UBP 4.3 (Short Form): Pediatrics – CDH and Prematurity

Question 1

What is the likely cause of this neonate’s respiratory distress?

(A neonate, born at 38 weeks gestation, begins experience respiratory distress with nasal flaring, sternal retraction, and cyanosis shortly after birth. On examination he has a scaphoid abdomen and absent breath sounds on the left. VS: P = 154, BP = 72/45 mmHg, R = 62, T = 36.8 C. ABG: pH = 7.24, PaCO2 = 57, and PaO2 = 43 on room air.)

Answer 1

The signs of respiratory distress such as nasal flaring and sternal retraction, combined with a scaphoid abdomen and absent breath sounds on the left, are consistent with –

the presence of a congenital diaphragmatic hernia.

The herniation of abdominal contents into the thoracic cavity results in impaired maturation of lung tissue with subsequent impaired gas exchange, intrapulmonary shunting, and pulmonary hypertension.

Pulmonary hypertension impairs the transition from fetal circulation.

The resultant extrapulmonary shunting through the patent foramen ovale and patent ductus arteriosus leads to worsening hypoxia, hypercarbia, and acidosis, which, in turn, further exacerbate pulmonary hypertension, setting up a vicious cycle.

Question 2

The PAO-2 -PaO2 difference is 57 mmHg.

What do you think is the cause of this?

(A neonate, born at 38 weeks gestation, begins experience respiratory distress with nasal flaring, sternal retraction, and cyanosis shortly after birth. On examination he has a scaphoid abdomen and absent breath sounds on the left. VS: P = 154, BP = 72/45 mmHg, R = 62, T = 36.8 C. ABG: pH = 7.24, PaCO2 = 57, and PaO2 = 43 on room air.)

Answer 2

Hypoplastic lung tissue results in intrapulmonary shunting and persistent pulmonary hypertension.

Pulmonary hypertension then causes extrapulmonary shunting through the foramen ovale and ductus arteriosus.

Thus, a high PAO2-PaO2 difference occurs in these patients secondary to both intrapulmonary and extrapulmonary shunting.

Clinical Note:

• A normal A-a gradient in a young adult non-smoker is < 10 mmHg.
• Since the A-a gradient is primarily utilized to evaluate pulmonary function, it would be of little help in the assessment of a patient with excessive extra-pulmonary shunting.
• Therefore, in practice, this measurement would not likely be utilized in the assessment of a newborn with suspected congenital diaphragmatic hernia.
• It is utilized in this question to lead to a discussion about the shunting associated with CDH.

Question 3

What would be your initial treatment?

(A neonate, born at 38 weeks gestation, begins experience respiratory distress with nasal flaring, sternal retraction, and cyanosis shortly after birth. On examination he has a scaphoid abdomen and absent breath sounds on the left. VS: P = 154, BP = 72/45 mmHg, R = 62, T = 36.8 C. ABG: pH = 7.24, PaCO2 = 57, and PaO2 = 43 on room air.)

Answer 3

I would intubate the neonate, provide supplemental oxygen, and insert a nasogastric or orogastric tube for stomach decompression.

I would avoid positive pressure mask ventilation, which can further compromise respiratory function by distending intrathoracic viscera.

Furthermore, I would –

• correct any hypothermia
  
  • (hypothermia can exacerbate pulmonary hypertension) and
• establish ventilator settings with the goal of resolving hypoxia, hypercarbia, and acidosis
  
  • (all of which can exacerbate pulmonary hypertension)
• while avoiding high airway pressures, which increase the risk of pneumothorax
  
  • (usually on the contralateral side).

Finally, I would order –

• an ABG,
• chest radiographs, and
• an echocardiogram, with the echocardiogram serving to identify congenital cardiac defects, right heart dysfunction, and/or pulmonary hypertension.

Question 4

Do you need to intubate the neonate, or would mask ventilation be acceptable?

(A neonate, born at 38 weeks gestation, begins experience respiratory distress with nasal flaring, sternal retraction, and cyanosis shortly after birth. On examination he has a scaphoid abdomen and absent breath sounds on the left. VS: P = 154, BP = 72/45 mmHg, R = 62, T = 36.8 C. ABG: pH = 7.24, PaCO2 = 57, and PaO2 = 43 on room air.)

Answer 4

Mask ventilation should be avoided since –

it may result in distension of intrathoracic viscera with further compromise of respiratory function.

While there are exceptions, most neonates with a significant congenital diaphragmatic hernia require intubation and controlled ventilation.

Question 5

What steps would you take to treat the pulmonary hypertension?

(A neonate, born at 38 weeks gestation, begins experience respiratory distress with nasal flaring, sternal retraction, and cyanosis shortly after birth. On examination he has a scaphoid abdomen and absent breath sounds on the left. VS: P = 154, BP = 72/45 mmHg, R = 62, T = 36.8 C. ABG: pH = 7.24, PaCO2 = 57, and PaO2 = 43 on room air.)

Answer 5

The steps I would take to treat his pulmonary hypertension would include: –

1. ensuring normothermia and
2. initiating a ventilation strategy to resolve any hypoxia, hypercarbia, and acidosis that may be contributing to pulmonary hypertension
   
   • (respiratory alkalosis can effectively reduce pulmonary vascular resistance).
3. Then, if metabolic acidosis secondary to tissue hypoxemia persisted, I would – consider administering intravenous bicarbonate.
4. At the same time, I would – provide a muscle relaxant to reduce oxygen consumption, and
5. administer benzodiazepines or opioids for sedation.
   
   • The latter would serve to reduce the release of catecholamines, which could lead to additional increases in pulmonary vascular resistance.
6. If these interventions were unsuccessful, I would – consider pulmonary vasodilator therapies, such as – prostaglandin E1, nitrates, and nitric oxide.
7. And, if all else failed, I would – give consideration to extracorporeal membrane oxygenation (ECMO).