Pediatric Anesthesia

Question 1

Is the oxyhemoglobin dissociation curve of the newborn shifted to the left or the right? Why?

Answer 1

It is shifted to the left because fetal Hgb which consists of two alpha and two gamma chains instead of two alpha and two beta chains (adult HgB) is unable to bind 2,3-DPG and therefore has a higher affinity for oxygen.

Question 2

By what age is fetal Hgb replaced by adult Hgb?

Answer 2

4-6 months of age in full-term infants. This can be delayed until up to 12 months for the preterm infant.

Question 3

At what conceptual age is surfactant developed?

Answer 3

It begins at 22-26 weeks gestation, peaking at 35-36 weeks.

Question 4

What intrapleural pressure is generated during the first breath of neonatal life?

Answer 4

The first breath of neonatal life is a gasp that generates a transpulmonary distending pressure of 40-80 cmH2O, in other words

Question 5

The adult lungs comprise from 300 million to 480 million alveoli; how many alveoli comprise the neonatal lungs?

Answer 5

About 30 million alveoli which is approximately 1/10th the number in the adult lungs. Most alveoli are formed by 18 months but maturation continues until about 8 years of age.

Question 6

Identify the two limitations of kidney function in the newborn. What is the significance of these limitations?

Answer 6

Neonates are obligate sodium excreters due to immature renal tubules. Therefore, the ability to concentrate urine is impaired. GFR is also diminished. Thus, infants do not tolerate large volumes of water and salts.

Question 7

When do liver enzymes become completely functional in the neonate?

Answer 7

The cytochrome P450 enzyme system is fully functional at 1 month of age.

Question 8

Where does the spinal cord end in the neonate?

Answer 8

Approximately L3 and it does not reach the adult location of L1 until 1 year of age.

Question 9

How do chest wall compliance and pulmonary lung compliance differ in the neonate compared with the young, healthy adult?

Answer 9

Chest wall compliance is increased and pulmonary compliance is decreased.

Question 10

In newborns, the closing capacity is greater than the FRC. What is the physiologic complication?

Answer 10

Small airway closure occurs during tidal volume breathing and thus there is less oxygen reserve in the FRC.

Question 11

What is the length of the infant trachea from the cords to the carina in centimeters?

Answer 11

It varies from 5-9 cm in infants and neonates and children up to 1 year of age.

Question 12

List 5 ways the neonatal airway differs from the adult airway and one anesthetic implication for each.

Answer 12

1) Larynx is more cephalad (C1-C2) 2) –> straight blade more useful than curved blade; 2) epiglottis is stubby, short, and omega-shaped –> control with laryngoscopy blade is more difficult; 3) tongue is larger –> increased risk for airway obstruction and may be difficult to displace with laryngoscopy; 4) vocal cords angled anteriorly –> ET tube may lodge in anterior commissure rather than slide into trachea; 5) larynx is funnel-shaped with the narrowest portion occurring at cricoid cartilage –> may be difficult to pass ET tube, may require smaller tube.

Question 13

At what age do the pediatric laryngeal cartilages reach adult proportions?

Answer 13

At age 10-12 years.

Question 14

What is the estimated blood volume of the preterm neonate (in mL/kg)? Of the neonate? of an infant 3 months to 3 years?

Answer 14

Preterm neonate: 90-100 mL/kg. Term neonate: 80-90 mL/kg. 3 months-3 years: 75-80 mL/kg.

Question 15

Describe the physiological anemia of the neonate and pediatric patient.

Answer 15

Normal hemoglobin levels in the full-term infant range from 14-20 g/dL. It progressively declines during the 9-12th week reaching a minimum of 10-11 g/dL with a hematocrit of 33%. After the 3rd months, hemoglobin levels stabilize at 1.5-12 g/dL until about 2 years of age then gradually increase to adult levels of 14-15.5 g/dL by puberty.

Question 16

Below what hemoglobin concentration is anemia sufficient to jeopardize oxygen carrying capacity in the neonate? Infant older than 3 months?

Answer 16

Hgb concentrations < 13 g/dL in the newborn and less than 10 g/dL in the pediatric patient older than 3 months jeopardizes oxygen-carrying capacity.

Question 17

A 3 month old infant, who is scheduled for surgery has a hemoglobin concentration of 10.5 g/dL. What action should be taken?

Answer 17

Nothing, this hemoglobin level is normal for this age.

Question 18

Why is cardiac output in infants dependent on HR and not stroke volume?

Answer 18

Because ventricular compliance is decreased which results in limited ability to increase myocardial contractility and stroke volume so the only way to alter cardiac output is to change heart rate.

Question 19

At what rate do infants consume oxygen? How does this compare to the adult?

Answer 19

Resting O2 consumption is about 6-8 mL/kg/min which is twice that of the adult.

Question 20

By what route do infants lost most of their body heat?

Answer 20

Most heat loss is by radiation (this applies to any age)

Question 21

Newborns produce heat primarily by what mechanism?

Answer 21

Non-shivering thermogenesis by metabolism of brown fat.

Question 22

What is the significance of brown fat? Where is brown fat located?

Answer 22

Infants respond to cold stress by increasing norepinephrine production which enhances metabolism of brown fat and increases body heat. Brown fat is located in the interscapular space and around large blood vessels, around the neck, the axilla, behind the sternum, and around the kidneys and adrenals.

Question 23

What controls non-shivering thermogenesis in infants?

Answer 23

The sympathetic nervous system activates NST in infants. Specifically, norepinephrine and thyroid hormone stimulate triglyceride and fatty acid metabolism of brown fat stores.

Question 24

At approximately what age does non-shivering thermogenesis cease to be clinically significant?

Answer 24

At about 2 years of age.

Question 25

What is the best way to warm an infant in the operating room?

Answer 25

Increasing operating room temperature.

Question 26

To what do preductal or postductal coarctation of the aorta refer?

Answer 26

Coarctation of the aorta refers to a discrete narrowing of the aorta immediately distal to the origin of the left subclavian artery. A preductal coarctation refers to the narrowing occurring proximal to the opening of the ductus arteriosus. Postductal coractations lie beyond the ductus arteriosus and are most commonly diagnosed in older children.

Question 27

Where should upper extremity blood pressure be monitored in the neonate with preductal coarctation of the aorta, on the right or left side?

Answer 27

Monitoring of blood pressure is best achieved by placing a catheter in the right radial artery.

Question 28

Where are pulse oximeters placed on the neonate to monitor preductal and postductal oxygenation?

Answer 28

Preductal oxygenation should be measured with a pulse oximeter on the right hand or finger and postductal oxygenation should be measured with a pulse oximeter on the left foot or toe.

Question 29

What is the purpose of a preductal pulse oximeter in the neonatal patient undergoing cardiac surgery?

Answer 29

Measurements of arterial oxygen saturation taken at the preductal location are a better index of neonatal cerebral oxygenation than those taken at a postductal location. A postductal pulse oximeter may be used in addition to the preductal pulse oximeter to quantitate the severity of a left to right shunt.

Question 30

What causes the foramen ovale to close in the newborn?

Answer 30

Closure is due to a decrease in PVR and increased pulmonary blood flow that occurs as the infant takes his/her first breaths and the alveoli expand. An increase in pulmonary blood flow and increase is left atrial pressure shuts the flap located on the left side of the foramen ovale.