Detection of inadequate anastomotic perfusion with handheld vital microscopy in two patients during colorectal surgery.

INTRODUCTION: Anastomotic leakage is one of the most feared complications after gastrointestinal surgery. Assessment of anastomotic viability during surgery remains challenging. Sufficient bowel tissue perfusion is a requisite for anastomotic healing. Handheld vital microscopy (HVM) is a non-invasive technique that can directly visualize the intestinal microcirculation during surgery. PRESENTATION OF TWO CASES: Two patients underwent elective laparoscopic colorectal surgery. During surgery HVM was used to assess bowel perfusion prior to creation of a primary anastomosis. Although the bowel macroscopically appeared to be well perfused, HVM showed a severely compromised microcirculation. The colon was re-internalized and during the following minutes cyanosis of the bowel occurred which was visually determined by the surgeon. After dissection towards cranially, a new site for the primary anastomosis was chosen. The postoperative period was uncomplicated. DISCUSSION: Sufficient bowel tissue perfusion is often mentioned as key in the pathophysiology of anastomotic leakage. HVM is a technique that could potentially aid surgeons in the assessment of microcirculatory perfusion of the bowel during surgery. CONCLUSION: We report two cases undergoing colorectal surgery in which HVM showed merit in detecting compromised bowel perfusion before creation of a primary anastomosis.

Association between serosal intestinal microcirculation and blood pressure during major abdominal surgery.

Background: In clinical practice, blood pressure is used as a resuscitation goal on a daily basis, with the aim of maintaining adequate perfusion and oxygen delivery to target organs. Compromised perfusion is often indicated as a key factor in the pathophysiology of anastomotic leakage. This study was aimed at assessing the extent to which the microcirculation of the bowel coheres with blood pressure during abdominal surgery. Methods: We performed a prospective and observational cohort study. In patients undergoing abdominal surgery, the serosal microcirculation of either the small intestine or the colon was visualized using handheld vital microscopy (HVM). From the acquired HVM image sequences, red blood cell velocity (RBCv) and total vessel density (TVD) were calculated using MicroTools and AVA software, respectively. The association between microcirculatory parameters and blood pressure was assessed using Pearson's correlation analysis. We considered a two-sided P-value of <0.050 to be significant. Results: In 28 patients undergoing abdominal surgery, a total of 76 HVM images were analyzed. The RBCv was 335 ± 96 µm/s and the TVD was 13.7 ± 3.4 mm/mm2. Mean arterial pressure (MAP) was 71 ± 12 mm Hg during microcirculatory imaging. MAP was not correlated with RBCv (Pearson's r = -0.049, P = 0.800) or TVD (Pearson's r = 0.310, P = 0.110). Conclusion: In 28 patients undergoing abdominal surgery, we found no association between serosal intestinal microcirculatory parameters and blood pressure.

Intestinal Mucosal and Serosal Microcirculation at the Planned Anastomosis during Abdominal Surgery.

INTRODUCTION: Intestinal blood flow is often named as a key factor in the pathophysiology of anastomotic leakage. The distribution between mucosal and serosal microperfusion during surgery remains to be elucidated. OBJECTIVE: The aim of this study was to assess if the mucosal microcirculation of the intestine is more vulnerable to a surgical hit than the serosal microcirculation during surgery. METHODS: In an observational cohort study (n = 9 patients), the microcirculation of the bowel serosa and mucosa was visualized with incident dark-field imaging during surgery. At the planned anastomosis, the following microcirculatory parameters were determined: microvascular flow index (MFI), percentage of perfused vessels (PPV), perfused vessel density (PVD), and total vessel density (TVD). Data are presented as median (interquartile range [IQR]). RESULTS: Perfusion parameters and vessel density were significantly higher for the mucosa than the serosal microcirculation at the planned site for anastomosis or stoma. Mucosal MFI was 3.00 (IQR 3.00-3.00) compared to a serosal MFI of 2.75 (IQR 2.21-2.94), p = 0.03. The PPV was 99% (IQR 98-100) versus 92% (IQR 66-94), p = 0.01. The TVD was 16.77 mm/mm2 (IQR 13.04-18.01) versus 10.42 mm/mm2 (IQR 9.36-11.81), p = 0.01, and the PVD was 15.44 mm/mm2 (IQR 13.04-17.78) versus 9.02 mm/mm2 (IQR 6.43-9.43), p = 0.01. CONCLUSIONS: The mucosal microcirculation was preserved, while lower perfusion of the serosa was found at the planned anastomosis or stoma during surgery. Further research is needed to link our observations to the clinically relevant endpoint of anastomotic leakage.

Mildly elevated lactate levels are associated with microcirculatory flow abnormalities and increased mortality: a microSOAP post hoc analysis.

BACKGROUND: Mildly elevated lactate levels (i.e., 1-2 mmol/L) are increasingly recognized as a prognostic finding in critically ill patients. One of several possible underlying mechanisms, microcirculatory dysfunction, can be assessed at the bedside using sublingual direct in vivo microscopy. We aimed to evaluate the association between relative hyperlactatemia, microcirculatory flow, and outcome. METHODS: This study was a predefined subanalysis of a multicenter international point prevalence study on microcirculatory flow abnormalities, the Microcirculatory Shock Occurrence in Acutely ill Patients (microSOAP). Microcirculatory flow abnormalities were assessed with sidestream dark-field imaging. Abnormal microcirculatory flow was defined as a microvascular flow index (MFI) < 2.6. MFI is a semiquantitative score ranging from 0 (no flow) to 3 (continuous flow). Associations between microcirculatory flow abnormalities, single-spot lactate measurements, and outcome were analyzed. RESULTS: In 338 of 501 patients, lactate levels were available. For this substudy, all 257 patients with lactate levels ≤ 2 mmol/L (median [IQR] 1.04 [0.80-1.40] mmol/L) were included. Crude ICU mortality increased with each lactate quartile. In a multivariable analysis, a lactate level > 1.5 mmol/L was independently associated with a MFI < 2.6 (OR 2.5, 95% CI 1.1-5.7, P = 0.027). CONCLUSIONS: In a heterogeneous ICU population, a single-spot mildly elevated lactate level (even within the reference range) was independently associated with increased mortality and microvascular flow abnormalities. In vivo microscopy of the microcirculation may be helpful in discriminating between flow- and non-flow-related causes of mildly elevated lactate levels. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01179243 . Registered on August 3, 2010.

Effect of nocturnal sound reduction on the incidence of delirium in intensive care unit patients: An interrupted time series analysis.

INTRODUCTION: Delirium in critically-ill patients is a common multifactorial disorder that is associated with various negative outcomes. It is assumed that sleep disturbances can result in an increased risk of delirium. This study hypothesized that implementing a protocol that reduces overall nocturnal sound levels improves quality of sleep and reduces the incidence of delirium in Intensive Care Unit (ICU) patients. METHODS: This interrupted time series study was performed in an adult mixed medical and surgical 24-bed ICU. A pre-intervention group of 211 patients was compared with a post-intervention group of 210 patients after implementation of a nocturnal sound-reduction protocol. Primary outcome measures were incidence of delirium, measured by the Intensive Care Delirium Screening Checklist (ICDSC) and quality of sleep, measured by the Richards-Campbell Sleep Questionnaire (RCSQ). Secondary outcome measures were use of sleep-inducing medication, delirium treatment medication, and patient-perceived nocturnal noise. RESULTS: A significant difference in slope in the percentage of delirium was observed between the pre- and post-intervention periods (-3.7% per time period, p=0.02). Quality of sleep was unaffected (0.3 per time period, p=0.85). The post-intervention group used significantly less sleep-inducing medication (p<0.001). Nocturnal noise rating improved after intervention (median: 65, IQR: 50-80 versus 70, IQR: 60-80, p=0.02). CONCLUSIONS: The incidence of delirium in ICU patients was significantly reduced after implementation of a nocturnal sound-reduction protocol. However, reported sleep quality did not improve.

Use of an Image Acquisition Stabilizer Improves Sidestream Dark Field Imaging of the Serosa during Open Gastrointestinal Surgery.

AIM: To investigate whether an image acquisition stabilizer (IAS) mounted on the sidestream dark field camera (SDF) during gastrointestinal surgery improves image stability and acquisition. METHODS: Serosal SDF imaging was compared with SDF imaging combined with an IAS (SDF + IAS) during gastrointestinal surgery. Stability was assessed as the image drift in pixels and the time to obtain stable images. The success rate was determined as the percentage of analyzable images after recording. The effect of negative pressure from the IAS was determined during single-spot measurements and by comparing microvascular parameters between groups. Data are presented as mean ± SD. RESULTS: Sixty serosal measurements were performed per group; 87% were successful in the SDF group and 100% in the SDF + IAS group (p = 0.003). Image drift in the SDF group was 148 ± 36 versus 55 ± 15 pixels in the SDF + IAS group; p < 0.001. Time to stable image was 96 ± 60 s in the SDF group versus 57 ± 31 s in the SDF + IAS group; p = 0.03. No effect of negative pressure was seen. CONCLUSION: The use of an IAS mounted on an SDF camera during serosal microvascular assessment improves the success rate of image acquisition and stability and reduces the time to stable image with no effect on the microcirculation.

International study on microcirculatory shock occurrence in acutely ill patients.

OBJECTIVES: Microcirculatory alterations are associated with adverse outcome in subsets of critically ill patients. The prevalence and significance of microcirculatory alterations in the general ICU population are unknown. We studied the prevalence of microcirculatory alterations in a heterogeneous ICU population and its predictive value in an integrative model of macro- and microcirculatory variables. DESIGN: Multicenter observational point prevalence study. SETTING: The Microcirculatory Shock Occurrence in Acutely ill Patients study was conducted in 36 ICUs worldwide. PATIENTS: A heterogeneous ICU population consisting of 501 patients. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Demographic, hemodynamic, and laboratory data were collected in all ICU patients who were 18 years old or older. Sublingual Sidestream Dark Field imaging was performed to determine the prevalence of an abnormal capillary microvascular flow index (< 2.6) and its additional value in predicting hospital mortality. In 501 patients with a median Acute Physiology and Chronic Health Evaluation II score of 15 (10-21), a Sequential Organ Failure Assessment score of 5 (2-8), and a hospital mortality of 28.4%, 17% exhibited an abnormal capillary microvascular flow index. Tachycardia (heart rate > 90 beats/min) (odds ratio, 2.71; 95% CI, 1.67-4.39; p < 0.001), mean arterial pressure (odds ratio, 0.979; 95% CI, 0.963-0.996; p = 0.013), vasopressor use (odds ratio, 1.84; 95% CI, 1.11-3.07; p = 0.019), and lactate level more than 1.5 mEq/L (odds ratio, 2.15; 95% CI, 1.28-3.62; p = 0.004) were independent risk factors for hospital mortality, but not abnormal microvascular flow index. In reference to microvascular flow index, a significant interaction was observed with tachycardia. In patients with tachycardia, the presence of an abnormal microvascular flow index was an independent, additive predictor for in-hospital mortality (odds ratio, 3.24; 95% CI, 1.30-8.06; p = 0.011). This was not true for nontachycardic patients nor for the total group of patients. CONCLUSIONS: In a heterogeneous ICU population, an abnormal microvascular flow index was present in 17% of patients. This was not associated with mortality. However, in patients with tachycardia, an abnormal microvascular flow index was independently associated with an increased risk of hospital death.

Is microvessel density correlated with anastomotic leakage after low anterior resection?

BACKGROUND/AIMS: Anastomotic leakage after low anterior resection may be the result of poor vascular supply from the proximal anastomotic loop. The purpose of this study was to investigate the correlation between colonic microvessel density and anastomotic breakdown. METHODOLOGY: Between 2006 and 2009, a consecutive series of 81 patients underwent double-stapled low anterior resection followed by a colorectal anastomosis. Symptomatic anastomotic leakage occurred in 14 patients (17%). In these patients, microvascular density was determined by image analysis of CD-31-immunostained sections from the proximal resection site. The results were compared with a sample of the remaining 67 patients without anastomotic leakage closely matched for age, gender, ASA-classification, pathological stage and neoadjuvant treatment. RESULTS: The mean percentage of anti-CD31 stained area, obtained from the proximal resection site was similar between patients with or without anastomotic leakage (4.0% +/- 1.8% versus 4.4% +/- 1.6% respectively, P = 0.53). With respect to neo-adjuvant therapy, no differences in the density of CD31 positive were observed (pre-operative radiotherapy = 4.3% +/- 1.8% versus pre-operative chemoradiotherapy 4.1% +/- 1.6%, P = 0.77). The mean vessel density reached borderline statistical significance in women (5.0% +/- 1.8%) compared to men (3.8% +/- 1.8%) (P = 0.06). CONCLUSIONS: Microvessel density quantification with immunohistochemical analysis of CD31 expression of the proximal anastomotic region did not show any correlation with anastomotic leakage in the clinical setting.

Electrical cardioversion for atrial fibrillation improves microvascular flow independent of blood pressure changes.

OBJECTIVE: This study tested the hypothesis that there is a discrepancy between global hemodynamic parameters and microvascular flow in patients before and after successful elective electrical cardioversion (ECV) for atrial fibrillation (AF). DESIGN: Prospective observational study. SETTING: Preanesthesia holding area in a teaching hospital. PARTICIPANTS: Adult patients who underwent successful elective ECV for AF. INTERVENTIONS: ECV. MEASUREMENTS AND MAIN RESULTS: Routine measurements of heart rate and noninvasive blood pressure were recorded and the sublingual microcirculation was visualized by sidestream darkfield imaging before and after the conversion of AF to sinus rhythm by elective ECV. The conversion to sinus rhythm significantly improved the microvascular flow index for smaller and larger microvessels. For smaller microvessels, perfused vessel density did not reach significance after conversion to sinus rhythm, whereas the proportion of perfused vessels was significantly larger and indices of heterogeneity for microvascular flow index decreased significantly. No correlation could be identified for the changes in mean blood pressure, perfused vessel density, and microvascular flow index for smaller microvessels. CONCLUSIONS: Successful ECV in patients with AF improves indices of sublingual microvascular perfusion. This change has no clear relation to the change in blood pressure and cannot be predicted from it. It may be prudent not to rely solely on global hemodynamic parameters to assess end-organ perfusion in this setting.

Microcirculation follows macrocirculation in heart and gut in the acute phase of hemorrhagic shock and isovolemic autologous whole blood resuscitation in pigs.

BACKGROUND: Disparity between the macro- and microcirculation is thought to occur as a result of (micro)vascular dysfunction in some types of shock. Whether this occurs during hemorrhagic shock, however, is unknown. We therefore investigated both macro- and microcirculatory variables in the heart as a vital organ and the gut as a nonvital organ. We hypothesized that the microcirculation in the gut would follow the macrocirculation in the acute phase of hemorrhagic shock and isovolemic autologous whole blood resuscitation, but that the microcirculation in the heart would be preserved even under conditions of macrocirculatory depression. STUDY DESIGN AND METHODS: Eleven pigs (23 ± 4 kg) were anesthetized and subjected to a controlled hemorrhagic shock (30 and 45% reduction of total blood volume) and isovolemic resuscitation with autologous blood. Quantitative measurement of microvascular oxygen pressures (µpO(2)) was performed by phosphorimetry on the gut and heart simultaneously. Measurements of systemic hemodynamic and regional oxygen-derived variables as well as µpO(2) were performed at baseline, after the first and second phases of hemorrhage, and after resuscitation. RESULTS: Five pigs responded to resuscitation, while six pigs died spontaneously within 20 to 30 minutes after reinfusion of the withdrawn blood, without significant differences in macro- or microcirculatory variables at baseline and after hemorrhage. Correlation analysis showed that microvascular pO(2) in the heart and the gut were closely related to macrocirculatory variables (cardiac index, mean arterial pressure, and oxygen delivery) during hemorrhage and resuscitation. CONCLUSIONS: This study demonstrated that the microcirculation in the gut (being a nonvital organ) and heart (being a vital organ) follow the macrocirculation in the acute phase of hemorrhagic shock and isovolemic autologous whole blood resuscitation.

Direct observation of the human microcirculation during cardiopulmonary bypass: effects of pulsatile perfusion.

OBJECTIVES: Possible benefits of pulsatile perfusion during cardiopulmonary bypass often are attributed to enhanced microvascular flow. However, there is no evidence to support this in humans. Therefore, the authors assessed whether pulsatile perfusion alters human microvascular flow. DESIGN: A prospective, randomized observational crossover study. SETTING: A tertiary cardiothoracic surgery referral center. PARTICIPANTS: Sixteen patients undergoing routine cardiopulmonary bypass for cardiac surgery. INTERVENTIONS: All patients underwent both pulsatile and nonpulsatile perfusion in random order. MEASUREMENTS AND MAIN RESULTS: The authors used sidestream dark-field imaging to record video clips of the sublingual human microcirculation. Perfusion was started either in the pulsatile (n = 8) or the nonpulsatile mode. After 10 minutes, microvascular recordings were made. The perfusion mode was then switched, and after 10 minutes, new microvascular recordings were taken. The authors quantified pulsatile perfusion-generated surplus hemodynamic energy by calculating pulse pressure and energy-equivalent pressure. Microvascular analysis included determination of the perfused vessel density (mean ± standard deviation). This did not differ between nonpulsatile and pulsatile perfusion (6.65 ± 1.39 v 6.83 ± 1.23 mm(-1), p = 0.58, and 2.16 ± 0.64 v 1.96 ± 0.48 mm(-1), p = 0.20 for small and large microvessels, respectively, cutoff diameter = 20 µm). Pulse pressure and energy-equivalent pressure was higher during pulsatile perfusion. However, there was no correlation between the difference in energy-equivalent pressure or pulse pressure and perfused vessel density (r = -0.43, p = 0.13, and r = -0.09, p = 0.76, respectively). CONCLUSION: Pulsatile perfusion does not alter human microvascular perfusion using standard equipment in routine cardiac surgery. Changes in pulse pressure or energy-equivalent pressure bear no obvious relationship with microcirculatory parameters.

Withdrawing intra-aortic balloon pump support paradoxically improves microvascular flow.

INTRODUCTION: The Intra-Aortic Balloon Pump (IABP) is frequently used to mechanically support the heart. There is evidence that IABP improves microvascular flow during cardiogenic shock but its influence on the human microcirculation in patients deemed ready for discontinuing IABP support has not yet been studied. Therefore we used sidestream dark field imaging (SDF) to test our hypothesis that human microcirculation remains unaltered with or without IABP support in patients clinically ready for discontinuation of mechanical support. METHODS: We studied 15 ICU patients on IABP therapy. Measurements were performed after the clinical decision was made to remove the balloon catheter. We recorded global hemodynamic parameters and performed venous oximetry during maximal IABP support (1:1) and 10 minutes after temporarily stopping the IABP therapy. At both time points, we also recorded video clips of the sublingual microcirculation. From these we determined indices of microvascular perfusion including perfused vessel density (PVD) and microvascular flow index (MFI). RESULTS: Ceasing IABP support lowered mean arterial pressure (74 ± 8 to 71 ± 10 mmHg; P = 0.048) and increased diastolic pressure (43 ± 10 to 53 ± 9 mmHg; P = 0.0002). However, at the level of the microcirculation we found an increase of PVD of small vessels <20 µm (5.47 ± 1.76 to 6.63 ± 1.90; P = 0.0039). PVD for vessels >20 µm and MFI for both small and large vessels were unaltered. During the procedure global oxygenation parameters (ScvO2/SvO2) remained unchanged. CONCLUSIONS: In patients deemed ready for discontinuing IABP support according to current practice, SDF imaging showed an increase of microcirculatory flow of small vessels after ceasing IABP therapy. This observation may indicate that IABP impairs microvascular perfusion in recovered patients, although this warrants confirmation.

Physicians' and nurses' opinions on selective decontamination of the digestive tract and selective oropharyngeal decontamination: a survey.

INTRODUCTION: Use of selective decontamination of the digestive tract (SDD) and selective oropharyngeal decontamination (SOD) in intensive care patients has been controversial for years. Through regular questionnaires we determined expectations concerning SDD (effectiveness) and experience with SDD and SOD (workload and patient friendliness), as perceived by nurses and physicians. METHODS: A survey was embedded in a group-randomized, controlled, cross-over multicenter study in the Netherlands in which, during three 6-month periods, SDD, SOD or standard care was used in random order. At the end of each study period, all nurses and physicians from participating intensive care units received study questionnaires. RESULTS: In all, 1024 (71%) of 1450 questionnaires were returned by nurses and 253 (82%) of 307 by physicians. Expectations that SDD improved patient outcome increased from 71% and 77% of respondents after the first two study periods to 82% at the end of the study (P = 0.004), with comparable trends among nurses and physicians. Nurses considered SDD to impose a higher workload (median 5.0, on a scale from 1 (low) to 10 (high)) than SOD (median 4.0) and standard care (median 2.0). Both SDD and SOD were considered less patient friendly than standard care (medians 4.0, 4.0 and 6.0, respectively). According to physicians, SDD had a higher workload (median 5.5) than SOD (median 5.0), which in turn was higher than standard care (median 2.5). Furthermore, physicians graded patient friendliness of standard care (median 8.0) higher than that of SDD and SOD (both median 6.0). CONCLUSIONS: Although perceived effectiveness of SDD increased as the trial proceeded, both among physicians and nurses, SOD and SDD were, as compared to standard care, considered to increase workload and to reduce patient friendliness. Therefore, education about the importance of oral care and on the effects of SDD and SOD on patient outcomes will be important when implementing these strategies. TRIAL REGISTRATION: ISRCTN35176830.

Aortic cross-clamping and reperfusion in pigs reduces microvascular oxygenation by altered systemic and regional blood flow distribution.

BACKGROUND: In this study, we tested the hypothesis that aortic cross-clamping (ACC) and reperfusion cause distributive alterations of oxygenation and perfusion in the microcirculation of the gut and kidneys despite normal systemic hemodynamics and oxygenation. METHODS: Fifteen anesthetized pigs were randomized between an ACC group (n = 10), undergoing 45 minutes of aortic clamping above the superior mesenteric artery, and a time-matched sham surgery control group (n = 5). Systemic, intestinal, and renal hemodynamics and oxygenation variables were monitored during 4 hours of reperfusion. Microvascular oxygen partial pressure (microPo(2)) was measured in the intestinal serosa and mucosa and the renal cortex, using the Pd-porphyrin phosphorescence technique. Intestinal luminal Pco(2) was determined by air tonometry and the serosal microvascular flow by orthogonal polarization spectral imaging. RESULTS: Organ blood flow and renal and intestinal microPo(2) decreased significantly during ACC, whereas the intestinal oxygen extraction and Pco(2) gap increased. The intestinal response to reperfusion after ACC was a sustained reactive hyperemia but no such effect was seen in the kidney. Despite a sustained high intestinal O(2) delivery, serosal microPo(2) (median [range], 49 mm Hg [41-67 mm Hg] versus 37 mm Hg [27-41 mm Hg]; P < 0.05 baseline versus 4 hours reperfusion) and the absolute number of perfused microvessels decreased along with an increased intestinal Pco(2) gap (17 mm Hg [10-19 mm Hg] versus 23 mm Hg [19-30 mm Hg]; P < 0.05). In contrast, the kidney showed a progressive O(2) delivery decrease accompanied by a decrease in renal cortex oxygenation (70 mm Hg [52-93 mm Hg] versus 57 mm Hg [33-64 mm Hg]; P < 0.05). CONCLUSION: Increased systemic and regional blood flow and oxygen supply after ACC does not ensure adequate regional blood flow and microcirculatory oxygenation in all organs.

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

OBJECTIVE: The behavior of the human microcirculation in the setting of cardiac arrest is largely unknown. Animal experiments have consistently revealed that global hemodynamics do not necessarily reflect microvascular perfusion. In addition, the time it takes for capillary blood flow to stop after the heart arrests is debated. Estimations range from 50 seconds to 5 mins, but data in humans are lacking. Aortic arch surgery frequently necessitates deep hypothermic circulatory arrest and subsequent selective antegrade cerebral perfusion. To elucidate microvascular behavior surrounding cessation of human circulation, we used sublingual microvascular imaging in this setting. DESIGN: Prospective, observational study. SETTING: Operating room of a large tertiary referral center for cardiac surgery. PATIENTS: Seven patients undergoing elective aortic arch repair. INTERVENTIONS: We used sidestream dark field imaging to study the sublingual microcirculation immediately before circulatory arrest, during circulatory arrest, and immediately after selective antegrade cerebral perfusion. MEASUREMENTS AND MAIN RESULTS: Results are reported as mean (sd) unless indicated otherwise. Before circulatory arrest, perfused vessel density was 6.41 (1.18) for small (<20 microm) and 1.57 (0.88) mm for large (>20 microm) microvessels. Microvascular flow index was a median of 3.0 (interquartile range 3.0-3.0) for both vessel sizes. After circulatory arrest, there was no equilibration of arterial and venous blood pressure before onset of selective antegrade cerebral perfusion after 59 (17) secs (range, 40-80 secs). Flow in small microvessels came to a complete stop after 45 (9) secs (range, 34-57 secs) after transition to circulatory arrest. However, flow in larger microvessels did not completely stop before selective antegrade cerebral perfusion started. Selective antegrade cerebral perfusion restored microvascular flow, reaching precirculatory arrest levels after 45 (27) secs (range, 20-85 secs). CONCLUSIONS: In a controlled surgical setting, circulatory arrest in humans induces a complete sublingual small microvessel shutdown within 1 min. However, flow in larger microvessels persists. Selective antegrade cerebral perfusion was able to restore microvascular flow to precirculatory arrest levels within a similar timeframe.

Imaging the human microcirculation during cardiopulmonary resuscitation in a hypothermic victim of submersion trauma.

The microcirculation is essential for delivery of oxygen and nutrients to tissue. However, the human microvascular response to cardiopulmonary resuscitation (CPR) is unknown. We report on the first use of sidestream dark field imaging to assess the human microcirculation during CPR with a mechanical chest compression/decompression device (mCPR). mCPR was able to provide microvascular perfusion. Capillary flow persisted even during brief mCPR interruption. However, indices of microvascular perfusion were low and improved vastly after return of spontaneous circulation. Microvascular perfusion was relatively independent from blood pressure. The microcirculation may be a useful monitor for determining the adequacy of CPR.

Microcirculatory imaging in cardiac anesthesia: ketanserin reduces blood pressure but not perfused capillary density.

OBJECTIVES: It has become possible to image the human microcirculation at the bedside using sidestream dark field (SDF) imaging. This may help the clinician when correlation between global and microvascular hemodynamics may not be straightforward. Ketanserin, a serotonin and alpha-1 adrenoceptor antagonist, is used in some countries to treat elevated blood pressure after extracorporeal circulation. This might hamper microcirculatory perfusion. Conversely, it is also conceivable that microcirculatory flow is maintained or improved as a result of flow redistribution. In order to introduce SDF imaging in cardiac anesthesia, the authors set out to directly observe the sublingual microcirculation in this setting. DESIGN: An observational study. SETTING: A large teaching hospital. PARTICIPANTS: Mechanically ventilated patients with elevated arterial blood pressure immediately after extracorporeal circulation (ECC). INTERVENTION: An intravenous bolus of ketanserin, 0.15 mg/kg. MEASUREMENTS AND MAIN RESULTS: Five minutes before and 10 minutes after ketanserin administration, global hemodynamic variables were recorded. In addition, the authors used SDF imaging to record video clips of the microcirculation. Analysis of these allowed for quantification of microvascular hemodynamics including determination of perfused vessel density (PVD) and microcirculatory flow index (MFI). After ketanserin administration, there was a significant reduction in systolic arterial blood pressure (129 +/- 9 to 100 +/- 15 mmHg, p = 0.0001). At the level of the microcirculation, the mean MFI did not change significantly for small (diameter <20 microm, 2.79 [interquartile range, 1.38-3] to 2.38 [1.88-2.75], p = 0.62) or large (diameter >20 microm, 2.83 [1.4-3] to 2.67 [0.35-2.84] p = 1.0) vessels. There was a significant increase in mean PVD for large vessels (1.23 +/- 0.63 to 1.70 +/- 79 mm(-1), p = 0.017) but not for small vessels (5.59 +/- 2.60 to 5.87 +/- 1.22 mm(-1), p = 0.72) where red blood cell flow was maintained. CONCLUSIONS: SDF imaging clearly showed a discrepancy between global and microvascular hemodynamics after the administration of ketanserin for elevated blood pressure after ECC. Ketanserin effectively lowers arterial blood pressure. However, capillary perfusion is maintained at a steady value. Both effects may be explained by an increase in shunting in the larger vessels of the microcirculation.

Hemoglobin-based oxygen carrier provides heterogeneous microvascular oxygenation in heart and gut after hemorrhage in pigs.

BACKGROUND: In this study, the hypothesis was tested that resuscitation with hemoglobin-based oxygen carriers (HBOCs) affects the oxygenation of the microcirculation differently between and within organs. To this end, we tested the influence of the volume of an HBOC on the microcirculatory oxygenation of the heart and the gut serosa and mucosa in a porcine model of hemorrhage. METHODS: In anesthetized open-chested pigs (n = 24), a controlled hemorrhage (30 mL/kg over 1 hour) was followed by resuscitation with 10, 20, or 30 mL/kg diaspirin-crosslinked hemoglobin (DCLHb) or isovolemic resuscitation with 30 mL/kg of a 6% hydroxyethyl starch solution (HAES). Measurements included systemic and regional hemodynamic and oxygenation parameters. Microvascular oxygen pressures (microPO2) of the epicardium and the serosa and mucosa of the ileum were measured simultaneously by the palladium-porphyrin phosphorescence technique. Measurements were obtained up to 120 minutes after resuscitation. RESULTS: After hemorrhage, a low volume of DCLHb restored both cardiac and intestinal microPO2. Resuscitation of gut microPO2 with a low volume of DCLHb was as effective as isovolemic resuscitation with HAES. Higher volumes of DCLHb did not restore cardiac microPO2, as did isovolemic resuscitation with HAES, but increased gut microPO2 to hyperoxic values, dose-dependently. Effects were similar for the serosal and mucosal microPo2. In contrast to a sustained hypertensive effect after resuscitation with DCLHb, effects of DCLHb on regional oxygenation and hemodynamics were transient. CONCLUSION: This study showed that a low volume of DCLHb was effective in resuscitation of the microcirculatory oxygenation of the heart and gut back to control levels. Increasing the volume of DCLHb did not cause an additional increase in heart microPO2, but caused hyperoxic microvascular values in the gut to be attained. It is concluded that microcirculatory monitoring in this way elucidates the regional behavior of oxygen transport to the tissue by HBOCs, whereas systemic variables were ineffective in describing their response.