Effect of Hypotension and Dobutamine on Gastrointestinal Microcirculations of Healthy, Anesthetized Horses

Horses undergoing abdominal exploratory surgery are at risk of hypotension and hypoperfusion. Normal mean arterial pressure is used as a surrogate for adequate tissue perfusion. However, measures of systemic circulation may not be reflective of microcirculation. This study measured the mean arterial pressure, cardiac index, lactate, and four microcirculatory indices in six healthy, anesthetized adult horses undergoing elective laparotomies. The microcirculatory parameters were measured at three different sites along the gastrointestinal tract (oral mucosa, colonic serosa, and rectal mucosa) with dark-field microscopy. All macro- and microcirculatory parameters were obtained when the horses were normotensive, hypotensive, and when normotension returned following treatment with dobutamine. Hypotension was induced with increases in inhaled isoflurane. The horses successfully induced into hypotension did not demonstrate consistent, expected changes in systemic perfusion or microvascular perfusion parameters at any of the three measured gastrointestinal sites. Normotension was successfully restored with the use of dobutamine, while the systemic perfusion and microvascular perfusion parameters remained relatively unchanged. These findings suggest that the use of mean arterial pressure to make clinical decisions regarding perfusion may or may not be accurate.

ASSESSMENT OF ABNORMAL SKELETAL MUSCLE PERFUSION BY CONTRAST-ENHANCED ULTRASOUND WITH PARAMETRIC IMAGING IN RATS AFTER SEVERE INJURY, HEMORRHAGIC SHOCK, AND WHOLE BLOOD RESUSCITATION

ABSTRACT

Background: After severe injury, optical measures of microvascular blood flow (MBF) decrease and do not normalize with resuscitation to normal blood pressure. These changes are associated with organ dysfunction, coagulopathy, and death. However, the pathophysiology is not well understood. Several possible pathways could also contribute to the development of trauma-induced coagulopathy (TIC). A small-animal model of trauma-related MBF derangement that persists after resuscitation and includes TIC would facilitate further study. Parametric contrast-enhanced ultrasound (CEUS) is particularly advantageous in this setting, because it noninvasively assesses MBF in large, deep vascular beds. We sought to develop such a model, measuring MBF with CEUS. Methods: Sixteen male Sprague-Dawley rats were anesthetized, ventilated, and cannulated. Rats were subjected to either no injury (sham group) or a standardized polytrauma and pressure-targeted arterial catheter hemorrhage with subsequent whole blood resuscitation (trauma group). At prespecified time points, CEUS measurements of uninjured quadriceps muscle, viscoelastic blood clot strength, and complete blood counts were taken. Results: After resuscitation, blood pressure normalized, but MBF decreased and remained low for the rest of the protocol. This was primarily driven by a decrease in blood volume with a relative sparing of blood velocity. Viscoelastic blood clot strength and platelet count also decreased and remained low throughout the protocol. Conclusion: We present a rat model of MBF derangement in uninjured skeletal muscle and coagulopathy after polytrauma that persists after resuscitation with whole blood to normal macrohemodynamics. Parametric CEUS analysis shows that this change is primarily due to microvascular obstruction. This platform can be used to develop a deeper understanding of this important process.

Assessment and comparison of microcirculation and macrocirculation in horses undergoing emergency exploratory celiotomy versus elective surgical procedures

OBJECTIVE

To assess oral buccal microcirculation by hand-held videomicroscopy in horses during colic surgery, comparing microcirculation values with macrocirculatory parameters and with those of healthy elective surgical horses.

STUDY DESIGN

Clinical prospective study.

ANIMALS

Client-owned horses (nine in the colic group; 11 in the elective group).

METHODS

In the colic group, buccal mucosal side stream dark-field microscopy (DFM) videos, cardiac output (CO), mean arterial pressure (MAP), and lactate were obtained at three timepoints under general anesthesia (30, 90, and 150 min after induction). Video analysis was used to determine total vessel density, proportion of perfused vessels, perfused vessel density, and heterogeneity index. Dark-field microscopy videos, MAP, and lactate were obtained at a single timepoint under general anesthesia (45 min after induction) in the elective group.

RESULTS

There were no differences in microcirculatory parameters between colic and elective horses, nor was there a difference across timepoints in the colic group. There was a weak negative correlation between microvascular parameters and CO (rho = -0.23).

CONCLUSION

The colic group did not have decreased microcirculation in comparison with the healthy elective group. Dark-field microscopy did not correlate well with macrocirculatory parameters in the colic group.

IMPACT

Dark-field microscopy may not be a sensitive enough indicator to detect differences in microcirculation between colic and elective groups. The lack of difference in microcirculation may be due to sample size, probe location, or variation in disease severity.

Assessment of microcirculation variables and endothelial glycocalyx using sidestream dark field videomicroscopy in anesthetized dogs undergoing cardiopulmonary bypass

Introduction

To evaluate microcirculation and endothelial glycocalyx (eGC) variables using sidestream darkfield (SDF) videomicroscopy in canine cardiopulmonary bypass (CPB).

Methods

Dogs undergoing CPB for surgical correction of naturally-occurring cardiac disease were prospectively included. Variables collected included patient demographics, underlying cardiac disease, red blood cell flow (Flow), 4-25 μm vessel density (Density), absolute capillary blood volume (CBVabs), relative capillary blood volume (CBVrel) and eGC width assessed by perfused boundary region (PBR). Anesthetized healthy dogs were used as control. Microcirculation and eGC variables were compared at baseline under anesthesia (T0), on CPB prior to cross clamping (T1), after cross clamp removal following surgical correction (T2) and at surgical closure (T3).

Results

Twelve dogs were enrolled, including 10 with a complete dataset. Median Flow was 233.9, 79.9, 164.3, and 136.1 μm/s at T0, T1, T2, and T3, respectively, (p = 1.00). Median Density was 173.3, 118.4, 121.0 and 155.4 mm/mm2 at T0, T1, T2, and T3, respectively, (p = 1.00). Median CBVabs decreased over time: 7.4, 6.6, 4.8 and 4.7 103μm3 at T0, T1, T2, and T3, respectively, (p < 0.01). Median CBVrel increased over time: 1.1, 1.5,1.1, and 1.3 103μm3 at T0, T1, T2, and T3, respectively, (p < 0.001). Median PBR increased over time: 1.8, 2.1, 2.4, 2.1 μm at T0, T1, T2, and T3, respectively, (p < 0.001). Compared to control dogs (n = 8), CPB dogs had lower CBVabs at T0.

Conclusion

Alterations in eGC thickness and microvascular occur in dogs undergoing CPB for naturally-occurring cardiac disease.

Rapid Patient-Side Evaluation of Endothelial Glycocalyx Thickness in Healthy Sedated Cats Using GlycoCheck® Software

The endothelial glycocalyx (EG) determines transvascular fluid fluxes, and influences inflammation, coagulation, and capillary blood flow. The GlycoCheck® software calculates EG thickness using sidestream dark field videomicroscopy recordings. This method has not been evaluated for use in cats. The aim of the present study was to evaluate the use of GlycoCheck® for estimating EG thickness in healthy cats, and to investigate the variability of EG thickness in this population. One hundred and one healthy research-purposed cats were included in the study. The cats were sedated, and a handheld videomicroscope, connected to GlycoCheck® software, was used to evaluate the sublingual microvasculature. The parameters measured included perfused boundary region (PBR, an indirect measurement of EG thickness) in vessels between 5 and 25 μm in diameter, valid vessel density, percentage red blood cell filling, and median red blood cell column width. Heart rate, respiratory rate, pulse oximetry and oscillometric blood pressure readings were also recorded. There were 35 neutered male cats, 11 intact males, 38 neutered females, and 17 intact females. The average age was 63 months (range, 11-160 months). Tolerance intervals for PBR (vessel diameter 5-25 μm) were 1.89-3.00 μm (95% CI, lower limit 1.76-2.04, upper limit 2.83-3.13 μm); for valid vessel density were 73.33-333.33 μm/mm2 (95% CI, lower limit 77.00-99.33, upper limit 312.67-350.33 μm/mm2); for percentage red blood cell filling were 59.85-85.07% (95% CI, lower limit 58.97-63.33, upper limit 83.07-88.20 %); and for median red blood cell column width were 5.63-8.59 μm (95% CI, lower limit 5.28-6.07, upper limit 8.14-9.51 μm). There was a negative association between median red blood cell column width and body weight (p = 0.007). The median red blood cell column was significantly wider in intact females when compared to spayed females (p = 0.033). The GlycoCheck® analysis was easily performed in healthy sedated cats. Clinical variables did not have an effect on the EG thickness. These results suggest that this technique could be valuable for evaluation of the EG and microvascular parameters in cats.

Evaluation of the sublingual microcirculation with sidestream dark field video microscopy in horses anesthetized for an elective procedure or intestinal surgery

OBJECTIVE

To compare the sublingual microcirculation between healthy horses anesthetized for elective procedures and horses with colic anesthetized for abdominal surgery and to determine the effect of mean arterial blood pressure (MAP) on the microcirculation.

ANIMALS

9 horses in the elective group and 8 horses in the colic group.

PROCEDURES

Sublingual microcirculation was assessed with sidestream dark field video microscopy. Videos were captured at 3 time points during anesthesia. Recorded microvasculature parameters were De Backer score (DBS), total density of perfused vessels (PVD) and small vessels (PVD-S), total proportion of perfused vessels (PPV) and small vessels (PPV-S), vascular flow index (MFI), and heterogeneity index (HI). Blood pressure during hypotensive (MAP < 60 mm Hg) and normotensive (MAP ≥ 60 mm Hg) episodes was also recorded.

RESULTS

During normotensive episodes, the elective group had significantly better PPV and PPV-S versus the colic group (median PPV, 76% vs 50%; median PPV-S, 73% vs 51%). In both groups, PPV decreased during anesthesia (elective group, -29%; colic group, -16%) but significantly improved in the elective group 15 minutes before the end of anesthesia (59%). During hypotensive episodes, PVD-S was better preserved in the colic group (11.1 vs 3.8 mm/mm²). No differences were identified for the microcirculatory parameters between normo- and hypotensive episodes in the colic group.

CONCLUSIONS AND CLINICAL RELEVANCE

Sublingual microcirculation was better preserved in healthy horses anesthetized for elective procedures than in horses with colic anesthetized for abdominal surgery despite resuscitation maneuvers. Results indicated that the macrocirculation and microcirculation in critically ill horses may be independent.

Fluid Therapy and the Microcirculation in Health and Critical Illness

Fluid selection and administration during shock is typically guided by consideration of macrovascular abnormalities and resuscitative targets (perfusion parameters, heart rate, blood pressure, cardiac output). However, the microcirculatory unit (comprised of arterioles, true capillaries, and venules) is vital for the effective delivery of oxygen and nutrients to cells and removal of waste products from the tissue beds. Given that the microcirculation is subject to both systemic and local control, there is potential for functional changes and impacts on tissue perfusion that are not reflected by macrocirculatory parameters. This chapter will present an overview of the structure, function and regulation of the microcirculation and endothelial surface layer in health and shock states such as trauma, hemorrhage and sepsis. This will set the stage for consideration of how these microcirculatory characteristics, and the potential disconnect between micro- and macrovascular perfusion, may affect decisions related to acute fluid therapy (fluid type, amount, and rate) and monitoring of resuscitative efforts. Available evidence for the impact of various fluids and resuscitative strategies on the microcirculation will also be reviewed.

Association between sublingual microcirculation, tissue perfusion and organ failure in major trauma: A subgroup analysis of a prospective observational study

INTRODUCTION

Previous studies described impaired microvascular perfusion and tissue oxygenation as reliable predictors of Multiple Organ Failure in major trauma. However, this relationship has been incompletely investigated. The objective of this analysis is to further evaluate the association between organ dysfunction and microcirculation after trauma.

MATERIALS AND METHODS

This is a retrospective subgroup analysis on 28 trauma patients enrolled for the Microcirculation DAIly MONitoring in critically ill patients study (NCT 02649088). Patients were divided in two groups according with their Sequential Organ Failure Assessment (SOFA) score at day 4. At admission and every 24 hours, the sublingual microcirculation was evaluated with Sidestream Darkfield Imaging (SDF) and peripheral tissue perfusion was assessed with Near Infrared Spectroscopy (NIRS) and Vascular Occlusion Test (VOT). Simultaneously, hemodynamic, clinical/laboratory parameters and main organ supports were collected.

RESULTS

Median SOFA score at Day 4 was 6.5. Accordingly, patients were divided in two groups: D4-SOFA ≤6.5 and D4-SOFA >6.5. The Length of Stay in Intensive Care was significantly higher in patients with D4-SOFA>6.5 compared to D4-SOFA≤6.5 (p = 0.013). Total Vessel Density of small vessels was significantly lower in patients with high D4-SOFA score at Day 1 (p = 0.002) and Day 2 (p = 0.006) after admission; the Perfused Vessel Density was lower in patients with high D4-SOFA score at Day 1 (p = 0.007) and Day 2 (p = 0.033). At Day 1, NIRS monitoring with VOT showed significantly faster tissue oxygen saturation downslope (p = 0.018) and slower upslope (p = 0.04) in patients with high D4-SOFA.

DISCUSSION

In our cohort of major traumas, sublingual microcirculation and peripheral microvascular reactivity were significantly more impaired early after trauma in those patients who developed more severe organ dysfunctions. Our data would support the hypothesis that restoration of macrocirculation can be dissociated from restoration of peripheral and tissue perfusion, and that microvascular alterations can be associated with organ failure.

Clinical use of plasma lactate concentration. Part 2: Prognostic and diagnostic utility and the clinical management of hyperlactatemia

OBJECTIVE

To review the current literature pertaining to the use of lactate as a prognostic indicator and therapeutic guide, the utility of measuring lactate concentrations in body fluids other than blood or plasma, and the clinical management of hyperlactatemia in dogs, cats, and horses.

DATA SOURCES

Articles were retrieved without date restrictions primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection.

HUMAN AND VETERINARY DATA SYNTHESIS

Increased plasma lactate concentrations are associated with increased morbidity and mortality. In populations with high mortality, hyperlactatemia is moderately predictive in identifying nonsurvivors. Importantly, eulactatemia predicts survival better than hyperlactatemia predicts death. Consecutive lactate measurements and calculated relative measures appear to outperform single measurements. The use of lactate as a therapeutic guide has shown promising results in people but is relatively uninvestigated in veterinary species. Increased lactate concentrations in body fluids other than blood should raise the index of suspicion for septic or malignant processes. Management of hyperlactatemia should target the underlying cause.

CONCLUSION

Lactate is a valuable triage and risk stratification tool that can be used to separate patients into higher and lower risk categories. The utility of lactate concentration as a therapeutic target and the measurement of lactate in body fluids shows promise but requires further research.

Analysis of skeletal muscle microcirculation in a porcine polytrauma model with haemorrhagic shock

Polytraumatised patients with haemorrhagic shock are prone to develop systemic complications, such as SIRS (systemic inflammatory response syndrome), ARDS (acute respiratory distress syndrome) and MOF (multiple organ failure). The pathomechanism of severe complications following trauma is multifactorial, and it is believed that microcirculatory dysfunction plays an important role. The aim of this study was to determine the changes in the microcirculation in musculature over time during shock and subsequent resuscitation in a porcine model of haemorrhagic shock and polytrauma. Twelve pigs (German Landrace) underwent femur fracture, liver laceration, blunt chest trauma, and haemorrhagic shock under standard anaesthesia and intensive care monitoring. Microcirculation data were measured from the vastus lateralis muscle using a combined white light spectrometry and laser spectroscopy system every 15 min during the shock and resuscitation period, and at 24, 48, and 72 h. Oxygen delivery and oxygen consumption were calculated and compared to baseline. The relative haemoglobin, local oxygen consumption, and saturation values in the microcirculation were observed significantly lower during shock, however, no changes in the microcirculatory blood flow and microcirculatory oxygen delivery were observed. After resuscitation, the microcirculatory blood flow and relative haemoglobin increased and remained elevated during the whole observation period (72 h). In this study, we observed changes in microcirculation during the trauma and shock phases. Furthermore, we also measured persistent dysfunction of the microcirculation over the observation period of 3 days after resuscitation and haemorrhagic shock. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1377-1382, 2018.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

Observational study of the effects of traumatic injury, haemorrhagic shock and resuscitation on the microcirculation: a protocol for the MICROSHOCK study

INTRODUCTION

The microcirculation is the physiological site of oxygen and substrate exchange. Its effectiveness during circulatory shock is vital for the perfusion of tissues, and has a bearing on subsequent organ function and prognosis. Microcirculatory dysfunction following traumatic haemorrhagic shock (THS) has been understudied compared with other pathologies such as sepsis. The aim of the MICROSHOCK study is to investigate changes seen in the microcirculation of patients following THS, and to assess its response to resuscitation. A greater understanding of the behaviour and mechanisms of microcirculatory dysfunction in this context may direct future avenues of goal-directed resuscitation for these patients.

METHODS AND ANALYSIS

This multicentre prospective longitudinal observational study includes patients who present as an emergency with THS. Microcirculatory parameters are recorded using sublingual incident dark field microscopy alongside measurements of global flow (oesophageal Doppler and transthoracic echocardiography). Patients are enrolled into the study as soon as feasible after they arrive in hospital, and then at subsequent daily time points. Blood samples are taken for investigation into the mechanisms of microcirculatory dysfunction. Sequential Organ Failure Assessment scores will be analysed with microcirculatory parameters to determine whether they correlate with greater fidelity than more conventional, global circulatory parameters.

ETHICS AND DISSEMINATION

Research Ethics Committee approval has been granted for this study (Reference: 14/YH/0078). Owing to the nature of THS, capacity for informed consent will be absent on patient enrolment. This will be addressed according to the Mental Health Capacity Act 2005. The physician in charge of the patient's care (nominated consultee) may consent on behalf of the patient. Consent will also be sought from a personal consultee (close relative or friend). After capacity is regained, the participant will be asked for their consent. Results will be submitted for publication in peer-reviewed journal format and presented at relevant academic meetings.

TRIAL REGISTRATION NUMBER

NCT02111109; Pre-results.

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.

Evaluation of a rapid bedside scoring system for microcirculation videos acquired from dogs

OBJECTIVE

To appraise a novel scoring system (Bedside Evaluation of Microcirculation [BEM]) to provide qualitative and semiquantitative assessment of canine microcirculatory videos generated by sidestream dark field imaging.

DESIGN

Prospective observational study.

SETTING

University teaching hospital.

ANIMALS

No animals were used in this study. Twenty microcirculatory videos (>20 s in length) acquired from the mucosa adjacent to the upper canine tooth of dogs were selected from a database of sidestream dark field microcirculatory videos with available current standard analysis (CSA).

INTERVENTION

Three observers were trained to evaluate 5 video quality parameters (stability, content, illumination, focus, and pressure) and four perfusion parameters (total vessel density [TVD], capillary vessel density [CVD], perfused vessel density [PVD] and microvascular flow index [MFI]). Quality parameters were scored (excellent [0], sufficient [1], and insufficient [2]) similar to CSA recommendations. Each perfusion parameter was subjectively scored (1 lowest - 5 highest) using sample clips from the training video for comparison. Videos passed quality analysis if no parameter was scored insufficient. Repeatability and reproducibility were evaluated by assessing all films in a random order three times daily for 3 days. Strength of correlation of BEM with CSA for both qualitative and semiquantitative parameters was assessed.

MEASUREMENTS AND MAIN RESULTS

The qualitative evaluation pass/fail assessment matched CSA 86% of the time with individual observer agreements of 84-88%. Agreement with CSA did not change significantly over the study period (84%, 88%, and 84% on days 1, 2, and 3, respectively). No significant correlations were demonstrated between any BEM perfusion parameter and the corresponding CSA values.

CONCLUSIONS

Rapid bedside assessment of microcirculatory video quality can be achieved. However, semiquantitative analysis by BEM demonstrated a lack of correlation with CSA for any of the perfusion parameters assessed.