4.1 RDS, Surfactant, TTN, and Transitional Respiratory Failure

RDS, Surfactant, TTN, and Transitional Respiratory Failure

Quick Answer: Respiratory distress syndrome (RDS) is surfactant-deficient lung disease of the preterm infant: grunting, retractions, tachypnea, a low-volume ground-glass chest radiograph with air bronchograms, and a need for CPAP, surfactant, or both. Transient tachypnea of the newborn (TTN) is delayed clearance of fetal lung liquid in term and late-preterm infants—especially after cesarean birth without labor—and is milder, with fluid in the fissures and recovery usually in 24–72 hours. Secondary apnea after prolonged perinatal asphyxia does not respond to stimulation and needs positive-pressure ventilation (PPV).

Respiratory problems are 15% of scored Clinical Judgment on the current Neonatal CCRN Test Plan (exams on or after November 12, 2025). This OpenExamPrep chapter is independent teaching on acute respiratory distress and failure, transitional respiratory problems (surfactant deficiency and secondary apnea), apnea of prematurity, RDS, and TTN. It does not claim endorsement by AACN Certification Corporation. OpenExamPrep provides independent CCRN Neonatal study material covering the patient problems listed on AACN Certification Corporation's current Neonatal CCRN Test Plan.

Meconium aspiration, congenital diaphragmatic hernia, and the full pulmonary-hypertension pathway belong in the next respiratory chapter. This section owns surfactant physiology, the RDS versus TTN split, and the NRP distinction between primary and secondary apnea.

Why the lung must transform in minutes

The fetal lung is a secretory organ. Type II epithelial cells pump chloride and water into the airspaces, so the lung is fluid-filled by design. At birth that fluid must leave and a gas–liquid interface must appear, or the infant cannot oxygenate. Labor catecholamines and glucocorticoids switch the epithelium toward sodium absorption through epithelial sodium channels (ENaC). The first effective breaths pull residual fluid into the interstitium and pulmonary lymphatics. If surfactant is missing, every expiration collapses alveoli and the next inspiration costs a huge opening pressure. If ENaC and lymphatic clearance are slow, alveoli are open but wet, and the infant tachypneas until the water leaves.

A useful split for the exam and the crib: RDS is a detergent problem (not enough surfactant to keep alveoli open at end-expiration). TTN is a plumbing problem (fetal lung liquid still occupying the airspace). Both present with tachypnea. Gestational age, labor history, the chest radiograph, and the 48-hour trajectory separate them.

Typical quiet respiratory rates you should be fluent with: about 40–60 breaths/min in an unassisted term infant and often 40–70 in a preterm infant who is working. Distressed infants commonly exceed 80. A rate of 110 in a pink late-preterm infant after cesarean birth is a TTN-range number until the film and oxygen need say otherwise. A rate of 80 with deep retractions and a grunt in a 26-week infant is RDS-range work, not a fluid-in-the-fissure story.

Surfactant physiology you must be able to teach

Pulmonary surfactant is a phospholipid–protein film secreted by type II pneumocytes. The dominant phospholipid is dipalmitoylphosphatidylcholine (DPPC), the lecithin of obstetric lung-maturity language. Surfactant proteins B and C organize the film so it spreads and re-spreads with each breath. Isolated SP-B deficiency is a rare genetic lethal respiratory failure in a term infant and is not ordinary prematurity RDS. SP-A and SP-D participate in innate immunity and are part of why an infected, protein-flooded lung stops responding to a surfactant dose.

Surfactant lowers surface tension most at low alveolar volume. The Laplace relationship (pressure = 2 × tension / radius) is the reason small alveoli would otherwise empty into larger ones. Without surfactant, atelectasis spreads, functional residual capacity (FRC) collapses, ventilation–perfusion mismatch widens, and the infant becomes hypoxemic, then hypercarbic, then exhausted. Compliance is low. The radiograph looks small-volume, not hyperinflated.

Lung-maturity testing (L/S ratio, phosphatidylglycerol) still appears in obstetric notes. An L/S ratio of about 2.0 or higher and the presence of phosphatidylglycerol historically predicted a lower RDS risk. You will not run those tests at the warmer. You will use gestational age, antenatal corticosteroids, maternal diabetes, and asphyxia as the risk stack.

Antenatal corticosteroids (commonly betamethasone 12 mg intramuscularly, two doses 24 hours apart, or an equivalent dexamethasone course) accelerate type II cell function and reduce RDS, IVH, and necrotizing enterocolitis risk in threatened preterm birth. The largest effect is when the course is completed about 24 hours to 7 days before delivery. Incomplete steroids do not make RDS impossible; they make it less likely. Insulin in the infant of a diabetic mother delays surfactant appearance, which is why a 36-week IDM can still have a true RDS film.

Surfactant appears in useful amounts mainly after about 34 weeks, with a late surge in phosphatidylglycerol near term. That is why a 26-week infant and a 36-week infant do not share a default differential even when both grunt.

Facts that change nursing, not just flashcards:

• Cold stress, acidosis, and hypoxemia impair surfactant function and recycling. Thermal and metabolic hygiene are lung therapy. Keep core temperature near 36.5–37.5 °C unless a specific protocol says otherwise, and treat hypoglycemia that is stealing the infant's work budget.
• Protein-rich edema inactivates surfactant. Pulmonary hemorrhage or a flooding PDA can look like RDS that stopped responding.
• Exogenous surfactant can be inactivated the same way. A dose is not a one-time charm if the lung is flooded, infected, or left atelectatic.

RDS: the preterm phenotype

RDS—hyaline membrane disease in older language—is the clinical expression of primary surfactant deficiency. Risk climbs as gestational age and birth weight fall. Extremely preterm infants have the disease until proven otherwise. Late-preterm infants can still have it, especially with no labor, no steroids, or diabetes. Term RDS is uncommon and should make you think of asphyxia, early pneumonia, surfactant-protein genetics, or mislabeled TTN or PPHN—not a shrug.

Bedside signs, often within minutes to a few hours of birth:

• Tachypnea, commonly 60–80+ breaths/min
• Grunting: partial glottic closure that creates auto-PEEP and defends FRC. Treat the cause; do not shush a grunt.
• Nasal flaring and retractions (subcostal, intercostal, sternal, suprasternal). A see-saw chest–abdomen pattern means the highly compliant preterm chest wall is collapsing inward while the abdomen pushes out.
• Cyanosis or a climbing oxygen need to keep saturations in the unit target (often 90–95% in preterm infants without a PPHN protocol)
• Diminished air entry; crackles if edema is present
• Fatigue: the infant who grunted and now has pauses is failing, not settling

Silverman–Andersen or similar work-of-breathing scores quantify retractions, nasal flare, and grunt. A climbing score plus rising FiO2 is an escalation trigger, not a chart decoration.

Chest radiograph: low lung volumes, diffuse ground-glass opacities, prominent air bronchograms (air-filled bronchi silhouetted against fluid-filled alveoli), and sometimes a bell-shaped thorax. Heart size is usually normal. If the film is patchy and hyperinflated in a post-term infant with meconium, you are not looking at classic RDS. If the abdomen is scaphoid and bowel is in the hemithorax, that is congenital diaphragmatic hernia (CDH), not white-out RDS.

Blood gas: hypoxemia first, then respiratory acidosis as CO2 rises. A 26-week infant with pH 7.19 and PaCO2 68 mm Hg on CPAP 7 cm H2O and FiO2 0.50 is not a little TTN. That infant is heading toward acute failure (section 4.2).

Exogenous surfactant, CPAP, and intubation

Modern RDS care is CPAP-first lung recruitment plus surfactant for infants who still meet failure criteria, not automatic intubation of every 30-week infant.

Nasal CPAP (typically 5–8 cm H2O, sometimes titrated toward 8–9 with caution for air leak) stents alveoli, preserves surfactant, and reduces intubation. Interfaces—binasal prongs or mask—need a seal without septal injury. Rotate pressure points, watch the philtrum, and treat a sudden deterioration with asymmetric chest or a brighter transillumination as pneumothorax until proven otherwise.

Exogenous surfactant preparations used in U.S. NICUs include poractant alfa (often 2.5 mL/kg first dose, subsequent 1.25 mL/kg), beractant (4 mL/kg), and calfactant (3 mL/kg). Follow the labeled volume and your unit protocol; do not invent a milliliter dose from adult memory. Give through an endotracheal tube or a thin catheter. Brief distribution breaths and position changes help the drug reach both lungs. Expect a rapid rise in compliance. If you leave a high PIP in place after the dose, you can create an air leak. Wean pressures and FiO2 as saturations climb.

INSURE (INtubate–SURfactant–Extubate to CPAP) is one sequence. LISA or MIST (less-invasive or minimally invasive surfactant administration) uses a thin catheter while the infant stays on CPAP, avoiding a full intubation–ventilation course when it works. Failure of LISA—persistent high FiO2, apnea, or severe acidosis—means intubate and ventilate rather than repeating a ritual that is not recruiting.

Intubation is indicated for apnea that is not brief and recoverable, extreme work of breathing, rising CO2 with acidosis, or oxygenation failure despite CPAP and surfactant. ETT size is weight- and gestation-based (often 2.5 mm internal diameter under about 1000 g, 3.0 near 1000–2000 g, 3.5 above that). Confirm with your unit table.

Nursing around the dose: confirm identity and milliliters per kilogram, pre-oxygenate as ordered, watch heart rate during laryngoscopy, auscultate after the dose, document FiO2 and mean airway pressure before and after, and do not disconnect the circuit for a casual listen that collapses FRC. Family presence and a one-sentence explanation (why the medicine, what the next hour looks like) are Clinical Judgment and Facilitation of Learning, not extras.

TTN: delayed lung-fluid clearance

Transient tachypnea of the newborn is the most common respiratory diagnosis in term and late-preterm infants. The mechanism is slow clearance of fetal lung liquid—immature or unstimulated ENaC—especially when there was no labor. Extra risk: late preterm (34–36 6/7 weeks), cesarean delivery, infant of a diabetic mother, male sex, and macrosomia in some series. Precipitous vaginal birth can also leave fluid behind because the catecholamine switch was short.

Picture: an infant who is often 36–40 weeks, frequently born by cesarean, who looks reasonably pink but breathes 80–120 times per minute with mild retractions and little or no grunt compared with RDS. Oxygen need is usually modest (hood, nasal cannula, or a short CPAP trial). Air entry is good. The infant is not collapsing between breaths the way a 25-week RDS infant is.

Radiograph: normal to increased volumes (not the microatelectatic RDS film), perihilar streaking, fluid in the minor fissure, a mildly large-looking heart from vascular prominence, and sometimes a small amount of pleural fluid. Air bronchograms are not the dominant motif.

Course: improvement over 24–72 hours as lymphatics clear water. Persistent high FiO2, a pre/post-ductal saturation gap, or a film that becomes patchy should reopen the differential: pneumonia, MAS, occult heart disease, or PPHN. Surfactant is not first-line TTN therapy. Antibiotics are a clinical decision when sepsis cannot be excluded. TTN is not a reason to skip a late-preterm infection evaluation if other risk factors exist.

RDS versus TTN at a glance

Primary versus secondary apnea in the delivery room

NRP physiology belongs here because the test plan lists secondary apnea with transitional respiratory failure.

After asphyxia, the infant may have a period of primary apnea: heart rate may fall, but stimulation and opening the airway often restore breathing. If the insult continues, the infant enters secondary apnea: gasping stops, heart rate stays low, and stimulation will not restart breathing. That infant needs PPV, not another round of drying as the only action. Secondary apnea is an acute perinatal event. It is not the same as apnea of prematurity on day 8 in a 27-week infant (section 4.3). Mixing those labels is a high-yield exam error.

A worked delivery-room contrast: a 39-week infant who is apneic after a nuchal cord, heart rate 50, and no response to drying needs PPV now. A 27-week infant on day 10 who pauses for 15 seconds, drops to SpO2 78% and heart rate 75, then restarts with a gentle stimulus is AOP until you have ruled out sepsis and anemia—not NRP secondary apnea.

Sort MAS, PPHN, and CDH without stealing chapter 5

You still have to sort look-alikes at the bedside so you do not treat them as RDS or TTN.

• Meconium aspiration syndrome (MAS): usually term or post-term, meconium-stained fluid, barrel chest, patchy infiltrates, hyperinflation, high PPHN risk. Not a 24-week ground-glass film.
• Persistent pulmonary hypertension of the newborn (PPHN): labile hypoxemia, right-hand (pre-ductal) saturation higher than a foot (post-ductal) saturation, loud second heart sound. Transitional PVR failed to fall (chapter 2 mechanism; chapter 5 management). RDS and TTN can trigger PPHN, but the shunt physiology is an extra diagnosis, not a synonym for tachypnea.
• CDH: scaphoid abdomen, bowel loops in the chest, usually left-sided. Immediate intubation is preferred over prolonged bag-mask ventilation that inflates viscera in the chest. Do not mistake that film for RDS.

Worked NICU examples

Example A. A 27-week, 890 g infant, incomplete steroids, grunting at 5 minutes of life, retractions, SpO2 82% in 40% oxygen. CPAP 6 cm H2O is started. At 2 hours FiO2 is 0.45, the film is ground-glass with air bronchograms, and PaCO2 is 62 mm Hg. This is RDS. Plan surfactant by the unit's INSURE or LISA pathway. Do not wait for a 72-hour TTN clock.

Example B. A 37-week infant after repeat cesarean without labor is 110 breaths/min at 2 hours, SpO2 94% in 25% oxygen, mild subcostal retractions, film with fluid in the fissure and streaky perihilar markings, good volumes. This is TTN. Support, evaluate for infection if indicated, expect improvement by the second day. Surfactant is not the opening move.

Example C. A 40-week infant is born after a tight nuchal cord, limp, apneic, heart rate 50. Stimulation does not produce a breath. This is secondary apnea—start PPV now. Calling it apnea of prematurity is wrong; the infant is not a day-old preterm with an immature brainstem.

Exam traps: treating every tachypnea as one disease; delaying PPV in secondary apnea because the infant might still be in primary apnea after a long asphyxial course; describing this OpenExamPrep section as official AACN procedure training. It is independent teaching covering listed patient problems. Mixed practice items are at /practice/ccrn-neonatal. Pediatric respiratory pages at /study-guides/ccrn-pediatric address older children, not this transitional hour.