Meconium Aspiration Syndrome Workup

Updated: Jun 28, 2023
  • Author: Gina M Geis, MD; Chief Editor: Dharmendra J Nimavat, MD, FAAP  more...
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Laboratory Studies

Acid-base status

Ventilation-perfusion (V/Q) mismatch and perinatal stress are prevalent in meconium aspiration syndrome (MAS); therefore, assessment of the infant's acid-base status is crucial.

Metabolic acidosis from perinatal stress is complicated by respiratory acidosis from parenchymal disease and persistent pulmonary hypertension of the newborn (PPHN).

Measurement of arterial blood gas (ABG) pH, partial pressure of carbon dioxide (pCO2), and partial pressure of oxygen (pO2), as well as continuous monitoring of oxygenation by pulse oximetry are necessary for appropriate management. The calculation of an oxygenation index (OI) can be helpful when considering advanced treatment modalities, such as extracorporeal membrane oxygenation (ECMO).

Serum electrolytes

Obtain sodium, potassium, and calcium concentrations at 24 hours of life in infants with MAS, because syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and acute renal failure are frequent complications of perinatal stress.

Complete blood cell (CBC) count

Note the following:

  • In utero or perinatal blood loss, as well as infection, contributes to postnatal stress.

  • Hemoglobin and hematocrit levels must be sufficient to ensure adequate oxygen-carrying capacity.

  • Thrombocytopenia increases the risk for neonatal hemorrhage.

  • Neutropenia or neutrophilia with left shift of the differential may indicate perinatal bacterial infection.

  • Polycythemia may be present secondary to chronic fetal hypoxia; polycythemia is associated with decreased pulmonary blood flow and may exacerbate the hypoxia associated with MAS and PPHN.

  • There is little evidence that empiric antibiotic therapy after obtaining a blood culture is beneficial, except in the case of prolonged rupture of the membranes and maternal fever.

Fetal scalp blood lactate sampling has not been shown to reduce the risk of respiratory distress syndrome in infants with meconium-stained amniotic fluid. [14]


Imaging Studies

Chest radiography

Chest radiography is essential in order to achieve the following:

  • Confirm the diagnosis of meconium aspiration syndrome (MAS) and determine the extent of the intrathoracic pathology

  • Identify areas of atelectasis and air leak syndromes

  • Ensure appropriate positioning of the endotracheal tube and umbilical catheters

See the images below.

Air trapping and hyperexpansion from airway obstru Air trapping and hyperexpansion from airway obstruction.
Acute atelectasis. Acute atelectasis.
Pneumomediastinum from gas trapping and air leak. Pneumomediastinum from gas trapping and air leak.
Left pneumothorax with depressed diaphragm and min Left pneumothorax with depressed diaphragm and minimal mediastinal shift because of noncompliant lungs.
Diffuse chemical pneumonitis from constituents of Diffuse chemical pneumonitis from constituents of meconium.



Echocardiography is necessary to ensure normal cardiac structure and for assessment of cardiac function, as well as to determine the severity of pulmonary hypertension and right-to-left shunting.

A prospective observational study of 117 newborns with MAS (and 100 controls) demonstrated that pulmonary ultrasonography may be a convenient, noninvasive, and accurate imaging modality for the diagnosis of MAS. [15] The primary features of MAS noted on sonograms included the following [15] :

  • Pulmonary consolidation with air bronchograms (all patients)

  • Pleural line anomalies and absence of the A-line (all patients)

  • Alveolar-interstitial syndrome or B-lines in nonconsolidated regions (all patients)

  • Atelectasis in severe MAS (16.2% of severe cases)

  • Pleural effusion (13.7% of patients)

Brain imaging studies

Later in the course of MAS, when the infant is stable and if the infant's neurologic examination is abnormal, imaging studies of the brain (eg, magnetic resonance imaging [MRI], computed tomography [CT] scanning, cranial ultrasonography) are indicated.