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Mechanisms of Pneumothorax in the Critically Ill
Air can accumulate in the pleural space in three ways:
- Rupture of the visceral pleura allowing air to travel from alveoli to the pleural space (an "internal" pneumothorax, as from barotrauma from mechanical ventilation, or the rupture of a bulla or bleb);
- Entry of air from the atmosphere into the pleural space, through trauma (as occurs in 50% of chest trauma victims) or a hole created by a doctor's needle during a procedure;
- Production of gas by organisms such as Clostridium within the pleural space; this is far less common.
Diagnosis of Pneumothorax in the ICU
Pneumothorax can be difficult to recognize in a critically ill patient. Physical exam and clinical signs and symptoms are unreliable and nonspecific, but may raise clinical suspicion for pneumothorax:
- Decreased breath sounds on one side
- Pulsus paradoxus
- Hemodynamic instability with tachycardia, hypotension
- Contralateral tracheal deviation
- Sudden increase in airway pressures (peak and plateau) in a mechanically ventilated patient
Because clinical signs are unreliable, radiography is required to diagnose pneumothorax.
Chest Ultrasound to Diagnose Pneumothorax
Mounting evidence suggests that thoracic ultrasonography by an experienced operator can be as accurate as chest X-ray at diagnosing pneumothorax. However, a brief training period is required.
The "lung point" (absence of sliding lung next to sliding lung) has a 100% specificity for pneumothorax, but its sensitivity is lower. The lung point sign is dependent on at least part of the lung contacting the chest wall -- therefore, it's better to diagnose small pneumothoraces and becomes less sensitive as a pneumothorax increases in size.
The presence of B-lines along with sliding lung has a 100% negative predictive value for pneumothorax at the point examined -- multiple areas must be examined to rule out pneumothorax with confidence.
Video tutorial on the bedside ultrasound for pneumothorax (thanks to the Hennepin County Department of Emergency Medicine):
Chest CT and Chest X-ray to Diagnose Pneumothorax
Chest CT is the gold standard for diagnosing pneumothorax, as well as determining size. Size is of less importance than clinical severity (hypoxia, distress, pain, hemodynamics) and pneumothorax size should not dictate management on its own.
Authors argue that chest X-rays have become effectively obsolete and should not be relied upon to diagnose pneumothorax in the critically ill patient. Pitfalls include potential loculated pneumothoraces occurring in heterogeneous ARDS or patients with pleural adhesions, as well as difficulties interpreting supine films. Although they essentially argue ultrasound should replace chest-X-rays, it's clear that most intensivists do not have this expertise.
Incidentally Discovered Pneumothorax in the ICU
Incidental or "occult" pneumothoraces are often discovered through CT scanning obtained without clinical suspicion of pneumothorax, especially on patients with trauma and/or on mechanical ventilation. Ideal management of these (evacuation with chest tube vs observation) is unknown. A recent multicenter observational study in mechanically ventilated patients (mainly surgical/trauma) suggested that observation of apparently stable incidentally discovered pneumothoraces, with placement of tube thoracostomy if the pneumothorax worsened or was causing significant problems, resulted in successful avoidance of unnecessary chest tubes without worsening outcomes.
Treating Pneumothorax in the ICU: Tube Thoracostomy
Standard practice is to place a chest tube for any pneumothorax occurring during mechanical ventilation, due to the risk of positive pressure expanding the pneumothorax into a tension pneumothorax. The British Thoracic Society explicitly recommends this, and also recommends tube thoracostomy for anyone with pneumothorax after trauma, surgery, or with tension physiology.
Authors consider small-bore chest tubes to be first-line therapy for pneumothorax in the ICU. Smaller-bore "pigtail" chest tubes have a lower rate of major complications than larger bore tubes, and work well for management of pneumothorax, including in mechanically ventilated patients. Evidence directly comparing small and large tubes is scant, but a retrospective review of >100 mechanically ventilated patients shows small-bore tubes work as well as in previous studies in larger-bore chest tubes, with no major complications.
Manual aspiration with thoracentesis (accepted practice for many cases of pneumothorax outside the ICU) has not been studied in critically ill patients and is not recommended.
Needle Decompression for (Suspected) Tension Pneumothorax
Suspect tension pneumothorax in patients:
- who are rapidly decompensating (hypoxemia, tachycardia, hypotension, suddenly high airway pressures);
- who have undergone CPR;
- who have a chest tube in place for prior pneumothorax (suspect tube blockage/kinking).
If there's a high clinical suspicion for tension pneumothorax, needle decompression should be performed with minimal delay. (If an experienced ultrasonographer is at hand, the diagnosis may be attempted that way first, if there are minutes to spare):
Insert a 14 to 16 gauge needle in the 2nd anterior intercostal space in the mid-clavicular line on the side suspected for pneumothorax.
If a patient is too obese for the needle to reach the pleural space, attempt needle decompression between the 4th and 5th intercostal spaces in the midaxillary line.
Place a tube thoracostomy as soon as feasible after needle decompression of tension pneumothorax.
Prolonged Air Leaks After Chest Tube for Pneumothorax
When to Consult Thoracic Surgery
British Thoracic Society guidelines suggest obtaining a thoracic surgery consult after 3-5 days of a persistent air leak after chest tube placement for pneumothorax; authors endorse this recommendation althoughthere is very little published data on surgical management of bronchopleural fistulas in critically ill or mechanically ventilated patients. If surgery is elected, the ACCP recommends VATS rather than open thoracotomy (in a non-evidence-based Delphi consensus statement).
Bronchoscopic Strategies for Management of Persistent Air Leaks
To avoid the morbidity of surgery, various bronchoscopic techniques have been introduced to manage persistent air leaks after chest tube placement for pneumothorax. One-way valves can be placed with an ordinary flexible bronchoscope without fluoroscopy and have been used successfully in non-critically ill patients with persistent air leaks. Attempts at leak closure using various glues, fibrin, metal coils, and other materials applied bronchoscopically have been reported, with insufficient data to recommend any of these.
Yarmus L, Feller-Kopman D. Pneumothorax in the Critically Ill Patient. Chest 2012;141:1098-1105.
MacDuff A et al. Management of spontaneous pneumothorax: British Thoracic Society pleural disease guideline 2010. Thorax 2010;65:ii18-ii31.