Ch 93 Pediatric Anesthesia Flashcards
What constitutes a low birthweight infant
<2500g
What electrolyte abnormalities are seen in preterm infants
hypoglycemia
hypocalcemia
hypomagnesemia
What contributes to increased pulmonary blood flow after birth?
- exposure of ductus arterioles to oxygenated blood causes it to close
- effects of lung expansion
- loss of low resistance through placental blood flow (increased peripheral resistance)
what is the mechanism of closure of the foramen ovale?
Increase in Left heart pressure (caused by increased peripheral vascular resistance)
Why does ductus arteriosis close? Why is patent DA seen more commonly in preterm infants?
Increased arterial oxygen concentration.
Arterial muscular tissue required for closure (not as available in preterm infants)
What is transitional circulation?
When the infant readily converts from adult to fetal circulation
-Causes rapid desaturation. Usually can improve with hyperventilation (decreased PaCO2 decreases pulmonary arterial pressure)
What are risk factors for prolonged transitional circulation?
- prematurity
- infection
- acidosis
- pulmonary disease resulting in hypercapnia or hypoxemia (e.g., meconium aspiration)
- hypothermia
- congenital heart disease
What are the physiological consequences of immature, less compliant myocardial structures in the neonate?
- Tendency toward biventricular failure
- sensitivity to volume loading
- poor tolerance of increased afterload
- HR dependent CO
Why is respiration less efficient in infants?
Smaller airways - more resistance
Highly compliant airways
Highly compliant chest wall, negative pressure poorly maintained (functional airway closure accompanies each breath due to these compliant states)
Immature diaphragmatic and intercostal muscles - easily fatigued
What are the 5 ways that infant airways differ from adults?
- large infant tongue - increased likelihood of obstruction and difficulties with laryngoscopy
- Higher (more cephalic) larynx
- Epiglottis is short, stubby, omega shaped and angled over larynx
- Angled vocal cords (a blind tube may be lodged in anterior commissure rather than slide into trachea)
- Funnel shaped larynx - narrowest at cricoid (may get caught up past cords)
Infants are obligate nasal breathers. Can they convert to oral breathing? When?
40% of term infants can covert to oral breathing if nasal airway obstructed (only 8% preterm)
By 5 months, almost all infants can easily convert to oral breathing.
When does kidney function completely mature?
2 years of age
Why is impaired glomerular and tubular function important in the neonate
Half life of medications prolonged (if they go through glomerular filtration)
Impaired ability to regulate large amounts of solutes and water
Why does the liver’s ability to metabolize medications improve as the infant grows?
- hepatic blood flow increases
2. Enzyme systems develop and are induced (Cytochrome P450)
How do plasma levels of albumin and other proteins compare in newborns versus infants? How does this effect pharmacology of drugs?
Newborns have lower plasma levels of albumin and other proteins necessary for drug binding than do infants.
Lower albumin levels results in less protein binding of some drugs –> greater levels of unbound drug
Are neonates at higher risk of GERD? Why?
Yes - ability to coordinate swallowing with respiration does not fully mature until 4-5months
Why are infants more vulnerable to hypothermia?
Thin skin, large ration of BSA to weight, limited ability to cope with cold stress (causes increased oxygen consumption and metabolic acidosis)
What is the principal method of heat production in infants < 3 months?
Non-shivering thermogenesis - metabolism of brown fat
Neonates have higher total body water content. How does this affect pharmacology?
Water soluble drugs have large volume of distribution, therefore requiring a larger initial dose (mg/kg) to achieve desired blood level. They also have delayed excretion secondary to larger VoDist.
Neonates have less fat. How does this affect pharmacology?
Drugs that depend on redistribution into fat for termination of action will have a long clinical effect. This is similar for drugs that redistribute into muscles.
How is does half life of most medications compare in older children to adults? Why
- Half life is shorter or equivalent to that of adults
- larger fraction of CO diverted to liver and kidneys (weight more in relation to body weight)
- mature renal and hepatic function
Why is uptake of volatiles more rapid in children?
Increased RR, cardiac index, and greater proportional distribution of cardiac output to vessel-rich organs
What is the MAC value for sevoflurane for neonates, infants (1-6months) and children >6 months?
Neonates: 3.3%
Infants: 3.2%
Children: 2.5%
How does sevoflurane affect RR and TV?
Decreases both
