70: Pneumothorax

An infant may have a pneumothorax (an abnormal accumulation of air or gas in the pleural space, between the visceral and parietal pleura). It can develop spontaneous or be secondary to trauma. A pneumothorax occurs more often in the neonatal period than any other time in life.

1. Spontaneous pneumothorax

   1. Primary spontaneous pneumothorax (PSP). Occurs when there is no obvious precipitating factor, no clear cause, it is idiopathic, without lung disease. Familial spontaneous pneumothorax is a rare cause in neonates.

   2. Secondary spontaneous pneumothorax (SSP). Occurs from underlying lung disease (respiratory distress syndrome [RDS], meconium aspiration syndrome [MAS], and others).

2. Traumatic pneumothorax

   1. Iatrogenic occurs from an accidental insult during a procedure such as central line placement or thoracentesis.

   2. Positive pressure ventilation (mechanical or noninvasive ventilation) can cause barotrauma.

   3. Chest trauma can occur when blunt or penetrating trauma occurs to the chest (rare in neonate).

3. Tension pneumothorax. A life-threatening condition that occurs when air is trapped in the pleural cavity under positive pressure. Air goes into the pleural cavity during inspiration, but no air is allowed to escape during expiration. It acts as a 1-way valve. Because air is trapped, intrathoracic positive pressure rises, lung volume decreases, and pressure compresses the mediastinum and causes a shift, with increased pulmonary vascular resistance. This results in an increase in central venous pressure, decrease in venous return to the heart, and a decrease in cardiac output. This causes displacement of mediastinal structures and cardiopulmonary compromise.

4. Persistent pneumothorax. A pneumothorax that persists >7 days in the absence of mechanical problems.

1. Are symptoms of tension pneumothorax present? A tension pneumothorax occurs when air is trapped in the pleural cavity under positive pressure. A tension pneumothorax presents as a medical emergency, and the patient's status will deteriorate acutely. The following signs may be seen with tension pneumothorax: cyanosis, hypoxia, tachypnea, a sudden decrease in heart rate with bradycardia, a sudden increase in systolic blood pressure followed by narrowing pulse pressure and hypotension, an asymmetric chest (bulging on the affected side), distention of the abdomen (secondary to downward displacement of the diaphragm), decreased breath sounds on the affected side, and shift of the cardiac apical impulse (most consistent finding) away from the affected side. A cyanotic upper half of the body with a pale lower half can be seen.

2. Is the patient asymptomatic? An asymptomatic pneumothorax is present in 1–2% of neonates. It occurs more frequently in males and term and post-term infants. It is usually unilateral. Most of these cases are discovered on chest radiograph at admission. Up to 15% of these infants were meconium stained at birth.

3. Is mechanical ventilation being used? The incidence of pneumothorax in patients receiving positive-pressure ventilation is 15–30%. A life-threatening tension pneumothorax may result from mechanical ventilation.

4. Are there risk factors for a pneumothorax? Neonates delivered between 30 and 36 weeks, moderately preterm, or term by caesarean section have a higher incidence of pneumothorax. The following are associated with an increased risk: male infant, low birthweight, premature, meconium-stained amniotic fluid, vacuum extraction, a low 1-minute Apgar score, ventilator treatment, perinatal asphyxia, cardiopulmonary resuscitation, transient tachypnea, RDS, MAS, pneumonia, pulmonary hypoplasia, urinary tract anomalies, infants who were resuscitated at birth, continuous positive airway pressure, and positive pressure ventilation. α1-Antitrypsin deficiency may play a role in some cases of spontaneous pneumothorax of the newborn.

Radiologically, the differential diagnosis can include pneumomediastinum, congenital lobar emphysema, atelectasis with compensatory hyperinflation, congenital diaphragmatic hernia, congenital cystic adenomatoid malformation, and a large pulmonary cyst. Clinically, it can present as any process that causes respiratory distress, and it is important to exclude other causes of respiratory distress in a neonate: RDS, endotracheal tube obstruction/displacement, aspiration, congenital heart disease, asphyxia, congenital diaphragmatic hernia (CDH), congenital cystic adenomatoid malformation (CCAM), or pleural effusions. Sudden rapid deterioration in a neonate can be from a tension pneumothorax, pneumopericardium, or a massive pericardial effusion/cardiac tamponade (umbilical venous catheter).

1. Pneumothorax

   1. Symptomatic pneumothorax (includes tension vs nontension pneumothorax). Nontension symptoms: irritability, grunting, pallor cyanosis, restlessness, apnea, mild tachypnea, respiratory distress. Tension symptoms are noted in Section II.A previously.

   2. Asymptomatic pneumothorax.

   3. Persistent pneumothorax.

2. Pneumomediastinum. Air in the mediastinal space that may be confused with a true pneumothorax. On the radiograph, mediastinal air can elevate the lobes of the thymus (called “angel wing” or “spinnaker sail” sign), and the air can also track within the extrapleural space and outline the inferior aspect of the heart (“continuous diaphragm sign”). See Figure 11–19.

3. Congenital lobar emphysema. A rare anomaly of lung development that presents with respiratory distress and pulmonary lobar hyperinflation. Overdistention of one lobe secondary to air trapping occurs most commonly (47–50%) in the left upper lobe. Other lobe involvement is right upper lobe (20%), right middle lobe (28%), and lower lobes (rare). The causes of congenital lobar emphysema are multifactorial.

4. Atelectasis with compensatory hyperinflation. Compensatory hyperinflation may appear as a pneumothorax on a chest radiograph.

5. Pneumopericardium. In neonates, pneumopericardium and tension pneumothorax can both present as sudden and rapid clinical deterioration. In pneumopericardium, the blood pressure drops, heart sounds are distant or absent, and pulses are muffled or absent. Massive abdominal distention can also be seen. In tension pneumothorax, the blood pressure may initially increase, but then hypotension follows. The chest radiograph easily differentiates the two. A pneumopericardium has a halo of air around the heart (see Figure 11–18). The more common event is a tension pneumothorax. If one is unsure and time does not permit radiographic verification, quick transillumination can be done. If not available or unsure of results, it is better to insert a needle in the chest on the suspected side. If no response, then a needle should be inserted on the other side. If there is still no response, then the diagnosis of pneumopericardium should be considered.

6. Congenital diaphragmatic hernia (CDH). A developmental defect in the diaphragm allows the abdominal viscera to protrude into the chest, which causes pulmonary hypoplasia and decreased pulmonary vasculature and dysfunction of the surfactant system. Ninety percent are on the left side. CDH is often mistaken as a left tension pneumothorax. Presents with respiratory distress, cyanosis, and circulatory insufficiency. It can be hard to differentiate a left-sided pneumothorax from a typically left-sided CDH. With CDH, the abdomen is scaphoid, and the spleen cannot be palpated. There can be a mediastinal shift on radiograph. If chest tubes are placed, there is a risk of perforating the herniated viscus.

7. Congenital cystic adenomatoid malformation (CCAM). This rare congenital abnormality of the lung results from abnormal embryogenesis and reduced alveolar growth. The infants present with respiratory distress. Tachypnea and cyanosis can be presenting signs that are similar to a pneumothorax. Many of these are detected on ultrasound prenatally. A chest radiograph usually identifies the mass containing air-filled cysts. (See Chapter 135.)

8. Congenital pulmonary cysts. These are space occupying, involve one or more lobes, have atelectasis of the adjacent lobe, and have symptoms similar to pneumothorax.

1. Physical examination. Specific findings are discussed in Section II.A. Transillumination is a useful rapid bedside technique in neonates (see Section IV.C and Chapter 40).

2. Laboratory studies. Blood gas levels may show decreased Pao₂ and increased Pco₂, with resultant respiratory acidosis.

3. Imaging and other studies

   1. Transillumination of the chest is a rapid bedside method to identify a pneumothorax. Always verify the diagnosis of pneumothorax by a chest radiograph if time permits. The room lights are lowered, and a fiber optic transilluminator is placed along the posterior axillary line on the side on which pneumothorax is suspected. If a pneumothorax is present, the chest “lights up” on that side. The transilluminator may be moved up and down along the posterior axillary line and may also be placed above the nipple. Transilluminate both sides of the chest and then compare the results. If severe subcutaneous edema is present, transillumination may be falsely positive. Premature infants with pulmonary interstitial emphysema may also have a false-positive transillumination. Large infants with thick chest walls do not transilluminate well.

   2. Chest radiographs are the method of choice for diagnosing pneumothorax. Early pneumothoraces are difficult to diagnose. Early on, there is separation of lung from the chest wall with no lung markings in that space. In infants there is a tendency of pleural air to cloak diaphragmatic and mediastinal surfaces. A pleural line is often not seen, but a well-defined costophrenic sulcus (deep sulcus sign) can be observed. The following films will aid the diagnosis:

      1. Anteroposterior (AP) view of the chest (see Figure 11–20) will show the following:

         1. A shift of the mediastinum away from the side of pneumothorax (with tension pneumothorax).

         2. Depression of the diaphragm on the side of the pneumothorax (with tension pneumothorax).

         3. Displacement of the lung on the affected side away from the chest wall by a radiolucent band of air.

      2. Cross-table lateral view will show a rim of air around the lung (“pancaking”). It will not help to identify the affected side. You must have an AP film to identify the side of the pneumothorax. This film must be considered together with the AP view to identify the involved side. Pleural air tends to collect anteriorly and may require the CT or lateral decubitus view.

      3. Lateral decubitus view (shot through the AP position) will detect even a small pneumothorax not seen on a routine chest radiograph. The infant should be positioned so the side of the suspected pneumothorax is up (eg, if pneumothorax is suspected on the left side, the film is taken with the left side up).

   3. Ultrasound examination of the lungs. The absence of lung sliding (grainy appearance) and comet tails (normal pleura reflecting sound waves) confirms the ultrasound diagnosis of a pneumothorax. The sensitivity and specificity of ultrasound is 100% and 93% for a complete pneumothorax, and 79% and 100% for a radio-occult pneumothorax. As a bedside tool, this is useful to diagnose a pneumothorax.

   4. Transcutaneous carbon dioxide (tcpCO₂) reference percentiles with changes over time can indicate a pneumothorax or a blocked or misplaced endotracheal tube.

   5. Echocardiography and renal ultrasound may be indicated in spontaneous pneumothorax in term infants, as some of these infants can have renal and cardiac anomalies.

1. Symptomatic pneumothorax

   1. Tension pneumothorax. Symptomatic (tension) pneumothorax is an emergency! A 1- to 2-minute delay could be fatal. If a tension pneumothorax is suspected, act immediately. It is better to treat in this setting, even if it turns out that there is no pneumothorax. There is no time for x-ray confirmation. If the patient's status is deteriorating rapidly, a needle or catheter over needle can be placed for aspiration, followed by formal chest tube placement. There is no specific sign that distinguishes a tension from a nontension pneumothorax. Signs of a tension pneumothorax from above can also occur in a nontension pneumothorax, except the signs and symptoms are more severe in a tension pneumothorax.

      1. Needle aspiration (see Figure 70–1) can be done as an emergency. Often times this is all that is necessary if the infant is not on a ventilator. If on a ventilator, a chest tube placement may need to be followed by needle aspiration.

         1. The site of puncture should be at the second intercostal space along the midclavicular line on the suspected side of pneumothorax. Cleanse this area with antibacterial solution. The fourth intercostal space at the anterior axillary line can also be used (needle would be inserted above the fifth rib).

         2. Connect a 23- or 25-gauge butterfly needle or a 22- or 24-gauge catheter over needle (Angiocath) to a 10–20-mL syringe with a stopcock attached.

         3. Palpate the third rib at the midclavicular line. Insert the needle (perpendicular to the chest surface) over the top of the third rib at the second intercostal space, and advance it until air is withdrawn from the syringe. Have an assistant hold the syringe to withdraw the air. The needle may be removed before the chest tube is placed if the infant is relatively stable, or it may be left in place for continuous aspiration while the chest tube is being placed. If an Angiocath is used, the needle can be removed and the catheter left in place.

      2. Chest tube placement is discussed in Chapter 27. This is necessary in most infants on mechanical ventilation with a tension pneumothorax.

      3. If the infant does not improve with a chest tube. Suspect extrapleural air leaks such as a pneumoretroperitoneum, which has been reported in infants with pneumothorax. If air is still present on the radiograph, consider these causes: obstruction of the tube with blood or pleural fluid, disconnected drainage tube, ineffective water seal, new air leak, or a lung perforation.

   2. Nontension pneumothorax. Depending on the infant, oxygen supplementation, needle aspiration, chest tube placement, or conservative management (oxygen, close observation) is done.

      1. Mild symptoms. Some require observation only.

      2. Symptomatic spontaneous pneumothorax (not on ventilator). Needle aspiration and possible chest tube placement. In one study the majority of infants did not require a needle aspiration or chest tube and could be managed with supplemental oxygen or close observation.

      3. Symptomatic spontaneous pneumothorax (on the ventilator). Needle aspiration and chest tube placement. Some infants on a ventilator who have a pneumothorax could be treated conservatively without a chest tube, but they usually are more mature, on lower ventilator settings, and had better gases at the time of the pneumothorax as compared with the infants who required a chest tube.

2. Asymptomatic pneumothorax

   1. If positive-pressure mechanical ventilation is being used:

      1. Needle aspiration/chest tube. A chest tube will probably need to be inserted because the ventilator pressure will prevent resolution of the pneumothorax, and tension pneumothorax may develop. Sometimes needle aspiration is all that is needed. If a pneumothorax develops in a patient who is ready to be extubated, clinical judgment must be used in deciding whether a chest tube should be placed.

      2. Expectant management. Recent studies are showing that some select infants on a ventilator can be managed without a chest tube.

   2. If positive-pressure mechanical ventilation is not being administered and there is no underlying lung pathology, these may be considered.

      1. Close observation with follow-up chest radiographs every 8–12 hours or sooner if the infant becomes symptomatic. The pneumothorax will likely resolve within 24–48 hours.

      2. Nitrogen washout therapy (controversial). Allows a more rapid resolution of the asymptomatic pneumothorax but is infrequently used due to the toxicity of 100% oxygen. The infant receives 100% oxygen for 8–12 hours; less nitrogen is able to enter the lungs, and at the same time absorption of nitrogen from the extrapleural space is increased and then exhaled. The total gas tension is decreased, which also facilitates absorption of nitrogen by the blood. The method should be used only in full-term infants in whom retinopathy of prematurity will not be a problem. Some NICUS give only enough oxygen to maintain a pulse oximetry reading >90% and have found resolution to be similar to the hyperoxic group.

3. Persistent pneumothorax. Generally defined as a pneumothorax that persists >7 days in the absence of mechanical problems. Sometimes infants who have chest tubes still have air leaks that persist for more than a week. These infants have episodes of instability when air reaccumulates; some require a new or replacement chest tube and an increase in their ventilator settings. These are treated to decrease the complications associated with air leaks (air embolus, hypotension, intracranial hemorrhage). The following have been used:

   1. High-frequency oscillatory ventilation (HFOV) or high-frequency jet ventilation (HFJV) can be used due to lower mean airway pressures.

   2. Unilateral lung intubation has been reported as an efficient and relatively safe therapy for pneumothorax. Duration of therapy should be a minimum of 48 hours.

   3. Fibrin glue, such as CryoSeal C (ThermoGenesis Corp., Rancho Cordova, CA), has been injected in the chest tube with a marked reduction in the air leak. Risks include hypercalcemia, localized tissue necrosis, bradycardia, diaphragmatic paralysis, and pneumothorax on the contralateral side. More studies are needed before this treatment can be routinely recommended.

4. Pneumomediastinum. May progress to a pneumothorax or pneumopericardium. Close observation is required.

5. Congenital lobar emphysema. If asymptomatic, conservative management with observation. If symptomatic or respiratory failure is occurring, the treatment is usually surgical excision of the affected lobe.

6. Atelectasis with compensatory hyperinflation

   1. Chest physiotherapy and postural drainage should be initiated. Chest physiotherapy should be used with caution in premature infants. A study showed an association with intraventricular hemorrhage and porencephaly in extreme premature infants.

   2. Treatment with bronchodilators is indicated.

   3. Positioning the infant with the affected (hyperinflated) side down may speed resolution.

   4. Bronchoscopy. May be necessary with mucous plug.

7. Pneumopericardium. This should be treated emergently by pericardiocentesis (see Chapter 38).

8. Cystic adenomatoid malformation or congenital cyst. Surgery is the treatment of choice.