Take a look at the table below from our Kidney News article, an editorial about a comparative study between a handheld ultrasound device (HUD) and a conventional ultrasound machine for lung and inferior vena cava POCUS in dialysis patients. This table provides a snapshot of the practical methods employed in clinical practice. Feel free to share your thoughts or suggestions in the comments section. Additionally, it’s worth noting that while we refer to volume status assessment broadly, POCUS primarily evaluates pressures in the hemodynamic circuit and flow patterns rather than volume directly.
| Method of volume status assessment | Advantages | Limitations |
| Physical Examination | Standard bedside evaluation: physicians do not require additional training. Positive findings are significant. | Poor sensitivity; misses a significant proportion of patients with volume overload. |
| Weight | Short-term changes in weight reflect fluid gain or loss. Can be done by the patient at their home. | Errors can occur due to inadequate calibration of the equipment or comparing readings from different scales. Changes in weight do not reflect congestion due to fluid redistribution. |
| Intake-output chart | Offers a snapshot of the patient’s fluid balance. | Errors in documentation are common, particularly outside of the intensive care unit. Does not reflect congestion due to fluid redistribution. |
| Bioimpedance | Provides information on total body, extracellular, and intracellular water enabling the calculation of absolute and relative fluid overload. | Cannot discriminate between compartmentalized edema (ascites, pericardial, and peritoneal fluid) and increased total body water. Does not assess intravascular volume. |
| Crit-Line® | Provides real-time data on relative changes in intravascular blood volume, allowing titration of the rate and volume of ultrafiltration. | Application is limited to patients on renal replacement therapy. Being a nurse or technician-driven modality, staff training is vital. Does not assess tissue congestion or extravascular lung water. |
| Pulmonary Artery Catheterization | Provides insight into hemodynamic variables such as right atrial pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, pulmonary vascular resistance, and cardiac output. | Invasive. Monitoring hemodynamic changes in response to therapy is not possible outside specialized intensive care units. Cannot provide information on the presence or absence of extravascular lung water (elevated pressure does not always imply volume). Does not provide information on the severity of venous congestion. Errors can occur due to improper transducer calibration, leveling, zeroing, and over/under inflation of the balloon. |
| Inferior Vena Cava (IVC) Ultrasound | Provides an estimate of right atrial pressure. Relatively easy to perform; most HUDs are adequate. | Unreliable to estimate right atrial pressure in mechanically ventilated patients. A plethoric IVC is not specific to volume overload (can be seen in conditions such as cardiac tamponade, pulmonary embolism, or pulmonary hypertension). A small, collapsible IVC does not differentiate between hypovolemia, euvolemia, and high output cardiac state. IVC can be small and collapsed despite elevated right atrial pressure in cases of intraabdominal hypertension. IVC collapsibility depends on the strength of breath, which is highly variable among patients. |
| Internal Jugular (IJ) Vein Ultrasound | Aids in the estimation of right atrial pressure. Particularly useful in cases where the IVC is inaccessible or unreliable (e.g., cirrhosis). HUDs generally provide adequate images. | Errors occur due to incorrect bed angle, excessive transducer pressure, and off-axis views. The belief that the right atrial depth is 5 cm from the sternal angle has been demonstrated to be incorrect. Precise estimation requires simultaneous focused cardiac ultrasound. Variations in scanning protocols throughout the literature. |
| Lung Ultrasound | Detects and quantifies extravascular lung water. More sensitive than a chest radiograph for cardiogenic pulmonary edema. HUDs provide adequate images. | B-lines are not specific for pulmonary edema (can be seen in lung fibrosis, infections, contusion, etc.). Some cases necessitate simultaneous measurement of left ventricular filling pressures using cardiac Doppler ultrasound to differentiate cardiogenic and non-cardiogenic pulmonary edema. |
| Venous Doppler/VExUS (hepatic, portal, intrarenal and femoral) | Detects and quantifies systemic venous congestion. Allows monitoring the response to decongestive therapy by repeating the measurements. | Advanced skill that requires competence in Doppler ultrasonography. Lack of simultaneous EKG may limit interpretation, particularly the hepatic vein waveform. Does not differentiate pressure and volume overload. Need high-end HUDs or cart-based machines. |
| Focused Cardiac Ultrasound | Provides information on cardiac pump function, chamber enlargement, pericardial effusion, and gross valvular lesions. Advanced users can estimate stroke volume, pulmonary artery pressure, and left ventricular filling pressures. | Advanced skill. Nephrologists performing Doppler assessments usually need certification in critical care echocardiography. Need high-end HUDs or cart-based machines. The reliability is contingent on having adequate acoustic windows, influenced by the patient’s body habitus. |