Microvascular hemodynamics in human hypothermic circulatory arrest and selective antegrade cerebral perfusion:

Haemodialysis Impairs the Human Microcirculation Independent from Macrohemodynamic Parameters

Hemodynamic changes during haemodialysis are common. Often these changes are associated with symptoms that are thought to be the result of reduced microcirculatory blood flow and oxygen delivery. The microcirculatory effect of hemodialysis is scarcely researched, though of possible influence on patient outcome. New techniques have become available to visualise and analyse microvascular blood flow. We performed an observational study using Sidestream Dark Field imaging, a microscopic technique using polarised light to visualise erythrocytes passing through sublingual capillaries, to analyse the effect of haemodyalisis on central microvascular blood flow. We showed that there is a substantial impairment of microvascular blood flow and a discrepancy between micro- and macro-vascular parameters.

Assessment of microcirculatory perfusion in healthy anesthetized cats undergoing ovariohysterectomy using sidestream dark field microscopy

OBJECTIVE

To: (1) determine the feasibility of using sidestream dark field microscopy (SDM) to measure microcirculatory parameters in healthy, anesthetized cats and (2) determine if surgical tissue manipulation and anesthesia time alter these parameters during ovariohysterectomy.

DESIGN

Prospective observational study.

SETTING

University teaching hospital.

ANIMALS

Eighteen healthy female cats.

INTERVENTIONS

Sublingual mucosa microcirculatory videos were obtained under general anesthesia preoperatively, intraoperatively, and postoperatively using an SDM device in healthy cats presenting for ovariohysterectomy. At each video acquisition point, macrovascular parameters (heart rate, blood pressure, pulse oximetry, end-tidal CO2) were recorded. Vascular analysis software was used to calculate standard microcirculatory parameters. Multivariate analysis was performed to compare microvascular and macrovascular parameters, as well as correlation with the effect of surgical manipulation and time under anesthesia.

MEASUREMENTS AND MAIN RESULTS

Twelve of 18 cats were included in final video analysis; 6 were removed for poor video quality. Values for total vessel density (TVD, 47.7 ± 8.39 mm/mm(2)), proportion of perfused vessels (PPV, 88.2 ± 5.95%), perfused vessel density (PVD, 43.0 ± 9.00 mm/mm(2)), microcirculatory flow index (MFI, 2.33 ± 0.33) were determined preoperatively. There were no significant changes in TVD, PPV, and PVD across intervention points. The MFI increased significantly from preoperative to intra- and postoperative data collection points. No correlation between microcirculatory parameters and length of anesthesia or macrocirculatory values was found.

CONCLUSIONS AND CLINICAL RELEVANCE

This study demonstrated that SDM can be utilized to obtain sublingual microvascular parameters in healthy, anesthetized cats. Limitations include difficulty in obtaining high quality images, presumed need for general anesthesia, and need for off-line video analysis. This technology has potential as a tool in experimental and clinical monitoring of microcirculatory changes in felines.

Impact of rapid ventricular pacing during TAVI on microvascular tissue perfusion

BACKGROUND

Rapid ventricular pacing (RVP) is an established technique to temporarily reduce left ventricular output during transcatheter aortic valve implantation (TAVI). The purpose of this study was to evaluate the impact of RVP on microvascular tissue perfusion (MTP) in patients undergoing TAVI.

METHODS AND RESULTS

We studied 42 patients (mean age 81.8 ± 6.9 years, n = 18 females. EuroSCORE 33 ± 12 %) during TAVI. MTP was analyzed using Sidestream-Darkfield imaging, of the sublingual microvasculature. Microvascular flow index (MFI) was continuously measured in small (10-25 μm)- and medium (26-50 μm)-sized vessels, starting 10 s before and ending 12 s after RVP. Further, perfused capillary density, total vessel density and the proportion of perfused vessels were assessed. After a mean RVP duration of 14.3 s (range 6-29), mean arterial pressure decreased from 68 ± 05 to 40 ± 7 mmHg (p < 0.001). This was associated with a significant decrease of MFI in small- and medium-sized vessels from 2.29 ± 0.64 and 2.36 ± 0.6 to 0.87 ± 0.66 (p < 0.001) and 1.0 ± 0.83 (p < 0.001), respectively. MFI remained significantly below baseline values (small: 1.75 ± 0.8, p = 0.001 vs. baseline; medium: 1.77 ± 0.85; p = 0.005 vs. baseline) at 12 s after end of RVP.

CONCLUSIONS

The study demonstrates a time-dependent effect of RVP on microflow, leading to 50 and 25 % of baseline at 8 and 18 s of RVP, respectively. In a substantial proportion of patients, RVP is associated with microcirculatory arrest and a delayed recovery of microflow. Although the impact of these findings on outcome is yet unclear, TAVI operators should be aware of the potentially adverse effects of even short periods of RVP.

Microcirculation and its relation to continuous subcutaneous glucose sensor accuracy in cardiac surgery patients in the intensive care unit

OBJECTIVE

Continuous glucose monitoring could be helpful for glucose regulation in critically ill patients; however, its accuracy is uncertain and might be influenced by microcirculation. We investigated the microcirculation and its relation to the accuracy of 2 continuous glucose monitoring devices in patients after cardiac surgery.

METHODS

The present prospective, observational study included 60 patients admitted for cardiac surgery. Two continuous glucose monitoring devices (Guardian Real-Time and FreeStyle Navigator) were placed before surgery. The relative absolute deviation between continuous glucose monitoring and the arterial reference glucose was calculated to assess the accuracy. Microcirculation was measured using the microvascular flow index, perfused vessel density, and proportion of perfused vessels using sublingual sidestream dark-field imaging, and tissue oxygenation using near-infrared spectroscopy. The associations were assessed using a linear mixed-effects model for repeated measures.

RESULTS

The median relative absolute deviation of the Navigator was 11% (interquartile range, 8%-16%) and of the Guardian was 14% (interquartile range, 11%-18%; P = .05). Tissue oxygenation significantly increased during the intensive care unit admission (maximum 91.2% [3.9] after 6 hours) and decreased thereafter, stabilizing after 20 hours. A decrease in perfused vessel density accompanied the increase in tissue oxygenation. Microcirculatory variables were not associated with sensor accuracy. A lower peripheral temperature (Navigator, b = -0.008, P = .003; Guardian, b = -0.006, P = .048), and for the Navigator, also a higher Acute Physiology and Chronic Health Evaluation IV predicted mortality (b = 0.017, P < .001) and age (b = 0.002, P = .037) were associated with decreased sensor accuracy.

CONCLUSIONS

The results of the present study have shown acceptable accuracy for both sensors in patients after cardiac surgery. The microcirculation was impaired to a limited extent compared with that in patients with sepsis and healthy controls. This impairment was not related to sensor accuracy but the peripheral temperature for both sensors and patient age and Acute Physiology and Chronic Health Evaluation IV predicted mortality for the Navigator were.

Inhaled nitric oxide improves systemic microcirculation in infants with hypoxemic respiratory failure

OBJECTIVES

To investigate the effect of inhaled nitric oxide on the systemic microcirculation. We hypothesized that inhaled nitric oxide improves the systemic microcirculation. Inhaled nitric oxide improves outcome in infants with persistent pulmonary hypertension of the newborn diagnosed by improving pulmonary blood flow and oxygenation. It reduces pulmonary vascular resistance without decline in systemic blood pressure. Inhaled nitric oxide is also utilized in the treatment of acute hypoxemic respiratory failure in children and adults. It is thought to improve regional ventilation perfusion by regional selective pulmonary vasodilation.

DESIGN

Pilot study.

SETTING

Intensive care unit of a level III university children's hospital.

PATIENTS

Consecutive ventilated patients who were treated with inhaled nitric oxide (20 ppm) were enrolled in this study. Eight patients (five boys, three girls) were included; five had congenital diaphragmatic hernia diagnosed, one had persistent pulmonary hypertension of the newborn diagnosed, one had acute respiratory distress syndrome diagnosed, and one had bronchiolitis diagnosed. The median age was 0 months (range, 0-38 months).

INTERVENTIONS

Inhaled nitric oxide administration.

MEASUREMENTS AND MAIN RESULTS

The microcirculation was assessed in the buccal mucosa within 1 hr before and within 1 hr after the start of inhaled nitric oxide using orthogonal polarization spectral imaging. The median functional capillary density before the inhaled nitric oxide was started was 4.0 cm/cm (range, 1.8-5.6 cm/cm) and improved to 4.9 cm/cm (range, 2.8-6.6 cm/cm; p = .017) after the start of inhaled nitric oxide.

CONCLUSIONS

Inhaled nitric oxide improves the systemic microcirculation in children with hypoxemic respiratory failure.

Rapid automatic assessment of microvascular density in sidestream dark field images

The purpose of this study was to develop a rapid and fully automatic method for the assessment of microvascular density and perfusion in sidestream dark field (SDF) images. We modified algorithms previously developed by our group for microvascular density assessment and introduced a new method for microvascular perfusion assessment. To validate the new algorithm for microvascular density assessment, we reanalyzed a selection of SDF video clips (n = 325) from a study in intensive care patients and compared the results to (semi-)manually found microvascular densities. The method for microvascular perfusion assessment (temporal SDF image contrast analysis, tSICA) was tested in several video simulations and in one high quality SDF video clip where the microcirculation was imaged before and during circulatory arrest in a cardiac surgery patient. We found that the new method for microvascular density assessment was very rapid (<30 s/clip) and correlated excellently with (semi-)manually measured microvascular density. The new method for microvascular perfusion assessment (tSICA) was shown to be limited by high cell densities and velocities, which severely impedes the applicability of this method in real SDF images. Hence, here we present a validated method for rapid and fully automatic assessment of microvascular density in SDF images. The new method was shown to be much faster than the conventional (semi-)manual method. Due to current SDF imaging hardware limitations, we were not able to automatically detect microvascular perfusion.