Shouldn't we also assess venous return flow to the heart in patients with suspected venous issues?

Assessment of Venous Return in Patients with Normal Cardiac Outflow

Yes, assessing venous return is physiologically essential when cardiac outflow is normal, as venous return equals cardiac output at steady state and abnormalities in venous return can significantly impact hemodynamic status. 1

Physiologic Rationale for Assessing Venous Return

Venous return is a major determinant of cardiac output and must equal cardiac output in steady-state conditions since the venous and arterial systems operate in series. 1 The venous system is a capacitive network with high compliance that contains unstressed blood volume serving as a reservoir that can be recruited during hemodynamic stress 1, 2.

Key Determinants of Venous Return (Guyton's Model)

The three critical factors that determine venous return are 1:

• Mean systemic filling pressure - the driving force for venous return
• Right atrial pressure - the back-pressure opposing venous return
• Resistance to venous return - impedance in the venous network

Preservation of mean circulatory filling pressure through mobilization of unstressed blood volume is the predominant mechanism for sustaining venous return and cardiac output during volume loss. 2

Clinical Scenarios Requiring Venous Return Assessment

Right Ventricular Dysfunction and Pulmonary Hypertension

Bedside cardiac ultrasonography should be performed to assess RV function when venous return abnormalities are suspected, as RV dysfunction can occur in up to 30% of septic patients and significantly impacts venous return dynamics. 3

• RV dysfunction assessment is recommended for all levels of training in critically ill patients to guide fluid, inotrope, and vasopressor therapy. 3
• Disproportionate RV dilation with sparing of the apex (McConnell's Sign) suggests acute pulmonary embolism in the appropriate clinical setting. 3

Suspected Venous Thrombosis

When venous obstruction is suspected, compression ultrasound of the proximal deep veins (common femoral and popliteal) should be performed as the initial diagnostic test. 3, 4

Diagnostic Algorithm for Suspected DVT:

For high pretest probability patients 3:

• Perform proximal compression ultrasound (CUS) initially
• If positive, initiate treatment without confirmatory venography
• If negative, perform additional testing with highly sensitive D-dimer, whole-leg ultrasound, or repeat proximal CUS in 1 week

For patients without risk stratification 3:

• Initial testing should be proximal CUS or whole-leg ultrasound
• If single proximal CUS is negative with positive D-dimer, perform repeat proximal CUS in 1 week or whole-leg ultrasound
• Withholding anticoagulation is safe when serial venous ultrasonography or impedance plethysmography results are normal. 5

Anomalous Venous Return (Congenital)

When anomalous pulmonary venous return is suspected after inadequate transthoracic echocardiography, CTA chest or MRA chest should be performed to define complete anomalous drainage pathways. 3

• MRA chest is excellent at identifying anomalous pulmonary vein anatomy and connections, with one study showing superior accuracy compared to echocardiography and cardiac catheterization. 3
• MRI heart function and morphology is the ideal noninvasive modality to quantify shunt amount through flow rate assessment in partial anomalous pulmonary venous connection (PAPVC). 3
• MRA abdomen may be helpful in infracardiac total anomalous pulmonary venous connection (TAPVC) or PAPVC to demonstrate drainage into hepatic or portal veins. 3

Common Pitfalls to Avoid

Failing to distinguish between acute DVT and chronic post-thrombotic changes can lead to inappropriate anticoagulation decisions. 4 Diagnosis of recurrent DVT requires evidence of new thrombus formation, such as a new noncompressible venous segment on ultrasound or conversion of normal impedance plethysmography to abnormal 5.

Overlooking isolated iliac vein thrombosis in patients with extensive unexplained leg swelling despite negative standard proximal CUS can lead to delayed diagnosis. 4 These patients should be considered for vascular surgery referral 4.

Venous insufficiency alone found on DVT ultrasound does not require vascular surgery referral and should be managed conservatively unless symptoms are severe or complications develop. 4

Duplex ultrasonography has 95% sensitivity and 100% specificity for femoral vein DVT, making it sufficiently accurate to initiate treatment without venography. 6 However, it is less accurate for isolated calf vein thrombosis 5.