Assessing Fluid Intolerance with Doppler Ultrasonography: A Physiological Framework

Figure 1. Basic ultrasonographic approach to shock. RA and LA are right and left atria; RV and LV are right and left ventricles. These are simplifications, obstructive shock may be due to pericardial effusion or tension pneumothorax in addition to pulmonary emboli or severe acute respiratory distress syndrome (ARDS). Additionally, shock is often multifactorial; e.g., a patient with septic shock from pneumonia complicated by severe ARDS may have all 4 etiologies occurring in concert.

Figure 2. Doppler ultrasound of the left ventricular outflow tract; 4 cardiac cycles obtained via transesophageal echocardiography. The dotted trace is the maximal velocity and the area under that trace is the velocity time integral (VTI).

Figure 3. Physiological Framework linking fluid ‘tolerance’ and ‘responsiveness’. See text for details. The graph is split into quadrants highlighting 4 physiological states where changing preload (∆x, fluid tolerance) compares with changing stroke volume (∆y, fluid responsiveness ). Doppler surrogates for preload may be right-heart based (e.g., systemic vein Doppler velocimetry, VExUS) or left-heart based (e.g., pulmonary vein Doppler velocimetry, E/e’ ratio, etc.).

Figure 4. Simultaneous venous and arterial Doppler from a wearable ultrasound. (A) shows the wearable technology on a healthy volunteer. (B) shows the effect of rising preload from left to right (arrows 1 & 2 are ↑ preload). The jugular wave is amorphous indicating jugular collapse, as preload rises, the morphology of the jugular vein becomes more pulsatile and forms the s and d waves described above; the x and y refer to the pressure descents of the CVP. The carotid VTI also rises from left to right suggesting that the SV is rising with preload (e.g., quadrant 1 to 2, Figure 3). (C) shows just the jugular morphology from inspiration to expiration, intimating jugular collapse on inspiration.

Figure 5. Summary of key learning points.