Pediatric Anesthesia Quiz #2 Flashcards
During fetal circulation, PVR is _____ and SVR is _____.
- PVR is high (the lungs are bypassed)
* SVR is low
What is the Foramen Ovale?
– Foramen ovale (“hole” in the atrial septum = connecting RA with LA) ->because PVR is high, blood shunts from
Right to Left (bypassing the lungs)
What is the Ductus Arteriosus?
– Ductus Arteriosus (connection between PA (Pulm. Artery) and Aorta = blood flows from RA – tricuspid valve
into RV->blood bypasses the lung again to take the short‐cut to the aorta(systemic circulation).
After birth, the neonate takes its first breaths, the lungs inflate and ___ reduces while the placenta is disconnected and blood is “not drained back to
mom” – increasing ___.
- PVR
- SVR
After birth….how do these pressure changes affect fetal circulation?
> With these pressure changes blood flows easier into the lungs and becomes oxygenated.
Also, the increased pressure in the LA (compared with RA) pushes the flap of the foramen ovale shut.
The increased pressure in the aorta allows some “back flow” of blood via the ductus arteriosus back into
the pulm. artery (PA) which causes additional oxygenation of the blood.
Eventually, the pressure changes within the two circulations and the reduced levels of prostaglandins
causes the closure of the ductus arteriosus (DA) and foramen ovale (FO) within days after birth.
What causes the foramen ovale to close in the newborn?
- the closure of the foramen ovale is due to the decrease in PVR and increase in pulmonary flow that accompanies with the infants first breaths and the expansion of the alveoli.
- the decrease in PVR is accompanied by contraction of the ductus arteriosus secondary to oxygenation
- this results in an increase in pulmonary blood flow and an increase in left arterial pressure
- the increased pressure in the LA shuts the flap, located on the left side of the foramen ovale
Identify 4 factors that may cause neonate/infant to return to fetal circulation?
- hypoxemia, acidosis, pneumonia and hypothermia are 4 primary precipitating factors in persistent fetal circulation.
- the pathologic mechanism common to all 4 factors is increased PVR and right-to-left shunting
What is the significance of the Ductus Venous?
-Ductus Venosus: (connection between the
umbilical vein and IVC) ‐ most umbilical venous
blood from the placenta bypasses the liver ->
IVC ->RA
-Blood supplied to heart / upper body has higher
oxygen content (65%) vs. that supplied to
abdominal organs, lower limbs, and placenta
(55%‐60%).
What happens as the infant is transitioning to breathing air?
Decreased PVR and increased SVR (loss of the umbilical circulation) are the two crucial events involved in the immediate transition from the fetal circulation to the
normal postnatal pattern.
The increase in systemic afterload causes an immediate closure of the flap valve mechanism of the foramen ovale and reverses the direction of shunt through the ductus arteriosus.
Blood shunts through what two structures in the neonate with persistent fetal circulation?
Blood shunts through the ductus arteriosus and the former ovale.
During the early neonatal period, reversion to the fetal circulation can occur: If hypoxia occurs, PVR
increases and reopens the ___ ___ which will lead to what?
- ductus arteriosus
- decline in arterial oxygenation which results in
acidosis which further increases PVR -> hypoxemia
If SVR remains higher than PVR -> left‐to‐right shunt (pink baby– transitionally ok!) but if PVR becomes more increased due to hypoxia and acidosis, previous fetal circulation may occur via patent foramen ovale
[PFO] and/ or patent ductus arteriosus [PDA] leading to this type of shunt and to this clinical picture.
- right-to-left shunt
- cyanotic baby
In the newborn, hypoxia causes what 4 things?
- pulmonary vasoconstriction
- systemic vasodilation
- bradycardia
- decreased cardiac output
Rapid intervention is necessary to prevent
this state from proceeding to cardiac arrest.
-> Give Atropine & 100% oxygen
List two ways the physiology of the cardiovascular system of the neonate differs from that of the adult?
- cardiac output is heart-rate dependent
2. left-ventricular compliance is decreased
What PaO2 and SaO2 are appropriate during anesthesia for the premature infant?
SaO2 in the 90-95%(PaO2 = 60-80 mmHg) is believed to be reasonable for the premature infant.
What is the normal heart rate of the term infant(term neonate)?
120 - 180 bpm
What is the estimated blood volume of the preterm neonate?
90 - 100 ml/kg
What is the estimated blood volume of the full-term neonate?
80 - 90 ml/kg
What is the estimated blood volume of an infant(
70 - 80 ml/kg
What is the estimated blood volume of a school-age child(
70 ml/kg
What is the estimated blood volume of a teenager(>12yrs)/Adult?
65 - 70 ml/kg
What is the estimated blood volume of an obese child?
60 - 65 ml/kg
The hypovolemic infant is unable to maintain an ___ ___, hence, accurate early volume replacement is essential.
-adequate CO
-The infant’s systolic arterial BP is closely related to the
circulating blood volume. Blood pressure is an
excellent guide to the adequacy of blood replacement
during anesthesia.
What is a neonates Hgb and Hct?
Hct=60%
Hgb=18-19 g/dl
At birth 50 - 70% of Hgb is _____ which has a higher affinity for oxygen —> picks-up more O2 but does not deliver it to the tissues(this describes what type of shift of the oxyhemoglobin dissociation curve?
- HgbF
- Shift to the left
What are the characteristics of H&H as the infant reaches 2-3 months old, 3 months to a year old?
And how are these characteristics affected if the infant was preterm?
- 2-3 months old-> H&H declines steadily -> Hgb 9-11 g/dl and HgbF is largely replaced by HgbA
- After 3 months to 1 year, HgbA increases to 12-13 g/dl
- In the preterm infant: earlier and greater fall in Hgb(7-8 g/dl)
Despite the reduction of Hgb, the oxygen delivery to the tissues may not be compromised d/t the oxygen-hemoglobin dissociation curve shift to the right(more HgbA)
The oxyhemoglobin dissociation curve of the newborn is shifted to the left or the right?
- Left!
- Fetal Hgb does not bind with 2,3 DPG. Thus the newborn’s oxyhemoglobin dissociation curve will be shifted to the left.
- This gives the fetus the advantage of loading more oxygen at low fetal oxygen partial pressures
What happens to the oxyhemoglobin dissociation curve during the first few months of life? why?
- The oxyhemoglobin dissociation curve shifts to the right.
- As fetal Hgb is replaced by adult Hgb(at 3-4 months of age, infants have increased levels of 2,3 DPG as compared to adults), the infants P50 increases(the curve shifts to the right) to approximate that of the adult, enhancing O2 delivery.
What is the hemoglobin concentration at 2 weeks of age, 2-3 months of age, and 2 years of age?
- At 2 weeks: Hgb is 13-19 g/100 ml of blood
- At 2-3 months: Hbg is less than 10-11 g/100 ml of blood
- At 2 years: Hgb is less than 12.5 g/100 ml of blood
Describe the physiological anemia of the neonate and pediatric patient.
The Hgb concentration progressively “bottoms out” during the 9th to 12th week reaching a minimum of 10-11 g/dl, with a hematocrit of 33%.
compare the physiological anemia in the preterm neonate to the full-term neonate.
In preterm infants, the decrease in Hgb level is greater and earlier, reaching the minimum Hgb concentration of 8 g/dl by 4-8 weeks(Hgb “bottoms out” earlier and lower)>
Below what Hgb concentration is anemia sufficient to jeopardize O2 carrying capacity(and hence cause you to cancel elective surgery) in the neonate and infant older than 3 months?
Less than 13 g/dl in the newborn and less than 10 gel in the pediatric patient older than 3 months
The 3 month old infant, who is scheduled for surgery has a Hgb of 10.5 g/dl. What action should be taken?
None. This Hgb level is normal for the age. At three months of age, Hgb concentration normally decreases to this level.
What are 4 altered pharmacokinetics seen in children that is different than in adults?
- altered protein binding(babies don’t have a lot of muscle mass)
- larger volume of distribution(think “yellyfish”-lots of water)
- smaller proportion of fat and muscle stores
- immature renal and hepatic function
What is the pediatric PO dose of midazolam?
0.5 - 0.7 mg/kg(max 20 mg)
What is the pediatric dose of IV cefazolin?
25 mg/kg
What is the pediatric dose of IV succinylcholine?
1.5 - 2 mg/kg