Neonatal Anesthesia Flashcards
Children
Ooxygenation, ventilation, airway management, and response to anesthetic agents and medications
The transition from fetal to neonatal physiology takes place during the first __-__ hours of life
24-72.
First 72 hrs the most important for cardiac, pulmonary, and renal systems.
A premature infant is born less than ___ weeks gestation
37
A postmature infant is born over ___ weeks gestation
42
Growth and development is massive in the first year of life. Body weight alone will increase by a factor of
3
Importance of catecholamines at birth
- Helps them prepare for birth, adapt to extrauterine life, and cope with hypoxia
- Animals deprived of a catecholamine surge at birth less likely to survive hypoxia
- Catecholamines aid in the clearance of liquid from the lungs, which improves lung compliance after birth
- Are important for the release of surface-active material from alveolar type II cells
- During asphyxia, catecholamines maintain cardiac output and redistribute blood flow from the periphery to the heart, brain, and adrenal glands
- They also increase arterial blood pressure and slow the heart rate, which reduces myocardial oxygen consumption
- Infants delivered by cesarean section without maternal labor have lower blood glucose concentrations and less blood flow to peripheral organs than after vaginal delivery and is related to plasma catecholamine concentrations
- Neonates with elevated catecholamine concentrations have higher Apgar scores than those who have low concentrations
- Catecholamines help to redistribute CO. Causes preferential redistribution to brain, heart, etc.
Immediate physiologic changes at birth
- Cessation of umbilical circulation
- Initiation of ventilation/lung expansion
- Stress and associated catecholamines
Fetal circulation
Fetal Circulation:
Oxygenated blood comes from placenta through the umbilical vein to IVC to Right Atrium
In RA, about 40% of this oxygenated blood mixes with desaturated blood returning from the upper body/head via the SVC. Then goes through the Right Ventricle and into the PA. Only 5-10% of this goes to the fetal lungs since PVR is HIGH. The rest is shunted through the DUCTUS ARTERIOSUS to the descending aorta
The remaining 60% of oxygenated blood that came from the placenta is shunted through the FORAMEN OVALE to the LA the LV and the ascending Aorta
Based on this, overall 60% of oxygenated blood goes to the upper body and 40% goes to the lower body.
Why is the pressure so high in the fetal pulmonary circulation?
1) Low pH promotes vasoconstriction
2) Low PaO2 promotes vasoconstriction
3) The alveoli are full of fluid, which compresses the blood vessels
The ductus arteriosus is dilated by
Low O2.
This is why it is open during fetal life, and closes once the lungs start functioning and the newborn experiences higher O2 concentrations.
Permanent closure of the foramen ovale occurs
after a few months.
However, 10-20% of the population will never have a truly anatomically closed FO.
True fibrotic closure of the ductus arteriosus doesn’t occur until
2-3 weeks of age
It can take longer if the child was born premature
What causes the ductus venosus to close?
Drop in portal pressure due to removal of the placenta
PVR decreases dramatically at birth due to
lung expansion, breathing, increased pH, and the increase in alveolar oxygen tension that occurs at birth
These factors can increase PVR
Hypoxia, acidosis, hypovolemia, hypoventilation, atelectasis, and cold increase PVR
Fetal circulation can be re-established if these factors occur during the first 2 weeks of life
Hypoxia, hypothermia, or acidosis
Why is hydration important in keeping normal circulation?
Because dehydration would drop the SVR and re-establish fetal circulation
Closure of the ductus arteriosus
Functional closure: within 1-2 days after birth.
–> O2(most important), catecholamines, and PSNS activation all encourage functional closure.
Anatomical closure: In 10-14 days in healthy neonate (up to several months in premature infants) the ductus arteriosus is replaced by connective tissue and is known as the ligamentum arteriosum.
How can we prevent the patient from reverting to fetal circulation?
Keep the patient warm, hydrated, normal PaO2, PaCO2, minimize myocardial depression related to anesthetic agents, maintain SVR*****
Myocardial depression will also cause BP to drop.
A baby’s first breath requires
40-60 cmH2O negative intrathoracic pressure.
Thus, if we have to ventilate, it’s a better idea to do so by intubating than mask ventilating
Surfactant production in the fetus and its importance in the newborn
Surface active material important for normal lung function. By 20 weeks’ gestation it is present within the alveolar lining cells,and by 28-32 weeks gestation, is present within airway lumens. Significant amounts don’t appear in terminal airways until 34-38 weeks gestation, unless SAM production and release stimulated by stress or steroids.
Administration of SAM decreases the incidence of hyaline membrane disease and the incidence of serious cardiopulmonary complications. Giving SAM at birth reduces the inflammatory response to mechanical ventilation and improves lung function.
Stimulation for breathing immediately after birth
. Stimulation of the respiratory centers by mild acidosis, hypercarbia, hypoxia, pain, cold, touch, noise, and clamping of the umbilical cord initiates and sustains rhythmic respiration. Severe acidosis, hypoxia, CNS damage, and maternal drugs (e.g., narcotics, barbiturates, local anesthetics, magnesium, alcohol) depress breathing. A few minutes after birth, the respiratory rate is 30 to 60 bpm - removes the increased CO2 produced by the high oxygen consumption of the neonate (about 6 mL/kg/min) and helps maintain a normal FRC by not allowing sufficient time for the FRC to be expired.
Normal FRC and ABG values are obtained within __ minutes after birth
10-20 minutes
Normal TV and MV are established within __ minutes after birth
5-10 minutes