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We dive into fluid resuscitation in sepsis, with Dr. Jon-Emile Kenny, pulmonary and critical care physician, author of the physiology textbook Heart-lung.org, and inventor of the FloPatch device.
Disclosures: Dr. Kenny appears here as both a clinician as well as a representative of his company and product, and should be presumed to retain a degree of bias in this discussion. However, his appearance is not part of a commercial relationship with our show; no compensation was provided, and neither he nor his company have any input in the episode’s content, nor the right to review it (or prevent its publication) after recording.
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Takeaway lessons
- Before giving IV fluids, ask: 1) Is there an indication to give fluids? 2) Is giving fluids safe? 3) Will giving fluids be effective?
- One of the most common misconceptions is that safety and efficacy are opposite ends of a spectrum, and efficacy necessarily implies safety. This is not so. Think instead of fluid like a drug, which could be effective, yet also dangerous (e.g. anaphylaxis), or vice versa. A volume overloaded patient could be fluid responsive, but giving fluid could be a poor idea.
- Interpreting heart function and cardiac output is difficult in sepsis, particularly on the venous or filling side. Many have some degree of diastolic dysfunction, which sepsis itself can induce.
- Kenny likes to phenotype patients into a 4-quadrant grid, similar to the traditional Diamond-Forrester heart failure classification, characterizing a patient as either wet/dry and normal/low cardiac output. POCUS can be used to assess both of these; LVOT VTI >17-20 is a normal-ish stroke volume and IVC is a surrogate for preload.
- The only phenotype likely to benefit from fluid is the cold, dry patient (warm patients don’t need fluid, wet patients are unlikely to respond and maybe shouldn’t have it even if they will), although in sepsis, 20-30% of even this group are not fluid responsive and fluid will simply congest them.
- Using BP response to fluid challenge is insensitive; in a significant number of patients, cardiac output will increase but BP will not. A marker of flow, e.g. doppler ultrasound, is more sensitive.
- The FloPatch is a wireless, wearable, continuous-wave doppler ultrasound. It adheres over the neck and continuously monitors both the carotid and jugular vessels. The jugular provides a CVP-like waveform for qualitative clinician inspection, while the carotid is used to automatically measure the systolic flowtime duration, which is associated with stroke volume (better evidence than calculating a stroke volume).
- The height of the carotid waveform may change with alterations in inotropy, afterload, and other factors, but if those are consistent, fluid responsiveness is best associated with the duration alone (base of the triangle).
- An increase in flowtime duration of >7 milliseconds after a preload challenge (Trendelenburg position or ~250-300 ml rapid fluid bolus) is associated with 10% increase in stroke volume. (This cutoff is meant to match existing literature on fluid responsiveness.)