Michael J. Massey

Impact of transfusion of autologous 7- versus 42-day-old AS-3 red blood cells on tissue oxygenation and the microcirculation in healthy volunteers.

BACKGROUND: Stored red blood cells (RBCs) accumulate biochemical and biophysical changes. Maximum storage duration is based on acceptable in vitro characteristics and 24‐hour survival, but not RBC function. Relatively little is known about the impact of RBC storage duration on oxygenation and the microcirculation.

Sublingual microcirculation is impaired in post-cardiac arrest patients

AIM We hypothesized that microcirculatory dysfunction, similar to that seen in sepsis, occurs in post-cardiac arrest patients and that better microcirculatory flow will be associated with improved outcome. We also assessed the association between microcirculatory dysfunction and inflammatory markers in the post-cardiac arrest state. METHODS We prospectively evaluated the sublingual microcirculation in post-cardiac arrest patients, severe sepsis/septic shock patients, and healthy control patients using Sidestream Darkfield microscopy. Microcirculatory flow was assessed using the microcirculation flow index (MFI) at 6 and 24h in the cardiac arrest patients, and within 6h of emergency department admission in the sepsis and control patients. RESULTS We evaluated 30 post-cardiac arrest patients, 16 severe sepsis/septic shock patients, and 9 healthy control patients. Sublingual microcirculatory blood flow was significantly impaired in post-cardiac arrest patients at 6h (MFI 2.6 [IQR: 2-2.9]) and 24h (2.7 [IQR: 2.3-2.9]) compared to controls (3.0 [IQR: 2.9-3.0]; p<0.01 and 0.02, respectively). After adjustment for initial APACHE II score, post-cardiac arrest patients had significantly lower MFI at 6-h compared to sepsis patients (p<0.03). In the post-cardiac arrest group, patients with good neurologic outcome had better microcirculatory blood flow as compared to patients with poor neurologic outcome (2.9 [IQR: 2.4-3.0] vs. 2.6 [IQR: 1.9-2.8]; p<0.03). There was a trend toward higher median MFI at 24h in survivors vs. non-survivors (2.8 [IQR: 2.4-3.0] vs. 2.6 [IQR: 2.1-2.8] respectively; p<0.09). We found a negative correlation between MFI-6 and vascular endothelial growth factor (VEGF) (r=-0.49, p=0.038). However, after Bonferroni adjustment for multiple comparisons, this correlation was statistically non-significant. CONCLUSION Microcirculatory dysfunction occurs early in post-cardiac arrest patients. Better microcirculatory function at 24h may be associated with good neurologic outcome.

A guide to human in vivo microcirculatory flow image analysis

Various noninvasive microscopic camera technologies have been used to visualize the sublingual microcirculation in patients. We describe a comprehensive approach to bedside in vivo sublingual microcirculation video image capture and analysis techniques in the human clinical setting. We present a user perspective and guide suitable for clinical researchers and developers interested in the capture and analysis of sublingual microcirculatory flow videos. We review basic differences in the cameras, optics, light sources, operation, and digital image capture. We describe common techniques for image acquisition and discuss aspects of video data management, including data transfer, metadata, and database design and utilization to facilitate the image analysis pipeline. We outline image analysis techniques and reporting including video preprocessing and image quality evaluation. Finally, we propose a framework for future directions in the field of microcirculatory flow videomicroscopy acquisition and analysis. Although automated scoring systems have not been sufficiently robust for widespread clinical or research use to date, we discuss promising innovations that are driving new development.

Lactate Clearance in Septic Shock Is Not a Surrogate for Improved Microcirculatory Flow.

BACKGROUND Failure to normalize lactate is associated with poor outcomes in septic shock. It has been suggested that persistently elevated lactate may result from regional ischemia due to disturbed and/or heterogenous microcirculatory blood flow. OBJECTIVES The goal of this study was to determine if lactate clearance (LC) may serve as a surrogate marker for changes in microcirculatory blood flow in patients with septic shock. METHODS This was a prospective observational study performed within a previously published clinical trial of l-carnitine for the treatment of vasopressor-dependent septic shock. Intravital video microscopy was performed at enrollment and 12 hours later, and microcirculatory flow index (MFI) was assessed. Associations between enrollment MFI, lactate, and Sequential Organ Failure Assessment (SOFA) score were determined, in addition to associations between ∆MFI, LC, and ∆SOFA. A preplanned subgroup analysis of only patients with an elevated initial lactate was performed. RESULTS We enrolled a total of 31 patients, 23 with survival and sufficient quality videos both at enrollment and at 12 hours. ∆MFI, LC, and ∆SOFA were 0.1 (interquartile range [IQR] = 0 to 0.3), 18% (IQR = -10% to 46%), and -2 (IQR = -4 to 0). Both ∆MFI and LC were associated with ∆SOFA (β = -5.3, p = 0.01; and β = -3.5, 0.047), but not with each other, even in the subgroup of patients with an initially elevated lactate. CONCLUSIONS We observed no association between degree of LC and change in microcirculatory blood flow in patients with septic shock. These data suggest against the hypothesis that LC may be used as a surrogate marker of microcirculatory blood flow.

A novel line detection method in space-time images for microvascular blood flow analysis in sublingual microcirculatory videos

Recent evidence suggests that quantitative assessment of microcirculatory dysfunction may indicate certain disease states [1, 2, 3]. Relevant microcirculatory hemodynamic parameters include total vessel density, density of perfused vessels, proportion of perfused vessels, and perfusion heterogeneity index. In one non-invasive, clinical approach, a handheld video microscope placed under the tongue records images of blood flow in small (<; 20μm) and medium (approximately 20-100μm) diameter vessels. Hemodynamic parameters are computed from measurements of vessel geometry and blood flow rates. Current technology is limited by poor dynamic range, low resolution, poor image stability, and pressure artifacts. Video images are analyzed quantitatively and semi-quantitatively by trained image analysts using a time-consuming, semi-automated techniques for vessel segmentation, and blood flow measurements. Space-time images are generated for quantitative velocity estimation. We propose a novel line detection method to automatically estimate the orientation of red blood cell (RBC) or plasma gap traces in space-time images. Velocities of RBCs can then be calculated based on the estimated orientation. The proposed automated method for velocity estimation was implemented for 80 vessels and compared with visual estimation of reference slope in space-time diagrams by a trained image analyst. Finally, the proposed method is compared with a Hough transform based velocity estimation method.

The impact of red blood cell storage duration on tissue oxygenation in cardiac surgery

Objective: Although storage alters red blood cells, several recent, randomized trials found no differences in clinical outcomes between patients transfused with red blood cells stored for shorter versus longer periods of time. The objective of this study was to see whether storage impairs the in vivo ability of erythrocytes to traverse the microcirculation and deliver oxygen at the tissue level. Methods: A subset of subjects from a clinical trial of cardiac surgery patients randomized to receive transfusions of red blood cells stored ≤10 days or ≥21 days were assessed for thenar eminence and cerebral tissue hemoglobin oxygen saturation (StO2) via the use of near‐infrared spectroscopy and sublingual microvascular blood flow via side‐stream darkfield videomicroscopy. Results: Among 55 subjects, there was little change in the primary endpoint (thenar eminence StO2 from before to after transfusion of one unit) and the change was similar in the 2 groups: +1.7% (95% confidence interval, −0.3, 3.8) for shorter‐storage and +0.8% (95% confidence interval, −1.1, 2.9) for longer‐storage; P = .61). Similarly, no significant differences were observed for cerebral StO2 or sublingual microvascular blood flow. These parameters also were not different from preoperatively to 1 day postoperatively, reflecting the absence of a cumulative effect of all red blood cell units transfused during this period. Conclusions: There were no differences in thenar eminence or cerebral StO2, or sublingual microcirculatory blood flow, in cardiac surgery patients transfused with red blood cells stored ≤10 days or ≥21 days. These results are consistent with the clinical outcomes in the parent study, which also did not differ, indicating that storage may not impair oxygen delivery by red blood cells in this setting.

Microvascular blood flow estimation in sublingual microcirculation videos based on a principal curve tracing algorithm

Microcirculatory perfusion is an important metric for diagnosing pathological conditions in patients. Capillary density and red blood cell (RBC) velocity provide a measure of tissue perfusion. Estimating RBC velocity is a challenging problem due to noisy video sequences, low contrast between the vessels and the background, and thousands of RBCs moving rapidly through video sequences. Typically, physicians manually trace small blood vessels and visually estimate RBC velocities. The task is labor intensive, tedious, and time-consuming. In this paper, we present a novel application of a principal curve tracing algorithm to automatically track RBCs across video frames and estimate their velocity based on the displacements of RBCs between two consecutive frames. The proposed method is implemented in one sublingual microcirculation video of a healthy subject.