Neonatal Respiratory Monitoring

According to NNPD, a neonate is said to have respiratory distress if there are ≥2 of the following: 

1. Tachypnea: RR ≥60/min 
2. Subcoastal or Intercostal recessions (chest retractions) 
3. Expiratory grunting (Groaning) 

Other signs: Nasal flaring, Suprasternal retractions, Reduced air entry

Assessment and Monitoring

It can be performed using: 

• Clinical examination 
• Respiratory distress scores 
• Oxygen saturation assessment 
• ABG analysis 
• Oxygenation indices 

1. Clinical Examination:

RR: Look for tachypnea 

Use of accessory respiratory muscles: Indicating Retractions / Recessions 

Increased A-P chest diameter: Indicates hyperinflation seen in TTN and Meconium aspiration syndrome. 

Abnormal sounds 

Stridor (Inspiratory>Biphasic): Indicates extrathoracic obstruction, seen in Laryngomalacia, subglottic stenosis, Pierre Robin sequence. 

Grunting (expiratory): A mechanism to increase FRC by the sudden closure of the glottis, seen in RDS.

Stertor / Snoring (Inspiratory): Naso-pharyngeal obstruction, seen in adenoid hypertrophy and Oro-pharyngeal obstruction in macroglossia/micrognathia 

Wheeze (Expiratory) 

Crepitations/Crackles (Inspiratory) 

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2. Respiratory Distress Scores

2 types of scores are used to monitor ongoing distress in neonates: 

Silverman Anderson score 

Downes-Vidyasagar score 

Serial monitoring is more important than one-time assessment. The higher the total score, the greater the severity, and the worse the prognosis. The Silverman Anderson score (SAS) correlates well with overall mortality. Downes' score correlates well with pH, (A-a) DO₂, and PaO2 values. Traditionally, Downes score is used in term and SAS in preterm neonates. 

Silverman Anderson Score 

3 grades and 5 entities: 

Upper chest: 

• Grade 0: Synchronized 
• Grade 1: The lower part of the chest lags on inspiration 
• Grade 2: See saw movement between chest and abdomen is observed 

Lower chest: 

• Grade 0: No retractions 
• Grade 1: Just visible retractions 
• Grade 2: Marked retractions 

Xiphoid retractions 

• Grade 0: No retractions 
• Grade 1: Just visible retractions 
• Grade 2: Marked retractions 

Nares Dilatation 

• Grade 0: No nasal dilatation 
• Grade 1: Minimal dilatation 
• Grade 2: Marked dilatation 

Expiratory grunt 

• Grade 0: No grunting 
• Grade 1: Audible on stethoscope only 
• Grade 2: Audible with the naked ear.

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Downes Vidyasagar Score

Interpretation of total scores: 

• 0: No distress 
• 1-4: Mild distress 
• 5-7: Moderate Distress 
• > 7: Severe distress or Impending respiratory failure

3. Oxygen Saturation Assessment

Performed using pulse oximetry: Both pre-ductal (Rt. Hand) and post-ductal (Rt. or left legs) SpO₂ are taken. 

• Normal target SpO₂ (pre-ductal): 91-95% 
• Hypoxia: If SpO₂ < 90% on room air 

If the difference between pre- and post-ductal SpO₂ is > 5%, it is termed PPHN (Persistent Pulmonary Hypertension of 2 Newborns). These patients have PDAs with large right-to-left shunts, causing differences in SpO₂.

Limitations of pulse-oximetry

Not good to identify hyperoxia (SpO₂ > 95% may occur with PaO₂ 80-300mm Hg). Not reliable when SpO₂ < 70%. External conditions interfere with SpO2 measurement, like: 

• Ambient light and limb movements 
• MetHb and CO-Hb 
• Poor peripheral perfusion: e.g., shock 

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4. ABG Analysis in Respiratory Distress

It is used in conjunction with clinical status and monitoring scores. It is useful for identifying respiratory failure and the need for medical ventilation. Normal values: pH: 7.35-7.45, PaO₂ : 50-70 mm Hg, PCO: 35-45 mm Hg, Bicarbonates: 20-24 mEq/L and Base deficit of 3-5 2 2

Respiratory failure presents when:

• Hypoxemia (PaO < 50 mmHg) 
• Hypercarbia (PaCO₂ > 60 mm Hg)- Better indicator to define Respiratory Failure than Hypoxemia 
• Acidosis (pH < 7.2)

5. Oxygenation Indices 

a. Alveolar-Arterial Oxygen Pressure Difference (A-a Do₂ ) 

(A-a) DO₂ = [Pₐ O₂ – Pₐ O₂ ]

0.8 is the respiratory quotient. The difference between Atmospheric pressure and alveolar water vapor pressure is 713 

760 – 47 = 713

A-a Do₂: Normal infants: <20 mm Hg on room air. If it is more than 20-30mm Hg or more, it indicates a ventilation-perfusion mismatch or shunts. Differentiating them by giving 100% O₂ for 5-10min. Recheck PaO₂: If PaO₂ rises, it indicates ventilation-perfusion mismatch, and if PaO₂ remains the same, it indicates shunts. If there is hypoxia but normal (A-a) DO2, it indicates low FiO2, or alveolar hypoventilation.

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b. Arterial to alveolar oxygen tension ratio (a/A ratio)

Normal: 0.75 to 1. If < 0.3: Indicates that the O2 transfer is abnormal. It is a good marker of Ventilation-perfusion Mismatch and Alveolar-Capillary Integrity

a/A ratio =

c. Oxygenation Index (OI)

It is a marker of hypoxemic respiratory failure (HRF) and it is invasive

Normal value: 0.75-1 

If OI >15: It indicates V/Q mismatch 

If OI >25: Indicates Hypoxia needing NO indication 

If OI ≥40: It is an indication of ECMO 

d. Oxygen Saturation Index (OSI)

It is non-invasive. It is correlated with OI. OI = 2 × OSI. This formula is valid when the oxygenation index is between 5 and 25.

Important points 

A neonate has impending respiratory failure but has relatively low to normal SAS or Downes scores Causes: 

• Hypothermia 
• Apnea 
• Poor perfusion: E.g., Shock

Also read: Anatomy And Basics Of Pediatric Pulmonology

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