Chapter 64 - preterm infant Flashcards

1
Q

how are newborns classified by gestational age?

A

Full term infant - 38 to 42 weeks

post term - > 42 weeks

pre term - < 37 weeks

extremely low gestational age newborn - 23 to 27 weeks

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2
Q

What cardiovascular changes are associated with neonate?

A

Cardiac

  • myocardium is stiff and poorly compliant
  • SV is fixed
    • (poorly developed contractile cells unable to stretch with inc volume)
  • CO dependent on HR only (since SV is fixed)
  • poorly developed sympathetic system
    • stress associated with vagotonic reflexes
    • bradycardia when stress encountered
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3
Q

What pulmonary changes are associated with neonate?

A

1) increase work of breathing

  • decrease lung compliance + increased chest wall compliance = unable to maintain open alveoli
  • high closing volume –> small airways close during normal TV

2) Increase MV
* due to increase RR
3) Increase O2 consumption
* rapid oxygen desaturation during apnea or airway obstruction
4) decrease type 1 muscle fiber in diaphragm and intercostal muscles
* early respiratory fatigue with increased work of breathing

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4
Q

how does the pediatric airway differ from the adult airway?

A

1) Large occiput

  • neck flexion leads to airway obstruction
  • require roll under shoulder for intubation

2) relatively large tongue

  • difficult mask ventilation
  • may require oral airway

3) cephalad larynx

  • difficult visualization of cords, consider straight blade
  • C4 position (adult is C5)

4) floppy epiglottis (omega shaped, broad)
* obstruct view of vocal cords, may need straight blade
5) vocal cords are slanted

  • anterior attachment of VC more caudad than posterior attachment
  • tracheal tube hung up at anterior commisure

6) cricoid cartilage narrowest portion of airway

  • perform leak test of tracheal tube
  • postextubation stridor
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5
Q

what are the renal, hepatic, and GI changes in neonates?

A

Renal

  • decrease GFR
    • decrease ability to excrete saline or water loads
    • decrease excretion of meds

Hepatic

  • decrease glycogen stores
    • periop glucose mainteance
  • immature hepatocyte enzymes and lower hepatic blood flow
    • decreased drug metabolism

GI

  • decrease lower esophageal sphincter tone
    • GERD
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6
Q

neonates and thermoregulation

A

thermoregulation

  • high surface to weight ratio
    • at risk for heat and water loss
  • unable to generate heat by peripheral vasoconstriction and shivering (like adults do)
  • nonshivering thermogensis
    • heat generated by metabolism of brown fat
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7
Q

Hematologic changes in neonate

A

1) fetal hemoglobin HbF

  • P50 is 19 mmHg (left shift)
  • high O2 affinity –> unloads less to tissue

2) physiologic anemia of newborn

  • occurs 9-12 weeks in full-term infants
  • hemoglobin nadir of 9-11 g/dL
  • HbF transitioned to HbA (adult)
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8
Q

What is infant respiratory distress syndrome?

A
  • occurs in preterm infants 2/2 to immature surfactant production
    • surfactant = needed to prevent closure of alveoli due to increase surface tension
  • s/sx
    • tachypneia, increase work of breathing, grunting, cyanosis, hypercarbic
  • Tx:
    • intubate, mechanical vent
    • exogenous surfactant admin
  • Complication
    • bronchopulmonary dysplasia - continuous O2 support and mech vent can lead to inflammation and scarring of lungs + interstital fibrosis
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9
Q

What CNS issues can preterm infants encounter?

A

Intraventricular hemorrhage

  • unable to autoregulate appropriately
  • changes in perfusion pressure not compensated –> hypoxic ischemia, cell death, necrosis and breakdown of blood vessel walls

Complication

  • death
  • hemorrohage blocking flow of CSF –> hydrocephalus –> long-term neurologic insult
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10
Q

what is retinopathy of prematurity?

A

ROP

  • disorganized growth of retinal blood vessels –> retinal detachment and blindness
  • multifactorial
    • supplemental oxygen is strongly associated with ROP

Prevention

  • avoid/limit supplemental oxygen to pre-term or full-term neonates < 44 weeks postconceptual age unless absolutelety necessary
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11
Q

how does MAC differ between neonates and adults?

A
  • MAC is lower for pre-term than full term infants
  • MAC value increases and peaks at 3-6 months of life, then decreases
    • not true sevo where peak is 0-30 days, and then decreases

Volatile Anes induction and excretion

  • fast induction - increase alveolar ventilation and increase CO
  • fast elimination - minimal fat reservoir along with increase CO and increase ventilation
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12
Q

what drug considerations are there for neonates compared to adults?

A

neonates

1) higher total body water content

  • large volume of distribution
  • water soluble meds (sux) require larger initial dose per kg

2) less fat and muscle content
* drugs that depend on redistribution for termination of effect (propofol) will have prolonged clinical effects
3) immature liver and kidneys
* slow drug metabolism, prolonged effects (roc)

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13
Q

what are methods of preventing heat loss in the OR?

A

Causes of heat loss:

  • neonates - thin skin, limited fat, inability to shiver or vasoconstrict
  • anesthesia
    • redistribution and loss of central heat to peripherary
    • inhibit nonshivering thermogenesis
  • conduction, convection, evaporative, radiation heat loss

1) conductive heat loss

  • forced air warming blanket
  • increase OR temp

2) convection heat loss

  • force air warming blanket
  • cover exposed areas of pt
  • transport in heated incubator

3) evaporative heat loss
* humidified air/gas
4) radiation
* radiant heat lamp

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14
Q

What are goals of oxygen admin intraopertively?

A
  • hyperoxia leads to oxygen free radicals
  • neonates have immature antioxidant enzme system to breakdown free radicals
  • O2 free radical damage –> ROP, BPD

Goal:

  • limit o2 supplementation (intubation/extubation)
  • use o2/air combination
  • maintain Spo2 < 95% ( >95% in preterm neonate is associated with ROP and BPD)
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15
Q

What is post-op apnea and how is it managed?

A

Post-op Apnea

pathophys

  • physical airway obstruction and/or central apnea

Risk factors

  • HgB < 10 g/dL
  • history of apnea
  • premature infants

Management

1) pre-term vs full term

  • preterm - delay elective surgery till > 60 weeks PCA
  • full term - delay elective surgery till > 44 weeks PCA

2) emergent surgery
* admit patients for continuous monitoring for at least 12 hours of apnea-free monitoring prior to sending home

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16
Q

Does regional anesthetisa elminiate the need for post-op apnea monitoring and therefore a quicker discharge home?

A

NO

  • although there is a decrease in apnea episodes using regional anes, it is not eliminated
  • patients should still be monitored for apnea for at least 12 hours
17
Q

what benefits can spinal anesthsia provide for a preterm infant who has BPD?

A
  • spinal anes will avoid need for tracheal intubation and mech vent –> can cause barotrauma, inflammation of lungs (benficial for already pre-existing lung damage)
  • avoids need for supplemental O2 (induction and emergence)
  • avoids need for CNS deppresants (sedation, inhaled anes)

Of note, spinal anes in neonates:

  • require higher dose per kg due to increase CSF volume
  • duration of anes is less than adult