Hemodialysis Graft Assessment Quiz

Pressure and Blood Flow

• Hydrostatic pressure: The weight of a blood column within veins when standing is called hydrostatic pressure.
• Systemic blood pressure: Related to arterial pressures in the body.
• Pulmonary pressure: Related to pressure within the pulmonary arteries.
• Poiseuille's Law: Vessel radius is the most significant factor affecting blood flow in a vessel. A small change in radius significantly affects blood flow.
• Potential hemodynamic changes: Factors related to potential hemodynamic changes within a vessel include vessel length, vessel radius, and blood viscosity.

Cardiovascular Applications of Bernoulli's Principle

• Flow separation within the carotid bulb: Bernoulli's Principle explains turbulence and flow separation within the carotid bulb.
• Increased resistance to flow: Bernoulli's principle explains increased resistance to flow at areas with focal stenosis.
• Relationship between vessel radius and flow volume: Explained by Bernoulli's principle.
• Doppler signal aliasing: At high velocities, Bernoulli's principle is the reason for aliasing of the Doppler signal.

Deep Venous System Pressure and Perforators

• Bi-directional flow: Perforators dilate, which leads to bi-directional flow when deep venous system pressure consistently exceeds the superficial system pressure.

Exercise and Lower Extremity Blood Flow

• Vasodilation and Resistance: Exercise causes vasodilation, which concurrently decreases resistance in the lower extremities to meet oxygen demands of the muscles. More blood flow is encouraged distally in the extremities. An increase in diastolic flow is anticipated when peripheral resistance drops.

Calf Muscle Relaxation and Blood Flow

• Blood flow from superficial to deep veins: Calf muscle relaxation causes blood to flow through perforators from the superficial to deep veins, refilling the deep system of veins.

Blood Oxygen Content and Veins

• Pulmonary veins: Carry highly oxygenated blood in the body from the lungs to the left atrium (for systemic circulation).

Response to Valsalva Maneuver

• Femoral vein flow: Flow will stop at the beginning of the Valsalva maneuver; upon release, flow will be slightly augmented towards the heart and will normalize.

Capillary Blush Response

• Pallor and return of normal skin coloring: The capillary blush response is tested by compressing the radial and ulnar arteries to create pallor in the hand, then releasing, to time the return to normal coloring in the hand; longer times indicate arterial problems or obstructions.
• Elevation of the arm: Another method is raising the arm above the head for 60 seconds to produce pallor, then returning to a neutral position to assess time for the return to normal coloring, which assesses possible ischemic disease.

Hemodynamically Significant Stenosis

• Celiac axis diagnosis: Diagnosed with the PSV greater than 2.0 m/s.
• Ultrasound contrast agent and microbubbles: Microbubbles in ultrasound contrast agents increase reflectivity of flowing blood.

Doppler Evaluation for Erectile Dysfunction (ED)

• Cavernous arteries and dorsal veins: Doppler evaluation for ED assesses cavernous arteries and dorsal veins, using pre- and post-medication injections (such as papaverine)

Venous Perforators (Diameter)

• Diameter > 4 mm: Venous perforators with a diameter greater than 4 mm will typically demonstrate reflux.

Renal Artery Stenosis

• Hemodynamic significance: Renal artery stenosis is considered hemodynamically significant when the stenosis is greater than 60%.

Common Femoral Artery Velocity and Stenosis

• Velocity increase and stenosis levels: If the common femoral artery velocity increases from 0.8 m/s to 2.2 m/s, this indicates a 50% stenosis.

Abnormal Response to Papaverine Injection (Impotence Exam)

• PSV and EDV of arterial inflow: PSV and EDV will decrease/decline with papaverine injection.

Renal-Aortic Ratio (RAR)

• Abnormality criteria: RAR is indicated to be abnormal (greater than 3.5) for renal artery stenosis.

Peak Systolic Velocity (PSV)

• SMA stenosis: Hemodynamically significant stenosis of the SMA is diagnosed when the PSV is greater than 2.75 m/s.

Parenchymal Resistance Ratio (PRR)

• Calculation: PRR = EDV (End Diastolic Velocity)/PSV (Peak Systolic Velocity)
• Normal values: PRR should be typically > 0.2; Values < 0.2 suggest increased parenchymal resistance.

Vertebral Artery Stenosis (and Related Symptoms)

• Bilateral Visual Symptoms: Vertebrobasilar disease is commonly associated with bilateral visual symptoms.

Collagen Disorders and Arterial Dissection Risk

• Marfan syndrome and Ehler-Danlos syndrome: These collagen disorders increase the risk of arterial dissection.

Transcutaneous Oximetry

• Normal Value: 70-80 mmHg.

Venous Insufficiency and Pain

• Dependent position: Pain relief from lower extremity venous insufficiency occurs with the legs in a dependent position.

Pulse Volume Recording (PVR) and Revascularization

• Increased amplitude: Following successful revascularization, a prominent increase in amplitude (by >50%) in the PVR tracing is an expected finding.

Popliteal Artery

• Location and Branches: This artery is found in the popliteal fossa, branching into the anterior and tibioperoneal trunks.
• Scan Approach: Best for imaging is positioning the probe posteriorly to the popliteal fossa, where the artery is situated behind the vein.

Test your understanding of hemodialysis graft assessment with this quiz that covers key concepts such as thrills, bruits, and venous pressure dynamics. Evaluate your knowledge on auscultation techniques and the physiological responses involved in dialysis graft function.