Chapter 64 - preterm infant Flashcards
how are newborns classified by gestational age?
Full term infant - 38 to 42 weeks
post term - > 42 weeks
pre term - < 37 weeks
extremely low gestational age newborn - 23 to 27 weeks
What cardiovascular changes are associated with neonate?
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
What pulmonary changes are associated with neonate?
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
how does the pediatric airway differ from the adult airway?
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
what are the renal, hepatic, and GI changes in neonates?
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
neonates and thermoregulation
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
Hematologic changes in neonate
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)
What is infant respiratory distress syndrome?
- 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
What CNS issues can preterm infants encounter?
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
what is retinopathy of prematurity?
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
how does MAC differ between neonates and adults?
- 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
what drug considerations are there for neonates compared to adults?
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)
what are methods of preventing heat loss in the OR?
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
What are goals of oxygen admin intraopertively?
- 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)
What is post-op apnea and how is it managed?
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
