Dr. Catherine Benny – Surgery resident at the University of Washington in Seattle (USA).
Dr. Johnny Wilkinson – Intensivist from Northampton, UK, and founder of Critical Care Northampton.
Dr. Manu Malbrain – Intensivist from Brussels, Belgium, and founder of International Fluid Academy Days.
They are at the 2018 International Fluid Academy Day in Amsterdam, discussing challenging topics in fluid management and perioperative care.
Context
After major surgery (or in an ICU setting), clinicians often track hemoglobin or hematocrit levels to detect potential bleeding. However, a drop in hemoglobin can stem from two main causes:
Ongoing blood loss (e.g., surgical bleeding or trauma)
Hemodilution (from fluid administration)
What the speakers say
Dr. Malbrain points out that relying on a single hemoglobin value to diagnose bleeding versus dilution is unreliable. In stable dialysis patients, you can sometimes interpret hemoconcentration or dilution from hematocrit because the fluid shifts are more controlled. But in surgical or trauma patients—especially those receiving rapid fluids or who might be actively bleeding—hemoglobin alone does not give a clear picture.
Multiple Parameters: He suggests correlating hemoglobin trends with:
Hemodynamic parameters (heart rate, blood pressure, mean arterial pressure)
Volumetric measures of preload (for example, advanced hemodynamic monitoring)
Point-of-care ultrasound
Bioelectrical impedance analysis (to look at total body water and fluid distribution)
Dr. Wilkinson reiterates that you want to look at trends rather than a single measurement. A sudden drop could indeed be concerning for active bleeding, but slow changes might just reflect fluid shifts, sampling frequency, or lab variation.
Context
Point-of-care ultrasound (POCUS) is commonly used to assess volume status by looking at the inferior vena cava (IVC)—specifically, how it changes with respiration. In spontaneously breathing patients, IVC collapsibility (or distensibility) can be an indicator of fluid responsiveness. However, this can be heavily confounded by factors like:
Mechanical ventilation
High PEEP (positive end-expiratory pressure)
Low tidal volumes
Right heart failure
Increased intra-abdominal pressure
What the speakers say
Dr. Wilkinson emphasizes that in the presence of high PEEP, altered lung mechanics, or increased abdominal pressure, IVC measurements become "entirely useless," at least as a sole measure of fluid responsiveness. He warns against focusing on just one parameter (e.g., IVC diameter) when multiple physiologic and machine-related factors can distort the reading.
The takeaway: IVC ultrasound can still be helpful in relatively stable or spontaneously breathing patients, but in a complex ICU scenario with mechanical ventilation and high PEEP, it should not be used on its own to guide fluid management.
Both Dr. Malbrain and Dr. Wilkinson keep coming back to the point that a single value—whether it's hemoglobin, hematocrit, or IVC measurement—cannot reliably guide fluid or transfusion decisions in isolation.
A patient's fluid status and/or bleeding risk should be inferred from multiple data points, including clinical exam (heart rate, blood pressure, capillary refill, etc.), continuous monitoring (CVP or advanced hemodynamic monitoring), imaging (POCUS, chest X-ray if needed), and laboratory trends (serial hemoglobin measurements, lactate, base deficit, etc.).
For a patient who is post-op in the ICU and has a dropping hemoglobin, the clinicians would:
Check for active bleeding (e.g., drains, wound sites, clinical stability).
Review fluid input to see if it might have caused dilutional changes.
Correlate with vital signs, ultrasound findings, and any advanced monitoring data.
Look at sequential trends in hemoglobin/hematocrit rather than making a decision based on a single-point drop.
In this short exchange, Drs. Benny, Wilkinson, and Malbrain highlight the pitfalls of relying on one-dimensional measures—like hemoglobin trends or IVC ultrasound—to guide fluid and transfusion decisions. They emphasize:
The need for trend analysis (multiple data points over time) rather than single-point values.
The value of combining parameters from clinical assessment, ultrasound, hemodynamic monitors, and advanced measurements (e.g., bioimpedance) to accurately gauge whether a patient is bleeding or simply experiencing fluid-induced hemodilution.
The limitations of IVC collapsibility in mechanically ventilated patients, especially with high PEEP or other complicating factors (right heart failure, increased abdominal pressure).
Ultimately, the conversation stresses an integrated, multimodal approach to patient assessment in critical care and perioperative settings, rather than placing too much faith in any single measurement tool.
