Ventilation-Perfusion Scan (V/Q Scan): Nursing Guide
A ventilation-perfusion (V/Q) scan is the paired nuclear medicine study nurses coordinate when pulmonary embolism is suspected and CT pulmonary angiography with iodinated contrast is avoided — for example when renal impairment, contrast allergy, or pregnancy concerns dominate the pathway. Focus on pregnancy and breastfeeding screening, radiotracer radiation safety, oxygen during transport, inhaler availability for aerosol ventilation phases, and urgent action when mismatch patterns or worsening hypoxemia appear before formal reports.
Contents
Quick Facts
Key Takeaway
The main nursing priority with a V/Q scan is confirming the PE indication and why CTPA was deferred, completing pregnancy and radiotracer safety screening, supporting aerosol cooperation and monitored transport with oxygen,
Imaging Parameters & Safety
Nurse quick-reference for imaging prep, safety screening, and transport.
Nuclear medicine — ventilation and perfusion lung imaging
No iodinated IV contrast for standard V/Q protocols — uses inhaled radiotracer gas or aerosol and IV radiotracer per nuclear medicine protocol
Uses radiotracer radiation; dose depends on tracer, protocol, and scanner — not specified as a single universal value in the published references
Ventilation and perfusion components may be performed separately or sequentially; total visit time includes IV placement, mask breathing, and camera imaging — not specified as one fixed interval in the published references
Sitting or supine under a gamma camera during ventilation mask breathing and perfusion imaging; position changes during acquisition per technologist protocol
No routine fasting requirement is specified for standard V/Q scans in the published references — follow the nuclear medicine order and local policy
What is Ventilation-Perfusion Scan (V/Q Scan)?
Ventilation-Perfusion Scan (V/Q Scan) is a paired nuclear medicine imaging study that evaluates how air moves through the lungs (ventilation) and how blood flows through pulmonary vessels (perfusion). A ventilation scan uses inhaled radioactive gas or aerosol; a perfusion scan uses IV-injected radiotracer that collects in lung blood vessels. Cameras detect tracer distribution to show matched or mismatched patterns. V/Q scanning is commonly used to evaluate suspected pulmonary embolism when CT pulmonary angiography is contraindicated or not selected, and may support evaluation of other ventilation–perfusion abnormalities per indication.
Overview
Nurses on emergency, medical-surgical, obstetric, and critical care units coordinate V/Q scans when patients have shortness of breath, pleuritic chest pain, or hemoptysis and clinicians pursue PE evaluation without iodinated contrast. Ward nurses do not prepare radiotracers or operate gamma cameras but are essential for order verification, pregnancy and breastfeeding screening, allergy and medicine review, chest radiograph correlation, IV access for perfusion tracer, inhaler availability when aerosol ventilation is planned, monitored transport, and communicating urgent preliminary reads.
Because PE can cause rapid hypoxemia, delays in safety screening or transport matter. Integrate V/Q reports with clinical probability, D-dimer context, leg examination, and arterial blood gas trends when ordered. A low-probability V/Q scan does not automatically exclude PE in every high-probability context per published PE/VTE guidelines — and matched defects from underlying lung disease can limit specificity. Pair results with deep vein thrombosis evaluation and anticoagulation pathways when indicated.
Before V/Q scan, verify why CTPA was deferred, screen pregnancy and breastfeeding status, review medicines and allergies, ensure IV access and inhaler availability when aerosol ventilation is ordered, and document baseline SpO₂. After the scan, encourage hydration per nuclear medicine instructions, monitor for tracer reactions, and escalate new respiratory distress, high-probability mismatch wording, or discordant low-probability results with worsening oxygenation according to facility policy.
Radiotracer, Aerosol, and PE Pathway Safety
V/Q scanning is time-sensitive in suspected pulmonary embolism, but radiotracer radiation screening and worsening hypoxemia must not be deferred for convenience. Treat falling SpO₂, incomplete pregnancy documentation, and high-probability preliminary reads as clinical priorities — not tasks to wait for formal reports.
- Transport to nuclear medicine before pregnancy or radiation screening is documented per protocol
- Preliminary high-probability mismatch with hypoxemia, tachycardia, or hypotension
- Marked deterioration despite low-probability or pending V/Q while clinical probability remains high
- Unable to cooperate with aerosol ventilation without prescriber or nuclear medicine plan for suboptimal study
Document: pregnancy and radiation screening, reason CTPA was deferred, transport time, baseline and trend SpO₂, aerosol tolerance, preliminary read communication, anticoagulation orders, and patient teaching.
What V/Q Scan Can and Cannot Tell You
This test can help identify:
- Ventilation–perfusion mismatch patterns suggesting acute pulmonary embolism when integrated with clinical probability
- Alternative PE imaging when iodinated contrast CTPA is contraindicated or not selected
- Regional ventilation and perfusion abnormalities in advanced pulmonary disease
- Need for urgent anticoagulation, monitoring, or further imaging when reports and symptoms align
This test cannot:
- Replace clinical probability assessment, D-dimer interpretation, or bedside monitoring
- Exclude every PE in all high-probability contexts — guideline pathways may require further testing
- Diagnose deep vein thrombosis without separate venous imaging when leg thrombosis is suspected
- Determine treatment alone — results must be integrated with examination, chest radiograph, and trends
Pre-scan Safety for V/Q and PE Workups
Verify
Clarify before proceeding when:
- Order does not match symptoms or duplicates recent adequate V/Q without clinical change
- Pregnancy or breastfeeding status is unknown before radiotracer administration
- Patient cannot tolerate aerosol mask or travel without monitored escort
- Preliminary read conflicts strongly with examination or D-dimer context
- Anticoagulation timing relative to scan is unclear — clarify with prescriber
- Severe COPD or acute asthma may invalidate ventilation phase — clarify with nuclear medicine
Reading V/Q Patterns With Clinical Probability
Integrate V/Q reports with pre-test probability, D-dimer, leg examination, chest radiograph, SpO₂ trends, heart rate, blood pressure, and anticoagulation response. Low-probability scans in high-probability patients may still need serial assessment or alternate imaging per published PE/VTE pathways.
| Clinical context | Pair with V/Q findings | Nursing focus |
|---|---|---|
| High probability + elevated D-dimer | High-probability mismatch or indeterminate read | Anticoagulation pathway, oxygen, bleeding precautions, ICU consult when massive PE suspected |
| Pregnancy with pleuritic pain + tachycardia | Pending or low-probability V/Q | Do not reassure based on deferred CTPA alone — track scan completion and symptoms |
| COPD with matched defects | Low-probability or nondiagnostic wording | Escalate discordant symptoms; further imaging may be required per protocol |
| Low-probability V/Q + worsening SpO₂ | Discordant result | Escalate per protocol — CTPA, leg ultrasound, or repeat assessment when clinically appropriate |
V/Q Probability Categories Nurses See on Reports
Radiology and nuclear medicine reports use probability language rather than numeric cutoffs. Exact wording varies by site — always read the formal report and local PE protocol.
| Report category (typical wording) | Pattern concept | Nursing implication |
|---|---|---|
| Normal / very low probability | Matched ventilation and perfusion without significant mismatch | May support excluding PE when probability was low — continue monitoring if symptoms persist |
| Low probability | Small perfusion defects with matched ventilation reduction | Often managed with clinical probability tools — escalate discordant deterioration |
| High probability | Segmental or larger perfusion defect with preserved ventilation (mismatch) | Treat as urgent PE pathway finding until prescriber reviews — anticoagulation and monitoring per orders |
| Indeterminate / nondiagnostic | Equal matched and mismatched defects or poor technical quality | Communicate limitation; further imaging or serial assessment may be ordered — not specified as one universal next step in reviewed references |
V/Q Scan Across ED, Maternity, and Medical Units
Diagnostic safety badge: High-acuity nuclear medicine imaging — radiation, aerosol cooperation, and PE pathway checks apply; high-probability preliminary reads and respiratory deterioration require immediate escalation.
Check-before-test protocol
- Identity + PE indication + reason CTPA deferred if applicable
- Pregnancy, breastfeeding, allergy, and medicine screening per policy
- IV access, inhaler plan, baseline SpO₂, and monitored transport plan
- Post-scan hydration teaching and preliminary read tracking
- Anticoagulation and bleeding precaution coordination when PE confirmed
Critical teach-back questions
- “Can you tell me why this lung scan with a mask and IV tracer is being done today?”
- “What symptoms — breathlessness, chest pain, leg swelling — should you report immediately?”
- “Do you understand we may start blood-thinning medicine quickly if the scan suggests a clot?”
Care coordination: prescriber, nuclear medicine, radiology, respiratory therapy, pharmacy, obstetrics when pregnant, and rapid response teams when ordered.
Why Ventilation-Perfusion Scan (V/Q Scan) is Ordered
V/Q scanning is ordered when clinicians need ventilation–perfusion pattern information — often for suspected PE when contrast CT is unsuitable or alternate imaging is selected.
| Clinical Indication | What the Test Answers | Nursing Rationale |
|---|---|---|
| Suspected acute pulmonary embolism when CTPA is contraindicated or not selected | Is there perfusion defect with preserved ventilation (mismatch) suggesting PE? | Supports anticoagulation and PE pathways when integrated with clinical probability, symptoms, and D-dimer context per specialty guidelines — not as an isolated yes/no diagnosis. |
| Pregnancy or breastfeeding concerns with suspected PE | Can V/Q provide PE evaluation when iodinated contrast CT risk must be weighed? | Risk–benefit discussion and imaging selection follow institutional PE and radiation protection policy — necessary studies should not be inappropriately delayed when PE is suspected. |
| Renal impairment or severe iodinated contrast allergy with PE suspicion | Is nuclear lung imaging an alternative when IV contrast CTPA is unsafe? | standard clinical references and RadiologyInfo describe V/Q as a lower-contrast alternative to pulmonary angiography in selected patients — final choice follows prescriber and radiology protocol. |
| Evaluation of regional lung function in advanced pulmonary disease | How do ventilation and perfusion distribute in chronic lung disease? | assessment of regional function in conditions such as COPD — interpretation must account for matched defects that can mimic or obscure PE patterns. |
Contraindications and Precautions
Absolute contraindications are patient- and protocol-specific. Nurses focus on precautions requiring prescriber or nuclear medicine clarification before radiotracer administration.
- Pregnancy or breastfeeding status unknown when radiation protection policy requires documented risk–benefit discussion before nuclear medicine studies.
- Unstable patient who cannot safely travel, tolerate mask ventilation, or lie still without monitored escort and oxygen plan.
- Order does not match clinical picture — for example routine V/Q without PE or pulmonary symptoms when CTPA would be appropriate and contrast screening is complete.
- Severe airflow limitation or inability to follow mask breathing may reduce ventilation scan quality — notify nuclear medicine and prescriber per protocol.
- Recent anticoagulation does not automatically cancel V/Q but affects pathway timing — document medicines on MAR and clarify hold parameters with prescriber.
- Underlying COPD, pneumonia, or prior embolism can produce matched or multiple defects — do not assume every abnormal pattern equals acute PE without radiology correlation.
- Preliminary or verbal read reporting high-probability mismatch with hypoxemia, tachycardia, or hypotension.
- Marked respiratory distress or falling SpO₂ despite supplemental oxygen while V/Q is pending or after a low-probability preliminary read.
- Suspected serious reaction during or after radiotracer — severe dyspnea, wheeze, hypotension, or urticaria beyond mild expected sensations.
Patient Preparation
V/Q preparation centers on radiotracer and radiation safety, pregnancy and breastfeeding screening, medicine and allergy review, IV access, aerosol cooperation support, and communicating clinical urgency to nuclear medicine and transport teams.
Pre-test checksReview anticoagulants, antiplatelets, bronchodilators, and any medicines nuclear medicine lists as interference per local protocol. Never withhold prescribed anticoagulation without prescriber orders — clarify timing relative to imaging and procedures.
Where the test is performed
This page is a Tests & Diagnostics guide for Ventilation-Perfusion Scan (V/Q Scan). It emphasizes why the test is ordered, how to interpret results, when to escalate, and preparation factors that affect validity — not step-by-step performance technique (those live under Nursing Procedures when available).
Ventilation-Perfusion Scan (V/Q Scan) is performed in the nuclear medicine department by trained technologists. Ward nurses focus on PE indication verification, pregnancy and breastfeeding screening, medicine and allergy review, inhaler availability when aerosol ventilation is used, IV access for perfusion tracer, safe transport with oxygen, post-scan radiation precautions, and urgent action on high-probability or discordant results — not radiotracer preparation or camera operation.
Use the preparation, results, and nursing responsibility sections below for safety checks, interpretation, escalation, and documentation — not equipment operation or departmental imaging protocols.
Result follow-up at a glance
Nursing workflow on this page — from order to safe action on results:
Results and Interpretation
V/Q results are descriptive nuclear medicine interpretations using probability language — not numeric laboratory values. Nurses integrate reports with symptoms, SpO₂ trends, hemodynamics, D-dimer context, chest radiograph, and pre-test probability.
Reference ranges, critical values, and protocols may vary by laboratory, institution, patient population, and testing method. Always follow local policy and the reporting laboratory’s reference range.
| Result | Range / Finding | Clinical Meaning | Nursing Action |
|---|---|---|---|
| No acute critical finding / as expected for indication | Normal or low probability for PE (report wording varies by site and protocol) | May support excluding PE when clinical probability was low — must fit the full clinical picture | Continue monitoring; escalate if dyspnea, SpO₂, or hemodynamics worsen despite reassuring wording |
| Equivocal / indeterminate finding | Intermediate, indeterminate, or nondiagnostic study | May need CTPA, leg ultrasound, repeat imaging, or serial assessment per protocol when suspicion remains | Communicate limitations to prescriber; do not assume PE is excluded when symptoms and probability remain high |
| Abnormal finding — clinically significant | High probability for PE — mismatch pattern (wording varies by site) | Often prompts anticoagulation, monitoring, and evaluation for massive PE or right-heart strain when paired with examination | Escalate urgent findings per policy; implement ordered anticoagulation and repeat assessment |
| Not applicable | Matched defects or perfusion defects with matched ventilation reduction | May reflect COPD, pneumonia, atelectasis, or prior embolism rather than acute PE — radiology correlation required | Integrate with chest radiograph and examination; escalate if acute PE remains likely despite matched pattern |
Urgent V/Q Findings and Escalation
Nuclear medicine reports do not use laboratory critical values, but certain V/Q probability categories and paired clinical signs require immediate action.
| Critical Finding | Threshold / Value | Immediate Action |
|---|---|---|
| High-probability PE pattern with hemodynamic compromise | Reported high-probability mismatch with hypotension, syncope, or severe hypoxemia | Escalate urgently per facility PE protocol; support ordered oxygen, anticoagulation, and advanced therapy pathways |
| Positive preliminary read with worsening oxygenation | High-probability or concerning mismatch wording with falling SpO₂ or increasing work of breathing | Notify prescriber/rapid response; titrate oxygen; prepare for anticoagulation and ICU transfer per orders |
| Discordant low-probability scan with high clinical suspicion | Low-probability or normal wording with rising heart rate, pleuritic pain, and falling SpO₂ | Escalate per protocol — further imaging, leg studies, or alternate diagnosis workup may be required |
Stop routine workflow and escalate according to facility policy when the patient develops severe respiratory distress, marked hypoxemia, hemodynamic instability, suspected serious tracer reaction, or when urgent V/Q findings conflict with rapid clinical deterioration.
Factors Affecting Results
V/Q interpretation can be affected by underlying lung disease, scan technique, timing, and clinical probability relative to symptoms.
- Matched perfusion and ventilation defects from COPD or pneumonia mimicking low-probability patterns
- Multiple subsegmental defects from prior embolism or pulmonary hypertension — formal radiology correlation required
- Technically limited ventilation scan from poor mask seal or non-cooperation misread on preliminary review
- Small subsegmental emboli below report threshold on technically limited studies
- PE present despite low-probability V/Q when clinical probability remains high — per guideline pathways
- Anticoagulation started before scan may alter clot appearance — document medicine timing
- Poor aerosol delivery or inability to hold breath during ventilation imaging
- COPD, pneumonia, atelectasis, or prior pulmonary embolism producing matched defects
- Timing relative to symptom onset, anticoagulation, and pre-test probability tools
V/Q scanning does not evaluate deep venous thrombosis without separate venous imaging. Radiotracer radiation and aerosol cooperation requirements carry distinct risks. Indeterminate scans are common in patients with underlying lung disease — further testing may be required per ESC and national clinical guidelines VTE guidance. Sensitivity and specificity thresholds are not specified as single universal values in the published references.
Nursing Responsibilities
Nursing care centers on radiotracer safety screening, aerosol and transport support, post-scan surveillance, timely preliminary read communication, and integrating results with PE pathways.
Before the TestDocumentation
Clear documentation supports PE pathway handoffs when preliminary nuclear medicine reads arrive before formal reports.
“STAT V/Q scan completed 0410. Two identifiers verified. Early pregnancy confirmed — radiation risk–benefit documented; CTPA deferred per prescriber. Pre-transport SpO₂ 92% on 3 L/min; patient used albuterol inhaler before aerosol phase per order. Preliminary read 0435: high-probability mismatch pattern. Prescriber notified with read-back; enoxaparin initiated per order. Formal report pending.”
- Indication, reason CTPA deferred, pregnancy/breastfeeding screen, and transport time
- IV access, aerosol tolerance, tracer administration tolerance, and any reaction treated
- Baseline and post-study SpO₂ with oxygen device and flow
- Preliminary and formal read communication with read-back if required
- Anticoagulation orders, bleeding precautions, and escalation calls
- Patient teaching on PE symptoms, leg swelling, hydration, and follow-up imaging or labs
Patient and Family Education
Use plain language about mask breathing, IV tracer injection, radiation, and symptoms that require immediate reporting.
Ventilation-Perfusion Scan (V/Q Scan) NCLEX practice questions
Practice NCLEX-style clinical judgment focused on Ventilation-Perfusion Scan (V/Q Scan) safety and nursing judgment. Use the case tabs (orders, results, assessment, nursing notes), then answer eight Next Gen–style items (including an ordered workflow step) and evaluate outcomes with the answer key.
Select a tab to view orders, results, assessment, and nursing note details for this case.
- Order: Ventilation-perfusion (V/Q) scan — STAT
- Indication: Pleuritic chest pain and dyspnea in early pregnancy; suspected pulmonary embolism; D-dimer elevated; CTPA deferred
- Timing: Ordered after bedside assessment and chest radiograph; anticoagulation not yet started
- Related orders: D-dimer elevated; chest radiograph performed; leg ultrasound pending; oxygen titration per protocol
- Result: V/Q scan not yet performed — preliminary read pending
- Trend / prior value: SpO₂ 93% on 2 L/min at 2100 → 87% on 4 L/min at 2245; RR rising
- Pending tests: V/Q scan, formal nuclear medicine report, and leg ultrasound
- Vital signs: HR 108/min, BP 104/62, RR 26/min, SpO₂ 87% on 4 L/min, T 37.0 °C
- Symptoms: Pleuritic chest pain, increasing dyspnea, mild anxiety, reports first trimester pregnancy
- Focused assessment: Clear lung bases; tachycardia; right calf tenderness reported; IV 20-gauge patent; inhaler at bedside
- Preparation notes: CTPA deferred due to pregnancy and prescriber preference for V/Q pathway. Breastfeeding not applicable. Albuterol inhaler available for aerosol phase.
- Collection events: Transport delayed awaiting escort; nuclear medicine notified about pregnancy documentation and inhaler plan
- Teaching gaps / safety concerns: Falling SpO₂ despite supplemental oxygen; pregnancy radiation documentation required; STAT V/Q not yet completed
Answer key & rationale
Frequently Asked Questions
FAQ
When is a V/Q scan ordered instead of CTPA?
V/Q scanning is often selected when clinicians need PE evaluation without iodinated IV contrast — for example when contrast allergy, renal impairment, or pregnancy concerns make CTPA less suitable. V/Q as a lower-risk alternative to pulmonary angiography in selected patients. Final imaging choice follows ACR Appropriateness Criteria, ESC/national clinical guidelines VTE guidance, and local PE protocols.
Does the patient need to fast before a V/Q scan?
No routine fasting requirement is specified for standard V/Q scans in the published references — follow the nuclear medicine order and institutional instructions.
What should nurses watch for during and after a V/Q scan?
Monitor for worsening dyspnea, hypoxemia, chest pain, hypotension, wheeze, or urticaria during aerosol and perfusion phases. Mild cough or brief discomfort may occur. Encourage hydration per nuclear medicine instructions after the study. Escalate according to facility policy for serious reactions or clinical deterioration.
How are V/Q results reported?
Reports use descriptive probability categories (such as normal, low probability, high probability, or indeterminate/nondiagnostic) rather than numeric laboratory values. Wording varies by site and protocol. Mismatched ventilation and perfusion patterns may suggest PE and require prompt medical treatment when clinically appropriate.
Can pregnant patients have a V/Q scan?
When PE is suspected, necessary imaging should not be withheld if benefits outweigh risks — imaging selection follows risk–benefit discussion per institutional radiation protection and PE protocols. Pregnancy status should always be assessed and documented before nuclear medicine studies.
Can a low-probability V/Q scan rule out pulmonary embolism?
A low-probability V/Q scan often supports excluding PE when clinical probability was low — but high-probability pathways may require further testing or serial assessment per published PE/VTE guidelines. Continue monitoring if symptoms worsen.
How quickly are V/Q scan results available?
Many urgent PE protocols receive preliminary communication the same shift, but formal report timing varies by site and acuity. Turnaround and screening rules vary by institution; follow local policy for a universal turnaround interval — follow local nuclear medicine workflow.
References
References
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U.S. National Library of Medicine. V/Q scan. MedlinePlus.https://medlineplus.gov/lab-tests/vq-scan/
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U.S. National Library of Medicine. Pulmonary ventilation/perfusion scan. MedlinePlus Medical Encyclopedia.https://medlineplus.gov/ency/article/003828.htm
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Radiological Society of North America. Pulmonary embolism. RadiologyInfo.org.https://www.radiologyinfo.org/en/info/pulmonary-embolism
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Radiological Society of North America. General nuclear medicine. RadiologyInfo.org.https://www.radiologyinfo.org/en/info/gennuclear
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American College of Radiology. ACR Appropriateness Criteria. ACR.https://www.acr.org/Clinical-Resources/Clinical-Tools-and-Reference/Appropriateness-Criteria
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Konstantinides SV et al.; ESC Scientific Document Group. 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism. Eur Heart J.https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Acute-Pulmonary-Embolism-Diagnosis-and-Management-of
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National Institute for Health and Care Excellence. Venous thromboembolic diseases: diagnosis, management and thrombophilia testing (NG158). NICE.https://www.nice.org.uk/guidance/ng158
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National Health Service. Diagnosis — pulmonary embolism. NHS.uk.https://www.nhs.uk/conditions/pulmonary-embolism/diagnosis/
Editorial Standards & Medical Review
About the author: Sid A. Abdala Balal, RN, writes evidence-based nursing education focused on diagnostic safety, clinical interpretation, and bedside nursing judgment.
Medical review: This guide is reviewed by Dr. Adam Sayedi, MD, for clinical accuracy, diagnostic safety, and alignment with current standards for Ventilation-Perfusion Scan (V/Q Scan).
Policies: Medical Review Process · Editorial Policy · Correction Policy