortic arch
Deoxygenated superior vena cava blood enters the
right atrium and primarily crosses the tricuspid valve into the right ventricle
-only a small amount of SVC blood enters the left atrium via the PFO
High pulmonary vascular resistance forces the right ventricular output to enter th
systemic circulation via the ductus arteriosus*******
The _______ originates from the pulmonary artery and inserts into the aorta at a point just distal to the origin of the left subclavian artery
ductus arteriosus
