Respiratory procedures: V/Q scan, bronchoscopy, thoracentesis, biopsy

Topic

The tests that look at lung blood flow, look inside the airways, drain fluid from the chest or take a piece of lung or pleura.

Updated Nov 13, 2026

What it is

When imaging and spirometry are not enough, a few procedures answer specific chest questions. The ventilation/perfusion (V/Q) scan compares air and blood reaching each lung region. Bronchoscopy looks inside the airways and collects washings and biopsies. Thoracentesis drains pleural fluid for analysis or relief, and pleural or transthoracic lung biopsy obtains tissue. Most carry a risk of bleeding or pneumothorax, so preparation and post-procedure monitoring are part of the test.

Key facts

Light criteria: the fluid is an exudate if pleural/serum protein is above 0.5, pleural/serum LDH is above 0.6, or pleural LDH is above two thirds of the upper normal serum value.
Transudates point to heart failure, cirrhosis or nephrotic syndrome; exudates to infection, cancer, tuberculosis or pulmonary embolism.
A pleural pH below about 7.2 or frank pus in a parapneumonic effusion indicates the need for drainage.
A lymphocytic exudate with high adenosine deaminase supports pleural tuberculosis, still common in Colombia.
The needle goes above the rib because the intercostal vein, artery and nerve run under the lower border of each rib.
CT pulmonary angiography has largely replaced the V/Q scan, which remains useful when iodinated contrast is a problem.

Step by step

Confirm indication, consent and identity; review platelets, coagulation tests and anticoagulant or antiplatelet use.
Record baseline vital signs and oxygen saturation; place a venous line for sedated procedures.
Position the patient (sitting and leaning forward for thoracentesis; supine or lateral for bronchoscopy as the team asks).
During the procedure, watch saturation, heart rate, cough and pain, and label samples correctly.
Afterwards, check breathing, saturation and the puncture site; obtain a chest X-ray if requested.
Report sudden dyspnea, chest pain, falling saturation, hemoptysis or hypotension at once (possible pneumothorax or bleeding).

Respiratory procedures and what the team watches for.

Procedure	What it shows or does	Chosen when	Preparation and nursing	Main risks
V/Q scan	Perfusion (injected labelled albumin) and ventilation (inhaled radioactive gas) images; a perfusion defect with normal ventilation (mismatch) suggests embolism	Suspected pulmonary embolism when CT angiography is unsuitable (contrast allergy, kidney disease, pregnancy in some protocols)	No fasting; recent chest X-ray needed to interpret it; remove metal	Small radiation dose; rare tracer allergy; often indeterminate with lung disease
Flexible bronchoscopy	Direct view of the airways; bronchoalveolar lavage, brushings, endobronchial and transbronchial biopsy; endobronchial ultrasound for mediastinal nodes	Hemoptysis, suspected tumour, non-resolving pneumonia, infection in the immunocompromised (tuberculosis, fungi), foreign body	Fasting for several hours; anticoagulants reviewed; topical throat anaesthesia and sedation; nothing by mouth until gag reflex returns; oxygen saturation monitoring	Bleeding, hypoxemia, pneumothorax after transbronchial biopsy, fever, sedation effects
Thoracentesis	Removes pleural fluid for diagnosis (appearance, protein, LDH, glucose, pH, cells, culture, cytology) or relief of dyspnea	New effusion of unknown cause, suspected infection (parapneumonic, empyema), large symptomatic effusion	Sitting, leaning forward on a table; ultrasound-guided site; needle above the upper border of the rib; record volume and appearance	Pneumothorax, bleeding, infection, vasovagal reaction, re-expansion pulmonary edema if a large volume is removed quickly
Pleural biopsy (closed needle, image-guided or thoracoscopic)	Pleural tissue for histology and culture	Exudate of unknown cause after fluid analysis, suspected tuberculosis or malignancy, mesothelioma	As for thoracentesis; thoracoscopy needs anaesthesia and usually a chest tube afterwards	Pneumothorax, bleeding, infection; thoracoscopy gives the highest yield
Transthoracic needle lung biopsy	Core or aspirate from a peripheral nodule or mass under CT or ultrasound guidance	Peripheral nodule or mass suspected to be cancer or infection, out of reach of the bronchoscope	Fasting, coagulation reviewed, antiplatelets and anticoagulants managed by the team; chest X-ray after	Pneumothorax (the most frequent, sometimes needing a chest tube), hemoptysis and bleeding

Test yourself

Think of the answer, then tap the question to see it.

Which V/Q scan pattern suggests pulmonary embolism?

A perfusion defect in a region with normal ventilation (a mismatch).

Why is the thoracentesis needle passed over the upper border of the rib?

Because the intercostal vein, artery and nerve run along the lower border of each rib.

What are the three Light criteria for a pleural exudate?

Pleural/serum protein above 0.5, pleural/serum LDH above 0.6, or pleural LDH above two thirds of the upper normal serum value.

What is the most frequent complication of a transthoracic needle lung biopsy?

Pneumothorax; a chest X-ray is taken afterwards to look for it, and a large one may need a chest tube.

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Educational content on the clinical exam; it is learned and practised under supervision. It does not replace assessment by a health professional and is not for self-diagnosis.

Sources: Pulmonary ventilation/perfusion scan (MedlinePlus, U.S. National Library of Medicine, 2026); Bronchoscopy: MedlinePlus Medical Encyclopedia (MedlinePlus, U.S. National Library of Medicine, 2026); Thoracentesis: MedlinePlus Medical Encyclopedia (MedlinePlus, U.S. National Library of Medicine, 2026); Lung needle biopsy: MedlinePlus Medical Encyclopedia (MedlinePlus, U.S. National Library of Medicine, 2026).

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