Pediatric & Neonatal anesthesia pathophysiology Part 2 Flashcards
Fetal circulation is characterized by
high PVR secondary to fluid filled lungs
- low systemic vascular resistance secondary to the large surface area of the low resistance utero-placental bed
The most oxygenated blood from the umbilical vein perfuses the
brain and heart by shunting across the liver via the ductus venosus and shunting across the right heart via the foramen ovale***
The umbilical vein PaO2 is
30-35 mmHg
-oxygen transport exists in relatively hypoxic environment
Fetal hemoglobin maintains the oxygen content of blood (CaO2) via two mechanism:
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
Transition from fetal to adult circulation occurs with
clamping of the umbilical cord and inflation of the lungs
-cord clamping removes the low resistance placenta and raises SVR
Lung inflation and increased PaO2 dramatically lowers
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
As PVR decreases, blood flow increases to the lungs, then blood flows into the left atrium increases via the pulmonary veins,
increasing LA pressure over RA pressure closes the atrial septum over the foramen ovale***
Placenta clamp ceases flow from this large, low-resistance vascular bed. This results in an
increase in SVR and a decrease in inferior vena cava blood flow and right atrium pressure
This increase in SVR and aortic pressure above the pulmonary artery pressure results in
reverse flow through the ductus arteriosus*****
The increase in oxygen concentration leads to a __________ causing closure of the ductus arteriosus
decrease in prostaglandins**
_______ closes the flap of tissue covering the patent foramen ovale
when left atrial pressure rises above right atrial pressure
Describe functional and anatomic closure of the foramen ovale.
functional- closure occurs quickly
anatomic- closure usually requires weeks
A PFO that is probe patent persists in 20-25% of adults
The ductus arteriosus remains patent in utero due to
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
Permanent anatomic closure of the ductus arteriosus, is usually complete in
5-7 days*** but may persist until 3 weeks
delayed closure is common in premature infants (esp. <34 weeks)
A PDA often occurs in premature infants with
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
Changes in systemic or pulmonary vascular resistance alter the direction of blood flow in patent ductus arteriosus, lead to
increase in PVR –> right to left shunting (bad)
can lead to congestive heart failure and low diastolic pressure
pulmonary edema from increased blood flow promotes (in patent ductus arteriosus)
pulmonary hypertension
-worsened with hypoxia, hypercarbia, acidosis, and hypothermia
Describe Pre ad post-ductal saturation monitoring:
preductal- pulse ox on the right hand
postductal- pulse ox on the lower limb
cerebral oximetry
Myelination of nerve fibers and cerebral cortex is
less incomplete and developed in premature infants
The blood brain barrier in the premature infant is
immature, rendering the developing brain more vulnerable to drugs or toxins
Neural pathways allowing for pain perception develop during
the first, second, and third trimesters
Developing cerebral vessels appear to be
more fragile than in the adult
cerebral auto-regulation is impaired in sick neonates and therefore blood flow is pressure dependent
Preterm infants have very fragile cerebral vessels- rupture leads to
intra-cerebral hemorrhage & intraventricular hemorrhage (IVH)***
Predisposing factors for IVH include:
hypoxia, hypercarbia, hypernatremia, fluctuations in pressure, low HCT, over transfusion, rapid administration of hypertonic fluids (i.e. NaBicarb or dextrose)
Intraventricular hemorrhage results in
spontaneous bleeding into and around the lateral ventricles of the brain
Intraventricular hemorrhage may result from
RDS, hypoxia, acute BP alterations, trauma, acidosis, distress
Symptoms of intraventricular hemorrhage include
hypotonia, apnea, seizures, loss of sucking reflex, bulging anterior fontanelle
IVH can progress to
hydrocephalus, parenchymal infarction, periventricular matter injury
_____ are high risk for IVH
small birth weight and preterm (as many as 1/3rd of micropremie infants)
Retinopathy of prematurity is the
arrest of normal retinal vascular development in exchange for neovascularization and fibrous tissue formation in the retina
Retinopathy of prematurity can lead to
retinal detachment and fibrosis
The anesthesia saturation goal to prevent retinopathy of prematurity is
90-94%****
ROP is associated with
low birth weight (<1000g), prematurity, oxygen exposure, apnea, blood transfusions, sepsis, CO2
The infant retina continues to mature until
42-44 weeks
________ may be more damaging than high oxygen tensions for patients with retinopathy of prematurity
fluctuating oxygen levels
Pediatric patients have an increased risk for heat loss due to
large surface area per kg than adults, thin skin, lower fat content, and higher surface area
The four routes of heat loss include
radiation>convection>evaporation>conduction***
Heat producing mechanisms include
- 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
What can be done to combat temperature loss for peds patients:
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
Hypothermia of pediatric patients can result in:
delayed awakening from volatile anesthetics cardiac instability respiratory depression increased pulmonary vascular resistance altered drug response
Volatiles & effect on temperature include
cutaneous vasodilation
- depress hypothalamus= reduction in already reduced ability to warm themselves
Neonates have very low _______
glycogen & body fat stores
- predisposed to hypoglycemia during stress (surgery)
- however decreased insulin production with infusion of dextrose predisposes to hyperglycemia
________ by the kidneys can work to offset low glycogen
impaired glucose excretion
Neonates should be maintained on IV ____ when NPO and close monitoring of blood glucose is vital
dextrose
normoglycemia is 45-90 mg/dL
In the premature infant, the renal system is
reduced
reduced ability to compensate for large swings in volume
renal clearance of drugs is reduced
reduced proximal tubular reabsorption of sodium and water
Describe the the important factors related to reduced proximal tubular reabsorption of salt and water.
monitoring of sodium and free water requirements is important during critical illness
Describe renal clearance of drugs being reduced.
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)
At term, functional maturity of the liver is
somewhat incomplete
The cytochrome P450 (phase 1 drug metabolism of liphophilic drugs) reaches
~50% adult values at birth
Phase II are
impaired until ~1 year of age
The hepatic system of the newborn has limited
glycogen stores
limited ability to handle large protein loads
& reduced albumin synthesis- greater levels of unbound drugs
In utero, ____ is actively transported across the placenta
calcium
After birth the infant relies on ________ for calcium
extracellular calcium & calcium reserves
however parathyroid function is not fully established, vitamin D stores may be inadequate, albumin and protein reserves are lower
Anticipate hypocalcemia especially in preterm due to
severe neonatal illness and following blood transfusion
Symptomatic hypocalcemia requires treatment with a slow infusion of either
calcium chloride or calcium gluconate
a central line is preferred as skin damage and sloughing may occur with calcium containing solutions administration
