Prematurity

Question 1

What is the definition of a premature infant?

Answer 1

Prematurity is defined as birth before 37 weeks gestation.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 733.

Question 2

What airway abnormalities commonly associated
with prematurity result in a decreased airway
diameter and increased resistance to airflow?

Answer 2

Premature infants have a high incidence of subglottic stenosis,
tracheal stenosis, and tracheobronchomalacia which are all
associated with a decrease in the airway diameter and
increased resistance to airflow.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 733.

Question 3

What are the normal vital signs for a preterm infant?

Answer 3

The normal preterm heart rate is between 120 and 160 BPM
and the normal respiratory rate is between 30 and 60/minute but
can increase to as much as 100 to 150 breaths per minute
depending on how severely the lung compliance is decreased.
The normal blood pressure depends on the birth weight of the
infant and ranges from about 50/25 for a 1000 gram infant to
70/40 for a 4000 gram infant.
Yao FF. Anesthesiology: Problem-Oriented Patient
Management. 7th ed. Philadelphia: Lippincott, Williams, and
Wilkins; 2012: 1015.

Question 4

Which agents are commonly used in the treatment of

apnea in the premature infant?

Answer 4

Theophylline (10 mg/kg) has been used historically for the
treatment of apnea in the premature infant. It was discovered in
1981 that the premature infant converts theophylline into
caffeine in the liver and that caffeine (6 mg/kg) had similar
advantages and a lower incidence of cardiovascular irritation.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1177-1178.

Question 5

What are the ventilatory goals during the anesthesia

of a premature infant?

Answer 5

These patients are susceptible to trauma from high inflation
volumes, oxygen toxicity, and bronchopulmonary dysplasia.
The current recommendation is to use a tidal volume of 4-6
mL/kg, higher respiratory rates, PEEP to avoid collapse of the
alveoli, and permissive hypercapnia (up to a PCO2 of 45-44
mm Hg).
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 734.

Question 6

What two significant conditions can occur due to the

presence of a patent ductus arteriosus?

Answer 6

Pulmonary hypertension and congestive heart failure
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 735.

Question 7

Why do premature infants have a decreased ability

to compensate for hypovolemia?

Answer 7

Cardiac contractility is limited due to the immaturity of the
contractile cells. Autoregulation is not yet matured, so the heart
rate does not respond sufficiently to hypovolemia. The
administration of anesthesia further blunts this already limited
coping mechanism making the premature infant more
susceptible to shock from hypovolemia.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 735.

Question 8

Does the premature infant’s heart exhibit a greater or

lesser sensitivity to catecholamines?

Answer 8

It is less sensitive to catecholamines because it is already near
the maximum level of beta-adrenergic stimulation.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 735.

Question 9

How does the heart of a premature infant differ from

that of a full-term neonate?

Answer 9

The fetal heart contains more connective tissue, the contractile
elements are less organized, and contractility has a greater
dependence upon the extracellular calcium concentration.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 735.

Question 10

What are the treatment regimens for postoperative

apnea in the premature infant?

Answer 10

The patient must have close cardiorespiratory monitoring.
Correction of anemia or hypovolemia should be performed.
Intravenous caffeine may be used to stimulate respiration.
Nasal CPAP or intubation and mechanical ventilation may be
required if these measures fail to produce the desired effect.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 735.

Question 11

Does regional anesthesia eliminate the risk for

postoperative apnea in the premature infant?

Answer 11

No, although regional anesthesia decreases the risk,
postoperative apnea can occur with regional techniques as well,
even if no general anesthetic medications were given.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 735.

Question 12

What are the factors that contribute to the
development of postoperative apnea in the
premature infant? What factor increase the risk for
apnea the most?

Answer 12

Postconceptual age is the greatest factor associated with an
increased risk for apnea. A postconceptual age (gestational
age + chronological age)

Question 13

What is the definition of postoperative apnea?

Answer 13

It is defined as apnea with a duration greater than 15 seconds
or apnea of a shorter duration that is accompanied by
bradycardia.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 734-735.

Question 14

What are the effects of increased pulmonary
vascular resistance on a patient with a patent ductus
arteriosus?

Answer 14

It will increase the right-to-left shunt.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 736.

Question 15

Describe the premature infant’s ventilatory response

to hypoxia.

Answer 15

Premature infants exhibit a biphasic ventilatory response to
hypoxia. The initial response is an increase in ventilation. After
several minutes, however, ventilation decreases and apnea
may occur.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 734.

Question 16

How do low surfactant levels in the premature infant

predispose the patient to hypoxia?

Answer 16

The low surfactant level results in decreased compliance and
reduced lung volumes. Intrapulmonary shunting and V/Q
mismatching occurs, resulting in hypoxia, especially during
anesthesia.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 734.

Question 17

When does surfactant production in the lungs begin?

Answer 17

It begins at 23-24 weeks gestation, but it is typically inadequate
until 36 weeks gestation.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 734.

Question 18

How does tracheobronchomalacia result in

increased airway resistance in the premature infant?

Answer 18

Tracheobronchomalacia results in collapse of the intrathoracic
airways during exhalation which increases airway resistance
and the work of breathing.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 733.

Question 19

Do subglottic stenosis and tracheal stenosis both

require a smaller endotracheal tube?

Answer 19

Subglottic stenosis requires a smaller endotracheal tube.
Tracheal stenosis usually occurs at the level of the carina and
does not require a smaller tube. Airway resistance is still higher
with tracheal stenosis, however, due to the smaller airway
diameter beyond the end of the endotracheal tube.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 733.

Question 20

What is the mortality rate for respiratory distress
syndrome in the premature infant? Why does it
occur?

Answer 20

Respiratory distress syndrome, also known as hyaline
membrane disease, is associated with a 50-75% mortality rate.
The condition is a result of inadequate surfactant in the alveoli.
This leads to alveolar collapse and shunting. Ultimately, arterial
hypoxia and acidosis occur which lead to death.
Yao FF. Anesthesiology: Problem-Oriented Patient
Management. 7th ed. Philadelphia: Lippincott, Williams, and
Wilkins; 2012: 1007-1020.

Question 21

What factors increase the risk for retinopathy of

prematurity?

Answer 21

A gestational age greater than 32 weeks demonstrates a
significantly decreased risk (zero risk in one study) of ROP. The
infant’s retinal vessels become maximally constricted at a PaO2
of 100 mmHg. A PaO2 of 100 mmHg to 150 mmHg for as little
as 1-2 hours has been shown to result in ROP, therefore, it is
recommended to maintain the infant’s PaO2 between 50 and 70
mmHg. Other factors associated with an increased risk include
respiratory distress, hypercarbia, acidosis, anemia, heart
disease, and infection.
Yao FF. Anesthesiology: Problem-Oriented Patient
Management. 7th ed. Philadelphia: Lippincott, Williams, and
Wilkins; 2012: 1012.

Question 22

Can digitalis be used to promote increased cardiac

contractility in the premature infant?

Answer 22

No. Digitalis is contraindicated in premature infants because no
resulting increase in contractility or ventricular ejection occurs,
but the heart rate does slow down, resulting in a decrease in
cardiac output.
Yao FF. Anesthesiology: Problem-Oriented Patient
Management. 7th ed. Philadelphia: Lippincott, Williams, and
Wilkins; 2012: 1010-1013.

Question 23

How are premature infants classified according to

birth weight?

Answer 23

Low birth weight is defined as an infant that weighs less than
2500 grams. Very low birth weight is defined as a weight less
than 1500 grams. Extremely low birth weight is defined as a
weight less than 1000 grams.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 733.

Question 24

Why is apnea common postoperatively in premature

infants?

Answer 24

The effects of the anesthetic combined with the underdeveloped
medullary respiratory control centers predispose the patient to
postoperative hypercapnia, hypoxia, and apnea after
anesthesia.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 734-735.

Question 25

How is evaporative heat loss prevented in the

premature infant?

Answer 25

By keeping the skin dry.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 26

What are the anesthetic implications for the

premature infant with regard to their liver function?

Answer 26

The liver function in a preterm infant is decreased. As a result,
the metabolism of many drugs may be prolonged. Also, the
liver is not able to produce albumin in normal quantities yet, so
the ‘free’ form of many drugs that are highly protein-bound will
be elevated.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 27

What is the most common surgical emergency in the

neonate?

Answer 27

Necrotizing enterocolitis is the most common surgical
emergency in the neonate. Premature infants are at the
greatest risk for developing it, but causes include umbilical
artery catheterization, systemic infections, perinatal asphyxia,
hypotension, exchange blood transfusions, patent ductus
arteriosus, cyanotic heart disease, respiratory distress
syndrome, and hyperosmolar feedings.
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 601-602.

Question 28

Why would indomethacin be administered to a

premature neonate?

Answer 28

Indomethacin, a potent prostaglandin inhibitor is administered
to stimulate closure of a patent ductus arteriosus.
Yao FF. Anesthesiology: Problem-Oriented Patient
Management. 7th ed. Philadelphia: Lippincott, Williams, and
Wilkins; 2012: 1010-1013.

Question 29

What inspired oxygen concentration should be used
to avoid the development of retinopathy of
prematurity?

Answer 29

The lowest possible inspired concentration that maintains an
oxygen saturation between 90% and 94% should be used.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 30

A premature infant is undergoing laparotomy for
necrotizing enterocolitis. What significant risk is
closely associated with this procedure?

Answer 30

Premature infants are at risk for spontaneous liver hemorrhage.
For some reason, this risk is particularly high during laparotomy
for necrotizing entercolitis. Recombinant factor VIIa may be
used to treat this condition.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 31

What is retinopathy of prematurity?

Answer 31

This is a retinopathy that occurs in about half of very low birth
weight infants (weight between 1000 and 1500 grams). The
exact mechanism that causes it is not known, but it is believed
to be related to vasoconstriction of retinal vessels in response
to high oxygen concentrations, the effect of free oxygen radicals
on retinal spindle cells, and induction of vascular endothelial
growth factor.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 736-737.

Question 32

How does hyperglycemia affect outcomes in
episodes of local and global cerebral ischemia in
premature infants?

Answer 32

In contrast to adults, hyperglycemia appears to exert a
neuroprotective effect during episodes of cerebral ischemia in
premature infants. It should also be noted that mild
hypoglycemia can result in brain damage in premature infants.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 33

Are premature infants at an increased risk for

developing hyperglycemia or hypoglycemia? Why?

Answer 33

Premature infants are at risk for developing both hyperglycemia
and hypoglycemia. Decreased stores of adipose tissue and
lower glycogen stores predispose them to hypoglycemia during
fasting. They also exhibit a decrease in insulin production, so
they are more susceptible to hyperglycemia from dextrose
infusions.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 34

Why would a premature infant be predisposed to

hyponatremia?

Answer 34

They have a reduced number of hormone receptors in the
proximal tubules that regulate sodium reabsorption. As a result,
they may excrete higher quantities of sodium through the
proximal tubules. Approximately 1/3 of extremely low birth
weight infants will develop hyponatremia.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 35

What form of heat loss is minimized by increasing

the operating room ambient temperature?

Answer 35

Convective heat loss
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737

Question 36

What form of heat loss does the placement of a

warming pad on the operating table prevent?

Answer 36

Conductive heat loss
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 37

What form of heat loss does a heat lamp prevent?

Answer 37

An overhead lamp reduces radiant heat loss.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 38

Why are premature infants more susceptible to

hypothermia?

Answer 38

There is little adipose tissue to act as insulation and the surface
area to mass ratio is very high. Regulation of skin blood flow in
response to changes in temperature is not well-developed.
Also, the non-shivering mechanism of thermogenesis
dependent upon brown fat is underdeveloped.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 737.

Question 39

Is nitrous oxide effective in premature infants?

Answer 39

Nitrous oxide is rarely used in this population. Nitrous oxide
must be given in a significant concentration to reduce MAC and
most premature infants do not tolerate the decreased inspired
oxygen concentration. Also, many premature infants undergo
surgery related to intestinal obstruction which makes nitrous
oxide a poor choice.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 739.

Question 40

In what premature infants would desflurane be a

poor choice for general anesthesia?

Answer 40

Because desflurane causes substantial airway irritation, it is not
recommended for use in premature infants with
bronchopulmonary dysplasia.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 738.

Question 41

Is fentanyl suitable for use in premature infants?

Answer 41

Yes. Doses between 30 and 50 mcg/kg administered during
surgery for ligation of a patent ductus arteriosus have been
noted to produce considerable hemodynamic stability. It should
be noted, however, that the half-life of fentanyl was significantly
prolonged (6-32 hours) in premature infants compared to the 2-
3 hours half-life in children and adults.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 39.

Question 42

Can remifentanil be used in premature infants?

Answer 42

Yes. Although it has not been studied in extremely pre-term
infants, the clinical effect and elimination half-life of remifentanil
have been shown to exhibit little difference in premature infants
compared to children and adults.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 739.

Question 43

How does the elimination half-life of propofol in
premature infants compare to that of children and
adults? Why?

Answer 43

The elimination half-life of propofol is longer because they have
less fat and muscle tissue available for redistribution of the drug.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 740.

Question 44

How does MAC compare between premature infants

and full-term infants?

Answer 44

MAC is considerably decreased in the premature infant.
Studies have demonstrated that the administration of 1 MAC of
isoflurane can reduce the systolic blood pressure by as much
as 30% in premature infants.
Cote CJ, Lerman J, & Anderson BJ. A Practice of Anesthesia
for Infants and Children. 5th Ed. Philadelphia: Elsevier
Saunders; 2013: 738.