Week 6 - Neonatal Anesthesia Flashcards
What are the classifications of Premature Infants?
Premature Infant = born before 37 weeks gestation
Moderate-Late Prematurity = 32-37 weeks
Very Premature = 28-<32 weeks
Extremely Premature = <28 weeks
Define:
- Gestational Age
- Chronological Age
- Postmenstrual Age
- Corrected Age
- Post Conceptual Age
-Gestational Age: weeks between 1st day of LMP, and
day of delivery
-Chronological Age: Time since birth
-Postmenstrual Age: Gestational Age + Chronological Age
-Corrected Age: Chronological Age reduced by the number of weeks born before 40 weeks gestation
-Post Conceptual Age: Time between conception and delivery (incorrect, should not be used)
Describe Fetal Circulation
– Relies on placenta for O2 and CO2 transport
– High pulmonary vascular resistance (deflated atelectatic lungs, hypoxic vasoconstriction)
– Low systemic circulatory resistance (high flow, low impedance of placental vessels)
– Extracardiac Shunts: Ductus Arteriosus (DA), Ductus Venosus (DV)
– Intracardiac Shunt: Foramen Ovale (FO)
Explain the transitional circulation of blood from from fetal to adult
- End of placental blood flow = Increase in aortic pressure
- Clamping umbilical vein = Doubles SVR
- Lungs Expand = Decrease PVR
- Increase in partial pressure of arterial O2 = Decrease in PVR
- Decrease in RA pressure + Increase in LA pressure = functional closure of the FO
- DA closes due to increase in SVR & decrease in PVR (kept open by prostaglandins)
- DV closure mechanism unknown
What factors maintain fetal circulation?
Anything that increases PVR: hypoxia, hypercarbia, acidosis, hypothermia
- May cause circulation to revert back to deoxygenated blood being shunted from right to left via PFO or PDA
- This explains why some babies are hypoxic despite adequate ventilation with 100% FiO2
How does the neonatal CV system differ from an adult?
- Fewer muscle cells, more connective tissue, fewer and unorganized myofibrils
- Immature contractile components (sarcoplasmic reticulum and T-tubule network)
- Neonate myocardium relies on free calcium for contractility — decreasing extracellular ionized calcium (citrate in PRBC, and albumin) decreases contractility!! (replace calcium frequently)
What is persistent pulmonary hypertension in neonates? What is its causes and treatment?
Failure of PVR to decrease at birth
-results in maintained right to left flow via PFO or PDA
Possible Causes: meconium aspiration, sepsis, asphyxia, increased muscularization of PA vessels, impaired endothelial nitric oxide release
Treatment: PEEP, exogenous serfactant, iNO, phosphodiesterase-5 inhibitor, inhaled prostaglandin-I2, endothelium receptor antagonists
What is the airway anatomy of a neonate?
Cephalad larynx at C3-4 (adults are C4-5)
Hyoid bone at C2-3
Base of tongue more superior to larynx = more acute angle between tongue and glottic opening
Epiglottis is narrow, omega shaped
**makes airway visualization more difficult
Immature lungs predispose neonates to what?
Alveolar Collapse and Hypoxia
- type II pneumocytes produce surfactant at 22-26 weeks and peaks at 35-36 weeks
- high risk of mechanical lung injury – nasal CPAP, high flow, ETT all common in NICU setting
What can apnea in the neonate lead to?
Bradycardia – heart rate 80 bpm or below
*usually at beginning of apnea spell –> then SpO2 falls (can be big trouble)
What is Bronchopulmonary Dysplasia?
Need for oxygen 28 postnatal days
- alveolarization begins at 36 weeks – prematurity interrupts this process = few, but large alveoli
- low surface area for gas exchange
- can lead to pulmonary hypertension, RV hypertrophy
- anesthetic goals: low FiO2, small TV, SpO2 90-94%
How can you help prevent intraventricular hemorrhage in neonates?
Avoid hypercarbia, hypoglycemia, hypothermia, rapid increases in BP
What is the renal function and considerations in neonates?
Full-term infants on have 30% of normal GFR
- renal excretion of antibiotics and NMBD is prolonged = increased duration of action, high blood concentrations
- interval between doses of antibiotics should be increased
- hyponatremia: neonates are obligate sodium excreters, very prone to hyponatremia
What are some liver function considerations in the neonate?
-Fetal liver can synthesize glycogen (98% of it is
used during first 48 hours) — Neonates at high risk of hypoglycemia
-Albumin levels are low = less ability to bind drugs to plasma proteins = increase in free drug
-Liver enzyme production low = low metabolism
-Hyperbilirubinemia common in term infants (Physiologic vs. Pathologic)
-7 days for clotting factors to reach adult levels (Vitamin K commonly given at birth)
What are GI considerations with the neonate?
- Fetal GI function develops late in gestation (intestinal motility increases 29-32 weeks)
- Prolonged gastric emptying, lower esophageal sphincters are incompetent
What is Necrotizing Enterocolitis?
Bowel necrosis due to harmful bacteria in a slow moving intestine that has little GI immune defenses
Early Signs are non-specific (temp instability, poor feeding, lethargy, apnea, bradycardia)
Late Signs = tachycardia, hypotension, metabolic acidosis, thrombocytopenia, peritonitis
What does anemia in a neonate increase the risk of?
Apnea
Intraparenchymal Brain Hemorrhage
Periventricular Leukomalacia
How are pharmacokinetics different in the neonate?
Cardiac output = 4x faster in neonate –> rapid IV drug onset, rapid metabolism (if liver/kidney function has matured)
Increased total body water and ECF –> water soluble drug dose is higher but can stay in CNS longer due to reduced redistribution
Decreased protein –> less binding sites = greater free drug
Decreased renal excretion due to decreased GFR and tubular function
