Pediatric & Neonatal anesthesia pathophysiology Part 2

Question 1

Fetal circulation is characterized by

Answer 1

high PVR secondary to fluid filled lungs

- low systemic vascular resistance secondary to the large surface area of the low resistance utero-placental bed

Question 2

The most oxygenated blood from the umbilical vein perfuses the

Answer 2

brain and heart by shunting across the liver via the ductus venosus and shunting across the right heart via the foramen ovale***

Question 3

The umbilical vein PaO2 is

Answer 3

30-35 mmHg

-oxygen transport exists in relatively hypoxic environment

Question 4

Fetal hemoglobin maintains the oxygen content of blood (CaO2) via two mechanism:

Answer 4

hgb F is left shifted and is more saturated than adult Hgb
hemoglobin levels in utero are elevated which also raises the CaO2
- the effect of left shifted hgb F** and polycythemia produce an oxygen carrying capacity in the fetus that nearly equal to adults

Question 5

Transition from fetal to adult circulation occurs with

Answer 5

clamping of the umbilical cord and inflation of the lungs

-cord clamping removes the low resistance placenta and raises SVR

Question 6

Lung inflation and increased PaO2 dramatically lowers

Answer 6

the PVR
- when the lungs expand and fill with gas pulmonary vascular resistance (PVR) decreases***** as a result of mechanical effects on the vessels and relaxation of vasomotor tone

Question 7

As PVR decreases, blood flow increases to the lungs, then blood flows into the left atrium increases via the pulmonary veins,

Answer 7

increasing LA pressure over RA pressure closes the atrial septum over the foramen ovale***

Question 8

Placenta clamp ceases flow from this large, low-resistance vascular bed. This results in an

Answer 8

increase in SVR and a decrease in inferior vena cava blood flow and right atrium pressure

Question 9

This increase in SVR and aortic pressure above the pulmonary artery pressure results in

Answer 9

reverse flow through the ductus arteriosus*****

Question 10

The increase in oxygen concentration leads to a __________ causing closure of the ductus arteriosus

Answer 10

decrease in prostaglandins**

Question 11

_______ closes the flap of tissue covering the patent foramen ovale

Answer 11

when left atrial pressure rises above right atrial pressure

Question 12

Describe functional and anatomic closure of the foramen ovale.

Answer 12

functional- closure occurs quickly
anatomic- closure usually requires weeks
A PFO that is probe patent persists in 20-25% of adults

Question 13

The ductus arteriosus remains patent in utero due to

Answer 13

hypoxia, mild acidosis, and placental prostaglandins

• removal of these factors after delivery causes functional closure
• the reverse flow pressure and increase in local PaO2 (>50-60 mmHg) causes the muscular wall of the ductus arteriosus to constrict

Question 14

Permanent anatomic closure of the ductus arteriosus, is usually complete in

Answer 14

5-7 days*** but may persist until 3 weeks

delayed closure is common in premature infants (esp. <34 weeks)

Question 15

A PDA often occurs in premature infants with

Answer 15

lung disease
- during the period before anatomic closure certain physiologic stressors (hypothermia, hypercarbia, acidosis, hypoxia, sepsis, raised PVR) can cause the newborn to revert to fetal circulation

Question 16

Changes in systemic or pulmonary vascular resistance alter the direction of blood flow in patent ductus arteriosus, lead to

Answer 16

increase in PVR –> right to left shunting (bad)

can lead to congestive heart failure and low diastolic pressure

Question 17

pulmonary edema from increased blood flow promotes (in patent ductus arteriosus)

Answer 17

pulmonary hypertension

-worsened with hypoxia, hypercarbia, acidosis, and hypothermia

Question 18

Describe Pre ad post-ductal saturation monitoring:

Answer 18

preductal- pulse ox on the right hand
postductal- pulse ox on the lower limb
cerebral oximetry

Question 19

Myelination of nerve fibers and cerebral cortex is

Answer 19

less incomplete and developed in premature infants

Question 20

The blood brain barrier in the premature infant is

Answer 20

immature, rendering the developing brain more vulnerable to drugs or toxins

Question 21

Neural pathways allowing for pain perception develop during

Answer 21

the first, second, and third trimesters

Question 22

Developing cerebral vessels appear to be

Answer 22

more fragile than in the adult

cerebral auto-regulation is impaired in sick neonates and therefore blood flow is pressure dependent

Question 23

Preterm infants have very fragile cerebral vessels- rupture leads to

Answer 23

intra-cerebral hemorrhage & intraventricular hemorrhage (IVH)***

Question 24

Predisposing factors for IVH include:

Answer 24

hypoxia, hypercarbia, hypernatremia, fluctuations in pressure, low HCT, over transfusion, rapid administration of hypertonic fluids (i.e. NaBicarb or dextrose)

Question 25

Intraventricular hemorrhage results in

Answer 25

spontaneous bleeding into and around the lateral ventricles of the brain

Question 26

Intraventricular hemorrhage may result from

Answer 26

RDS, hypoxia, acute BP alterations, trauma, acidosis, distress

Question 27

Symptoms of intraventricular hemorrhage include

Answer 27

hypotonia, apnea, seizures, loss of sucking reflex, bulging anterior fontanelle

Question 28

IVH can progress to

Answer 28

hydrocephalus, parenchymal infarction, periventricular matter injury

Question 29

_____ are high risk for IVH

Answer 29

small birth weight and preterm (as many as 1/3rd of micropremie infants)

Question 30

Retinopathy of prematurity is the

Answer 30

arrest of normal retinal vascular development in exchange for neovascularization and fibrous tissue formation in the retina

Question 31

Retinopathy of prematurity can lead to

Answer 31

retinal detachment and fibrosis

Question 32

The anesthesia saturation goal to prevent retinopathy of prematurity is

Answer 32

90-94%******

Question 33

ROP is associated with

Answer 33

low birth weight (<1000g), prematurity, oxygen exposure, apnea, blood transfusions, sepsis, CO2

Question 34

The infant retina continues to mature until

Answer 34

42-44 weeks

Question 35

________ may be more damaging than high oxygen tensions for patients with retinopathy of prematurity

Answer 35

fluctuating oxygen levels

Question 36

Pediatric patients have an increased risk for heat loss due to

Answer 36

large surface area per kg than adults, thin skin, lower fat content, and higher surface area

Question 37

The four routes of heat loss include

Answer 37

radiation>convection>evaporation>conduction***

Question 38

Heat producing mechanisms include

Answer 38

- non-shivering thermogenesis during the first 3 months of life - metabolism of brown fat- shivering is severely limited in premature infants; thermogenesis is inhibited by volatile anesthetics - crying - movement

Question 39

What can be done to combat temperature loss for peds patients:

Answer 39

transport the child in an incubator or on a heating pad warm the OR (78-80 degrees) & fluids limit skin exposure cover the child's head use of forced air devices & warmers at all times heat lamps

Question 40

Hypothermia of pediatric patients can result in:

Answer 40

``` delayed awakening from volatile anesthetics cardiac instability respiratory depression increased pulmonary vascular resistance altered drug response ```

Question 41

Volatiles & effect on temperature include

Answer 41

cutaneous vasodilation | - depress hypothalamus= reduction in already reduced ability to warm themselves

Question 42

Neonates have very low _______

Answer 42

glycogen & body fat stores - predisposed to hypoglycemia during stress (surgery) - however decreased insulin production with infusion of dextrose predisposes to hyperglycemia

Question 43

________ by the kidneys can work to offset low glycogen

Answer 43

impaired glucose excretion

Question 44

Neonates should be maintained on IV ____ when NPO and close monitoring of blood glucose is vital

Answer 44

dextrose | normoglycemia is 45-90 mg/dL

Question 45

In the premature infant, the renal system is

Answer 45

reduced reduced ability to compensate for large swings in volume renal clearance of drugs is reduced reduced proximal tubular reabsorption of sodium and water

Question 46

Describe the the important factors related to reduced proximal tubular reabsorption of salt and water.

Answer 46

monitoring of sodium and free water requirements is important during critical illness

Question 47

Describe renal clearance of drugs being reduced.

Answer 47

ability to handle free water and solute loads may be impaired in neonates half-life of medications excreted by GFR will be prolonged (i.e. antibiotics)

Question 48

At term, functional maturity of the liver is

Answer 48

somewhat incomplete

Question 49

The cytochrome P450 (phase 1 drug metabolism of liphophilic drugs) reaches

Answer 49

~50% adult values at birth

Question 50

Phase II are

Answer 50

impaired until ~1 year of age

Question 51

The hepatic system of the newborn has limited

Answer 51

glycogen stores limited ability to handle large protein loads & reduced albumin synthesis- greater levels of unbound drugs

Question 52

In utero, ____ is actively transported across the placenta

Answer 52

calcium

Question 53

After birth the infant relies on ________ for calcium

Answer 53

extracellular calcium & calcium reserves however parathyroid function is not fully established, vitamin D stores may be inadequate, albumin and protein reserves are lower

Question 54

Anticipate hypocalcemia especially in preterm due to

Answer 54

severe neonatal illness and following blood transfusion

Question 55

Symptomatic hypocalcemia requires treatment with a slow infusion of either

Answer 55

calcium chloride or calcium gluconate | a central line is preferred as skin damage and sloughing may occur with calcium containing solutions administration