Indications for Fluoroscopy-Guided Sniff Test with Chest Fluoroscopy
Fluoroscopy-guided sniff test is primarily indicated for evaluating diaphragmatic motion and function in patients with suspected diaphragmatic paralysis or dysfunction, particularly when mechanical prosthetic cardiac valves need assessment.
Primary Indications
Evaluation of Diaphragmatic Function
- Assessment of suspected diaphragmatic paralysis
- Evaluation of diaphragmatic excursion during respiratory maneuvers
- Monitoring diaphragmatic motion in patients with respiratory symptoms of unclear etiology
Cardiac Valve Assessment
- Evaluation of mechanical prosthetic cardiac valves, particularly when endocarditis is suspected 1
- Detection of excess mobility of mechanical prosthetic valves during cardiac cycle (suggesting valve dehiscence) 1
- Assessment of immobility of mechanical prosthetic valve leaflets due to infected pannus or thrombus 1
Clinical Scenarios Where Fluoroscopic Sniff Test is Valuable
Prosthetic Heart Valve Evaluation
- When echocardiography results are inconclusive or suboptimal
- For evaluating mechanical valve function when valve dysfunction is suspected 1
- To detect abnormal tilting or rocking of the base ring (indicative of valve dehiscence) 1
- For measuring opening and closing angles of mechanical valve leaflets 1
Respiratory Assessment
- In patients with unexplained dyspnea where diaphragmatic dysfunction is suspected
- To distinguish between paradoxical and normal diaphragmatic movement
- For assessment of respiratory gating in patients undergoing radiation therapy 2
Technical Considerations
Positioning and Views
- Supine position is generally used for the examination
- Multiple projections may be required:
- Postero-anterior (0°) and lateral (90°) projections to identify valve orientation
- "In profile" projection (beam parallel to valve ring plane and tilting axis)
- "En face" projection for mitral prostheses 1
Advantages of Fluoroscopy
- Real-time visualization of dynamic structures
- Ability to observe diaphragmatic movement during various respiratory maneuvers
- Lower radiation dose compared to CT-guided procedures (mean effective dose of 0.029 mSv, approximately equivalent to one chest X-ray) 3
- Ability to vary patient positioning during examination 4
Limitations and Precautions
- Does not provide hemodynamic assessment or information about the etiology of reduced disc mobility in valve assessment 1
- Radiation exposure should be minimized through:
- Intermittent exposures
- Last image hold
- Beam filtration
- Pulsed fluoroscopy 5
- Limited value for native valve endocarditis assessment 1
Alternatives to Consider
- Echocardiography remains the first-line imaging for cardiac valve assessment 1
- MRI may be considered for evaluation of diaphragmatic function in cases where radiation exposure is a concern
- CT may provide better anatomical detail but lacks the real-time functional assessment that fluoroscopy offers 4
Fluoroscopy-guided sniff test remains a valuable diagnostic tool that provides unique functional information about diaphragmatic motion and mechanical valve function that cannot be easily obtained with other imaging modalities.