Neonates Flashcards
Why is phenylephrine not a good choice for neonates?
Their hearts are immature and unable to increase contractility to overcome increases in after load.
Why do infant have such a high respiratory rate?
- To compensate for their high metabolic rate (twice the rate of O2 consumption and CO2 production as adults)
- Thus the neonate must increase their minute ventilation accordingly.
- Also, neonates only have about 1/3 the alveolar surface area of adult.
- Metabolically, it’s more efficient to increase RR than TV
In the setting of hypovolemia and bradycardia, which is better for the neonate, EPI or atropine?
EPI
Will increase HR and will increase contractility (even though only by a little bit)
How does contractility improve over time in neonates?
Neonates are initially born with very low SVR, but this begins to rise over time.
The LV has to push against a higher after load, so contractile elements multiple and mature, thus improving contractility. Over time, this means that kids become less dependent on HR for CO.
Baroreceptor response in neonates
Immature.
Because of this, the reflex will not increase HR in the setting of hypovolemia and can vastly worsen BP.
The number of alveoli continue to rise until this age
8-10 years of age
Why do neonates have very fast inhalation inductions?
High minute ventilation and low FRC
Type I and Type II muscle fibers
II = Fast twitch (strong, but tire easily) I = Slow twitch (endurance)
Muscles of inspiration
DIAPHRAGM IS MAIN ONE
Intercostals are immature (ribs thus more horizontal and unable to significantly increase thoracic volume)
Newborn lungs are compliant or noncompliant?
None-compliant
The CHEST WALL is very compliant d/t cartilaginous ribs
Why does chest wall collapse on inspiration occur in neonates?
Low lung compliance + high chest wall compliance
Diaphragm has to work hard to expand the lung. High negative intrathoracic pressures lead to chest wall collapse
FRC and CC in newborns
CC overlaps with FRC, causing small airway collapse with tidal breathing
Clamping of the cord causes this in the newborn
Rhythmic breathing
Acute rise in ____ promotes continuous breathing in the newborn
Acute rise in O2 promotes continuous breathing
Hypoxia causes apnea.
Respiratory control doesn’t mature until this age
42-44 weeks
BEFORE this time, hypoxia will cause apnea.
AFTER this time, hypoxia stimulates breathing.
Lifespan of RBCs with HgbF
70-90 days
Compared to 120 days with HgbA
P50 of HgbF and HgbA
HgbF = 19mmHg
HgbA = 26.5mmHg
HbF’s ability to bind 2,3-DPG
HgbF is unable to bind 2,3-DPG, which is why it has a higher affinity for O2 and lower partial pressure in the tissues
When is HgbF replaced by HgbA?
First 2 months of life
RBC transfusion guidelines
Depends on if patient is older or younger than 4 months old
Younger than 4 months:
- Kids still have HgbF, so transfusion trigger is higher (their Hgb isn’t as efficient in delivering O2!)
- Trigger of 10 for kid having major surgery or if they have moderate CP disease
- Trigger of 13 (earlier transfusion) for kids with SEVERE CP disease
Older than 4 months:
- Same guidelines for adults (6-10g/dL stuff)
FFP transfusion guidelines
For coagulopathies only (not volume expansion). Give if:
- Need to quickly reverse warfarin
- PT > 1.5 or increased PTT
- To correct coagulopathic bleeding if > 1 blood volume has been replaced and you can’t get coats drawn easily
This pH abnormality is associated with massive transfusion
Either may happen
1) Acidosis from poor oxygenation and increased lactate
2) Alkalosis from metabolism of citrate to bicarbonate in the liver
Massive transfusion may have this effect on GB
Hyperglycemia 2/2 dextrose in the blood
Why are PRBCs radiated?
To destroy leukocytes, which can cause graft-vs-host disease
Newborns and ABO antigens
ABO antigens are poorly expressed in newborns. Some say they can be given uncross matched blood. q
Renal function in the neonate and it’s implications
Compared to the adult, the neonatal kidney has:
1) Decreased perfusion pressure
2) Decreased GFR
3) Decreased ability to concentrate ruin
As a result, the neonate is bad at handling fluids:
- Bad at concentrating urine, so it loses lots of water 2/2 lack of sodium reabsorption (bad at handling fluid restriction)
- However, low GFR, so unable to excrete large volumes, and are bad at handling fluid overload as well
- Fluid management is essential!
Solutes:
- Tend to lose sodium and glucose
Renal maturation
1) GFR reaches adult levels at 8 months - 2 years
2) Renal tubular function achieves full concentrating ability at 2 years
Total body water distribution is the same as adults by this age
1 year
Third space losses
Minimal surgical trauma = 3-4cc/kg/hr
Moderate = 5-6
Major = 7-10
Neonatal CO
CO is 200mL/kg/min
This is faster than the adult and results in faster circulation time compared to adults
Protein binding in neonates
Decreased d/t low levels of circulating proteins
Effect of fat soluble drugs
Drugs that rely on fat for redistribution and termination of effect will have a prolonged DOA 2/2 decreased body fat content.
These bitches are 80% water.
Neonates and bilirubin
Neonates cannot conjugate bilirubin 2/2 a lack of glucuronyl transferase. This is the same enzyme that metabolizes tylenol.
BBB in neonates
Immature.
Allows more drugs to pass. May explain the increased sensitivity to sedative hypnotics.
Muscle relaxant dosing in neonates
Sux = NEED MORE! 2mg/kg (higher Vd + equal sensitivity to sux at the NMJ)
NDMRs = same as adult dosing (this is because even though there is a higher Vd, the NMJ is immature and more sensitive to NDMRs)
Sux dosing
IV = 2mg/kg
IM = 5mg/kg for neonates and infants
4mg/kg for older children
Sux and bradycardia
Happens in children
This is the only NDMR that can be given IM
Roc
IM dose is 1mg/kg for kids 1 year
This is an indication in the mother that their child might have TEF
Polyhydramnios (kid isn’t swallowing amniotic fluid)
TEF is associated with these other congenital anomalies (25-50% of those with TEF will have another anomaly)
VACTERL
Vertebral defects Imperforate Anus Cardiac Abnormalities TEF Esophageal atresia Renal Dysplasia Limb anomalies
20% will have a significant cardiac defect. Pre-op ECHO should be performed
When is surfactant made during gestation?
Begins at 22-26 weeks
Peaks at 35-36 weeksq
This medication can hasten fetal lung development. When does it work?
Betamethasone
Starts to work at 18 hours
Peaks at 48 hours
Another same for surfactant is
Lecithin
How can we get an idea of how mature a fetus’s lungs are?
Do an amniocentesis to look at the L/S ratio.
Looks at ratio of lecithin (surfactant) to sphingomyelin (surfactant precursor).
L/S ratio > 2 means adequate maturation
Risk factors for developing respiratory distress syndrome (RDS)
Prematurity Low birth weight O2 Toxicity Intubation Barotrauma from PPV Maternal DM
pH imbalances with pyloric stenosis
Causes initial metabolic ALKALOSIS.
Patient continues to lose fluid, and if hypovolemia is not corrected, impaired tissue perfusion results in lactate production and metabolic ACIDOSIS.
Symptoms of pyloric stenosis first appear when?
At 2-12 weeks
More common in males.
Vomiting depletes these things
Water, H+, Na+, Cl-, and K+
Why is urine acidic in pyloric stenosis?
Losing lots of fluid. RAAS activated and aldosterone is released. Kidney reabsorbs Na+, but loses H+ to maintain electroneutrality
Anesthetic management of pyloric stenosis
- Postpone surgery until fluids and electrolytes are optimized.
- Correct severe dehydration with 20mL/kg of NS
- Maintenance fluids should be D5 1/2NS at 1.5x calculated rate (volume depleted and poor nutritional status)
- Anticipate full stomach (RSI or awake intubation). Extubatne awake.
- Post-op apnea is common (could be b/c the CSF remains alkalotic even though serum pH has normalized)
Patho of retinopathy of prematurity
Immature BVs are at risk of vasoconstriction and hemorrhage. Dysfunctional healing then causes scars. As the scars retract, they pull on the retina, causing detachment and blindness.
Risk factors for retinopathy of prematurity
Prematurity High FiO2 Mechanical ventilation Intraventricular hemorrhage Sepsis Vitamin E deficiency
For how long do kids need to be given a low FiO2?
Until retinal maturation is complete (44 weeks post-conception)
Until then, keep SpO2 between 85-93%
What drugs may cause neural apoptosis?
Those that stimulate GABA and inhibit NMDA:
- Ketamine*
- Midazolam*
- Propofol
- Etomidate
- VAs
- N2O
- Barbs
- Other benzos
What are the Dubowitz and Ballard scoring systems?
Ways of estimating gestational age AFTER the baby has been born!
How old is dis baby?
Most accurate 30-42 hours after birth
What is the MOST ACCURATE way to measure gestational age in a fetus?
Crown-rump length via ultrasound
