9.6 Surfactant Administration & Response

9.6 Surfactant Administration & Response

Surfactant Administration Modalities

                      SURFACTANT DELIVERY STRATEGIES

    TRADITIONAL ETT INSTILLATION              LISA / MIST METHOD
    ┌──────────────────────────────┐          ┌──────────────────────────────┐
    │ Intubated neonate            │          │ Spontaneously breathing      │
    │ Positive pressure vent       │          │ Noninvasive Bubble CPAP      │
    │ Instilled via multi-access   │          │ Thin vascular catheter / tube│
    │ catheter or dual-lumen ETT   │          │ passed through vocal cords   │
    │ Administered in 2–4 aliquots │          │ Surfactant instilled over    │
    │ with position changes        │          │ 1–3 min; catheter removed    │
    └──────────────┬───────────────┘          └──────────────┬───────────────┘
                   │                                         │
                   ▼                                         ▼
    INSURE (INtubate-SURfactant-Extubate)     AVOIDS MECHANICAL VENTILATION
    • Intubate ──► Dose ──► Extubate to CPAP  • Limits planned ETT ventilation
    • Target extubation within 30–60 min      • Reduces BPD & pneumothorax

1. Traditional Endotracheal Instillation via Side-Port / Multi-Access Catheter

• The infant is intubated with an endotracheal tube.
• A dedicated multi-access closed suction catheter or side-port delivery adapter is attached.
• The calculated dose is drawn into a syringe and instilled directly into the trachea in 2 to 4 aliquots.
• Historically, the infant was rotated into right and left lateral decubitus positions between aliquots to facilitate gravity-assisted lobar distribution. Modern practice recognizes that rapid fluid capillary action distributes surfactant effectively without requiring extreme patient repositioning.

2. The INSURE Technique (INtubate - SURfactant - Extubate)

• Designed to deliver surfactant while avoiding prolonged mechanical ventilation.
• Preterm infants demonstrating moderate-to-severe RDS on CPAP are electively intubated, administered surfactant via ETT, briefly ventilated to ensure alveolar dispersion, and extubated directly back to nasal CPAP within $30\text{ to }60\text{ minutes}$.

3. Less Invasive Surfactant Administration (LISA) / Minimally Invasive Surfactant Therapy (MIST)

• A preferred option for selected infants: Many neonatal guidelines favor LISA/MIST for spontaneously breathing preterm infants on CPAP when the team has suitable expertise; eligibility and technique remain protocol-dependent.
• Technique:
  1. The preterm infant remains spontaneously breathing on continuous noninvasive positive airway pressure (typically Bubble CPAP at $6\text{ to }8\text{ cmH}_2\text{O}$).
  2. Under direct laryngoscopy or video laryngoscopy, a thin, flexible small-bore catheter (e.g., a 16–18 gauge Angiocath or a 4–5 Fr feeding tube) is gently advanced through the vocal cords into the upper trachea.
  3. Surfactant (preferably high-concentration Poractant alfa due to its low volume) is slowly instilled into the trachea over $1\text{ to }3\text{ minutes}$ while the infant continues spontaneous breathing.
  4. The spontaneous negative inspiratory thoracic pressure draws the surfactant droplets down into the bronchial tree, while CPAP preserves functional residual capacity.
  5. The catheter is removed immediately upon completion of instillation.
• Clinical Benefits and limits: LISA can reduce exposure to endotracheal positive-pressure ventilation and may reduce mechanical-ventilation-related complications in appropriate infants. It still requires laryngoscopy and tracheal catheterization, and apnea, treatment failure, or deterioration may require rescue ventilation or intubation.

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Acute Physiological Responses, Hazards & Ventilator Management

Administering exogenous surfactant triggers immediate, profound biomechanical changes within the neonatal lung. The respiratory therapist must anticipate these changes and intervene instantly at the bedside.

                  ACUTE POST-SURFACTANT PHYSIOLOGICAL CASCADE

                          [SURFACTANT INSTILLATION]
                                     │
                     Surfactant Spreads Rapidly & Lowers
                          Alveolar Surface Tension
                                     │
                                     ▼
              RAPID IMPROVEMENT IN COMPLIANCE & OXYGENATION
                    (Magnitude and timing vary by infant)
                                     │
           ┌─────────────────────────┴─────────────────────────┐
           ▼                                                   ▼
   IF VENTILATOR SETTINGS                             IF VENTILATOR SETTINGS
       REMAIN UNCHANGED                               ARE PROMPTLY REDUCED
           │                                                   │
  • Massive Tidal Volume Spikes                      • PIP titrated down rapidly
    (VT jumps 4 mL/kg ──► 12 mL/kg)                  • Target VT (4–6 mL/kg) preserved
  • Severe Alveolar Overdistension                   • FiO2 rapidly weaned
  • PULMONARY INTERSTITIAL EMPHYSEMA (PIE)           • Normocarbia maintained
  • TENSION PNEUMOTHORAX                             • SAFE LUNG RECOVERY
  • SEVERE HYPOCARBIA (PaCO2 < 25 mmHg)
    (Triggers Cerebral Vasoconstriction & PVL)

1. Immediate Reassessment and Ventilator Actions

• Ventilator reassessment: Compliance and oxygenation may improve rapidly, so the same pressure can produce a larger tidal volume. Continuously monitor exhaled volume and chest movement and reduce pressure promptly when indicated; do not make an automatic fixed reduction before observing the response.
• FiO2 titration: Oxygenation may improve quickly. Reduce FiO2 promptly as indicated to remain within the infant’s prescribed gestation- and condition-specific saturation range and avoid hyperoxemia.
• Prevention of Hypocarbia: Over-ventilation plunges $PaCO_2$ rapidly below $25\text{ to }30\text{ mmHg}$. Severe hypocarbia causes profound cerebral arteriolar vasoconstriction, resulting in cerebral ischemia and Periventricular Leukomalacia (PVL).

2. Peri-Administration Complications & Interventions

• Transient Airway Obstruction & Desaturation: Instilling a fluid bolus into a $2.5\text{ or }3.0\text{ mm}$ ETT creates a liquid meniscus that transiently obstructs gas flow, causing acute cyanosis and vagal bradycardia.
  • Action: Immediately pause instillation. Increase ventilator PIP by $2\text{ to }3\text{ cmH}_2\text{O}$ and transiently increase $FiO_2$ until the heart rate recovers ($> 100\text{ bpm}$) and saturations stabilize. Once cleared, resume instillation at a slower pace.
• Post-dose suctioning:
  • Avoid routine endotracheal suctioning during the interval specified by the surfactant manufacturer and local protocol; for some products this is about 1 hour.
  • If ventilation is impaired by suspected tube obstruction, assess patency and intervene without delaying necessary airway care.
• Pulmonary Hemorrhage Risk: A recognized complication of surfactant therapy occurring primarily in extremely low-birth-weight (ELBW, $< 1000\text{ g}$) infants with a large patent ductus arteriosus (PDA). As PVR falls rapidly post-surfactant, left-to-right ductal shunting surges, flooding the pulmonary capillaries and causing capillary stress failure. This requires immediate neonatal critical-care escalation: stabilize the airway and gas exchange, titrate PEEP and oxygen to the infant’s response, correct hemodynamic or coagulation problems, and individualize any repeat surfactant decision.

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Worked Clinical Calculation: Surfactant Dosing Formulation

Clinical Scenario

A 27-week gestational age female infant weighing $800\text{ grams}$ ($0.80\text{ kg}$) is delivered via urgent cesarean section for maternal pre-eclampsia. The infant develops severe respiratory distress syndrome requiring endotracheal intubation. The physician orders Poractant alfa (Curosurf) for the initial therapeutic dose.

Step-by-Step Dosing Calculation

1. Determine Initial Weight-Based Dose:

   • Recommended initial dose of Poractant alfa $= \mathbf{200\text{ mg/kg}}$ ($2.5\text{ mL/kg}$).

2. Calculate Total Dose in Milligrams (mg): $\text{Total Dose (mg)} = 0.80\text{ kg} \times 200\text{ mg/kg} = \mathbf{160\text{ mg}}$

3. Calculate Total Volume to Administer in Milliliters (mL):

   • Poractant alfa concentration $= 80\text{ mg/mL}$. $\text{Total Volume (mL)} = \frac{160\text{ mg}}{80\text{ mg/mL}} = \mathbf{2.0\text{ mL}}$ (Cross-check via volume multiplier: $0.80\text{ kg} \times 2.5\text{ mL/kg} = 2.0\text{ mL}$).

4. Calculate Subsequent Repeat Doses (if required at 12 hours):

   • Repeat dose $= 100\text{ mg/kg}$ ($1.25\text{ mL/kg}$). $\text{Repeat Dose (mg)} = 0.80\text{ kg} \times 100\text{ mg/kg} = \mathbf{80\text{ mg}}$ $\text{Repeat Volume (mL)} = 0.80\text{ kg} \times 1.25\text{ mL/kg} = \mathbf{1.0\text{ mL}}$

Therapist Execution: The therapist warms a vial of Curosurf to room temperature, gently inverts it, draws up precisely $2.0\text{ mL}$ into a sterile syringe, and delivers it via a side-port catheter while continuously monitoring heart rate, $SpO_2$, and expired tidal volume.

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NPS Exam Traps

[!WARNING]

Exam Trap 1: The "Post-Surfactant Pneumothorax"

After surfactant, rapidly improving compliance can make previously appropriate pressure deliver excessive tidal volume. Reassess pressure, volume, FiO2, and chest symmetry immediately. Sudden unilateral absent sounds with shock should be treated as tension pneumothorax without waiting for imaging; the teaching point is active titration to response, not an automatic fixed pressure reduction in every infant.

Exam Trap 2: Post-Surfactant Endotracheal Suctioning

Avoid routine suctioning during the product- and protocol-specified post-dose interval when ventilation is effective. Coarse sounds alone do not require suction, but suspected ETT obstruction with impaired ventilation warrants immediate patency assessment and necessary airway care.

Exam Trap 3: The Refractory Full-Term Infant

In a term infant with severe diffuse disease and little sustained response to exogenous surfactant, include inherited surfactant dysfunction such as SFTPB disease in the differential. Infection, pulmonary hypertension, structural disease, and other genetic disorders must also be evaluated. Genotype and residual protein influence phenotype, so nonresponse alone is not diagnostic and specialist genetic testing is required.