Assessing Fluid Status with POCUS
Cardiac Assessment
- The American College of Cardiology recommends evaluating left ventricular function and stroke volume using velocity time integral (VTI) measurements, with a normal LVOT VTI of 18-22 cm in adults, and abnormally low VTI <15 cm indicating potential hemodynamic compromise 1
- Severely reduced VTI (≤2.5 cm) indicates significant hemodynamic compromise from severe cardiac dysfunction, significant volume depletion, or hypovolemia, with a strength of evidence based on clinical guidelines 1
- Stroke Volume can be calculated as LVOT Cross-Sectional Area × LVOT VTI, with serial VTI measurements assessing response to fluid administration, and VTI variation >15% during respiratory cycle predicting fluid responsiveness 1
Lung Ultrasound for Extravascular Fluid
- Lung ultrasound detects pulmonary edema and extravascular lung water through B-line assessment, with B-lines indicating extravascular lung fluid and interstitial syndrome, and counting B-lines in multiple lung zones for semi-quantitative assessment 2, 3, 4
- Important caveat: Lung ultrasound cannot distinguish between cardiogenic and non-cardiogenic edema, with a strength of evidence based on multiple studies 2, 3, 4
- Validated lung ultrasound aeration scores incorporate A-lines, alveolar-interstitial patterns, and consolidations, rather than simple B-line counts, to better describe lung aeration and have been validated with various techniques 4, 5
Special Populations
- In pediatric patients, POCUS detects optic nerve sheath diameter changes indicative of raised intracranial pressure in children with fused skull bones, with a strength of evidence based on clinical studies 7, 8
- Cranial ultrasonography is the preferred initial imaging modality for intracranial pressure assessment in neonates, with a strength of evidence based on clinical guidelines 8