9.3 Pleural Space Abnormalities: Pneumothorax, Effusion and Hemothorax

Why the Pleural Space Belongs on the CMC Blueprint

Test-plan item II.A.3 is not a thoracic-surgery lecture. Cardiac patients accumulate pleural fluid because their hearts fail, they develop pneumothoraces because we put catheters and leads into their chests, and they die of tension physiology and clotted mediastinal drains that a nurse could have caught. Every pleural problem in this section is either caused by cardiac disease, caused by cardiac procedures, or mistaken for cardiac decompensation.

Pleural Effusion: Transudate versus Exudate

The first fork in the road is whether the fluid crossed an intact membrane because of pressure (transudate) or leaked through an injured, inflamed membrane (exudate).

Light's Criteria

Fluid is an exudate if ANY ONE of the following is met:

Light's criteria are about 98% sensitive for exudate but only about 80% specific, and the failure mode is precisely the patient you care for: a heart failure effusion that has been diuresed concentrates protein and LDH in the pleural fluid and gets misclassified as an exudate in roughly 25-30% of cases. When the clinical picture is clearly heart failure but Light's says exudate, the confirming tests are:

• Serum-to-pleural-fluid albumin gradient greater than 1.2 g/dL (transudate), or
• Serum-to-pleural-fluid protein gradient greater than 3.1 g/dL (transudate), or
• Pleural fluid NT-proBNP above roughly 1,500 pg/mL, which supports a cardiac origin.

The Effusions You Will Actually See

• Heart failure effusion. Bilateral in 55-70% of cases; when unilateral, right greater than left; transudative, clear and straw-colored; resolves with decongestion. A unilateral left-sided effusion, an effusion with fever or pleuritic pain, or one that fails to respond to diuresis deserves a different explanation — do not attribute it to heart failure by default.
• Post-cardiac-surgery effusion. Typically left-sided after CABG with internal mammary artery harvest and pleurotomy; usually small and self-limited. A late effusion appearing 2-4 weeks post-operatively with fever, pleuritic pain, elevated inflammatory markers and often a pericardial effusion suggests post-cardiac injury (Dressler) syndrome, which is exudative, often eosinophilic, and treated with NSAIDs plus colchicine rather than antibiotics.
• Parapneumonic effusion and empyema. Uncomplicated parapneumonic effusions are free-flowing with pH above 7.20, glucose above 60 mg/dL and LDH under 1,000 IU/L, and respond to antibiotics alone. Complicated effusions (pH under 7.20, glucose under 60 mg/dL, LDH above 1,000, positive Gram stain, or loculation) require drainage. Empyema is frank pus or organisms on Gram stain and requires a chest tube, often with intrapleural alteplase 10 mg plus dornase alfa 5 mg twice daily for 3 days, or VATS decortication. This is a real complication of prolonged intubation and post-operative pneumonia in cardiac surgery patients.
• Hemothorax. Pleural fluid hematocrit 50% or more of the serum hematocrit. Causes in the cardiac unit: subclavian or internal jugular line placement, pacemaker or ICD lead placement, pericardiocentesis, thoracentesis, chest compressions, anticoagulation with a small pleural injury, and rupture of a thoracic aortic aneurysm. Surgical exploration is indicated for an immediate drainage of 1,500 mL or more, or ongoing drainage above 200 mL/h for 2-4 hours.
• Chylothorax. Milky, non-clearing drainage after thoracic duct injury — thoracic or cardiac surgery, high left internal jugular or subclavian cannulation, or central venous thrombosis. Confirmed by pleural fluid triglycerides above 110 mg/dL with chylomicrons present. Management: drainage, a low-fat diet with medium-chain triglycerides or total parenteral nutrition, octreotide, and lymphangiography with duct embolization or ligation if output persists. High-output chylothorax depletes protein, immunoglobulins and lymphocytes — nutrition and infection risk are nursing concerns.

Pneumothorax

Classification and the Cardiac Causes

• Primary spontaneous: tall, thin, young, smoker; ruptured apical bleb.
• Secondary spontaneous: underlying lung disease (COPD, cystic fibrosis, interstitial disease) — much less well tolerated because there is no reserve.
• Iatrogenic — the cardiac-unit list: subclavian and internal jugular central venous catheter insertion, pulmonary artery catheter placement, permanent pacemaker and ICD lead implantation via subclavian puncture, subxiphoid pericardiocentesis, transbronchial or pleural biopsy, barotrauma from positive-pressure ventilation, and chest compressions. A post-device-implant pneumothorax may not be visible on the immediate post-procedure film and can declare itself 24-48 hours later, so a normal post-procedure chest radiograph does not close the question if the patient becomes dyspneic on day 2.
• Traumatic, including after rib fractures from CPR.

Tension Pneumothorax: Obstructive Shock

A one-way valve traps air in the pleural space with each breath. Rising intrapleural pressure shifts the mediastinum, kinks and compresses the superior and inferior vena cava, and destroys venous return. Note the physiology trap: the CVP is high while true RV preload is low — the number lies about the volume status, exactly as it does in tamponade.

Findings:

• Acute hypotension with tachycardia, then bradycardia and arrest
• Severe hypoxemia and respiratory distress
• Absent or markedly diminished breath sounds on the affected side with hyperresonance to percussion
• Tracheal deviation away from the affected side — a late and insensitive sign; its absence does not exclude tension
• Distended neck veins / rising CVP
• In a ventilated patient: an abrupt rise in peak and plateau airway pressures, a falling delivered tidal volume in pressure-controlled modes, and a falling end-tidal CO2

Tension pneumothorax is a clinical diagnosis and is treated before imaging. Immediate needle decompression with a 14-gauge catheter at least 5 cm long, placed at the fourth or fifth intercostal space in the anterior axillary line (the current preferred adult site, because the traditional second intercostal space at the midclavicular line fails to reach the pleura in a large proportion of adults), followed immediately by chest tube placement. A nurse who sends this patient to radiology instead has answered the item wrong.

Bedside discrimination from cardiac tamponade — both are obstructive shock with hypotension and elevated jugular venous pressure:

Imaging Findings Worth Memorizing

• Chest radiograph: an upright film shows a visceral pleural line with absent lung markings peripherally. A supine ICU film often hides a pneumothorax — look for the deep sulcus sign (an abnormally deep, lucent costophrenic angle). An effusion needs roughly 200 mL to blunt the costophrenic angle on a PA film but only about 50 mL on a lateral decubitus view.
• Lung ultrasound (faster and more sensitive than a portable radiograph):
  • Normal: lung sliding present, "seashore sign" on M-mode; the presence of B-lines at that site rules out pneumothorax there.
  • Pneumothorax: absent lung sliding, absent B-lines, "barcode" or "stratosphere" sign on M-mode; the lung point — the exact location where sliding reappears — is essentially 100% specific and also estimates size.
  • Effusion: anechoic space above the diaphragm, the spine sign (vertebral bodies visible above the diaphragm), with swirling debris or septations suggesting exudate or empyema.

Drainage Procedures and Nursing Management

Thoracentesis

Ultrasound-guided, positioned sitting and leaning forward or lateral decubitus if unable. Limit removal to 1,000-1,500 mL in a single session, and stop earlier for chest tightness, intractable cough, or a pleural pressure below -20 cmH2O. Exceeding this risks re-expansion pulmonary edema — unilateral edema and hypoxemia developing within 1-24 hours of rapid re-expansion, occasionally with hypotension; treatment is supportive oxygenation and ventilation, not diuresis alone. Other complications: pneumothorax (2-6%, much lower with ultrasound guidance), bleeding, and liver or spleen puncture. Post-procedure nursing: vital signs and SpO2, assess for new dyspnea or chest pain, apply an occlusive dressing, and obtain a chest radiograph only if the patient is symptomatic, air was aspirated, multiple passes were made, or the patient is mechanically ventilated.

Chest Tubes and Pigtail Catheters

Large-bore tubes (24-32 Fr) are used for hemothorax and thick empyema; small-bore pigtail catheters (8-14 Fr) are equally effective for pneumothorax and free-flowing effusion and are far better tolerated — the main nursing difference is that small catheters clot and kink more easily and require scheduled flushing per protocol.

The classic drainage system has three compartments: the collection chamber, the water seal (a one-way valve, normally filled to 2 cm), and the suction control (a water column set to -20 cmH2O, or a dry regulator dial).

Water seal versus suction. Suction, usually -20 cmH2O, accelerates evacuation; transitioning to water seal (gravity drainage) is the standard test of whether an air leak has resolved before removal. Do not change a post-operative mediastinal tube between suction and water seal without an order.

Removal criteria and technique: no air leak, lung re-expanded on chest radiograph, drainage below the unit threshold (commonly under 100-200 mL/24 h, or roughly 2 mL/kg/day), and ideally the patient off positive-pressure ventilation. Premedicate for pain, have the patient perform a Valsalva maneuver or hold at end-expiration (the critical point is that the patient must not inhale during withdrawal), withdraw swiftly, and apply an occlusive petroleum-gauze dressing immediately. Obtain a chest radiograph within 1-4 hours, or sooner if the patient becomes symptomatic, and monitor for recurrent pneumothorax and subcutaneous emphysema.

Post-Cardiac-Surgery Mediastinal and Pleural Drains

Expect brisk initial output that tapers — commonly under 100-150 mL/h in the first hours. The scenario CMC tests is the opposite of hemorrhage: a previously brisk mediastinal tube that suddenly stops draining in a patient whose CVP is rising, pulse pressure is narrowing, heart rate is climbing and cardiac index is falling has a clotted tube and evolving tamponade. Notify the surgeon immediately and prepare for bedside echocardiography and possible re-exploration; follow unit policy on gentle milking, and do not perform vigorous stripping, which generates dangerously high negative pressures. Recognize that post-operative tamponade is often localized clot, so the textbook echocardiographic findings of right atrial and right ventricular diastolic collapse and a large circumferential effusion may be absent, pulsus paradoxus may be absent, and the diagnosis rests on the hemodynamic trend plus the chest tube output pattern — the two things the nurse owns.