Summary written by Dr. Scott Sullivan
Today it is my pleasure to welcome Dr. Michael Massey. Dr. Massey got his Master’s Degree at MIT, as well as a PhD in physics at University of Michigan. Over the past number of years, he has been working closely with Dr. Nathan Shapiro at Beth Israel Deaconess Medical Center looking at sublingual microvascular circulation in a variety of settings, particularly sepsis. We thought this would be a great opportunity for him to come down here and tell us about it and how to use it at the bedside!
Clinical Pearls
- Microvascular
Circulation
- Persistent microcirculatory derangements are prognostic of poor outcomes
- Various commercial ventures, these devices remain expensive research tools
- Summary of Points
- Microcirculation acts as an organ system
- Noninvasive visual window into shock state
- Microvascular dysfunction is hard to evaluate
- Image quality and user skill are challenges
- Software and image processing is under development, and more DATA is needed
- Handheld Video Microscopes
currently approved
- Cytocam Incident Darkfield (IDF)
- Microscan Sidestream Darkfield (SDF)
- These devices go under the tongue and are noninvasive
- Use LEDs in a ring and optics in the center, green light is absorbed by hemoglobin which is why the RBCs appear dark on a light background
- The image quality is highly user-dependent
- Microcirculation Model
- Capillary network is <100 microns in diameter
- The vessels <20 microns are the primary site of Oxygen diffusion into the tissue
- Oxygen Utilization
- Macrocirculation (Oxygen Supply/Delivery) Ã Microcirculation (Oxygen extraction/diffusion) Ã Mitochondria (Oxygen Use)
- In sepsis, the theory is that the microcirculation fails
- The macrocirculation may be adequate
- Physiological shunting
- Maldistributed flow
- Disrupted perfusion in the small vessels
- Microvascular Hemodynamics
- Flow = Pressure Gradient / Vascular Resistance
- Endothelial Dysfunction
- Very large surface area
- Intimately related to the systemic inflammatory response syndrome (SIRS)
- ProCESS Microcirculatory Flow Ancillary Study
- Vascular densities showed correlation with mortality at 24 and 72 hours
- Leukocyte Adhesion
- In sepsis, the immune response leads to endothelial cell injury
- Increased numbers of rolling and adhered leukocytes
- Sublingual SDF is a non-invasive method to visualize leukocyte adhesion
- Cytokine Release Syndrome
- This is a form of SIRS
- Occurs when WBCs and endothelium are activated
- Released inflammatory cytokines in turn activate more WBCs
- The leukocytes in the microcirculation are predominantly neutrophils and visible in the sublingual circulation.
- Organ Failure and Neurotoxicity in sepsis and at the microcirculatory level
- Leukocytes release reactive oxygen species into the intercellular space which kills good cells, releasing more cytokines, and perpetuating the cycle.Â
