Identifying a sublingual triangle as the ideal site for assessment of sublingual microcirculation.

The sublingual mucosa is a commonly used intraoral location for identifying microcirculatory alterations using handheld vital microscopes (HVMs). The anatomic description of the sublingual cave and its related training have not been adequately introduced. The aim of this study was to introduce anatomy guided sublingual microcirculatory assessment. Measurements were acquired from the floor of the mouth using incident dark-field (IDF) imaging before (T0) and after (T1) sublingual cave anatomy instructed training. Instructions consists of examining a specific region of interested identified through observable anatomical structures adjacent and bilaterally to the lingual frenulum which is next to the sublingual papilla. The anatomical location called the sublingual triangle, was identified as stationed between the lingual frenulum, the sublingual fold and ventrally to the tongue. Small, large, and total vessel density datasets (SVD, LVD and TVD respectively) obtained by non-instructed and instructed measurements (NIN (T0) and IM (T1) respectively) were compared. Microvascular structures were analyzed, and the presence of salivary duct-related microcirculation was identified. A total of 72 video clips were used for analysis in which TVD, but not LVD and SVD, was higher in IM compared to NIM (NIM vs. IM, 25 ± 2 vs. 27 ± 3 mm/mm2 (p = 0.044), LVD NIM vs. IM: 7 ± 1 vs. 8 ± 1mm/mm2 (p = 0.092), SVD NIM vs. IM: 18 ± 2 vs. 20 ± 3 mm/mm2 (p = 0.103)). IM resulted in microcirculatory assessments which included morphological properties such as capillaries, venules and arterioles, without salivary duct-associated microcirculation. The sublingual triangle identified in this study showed consistent network-based microcirculation, without interference from microcirculation associated with specialized anatomic structures. These findings suggest that the sublingual triangle, an anatomy guided location, yielded sublingual based measurements that conforms with international guidelines. IM showed higher TVD values, and future studies are needed with larger sample sizes to prove differences in microcirculatory parameters.

Increased Hepatic Microvascular Density, Oxygenation, and VEGF in the Hypertrophic Lobe following Portal Vein Embolization in Rabbits.

INTRODUCTION: The microvascular events following portal vein embolization (PVE) are poorly understood despite the pivotal role of the microcirculation in liver regeneration and tumor progression. We aimed to assess the changes in hepatic microvascular perfusion and neo-angiogenesis after experimental PVE. METHODS: PVE of the cranial liver lobes was performed in 12 New Zealand White rabbits divided into 2 groups of permanent (P-PVE) and reversible PVE (R-PVE), respectively. Hepatobiliary scintigraphy and CT were used to evaluate hepatic function and volume. Hepatic microcirculation was assessed using a handheld vital microscope (Cytocam) to measure microvascular density (total vessel density; TVD) before PVE, right after PVE, and 20 min after PVE, as well as at 14 days (D14 post-PVE) and 35 days (D35 post-PVE). Additionally, on D35, microvascular PO2 and liver parenchymal VEGF were assessed. RESULTS: Eleven rabbits were included after PVE (R-PVE, n = 5; P-PVE, n = 6). TVD in the nonembo-lized (hypertrophic) lobes was higher than in the embolized (atrophic) lobes of the P-PVE group at D35 post-PVE (36.7 ± 7.2 vs. 23.4 ± 4.9 mm/mm2; p < 0.05). In the R-PVE group, TVD in the nonembolized lobes was not increased at D35. Function and volume were increased in the nonembolized lobes of the P-PVE group compared to the embolized lobes, but not in the R-PVE group. Likewise, the mmicrovascular PO2 and VEGF staining rate were higher in the nonembolized lobes of the P-PVE group at D35 post-PVE. DISCUSSION/CONCLUSION: Successful volumetric and functional hypertrophy of the nonembolized lobe was accompanied by microvascular alterations featuring increased neo-angiogenesis, microvascular density, and microvascular oxygen pressure following P-PVE.

Intraoperative Imaging Techniques to Visualize Hepatic (Micro)Perfusion: An Overview.

The microcirculation plays a crucial role in the distribution of perfusion to organs. Studies have shown that microcirculatory dysfunction is an independent predictor of morbidity and mortality. Hence, assessment of liver perfusion offers valuable information on the (patho)physiological state of the liver. The current review explores techniques in perfusion imaging that can be used intraoperatively. Available modalities include dynamic contrast-enhanced ultrasound, handheld vital microscopes, indocyanine green fluorescence angiography, and laser contrast speckle imaging. Dynamic contrast-enhanced ultrasound relays information on deep tissue perfusion and is a commonly used technique to assess tumor perfusion. Handheld vital microscopes provide direct visualization of the sinusoidal architectural structure of the liver, which is a unique feature of this technique. Intraoperative fluorescence imaging uses indocyanine green, a dye that is administered intravenously to visualize microvascular perfusion when excited using near-infrared light. Laser speckle contrast imaging produces non-contact large surface-based tissue perfusion imaging free from movement- or pressure-related artefacts. In this review, we discuss the intrinsic advantages and disadvantages of these techniques and their clinical and/or scientific applications.

Interpatient heterogeneity in hepatic microvascular blood flow during vascular inflow occlusion (Pringle manoeuvre).

BACKGROUND: Vascular inflow occlusion (VIO) during liver resections (Pringle manoeuvre) can be applied to reduce blood loss, however may at the same time, give rise to ischemia-reperfusion injury (IRI). The aim of this study was to assess the characteristics of hepatic microvascular perfusion during VIO in patients undergoing major liver resection. METHODS: Assessment of hepatic microcirculation was performed using a handheld vital microscope (HVM) at the beginning of surgery, end of VIO (20 minutes) and during reperfusion after the termination of VIO. The microcirculatory parameters assessed were: functional capillary density (FCD), microvascular flow index (MFI) and sinusoidal diameter (SinD). RESULTS: A total of 15 patients underwent VIO; 8 patients showed hepatic microvascular perfusion despite VIO (partial responders) and 7 patients showed complete cessation of hepatic microvascular perfusion (full responders). Functional microvascular parameters and blood flow levels were significantly higher in the partial responders when compared to the full responders during VIO (FCD: 0.84±0.88 vs. 0.00±0.00 mm/mm2, P<0.03, respectively, and MFI: 0.69-0.22 vs. 0.00±0.00, P<0.01, respectively). CONCLUSIONS: An interpatient heterogeneous response in hepatic microvascular blood flow was observed upon VIO. This may explain why clinical strategies to protect the liver against IRI lacked consistency.

Leukocyte-Endothelium Interaction in the Sublingual Microcirculation of Coronary Artery Bypass Grafting Patients.

OBJECTIVE: The aim of this study was to apply an innovative methodology to incident dark-field (IDF) imaging in coronary artery bypass grafting (CABG) patients for the identification and quantification of rolling leukocytes along the sublingual microcirculatory endothelium. METHODS: This study was a post hoc analysis of a prospective study that evaluated the perioperative course of the sublingual microcirculation in CABG patients. Video images were captured using IDF imaging following the induction of anesthesia (T0) and cardiopulmonary bypass (CPB) (T1) in 10 patients. Rolling leukocytes were identified and quantified using frame averaging, which is a technique that was developed for correctly identifying leukocytes. RESULTS: The number of rolling leukocytes increased significantly from T0 (7.5 [6.4-9.1] leukocytes/capillary-postcapillary venule/4 s) to T1 (14.8 [13.2-15.5] leukocytes/capillary-postcapillary venule/4 s) (p < 0.0001). A significant increase in systemic leukocyte count was also detected from 7.4 ± 0.9 × 109/L (preoperative) to 12.4 ± 4.4 × 109/L (postoperative) (p < 0.01). CONCLUSION: The ability to directly visualize leukocyte-endothelium interaction using IDF imaging facilitates the diagnosis of a systemic inflammatory response after CPB via the identification of rolling leukocytes. Integration of the frame averaging algorithm into the software of handheld vital microscopes may enable the use of microcirculatory leukocyte count as a real-time parameter at the bedside.