A Delayed Occurrence of Surfactant Proteins in An Extremely Preterm Infant

We report an infant with significantly delayed pulmonary surfactant protein secretion, whose clinical course is clearly different from that of a newborn infant with congenital alveolar proteinosis due to abnormalities of pulmonary surfactant protein (SP) B and SP-C genes. The case was female infant born weighting 1049 g at 26 weeks of gestation. After instillation of artificial lung surfactant as neonatal respiratory distress syndrome in the early postnatal period, respiratory management was started with high-frequency oscillation ventilation. Although the respiratory setting was temporarily weaned after that, the respiratory condition worsened from 3 days of age. As a result, it was necessary to instill the artificial lung surfactant 32 times in total by 35 days of age. This case was clinically inconsistent with congenital alveolar proteinosis based on both the fact that there was no increase in tracheal secretions in abnormal surfactant proteins and the concentrations and changes of serum KL-6, SP-A and SP-D. Pulmonary surfactant protein analysis of tracheal aspirate revealed a significantly delayed secretion of SP-C. The patient was discharged at 134 days of age without home oxygen therapy and is now well at age 2 years with normal growth and development. There is no respiratory infection that requires hospitalization. Unlike the usual clinical course such as RDS and congenital pulmonary alveolar proteinosis, this case is the second case suggesting a new specific disease as extreme delayed secretion of SP-C.


Case Report
A 1049-g female infant was born to a 40-year-old G2P1 mother at 26 weeks gestation via emergency cesarean section due to an indication of placental abruption. After birth, the infant underwent immediate tracheal intubation, and the first dose of artificial lung surfactant (Surfacten®) was instilled. High-Frequency Oscillatory (HFO) ventilation mode was selected as the initial ventilator setting.
However, further improvement of respiratory distress syndrome (RDS) was necessary (Figure 1), and two additional doses of artificial lung surfactant were given on the same day. The HFO mode was combined with intermittent mandatory ventilation to stabilize the infant's respiratory condition as a rescue mode. Because she required an F I O 2 of 0.5 from the age of 3 days to maintain an SpO 2 above 90%, additional surfactant was required. She required 32 doses of surfactant up to 35 days of age. Thereafter, we were able to gradually reduce the respiratory settings and succeeded in planned extubation at age 50 days.
Oxygen administration was stopped at age 91 days ( Figure   2), and she was discharged well at age 134 days. Her corrected gestational age was 46 w 0 d, and she weighed 4842g ( Figure 3).
Tracheal aspirates (TA) were obtained as follows. After instillation of 0.5mL saline, the airway was suctioned with a 4F catheter attached to a suction trap to recover the aspirates. The suction catheter lumen was then rinsed with saline, of which about 2mL in total was added to the trap. All TA were frozen at -20°C until assayed.
Tricine/sodium dodecyl sulfate polyacrylamide gel electrophoresis was performed with 20 µg of total protein, and immunoblotting was performed for surfactant protein (SP)-B and SP-C as previously described [1]. Commercially available ELISA kits for SP-A and SP-D of TA and serum were used. Data for SP concentrations are expressed as the standard value divided by albumin (µg/mg albumin). This study was approved by the ethics committee of the Japanese Red Cross Musashino Hospital.   Very little SP-A was detected in blood and TA, but it gradually increased after this age ( Figure 5). KL-6 and urinary β2MG levels increased up to the age of 30 days and then decreased ( Figure 6). We already reported in this journal an extremely preterm infant with no SP gene abnormalities but with a markedly delayed appearance of SP-B and SP-C in TA [2]. The present case is characterized by normal secretion of SP-B and SP-D but insufficient secretion of SP-A and SP-C for about 1 month. Currently, comprehensive gene testing is becoming popular, and urgent genetic testing is recommended for unexplained neonatal respiratory disorders [3].  In patients with congenital alveolar proteinosis, serum levels of SP-A and SP-D increase to several 100 or several 1000ng/mL, but this infant's SP-A remained low for a period of one month after birth before increasing. The level was maintained thereafter, and SP-D also increased by a factor of 2-3 to normalize at 3 months of age. shown to have almost no effect. [5] In the present patient, not SP-A, but only serum SP-D and KL-6 mildly increased, gradually decreased, and then remained within the normal range until the day of discharge, indicating that this is not the diagnosis for this patient. When surfactant was administered, FIO2 could be reduced for about 1 day as shown in Figure 2. The infant no longer required repeated doses of artificial lung surfactant from about 1 month after birth, when sufficient SP-C was found in her TA, and at the same time, the administered FIO2 could be reduced. It is possible that the lung tissue damage was minimized by frequent administration of artificial lung surfactant, which may have improved the prognosis.