Peds anesthesia Flashcards
What is considered pre-term?
Prior to 37 weeks gestational age
What is considered the neonate?
1-28 days
What is an infant?
28 days to 1 year
What is a child considered?
greater than 1 year
The most significant transition occurs within:
24-72 hours after birth
What are some of the adaptive changes that occur?
-Establish FRC
-Convert circulation
-Recover from birth asphyxia
-Maintain core temp
During fetal respiration, where does gas exchange occur?
Placenta
O2 transport is accomplished by fetal Hgb which totals:
70-90%
Fetal Hgb shifts the oxyhemoglobin dissociation curve to the:
LEFT
(increased o2 loading in the lungs/placenta, decreased O2 unloading at the tissues)
Hemoglobin in the full term neonate is:
18-20g/dL
What fetal lung changes occur at 4 weeks?
Primitive lung buds develop from the foregut
What fetal lung changes occur at 16 weeks?
Branching of the bronchial tree complete to 28 divisions, no further formation of cartilaginous airways
What fetal lung changes occur at 24 weeks?
primitive alveoli (saccules) and type 2 cells present: SURFACTANT DETECTABLE survival possible with artificial ventilation
What fetal lung changes occur at 28-30 weeks?
capillary network surrounds saccules; unsupported survival possible
What fetal lung changes occur at 36-40 weeks?
True alveoli present- roughly 20 million at birth
What lung changes occur from birth to 3 months?
PaO2 rises as R to L mechanical shunts close
What lung changes occur until 6 years?
Rapid increase in alveoli- 350 million at age 6
How fast can the fetus “guppy breath in utero” at 30 weeks?
30% of the time- breathing at a rate of 60 breaths per min
Does the fetus respond to chemical stimuli?
yes
Normal blood gas value for newborn at term:
pH: 7.2
PO2: 50
PCO2: 48
Normal blood gas value for fetus at term at the end of labor:
pH: 7.25
Po2: 10-20
PCO2: 55
What are the changes with the onset of ventilation?
PVR decreases
Pulmonary blood flow increases
increase in PO2
decrease in Co2
When does rhythmic breathing occur?
With clamping of the umbilical cord and increasing o2 tensions from air breathing
What is the primary event of the respiratory system transition?
Initiation of ventilation
What changes do the alveoli undergo?
alveoli go from fluid-filled to air-filled
How are large surface tension forces overcome?
By the small radius of the curvature of the diaphragm
infants must generate a high negative pressure: -70cm H2O, to inflate the lungs
What is the infants FRC?
approx 25-30mL/kg
Established to act as a buffer against cyclical alterations in the PO2 and PCO2 btwn breaths
What are the neonate and infant lungs prone to?
Collapse:
weak elastic recoil, weak intercostal muscles, intra-thoracic airways collapse during exhalation
What encroaches upon FRC?
High closing volumes
- small airway closure begins at volumes at or above FRC leading to lung collapse and V/Q mismatch
Why don’t infants have lung collapse all the time?
Infants terminate the expiratory phase of breathing before reaching their true FRC which results in intrinsic PEEP and a higher FRC.
What can help maintain FRC/lung inflation in the neonate during anesthesia?
PEEP of 5cm H2O
When does the respiratory system become normal?
3-4 weeks of age (but likely remains immature for some time especially in pre-term babies)
Why can neonates respond to hypercarbia?
Chemoreceptor control is present at birth
How do newborns respond to hypercarbia?
increase ventilation
But the slope of the response curve is decreased
How does hypoxia affect a neonates response to CO2?
Depresses the response to CO2
Response to hypoxia is_______.
Biphasic
Initial hyperpnea–> depression of respiration in about 2 mins
Why is the initial hyperpneic response abolished?
its abolished by HYPOTHERMIA and LOW LEVELS OF ANESTHETIC GAS
What is the most common response to hypoxia in the newborn?
APNEA
especially in pre-term infants
By 3 weeks of age, hypoxia produces:
Sustained HYPERVENTILATION
Respiratory pauses exceeding _____ or those accompanied by bradycardia or cyanosis = apnea
20 seconds
Hypoxia causes profound_____ in babies
BRADYCARDIA
Increased work of breathing =
FATIGUE
very compliant upper airway structures and ribcage which tend to collapse during inspiration
Inefficient diaphragmatic contraction
Only 25% of muscle fibers in the diaphragm are ______ fatigue-resistant work horse fibers vs. adults 55%
Type 1
What are the factors that contribute to apnea in infancy?
-Increase O2 consumption 6mL/kg
-Decreased FRC (non-functional residual capacity)
-Increased closing volume
Once hypoxia ensues, these factors will result in abnormal breathing patterns and apnea much more quickly than in the older child or adult
Where does gas exchange occur in the fetus?
Placenta
in the fetus, how much of the cardiac output do the lungs require?
5-10%
Why do fetal intracardiac and extracardiac shunts exist?
To minimize blood flow to the lungs while maximizing flow/O2 delivery to organ systems
What are the fetal shunts?
-Ductus Venosus
-Foramen Ovale
-Ductus Arteriosus
The fetal circulation is _____
PARALLEL
Deoxygenated blood travels the ______ _____ to the ____ _____ to the ______ (very low resistance to flow)
deoxygenated blood travels the descending aorta—> umbilical arteries –> placenta
Oxygenated blood returns via the _____ ______ (PO2 35 mmHg)
Umbilical vein
The _____ _____ diverts approx 50% of blood away from the liver into the IVC then to the RA
Ductus venosus
What connects the right and left atrium?
Foramen ovale
Preferential streaming causes O2 rich blood to be directed across the foramen ovale which connects the right and left atrium
O2 right blood fed to the _____ and ejected into the _____ thereby feeding the coronary and cerebral circulations
O2 rich blood fed to the LV and ejected into the aorta, thereby feeding the coronary and cerebral circulations
SVC and hepatic venous flow is delivered to the:
RV
In the fetal circulation PVR is:
HIGH
In fetal circulation, RV output is delivered across the _____ ____ which connects the PA to the descending aorta
RV output is delivered across the ductus arteriosus which connects the PA to the descending aorta
Blood entering the descending aorta returns to the _____ and feeds the lower body (PO2 22mmHg)
Blood entering the descending the aorta returns to the placenta and feeds the lower body (PO2 22mmHg)
What causes the reversal of shunts?
Umbilical cord cut:
increased SVR
onset of breathing (decreased PVR)
fetal circulation changes from parallel to _____ in transitional circulation
Fetal circulation changes from parallel to SERIES in transitional circulation
Initiation of ventilation increases arterial and alveolar PO2 which dilates pulmonary vasculature which has what effect?
PVR decreases
Pulmonary blood flow increases (450%)
____ pressure increases, ______ pressure decreases
LA pressure increases, RA pressure decreases
What percent of adults have a patent foramen ovale?
25-30%
Why does the ductus arteriosus constrict within several minutes?
D/t increases PO2, and decreased circulation prostaglandins (PGI2, PGE1)
When does the physiologic closure of the ductus arteriosus occur?
10-15hrs
When does anatomic closure of the ductus arteriosus closer?
2-3 weeks