How do I assess a patient's fluid status?

Assessing Fluid Status in Patients

Begin with a systematic bedside assessment combining clinical examination, point-of-care ultrasound (POCUS), and dynamic hemodynamic testing—static measures like CVP alone are unreliable and should never guide fluid decisions. 1, 2

Clinical Bedside Assessment

Physical Examination Findings

Assess for congestion using a graded approach:

• Jugular venous pressure (JVP): Measure in cm above the sternal angle. JVP <8 cm with no hepatojugular reflux suggests euvolemia; 8-10 cm or positive hepatojugular reflux indicates mild congestion; 11-15 cm moderate; >16 cm severe congestion. 1

• Orthopnea severity: Grade as none, mild (one pillow), moderate (multiple pillows), or severe (sleeps seated/in chair). This directly correlates with elevated filling pressures. 1

• Peripheral edema: Grade from none to 1+ through 4+. However, edema alone is nonspecific—must be interpreted with other congestion markers. 1

• Hepatomegaly: Palpate for liver edge enlargement and assess for pulsatility. Massive tender enlargement extending to midline indicates severe right-sided congestion. 1

• Pulmonary crackles/crepitations: This is the critical threshold sign—immediately stop fluid administration when crackles develop, as they signal either fluid overload or cardiac dysfunction. 2

Dynamic Maneuvers for Volume Assessment

Orthostatic vital signs provide functional assessment of volume status:

• Measure blood pressure and heart rate supine (after 2 minutes) then standing (after 1 minute). 1

• In hypovolemic patients: expect ≥20 mmHg systolic BP drop and ≥10-30 bpm heart rate increase. 1

• Paradoxical response in heart failure: Patients with elevated filling pressures may show increased systolic BP with standing due to improved cardiac output from reduced preload. Loss of this paradoxical increase suggests achievement of euvolemia. 1

Valsalva maneuver assessment:

• Normal response shows initial BP rise (Phase 1), drop during strain (Phase 2), brief reduction after release (Phase 3), then overshoot above baseline (Phase 4). 1

• "Absent overshoot" pattern (Phases 1-3 normal, no Phase 4) indicates mild heart failure. 1

• "Square wave" pattern (BP stays elevated throughout strain) indicates advanced heart failure with high filling pressures. 1

Point-of-Care Ultrasound (POCUS) Assessment

POCUS provides objective hemodynamic data that refines physical examination—use a multi-organ approach integrating cardiac, vascular, and extravascular findings. 3, 4

Cardiac Assessment

Echocardiography for filling pressures:

• Measure E/E' ratio using pulse-wave Doppler (E-wave) and tissue Doppler imaging (E'-wave). E/E' ratio correlates well with pulmonary capillary wedge pressure and predicts adverse outcomes. 1

• Limitation: Correlation is less robust in patients with mitral regurgitation. 1

• Assess left ventricular ejection fraction and stroke volume to differentiate cardiogenic from other shock types. 1

Inferior Vena Cava (IVC) Assessment

• Measure IVC diameter and collapsibility with respiration to estimate central venous pressure and right heart preload. 1, 3, 5

• Integrate IVC findings with other POCUS parameters—IVC alone has limitations and should not be used in isolation. 3, 4

Lung Ultrasound

Scan intercostal spaces for B-lines ("ultrasound lung comets"):

• Number of B-lines correlates with pulmonary congestion on chest X-ray, interstitial edema on CT, extravascular lung water, and PCWP. 1

• This technique detects pulmonary congestion earlier and more sensitively than physical examination or chest radiography. 1, 4

Laboratory Assessment

Natriuretic peptides complement clinical assessment:

• BNP thresholds for congestion grading: <100 pg/mL (none), 100-299 (mild), 300-500 (moderate), >500 (severe). 1

• NT-proBNP thresholds: <400 pg/mL (none), 400-1500 (mild), 1500-3000 (moderate), >3000 (severe). 1

• Caveat: Interpretation is complicated by presence of cardiac disease, renal dysfunction, and obesity. 5

Dynamic Assessment of Fluid Responsiveness

After initial resuscitation, use dynamic measures to determine if additional fluid will improve cardiac output—this prevents both under-resuscitation and harmful fluid overload. 1, 2

Passive Leg Raise (PLR) Test

PLR is the preferred bedside test when advanced monitoring is unavailable:

• Mobilizes approximately 300 mL of blood from lower extremities to central circulation, creating a reversible fluid challenge. 6, 2

• Positive test: ≥10-15% increase in stroke volume (measured by POCUS velocity-time integral), cardiac output, or pulse pressure indicates fluid responsiveness. 6, 2

• Diagnostic performance: Positive likelihood ratio of 11 (95% CI 7.6-17) and specificity of 92%—far superior to CVP. 6

• Contraindication: Do not rely on PLR in patients with intra-abdominal hypertension or abdominal compartment syndrome. 6

Pulse Pressure Variation (PPV) / Stroke Volume Variation (SVV)

• In mechanically ventilated patients with controlled ventilation (tidal volume 8 mL/kg, no arrhythmias): PPV shows sensitivity 0.72 and specificity 0.91 for predicting fluid responsiveness. 1, 2

• Limitation: Requires specific ventilator settings and cannot be used in spontaneously breathing patients or those with arrhythmias. 2

Algorithmic Approach by Clinical Scenario

Hypotension/Shock

1. Initial assessment: Perform focused physical exam (JVP, lung auscultation, skin perfusion, mental status) and POCUS (cardiac function, IVC, lung B-lines). 1, 3

2. Initial resuscitation: Administer 30 mL/kg crystalloid bolus within 3 hours for septic shock or tissue hypoperfusion. 1, 6, 2

3. Reassess after initial bolus: Perform PLR test. If positive (≥10-15% stroke volume increase), give additional 250-1000 mL boluses and reassess after each. 6, 2

4. If PLR negative: Initiate vasopressors targeting MAP 65 mmHg rather than continuing fluids. 1, 2

5. Stop fluids immediately if: Pulmonary crackles develop, JVP rises significantly, or new peripheral edema appears. 2

Acute Heart Failure/Congestion

1. Grade congestion systematically using the scoring system: orthopnea severity, JVP measurement, hepatomegaly assessment, peripheral edema grading, and natriuretic peptide level. 1

2. Congestion score interpretation: <1 (none), 1-7 (mild), 8-14 (moderate), 15-20 (severe). 1

3. Lung ultrasound: Quantify B-lines to objectively assess pulmonary congestion and monitor decongestive therapy response. 1, 4

4. Do not discharge until euvolemia is achieved—unresolved edema increases readmission risk. 2

Acute Kidney Injury

1. Differentiate pre-renal from other causes: Use POCUS to assess cardiac function, IVC diameter/collapsibility, and presence of hydronephrosis. 1, 3

2. If hypovolemic (collapsed IVC, low stroke volume): Administer fluid boluses with frequent reassessment. 1, 3

3. If euvolemic/hypervolemic (dilated IVC, B-lines present): Avoid fluids; consider diuretics or renal replacement therapy. 1, 2

Critical Pitfalls to Avoid

• Never use CVP alone to guide fluid decisions—it has <50% positive predictive value for fluid responsiveness and can lead to under-resuscitation, organ dysfunction, and increased mortality. 1, 6, 2

• Do not continue fluids once pulmonary crackles develop—this is the clinical threshold where fluid becomes harmful. 2

• Do not delay fluid administration in obviously hypovolemic patients to perform echocardiography—clinical judgment supersedes protocol-driven care. 2

• Recognize high-risk populations: Patients with heart failure, chronic kidney disease, and chronic lung disease tolerate less fluid and require more frequent reassessment with smaller bolus volumes (250-500 mL). 2

• In cirrhosis with ACLF: Use bedside transthoracic echocardiography to assess cardiac function and IVC; monitor dynamic changes in stroke volume with fluid boluses or PLR to guide resuscitation and avoid overload. 1