- A neonatology team was called to evaluate a full-term male infant with
severe respiratory distress and cyanosis at a few minutes of age. The infant
had been born by vaginal delivery after his mother presented in spontaneous
labor. Labor was complicated by maternal fever.Upon arrival, the pediatric resident initiates continuous positive airway
pressure (CPAP) with 21% F IO 2 using a bag-mask. The infant’s work of
breathing decreases and the baby appears pink with a right-arm pulse
oximetry reading of 94%. The infant’s physical examination reveals
decreased aeration bilaterally. The infant is then admitted to the Neonatal
Intensive Care Unit for further care. -
In the intensive care unit, the baby is placed on a cardiovascular monitor.
The infant’s vital signs are:
• HR = 160 beats per minute
• RR = 84 breaths per minute
• BP = 60/40 mm Hg
• T = 100.9°F (38.3°C)
The nurse sends a complete blood count, blood culture, and an arterial
blood gas. She also places an IV and administers intravenous ampicillin and
gentamicin.
1. Of the following (noted in the table below), the normal arterial blood gas results in a newborn in room air are:ABG NB -
The infant’s arterial blood gas results while receiving CPAP with a positive
end-expiratory pressure (PEEP) of 5 cm H 2 O and 21% F IO 2 are shown
below:
pH = 7.17, Paco 2 = 75 mm Hg, Pao 2 = 32 mm Hg, HCO 3 = 26 mEq/L,
base excess = –1.3 mEq/L
2. Of the following, the most likely interpretation of this infant’s arterial
blood is a:A. Metabolic acidosis
B. Metabolic alkalosis
C. Respiratory acidosis
D. Respiratory alkalosis
The infant’s clinical examination worsens, and the infant has severe
respiratory distress and decreasing oxygen saturations. Even though the
team increases the F IO 2 to 100% and increases the PEEP to 7 cm H 2 O, the
infant remains cyanotic and has persistent respiratory distress. The infant is
then intubated and placed on spontaneous intermittent mechanical
ventilation with the following settings:
• Peak inspiratory pressure (PIP) of 26 cm H 2 O
• PEEP = 6 cm H 2 O
• Rate = 25 breaths per minute
• F IO 2 = 100%
A chest radiograph shows that the endotracheal tube is appropriately positioned and the lung fields reveal bilateral pneumonia. There is noevidence of a pneumothorax or pleural effusions. An echocardiograph
reveals a structurally normal heart with normal function and a patent ductusarteriosus with left-to-right (aorta to pulmonary artery) shunting. -
A repeat arterial blood gas is obtained and the results are:
pH = 7.08, Paco 2 = 95 mm Hg, Pao 2 = 38 mm Hg, HCO 3 = 27 mEq/L,
base excess = –1.8 mEq/L
The infant’s complete blood count results are:
• White blood cell count = 3 × 10 3 /μl (neutrophils 20%, bands 20%,
lymphocytes 60%)
• Hemoglobin = 11g/dL (mmol/L)
• Hematocrit = 33% (0.33)
• Platelet count = 150 × 10 3 /μl (150 × 10 9 /L) -
3. Of the following, the most effective next step to improve this infant’s
oxygenation is to:
87
A. Increase the inspiratory time
B. Increase the PEEP
C. Increase the PIP
D. Increase the rate -
4. Of the following, the most effective next step to decrease this infant’s
carbon dioxide concentration is to:
A. Decrease the flow
B. Decrease the PIP
C. Increase the PEEP
D. Increase the rate -
In the setting of respiratory failure, the team attempts multiple strategies to
improve this infant’s oxygenation, including:
• Ventilator change to a high-frequency oscillator
• Frequent endotracheal suctioning
• Packed red blood cell transfusion to increase the infant’s oxygen-
carrying capacity
• Sedation to prevent the infant from breathing against the ventilator
• Placement of an arterial line for frequent arterial gas monitoring
Because this infant has severe respiratory failure with persistent hypoxemia
that has not responded to any medical interventions, the neonatal team
consults the pediatric surgeon to place the infant on extracorporeal
membrane oxygenation (ECMO).
5. Of the following, the type of ECMO that is most indicated in this infant
is:
A. Arterio-arterial (AA)
B. Arteriovenous (AV)
C. Venoarterial (VA)
D. Veno-venous (VV)The infant is placed on ECMO for 5 days, and with resolution of the pneumonia, the baby is able to be decannulated without difficulty. The infant is discharged home at 3 weeks of age with close neurologic follow-
up.
ANSWERS
- 1. B. pH = 7.39, Paco 2 = 44, Pao 2 = 70
The normal pH of a neonate ranges between ~7.35 and 7.43. Normal Pao 2
(i.e., arterial Po 2 ) values range between 60 and 90 mm Hg and Paco 2 (i.e.,
arterial Pco 2 ) values range between 35 and 45 mm Hg. Thus, the arterial
blood gas with a pH = 7.39, Paco 2 = 44, and Pao 2 = 70 is normal for an
infant.
An infant with an arterial Po 2 of 30, as shown in option A, has
hypoxemia. Because an infant is unable to achieve a Pao 2 of 140 in room
air, option D is not possible. However, if an infant receives supplemental
oxygen, the Pao 2 can be greater than 150 if the baby does not have cardiac
or respiratory disease. If an infant has an arterial Pco 2 that is too low, as in
option C, this may lead to cerebral vasoconstriction. - 2. C. Respiratory acidosis
- The infant in this vignette has severe cyanosis and respiratory distress. An arterial blood gas is helpful to assess an infant’s ventilation andoxygenation. If the pH is low (i.e., acidotic) and the Paco 2 is high, this is
consistent with a respiratory acidosis and demonstrates that an infant is notventilating effectively because of lung disease. This infant’s blood gas isconsistent with a respiratory acidosis.In contrast, if the pH is high (i.e., Alkalotic) and the Paco 2 is low, this is consistent with a respiratory alkalosis. A respiratory alkalosis is sometimes observed in infants with a urea cycle defect.
Metabolic acidosis is associated with a low pH and a low Paco 2 . Theinfant’s anion gap can be helpful to determine the cause of an infant’s metabolic acidosis. The anion gap is calculated by the difference between
cations and anions:
Anion gap = [Na + ] – ([Cl – ] + [HCO3 – ])A metabolic acidosis with an elevated anion gap is associated with shock, sepsis, renal failure, and metabolic disorders. A metabolic acidosis with a normal anion gap can result from renal tubular acidosis, diarrhea, and
congenital adrenal hyperplasia. A metabolic alkalosis is associated with an elevated pH and Paco 2 . A
metabolic alkalosis can be found in infants with emesis, diuretic use, and
Bartter syndrome.
3. B. Increase the PEEP
Oxygenation is most dependent on mean airway pressure. The most
effective way to increase mean airway pressure is by increasing the PEEP.
However, as the PEEP increases, the tidal volume decreases and can
compromise ventilation.
Increasing the PIP or increasing the inspiratory time will also increase
mean airway pressures, but not as effectively. By increasing the flow or rate
on a ventilator, a small increase in mean airway pressure may occur. -
4. D. Increase the rate
There are several ventilator strategies to decrease an infant’s Paco 2 ,
including:
• Increase the rate
• Increase PIP (note: if the PEEP stays constant, an increase in PIP will
increase tidal volume)
• Decrease PEEP (note: if the PIP stays constant, a decrease in PEEP
will increase tidal volume)
• Increase flow
• Increase the expiratory time
However, each of these changes can lead to secondary consequences. For
example, by increasing the ventilator rate, stacked breaths or inadvertent
PEEP can occur, which may decrease tidal volume and increase Paco 2 . An
increase in PIP or flow can induce barotrauma. While an infant’s tidal
volume will increase with a decrease in PEEP, the mean airway pressure
will also decrease, and this may lead to worsening hypoxemia. Similarly, anincrease in expiratory time can decrease mean airway pressure and worsen
an infant’s oxygenation.
5. D. Veno-venous (VV) - Despite multiple strategies to treat the infant in this vignette, the infant
- remains hypoxemic. ECMO is an option for infants who fail maximal
ventilator support with 100% F IO 2 and have an elevated alveolar–arterial
O 2 gradient and a high oxygenation index. ECMO is contraindicated in the
following infants:
• Premature infants (typically those infants who are <34 weeks’
gestation)
• Irreversible lung disease
• Irreversible severe neurologic abnormalities
• Severe intraventricular hemorrhage
• Significant coagulopathy
• Congenital anomalies incompatible with a good long-term outcome
There are two types of ECMO: VV and VA. In VV ECMO, blood from an
infant’s vein is circulated outside of the infant, oxygenated, and returned
back to the infant’s venous circulation. In VA ECMO (see Figure 1), blood
is similarly removed from an infant’s vein and oxygenated outside of the
body. However, blood is returned back to the infant’s arterial circulation,
bypassing the infant’s heart. VA ECMO is used when an infant’s cardiac
dysfunction is partly responsible for the infant’s hypoxemia. Because the
infant in this vignette has hypoxemia primarily resulting from a respiratory
process, VV ECMO will be effective at oxygenating and ventilating this
baby.
Superintendent, ICH.