Prematurity Flashcards
What is the definition of a premature infant?
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.
What airway abnormalities commonly associated
with prematurity result in a decreased airway
diameter and increased resistance to airflow?
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.
What are the normal vital signs for a preterm infant?
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.
Which agents are commonly used in the treatment of
apnea in the premature infant?
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.
What are the ventilatory goals during the anesthesia
of a premature infant?
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.
What two significant conditions can occur due to the
presence of a patent ductus arteriosus?
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.
Why do premature infants have a decreased ability
to compensate for hypovolemia?
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.
Does the premature infant’s heart exhibit a greater or
lesser sensitivity to catecholamines?
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.
How does the heart of a premature infant differ from
that of a full-term neonate?
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.
What are the treatment regimens for postoperative
apnea in the premature infant?
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.
Does regional anesthesia eliminate the risk for
postoperative apnea in the premature infant?
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.
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?
Postconceptual age is the greatest factor associated with an
increased risk for apnea. A postconceptual age (gestational
age + chronological age)
What is the definition of postoperative apnea?
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.
What are the effects of increased pulmonary
vascular resistance on a patient with a patent ductus
arteriosus?
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.
Describe the premature infant’s ventilatory response
to hypoxia.
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.
How do low surfactant levels in the premature infant
predispose the patient to hypoxia?
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.
When does surfactant production in the lungs begin?
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.
How does tracheobronchomalacia result in
increased airway resistance in the premature infant?
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.
Do subglottic stenosis and tracheal stenosis both
require a smaller endotracheal tube?
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.
What is the mortality rate for respiratory distress
syndrome in the premature infant? Why does it
occur?
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.
What factors increase the risk for retinopathy of
prematurity?
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.
Can digitalis be used to promote increased cardiac
contractility in the premature infant?
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.
How are premature infants classified according to
birth weight?
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.
Why is apnea common postoperatively in premature
infants?
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.
