Low Flow States Research Articles

Prophylactic Sacral Dressing for Pressure Ulcer Prevention in High-Risk Patients.

Patients in intensive care units are likely to have limited mobility owing to hemodynamic instability and activity orders for bed rest. Bed rest is indicated because of the severity of the disease process, which often involves intubation, sedation, paralysis, surgical procedures, poor nutrition, low flow states, and poor circulation. These patients are predisposed to the development and/or the progression of pressure ulcers not only because of their underlying diseases, but also because of limited mobility and deconditioned states of health. To assess whether treating high-risk patients with a prophylactic sacral dressing decreases the incidence of unit-acquired sacral pressure ulcers. An evidence-based tool for identifying patients at high risk for pressure ulcers was used in 3 intensive care units at an urban tertiary care hospital and academic medical center. Those patients deemed at high risk had a prophylactic sacral dressing applied. Incidence rates were collected and compared for the 7 months preceding use of the dressings and for 7 months during the trial period when the dressing was used. After the sacral dressing began being used, the number of unit-acquired sacral pressure ulcers decreased by 3.4 to 7.6 per 1000 patient days depending on the unit. A prophylactic sacral dressing may help prevent unit-acquired sacral pressure ulcers. Implementation of an involved care team with heightened awareness and increased education along with a prophylactic sacral dressing in patients deemed high risk for skin breakdown are all essential for success.

The Cytocam video microscope. A new method for visualising the microcirculation using Incident Dark Field technology.

We report a new microcirculatory assessment device, the Braedius Cytocam, an Incident Dark Field (IDF) video microscope, and compare it with a precursor device utilising side stream dark field (SDF) imaging. Time matched measurements were made with both devices from the sublingual microcirculation of pigs subjected to traumatic injury and hemorrhagic shock at baseline and during a shock phase. Images were analysed for vessel density, microcirculatory flow and image quality. There were no differences in density or flow data recorded from the two devices at baseline [TVD IDF 14.2 ± 2.4/TVD SDF 13.2 ± 2.0, p 0.17] [MFI IDF 3 (2.8-3.0)/MFI SDF 3 (2.9-3.0), p 0.36] or during the shock state [TVD IDF 11.64 ± 3.3/TVD SDF 11.4 ± 4.0 p = 0.98] [MFI IDF 1.9 (0.6-2.7)/MFI SDF 1.7 (0.3-2.6) p 0.55]. Bland and Altman analysis showed no evidence of significant bias. Vessel contrast was significantly better with the IDF device for both capillaries [17.1 ± 3.9 (IDF) v 3.4 ± 3.6 (SDF), p = 0.0006] and venules [36.1 ± 11.4 (IDF) v 26.4 ± 7.1 (SDF) p 0.014] The Braedius Cytocam showed comparable vessel detection to a precursor device during both baseline and low flow (shock) states.

Cell Impermeant-based Low-volume Resuscitation in Hemorrhagic Shock: A Biological Basis for Injury Involving Cell Swelling.

To determine the role of cell swelling in severe hemorrhagic shock and resuscitation injury. Circulatory shock induces the loss of energy-dependent volume control mechanisms. As water enters ischemic cells, they swell, die, and compress nearby vascular structures, which further aggravates ischemia by reducing local microcirculatory flow and oxygenation. Loading the interstitial space with cell impermeant molecules prevents water movement into the cell by passive biophysical osmotic effects, which prevents swelling injury and no-reflow. Adult rats were hemorrhaged to a pressure of 30 to 35 mm Hg, held there until the plasma lactate reached 10 mM, and given a low-volume resuscitation (LVR) (10%-20% blood volume) with saline or various cell impermeants (sorbitol, raffinose, trehalose, gluconate, and polyethylene glycol-20k (PEG-20k). When lactate again reached 10 mM after LVR, full resuscitation was started with crystalloid and red cells. One hour after full resuscitation, the rats were euthanized. Capillary blood flow was measured by the colored microsphere technique. Impermeants prevented ischemia-induced cell swelling in liver tissue and dramatically improved LVR outcomes in shocked rats. Small cell impermeants and PEG-20k in LVR solutions increased tolerance to the low flow state by two and fivefold, respectively, normalized arterial pressure during LVR, and lowered plasma lactate after full resuscitation, relative to saline. This was accompanied by higher capillary blood flow with cell impermeants. Ischemia-induced lethal cell swelling during hemorrhagic shock is a key mediator of resuscitation injury, which can be prevented by cell impermeants in low-volume resuscitation solutions.

Partial caecal necrosis

Non-occlusive caecal infarction is a rare condition that has been described in association with a variety of clinical entities, generally due to a low-flow state, and has been reported to occur in association with chronic heart disease, open-heart surgery, certain drugs, and haemodialysis.

Portal Venous Gas in a Patient with End-Stage Renal Disease

An 86-year-old man with end-stage renal disease presented with acute epigastric pain during a hemodialysis session. Computed tomography on admission demonstrated extensive gaseous distension of the portal venous system and signs of ileus without bowel necrosis. His constipation and portal venous gas (PVG) completely resolved with conservative management. While PVG can often signal impending decompensation in critically ill patients, it can also be observed in relatively benign processes and does not necessarily correlate with the acuity of illness. Its occurrence in patients undergoing hemodialysis may begin with a low-flow state, which can lead to ischemic injury.

Complement C5a inhibition improves late hemodynamic and inflammatory changes in a rat model of nonocclusive mesenteric ischemia

Nonocclusive mesenteric ischemia (NOMI) can evolve in a variety of low-flow states. Although the mechanisms leading to NOMI-related intestinal necrosis are largely unknown, circumstantial evidence suggests that excessive vasoconstriction and complement activation both play important roles in this process. Because targeting of the circulatory malfunction of the splanchnic area could be of therapeutic relevance, we set out to investigate the long-term effects of treatment with a complement C5a antagonist in a rat model of partial aortic occlusion (PAO)-induced transient mesenteric hypoperfusion. The mean arterial pressure of the splanchnic area was kept between 30 and 40 mm Hg by 60 minutes of PAO in anesthetized male Sprague-Dawley rats. C5a inhibitor acetyl-peptide-A (AcPepA; 4 mg kg(-1) intravenously) or vehicle administration was initiated at the 45th minute of PAO. After 24 hours, the animals were reanesthetized to record the macrohemodynamics and ileal microcirculation, and plasma and tissue samples were taken for determination of high-mobility group box protein-1 (HMGB-1), endothelin-1, tumor necrosis factor (TNF)-α levels, and small intestinal leukocyte infiltration. Epithelial structural changes were visualized by in vivo confocal laser scanning endomicroscopy. At 24 hours after PAO, mean arterial pressure, heart rate, and cardiac output were significantly greater, the intestinal intramural microcirculation was significantly impaired, and plasma HMGB-1, endothelin-1, TNF-α levels, the degree of epithelial damage and leukocyte infiltration was increased. The AcPepA treatment moderated the hemodynamic and microcirculatory changes, and decreased inflammatory activation and histologic signs of mucosal damage. C5a inhibition ameliorated the potentially harmful local mesenteric hypoperfusion and global long-term inflammatory consequences of PAO. This approach is of promise for use in NOMI-associated situations.

Methodological inaccuracies in clinical aortic valve severity assessment: insights from computational fluid dynamic modeling of CT-derived aortic valve anatomy

Aortic stenosis is the most common valvular heart disease. Assessing the contribution of the valve as a portion to total ventricular load is essential for the aging population. A CT scan for one patient was used to create one in vivo tricuspid aortic valve geometry and assessed with computational fluid dynamics (CFD). CFD simulated the pressure, velocity, and flow rate, which were used to assess the Gorlin formula and continuity equation, current clinical diagnostic standards. The results demonstrate an underestimation of the anatomic orifice area (AOA) by Gorlin formula and overestimation of AOA by the continuity equation, using peak velocities, as would be measured clinically by Doppler echocardiography. As a result, we suggest that the Gorlin formula is unable to achieve the intended estimation of AOA and largely underestimates AOA at the critical low-flow states present in heart failure. The disparity in the use of echocardiography with the continuity equation is due to the variation in velocity profile between the outflow tract and the valve orifice. Comparison of time-averaged orifice areas by Gorlin and continuity with instantaneous orifice areas by planimetry can mask the errors of these methods, which is a result of the assumption that the blood flow is inviscid.

Is hyperlactatemia a useful screening marker of severe sepsis in hemato-oncologic malignant patients?

Hyperlactatemia is often associated with poor clinical outcomes. Mortality is increased when lactic acidosis with low-flow states or sepsis. For improving poor prognosis, early detection and intervention of hyperlactatemia are important. There are call for monitoring blood lactate level. However, hyperlactatemia is often associated with type II lactic acidosis in hemato-oncologic malignant patients.

Chronic LDH Elevation after Left Ventricular Assist Device Implantation


 
 
 A 61-year-old woman who underwent HeartMate II left ventricular assist device placement for non-ischemic cardiomyopathy developed elevated lactate dehydrogenase within two weeks after implantation. After eight months of observation and several hospital admissions during which there was no evidence of pump thrombosis, she presented with clinically manifest hemolysis. During pump exchange there was notable pannus formation on the inflow cannula of the left ventricular assist device. The pannus around the inflow likely existed for several months, limiting the flow and creating a low- grade hemolysis and this low flow state stimulated thrombus formation triggering gross hemolysis. Thoratec analysis of the pump confirmed that the clot was present for about 5 days. Lactate dehydrogenase normalized after pump exchange.
 
 

Evaluation of aortic stenosis: an update--including low-flow States, myocardial mechanics, and stress testing.

Degenerative aortic stenosis (AS) is one of the most frequent valvular heart diseases in Western countries. Echocardiography plays a central role in the evaluation and management of patients with AS. To overcome the inherent inconsistencies between the echocardiographic parameters defining severe AS and to unify concepts, a new classification based on the interplay between flow and gradients has recently been adopted. Outcome studies of asymptomatic patients with preserved left ventricular ejection fraction (LVEF), as classified by this new approach, have shown that low-flow (LF) states are associated with poor outcome, that the classical normal-flow/high-gradient pattern has an intermediate outcome, while normal-flow/low-gradient severe AS seems to have an outcome comparable to moderate AS and such patients do not benefit from aortic valve replacement. Patients with LF/low-gradient severe AS with preserved LVEF, also known as "paradoxical LF/low-gradient AS," have the worst outcome and benefit greatly from surgical or percutaneous valve replacement, provided that severity is proven. In patients with LF/low-gradient and depressed LVEF, dobutamine stress echocardiography has an important role to distinguish severe from pseudo-severe AS and to assess surgical risk. Assessment of aortic valve calcium score, as well as computation of projected effective orifice aortic area at normal trans-valvular flow rates, has proved to be very useful to distinguish severe from pseudo-severe AS in LF/low-gradient AS with both reduced and preserved LVEF. Asymptomatic patients with normal flow/gradient should be submitted to an exercise test; exercise echocardiography can identify patients at increased risk when mean gradient increases by >18-20 mmHg and/or pulmonary arterial hypertension develops during exercise.

SYSTOLIC STRAIN DYSFUNCTION PATTERNS IN LOW FLOW VERSUS HIGH FLOW SEVERE AORTIC STENOSIS WITH PRESERVED EJECTION FRACTION

We hypothesize subclinical strain dysfunction is the cause of the paradoxical Low Flow (LF) state, defined as an indexed stroke volume (SVi) ≤35ml/m2, in some patients with severe aortic stenosis and normal ejection fraction (AS). To test this hypothesis we performed an in depth strain analysis in

The salutary effects of diphenyldifluoroketone EF24 in liver of a rat hemorrhagic shock model.

BackgroundLiver is a target for injury in low flow states and it plays a central role in the progression of systemic failure associated with hemorrhagic shock. Pharmacologic support can help recover liver function even after it has suffered extensive damage during ischemia and reperfusion phases. In this work we assessed the efficacy of a diphenyldifluoroketone EF24, an IKKβ inhibitor, in controlling hepatic inflammatory signaling caused by hemorrhagic shock in a rat model.MethodsSprague Dawley rats were bled to about 50% of blood volume. The hemorrhaged rats were treated with vehicle control or EF24 (0.4 mg/kg) after 1 h of hemorrhage without any accompanying resuscitation. The study was terminated after additional 5 h to excise liver tissue for biochemical analyses and histology.ResultsEF24 treatment alleviated hemorrhagic shock-induced histologic injury in the liver and restored serum transaminases to normal levels. Hemorrhagic shock induced the circulating levels of CD163 (a marker for macrophage activation) and CINC (an IL-8 analog), as well as myeloperoxidase activity in liver tissue. These markers of inflammatory injury were reduced by EF24 treatment. EF24 treatment also suppressed the expression of the Toll-like receptor 4, phospho-p65/Rel A, and cyclooxygenase-2 in liver tissues, indicating that it suppressed inflammatory pathway. Moreover, it reduced the hemorrhagic shock-induced increase in the expression of high mobility group box-1 protein. The evidence for apoptosis after hemorrhagic shock was inconclusive.ConclusionEven in the absence of volume support, EF24 treatment suppresses pro-inflammatory signaling in liver tissue and improves liver functional markers in hemorrhagic shock.

Abstract T P181: Static And Dynamic Cerebral Autoregulation Dissociate In Asymptomatic Carotid Artery Disease

Background: High grade internal carotid artery (ICA) disease can alter cerebral autoregulation and thus increase risk for ischemia. We aimed to differentiate two types of autoregulation - dynamic cerebral autoregulation (DCA), thought to be a homeostatic process, and vasomotor reactivity (VMR), which determines cerebrovascular reserve - in patients with asymptomatic ICA stenosis. Methods: Twenty-two patients (age 50-93, 16M) with unilateral 80-100% ICA occlusion but no stroke underwent quantitative CBF measurements using continuous arterial spin labeling (CASL) MRI. DCA was performed by continuous insonation of both middle cerebral arteries with transcranial Doppler for 10 minutes at depth 56mm using a standard head frame. Phase shift (PS) between spontaneous oscillations in blood pressure (measured with finger photoplethysmography (Finapres)) and MCA mean flow velocities (MFV) at frequencies .06-.12 Hz was calculated for each hemisphere using transfer function analysis. Lower degree of PS indicated worse autoregulation (abnormal <24deg1). VMR was determined as a response to 2 minutes of 5% CO2 inhalation (abnormal <2% rise in MCA MFV per mmHg PCO2 by Doppler-integrated inline capnometer (Spencer Technologies)). T-test Chi-square, and multivariable linear regression were used to look for associations between VMR, DCA, and hemispheral CBF (SPSS v.22). Results: MCA MFV (p<.001), VMR (p=.002), and CBF (p<.003), were lower in the ICA occlusion hemisphere. DCA difference approached significance (p=0.064). Controlling for age and anterior circle of Willis collateral cross-filling, DCA (p=0.024), but not VMR (p=0.079) on the occluded side was associated with greater hemispheral CBF asymmetry (F=6.87, p=0.024). VMR and DCA were not correlated (Fisher exact =.61). Conclusions: DCA but not VMR correlated with a low flow state produced by high grade ICA disease in asymptomatic patients. Our results suggest that in ICA stenosis dynamic/homeostatic mechanisms may be affected without substantially altering the static/protective mechanism of cerebrovascular reserve. Ongoing studies will investigate the effect of these two autoregulatory mechanisms on vascular cognitive impairment. 1 Ortega-Gutierrez S, et al. J Neuroimaging. 2014 24:379-86

Near infrared spectroscopy for evaluation of skeletal muscle tissue oxygenation in different types of shock

Clinical examination is non-invasive, but has well-recognized limitations in detecting compensated and uncompensated low flow states and their severity.This paper describes the principles of near infra-red spectroscopy (NIRS) and the basis for its proposed use, in hypovolaemic, cardiogenic and septic shock, for assessing global and regional tissue oxygenation. The vascular occlusion test is explained. Limitations of NIRS, current controversies, and what is necessary in the future to make this technology a part of the initial and ongoing assessment of a patient, are discussed as well. The ultimate goal of such techniques is to prevent miss-assessment and inadequate resuscitation of patients, two major initiators in the development of multisystem organ failure and death.

Effect of coronary artery bypass grafting surgery with a pump on cerebral blood flow in high-risk patients

Coronary artery bypass grafting (CABG) surgery usually improves myocardial contractility, reducing cardiovascular events. However, it is a high-risk procedure associated with significant neurological complications, including stroke, delirium and cognitive impairment. The pathophysiology of these complications is not very well known, and may include low flow state after surgery, low cardiac output, embolism and reperfusion lesion. The aim of this study is to prospectively evaluate the cerebral hemodynamics through transcranial color and spectral Doppler sonography in high-risk patients undergoing cardiac surgery with a pump.

CPR flow to prime the ischemic heart during cardiac arrest?

Cardiac arrest is unique among cardiac ischemic syndromes in that all circulation must be generated external to the heart. Although, chest compressions deliver limited blood flow, it may be possible to take advantage of this cardiopulmonary resuscitation (CPR) low-flow state to “prime” the heart in advance of return of restoration of spontaneous circulation. Prior investigation has demonstrated improved cardiac function after perfusing the globally ischemic heart with a cardioprotective agent under low-flow perfusion conditions (modeling CPR flow). These results raise the question as to whether CPR-generated flow can be utilized to induce pharmacological post-conditioning in the arrested heart.

Laryngo-tracheal ultrasonography to confirm correct endotracheal tube and laryngeal mask airway placement.

Waveform capnography was recommended as the most reliable method to confirm correct endotracheal tube or laryngeal mask airway placements. However, capnography may be unreliable during cardiopulmonary resuscitation and during low flow states. It may lead to an unnecessary removal of a well-placed endotracheal tube, re-intubation and interruption of chest compressions. Real-time upper airway (laryngo-tracheal) ultrasonography to confirm correct endotracheal tube placement was shown to be very useful in cadaveric models and during emergency intubation. Tracheal ultrasonography does not interrupt chest compressions and is not affected by low pulmonary flow or airway obstruction, but is limited by ultrasonography scattering and acoustic artifacts generated in air – mucosa interfaces. Sonographic upper airway assessment emerges as a rapid and easily available method to predict difficult intubation, to assess the laryngeal and hypopharyngeal size and visualize the position of the laryngeal mask airway in situ. This study demonstrates that the replacement of air with saline in endotracheal tube or laryngeal mask airway cuffs and the use of the contrast agents enables detection of cuffs in the airway. It also allows visualization of the surrounding structures or tissues as the ultrasound beam can be transmitted through the fluid – filled cuffs without being reflected from air – mucosal interfaces.

Differing effects when using phenylephrine and norepinephrine to augment cerebral blood flow after traumatic brain injury in the immature brain.

Low cerebral blood flow (CBF) states have been demonstrated in children early after traumatic brain injury (TBI), and have been correlated with poorer outcomes. Cerebral perfusion pressure (CPP) support following severe TBI is commonly implemented to correct cerebral hypoperfusion, but the efficacy of various vasopressors has not been determined. Sixteen 4-week-old female swine underwent nonimpact inertial brain injury in the sagittal plane. Intraparenchymal monitors were placed to measure intracranial pressure (ICP), CBF, brain tissue oxygen tension (PbtO2), and cerebral microdialysis 30 min to 6 h post-injury. One hour after injury, animals were randomized to receive either phenylephrine (PE) or norepinephrine (NE) infusions titrated to a CPP>70 mm Hg for 5 h. Animals were euthanized 6 h post-TBI, and brains were fixed and stained to assess regions of cell and axonal injury. After initiation of CPP augmentation with NE or PE infusions, there were no differences in ICP between the groups or over time. Animals receiving NE had higher PbtO2 than those receiving PE (29.6±10.2 vs. 19.6±6.4 torr at 6 h post-injury, p<0.05). CBF increased similarly in both the NE and PE groups. CPP support with PE resulted in a greater reduction in metabolic crisis than with NE (lactate/pyruvate ratio 16.7±2.4 vs. 42.7±10.2 at 6 h post-injury, p<0.05). Augmentation of CPP to 70 mm Hg with PE resulted in significantly smaller cell injury volumes at 6 h post-injury than CPP support with NE (0.4% vs. 1.4%, p<0.05). Despite similar increases in CBF, CPP support with NE resulted in greater brain tissue oxygenation and hypoxic-ischemic injury than CPP support with PE. Future clinical studies comparing the effectiveness of various vasopressors for CPP support are warranted.

A Rare Cause of Abdominal Pain, Nausea, and Vomiting: “Black” Esophagus

Introduction: A 30-year-old male with a past medical history of HIV on HAART, type 1 diabetes mellitus, end stage renal disease on chronic hemodialysis and blindness presented with two days of epigastric abdominal pain, nausea and non-bloody, non-bilious vomiting. He also endorsed odynophagia to solids. The patient was admitted to the hospital two other times within the last three months for similar complaints of abdominal pain associated with vomiting and anorexia. His symptoms were always thought to be secondary to underlying diabetic ketoacidosis and they would largely resolve with aggressive intravenous fluids and insulin. On this admission, physical examination was significant for mild epigastric tenderness. CT scan of his abdomen revealed circumferential wall thickening of the distal esophagus compatible with esophagitis. The patient underwent an EGD which showed circumferential, blackening of the distal esophagus consistent with acute esophageal necrosis. Biopsies were obtained, which revealed necro-inflammatory mucosa with multiple fungal forms consistent with Candida species. The patient was treated with intravenous esomeprazole and an oral sucralfate suspension, along with fluconazole given the findings of fungal infection on mucosal biopsy. The patient’s symptoms markedly improved. The patient was discharged home with complete resolution of his presenting symptoms to have close endoscopic follow-up at a later date. Acute esophageal necrosis, or the so-called “black esophagus,” is a rare finding first described in 1990 by Goldenberg et al, with an estimated prevalence reported in one autopsy study to be 0.2%. The exact pathogenesis remains unknown but ischemia is believed to be the main inciting event. Low-flow states such as diabetic ketoacidosis, as seen in our patient, result in hypo-perfusion of the distal esophagus, a region that is more “watershed” and less vascularized than the proximal portions of the esophagus. Treatment is largely supportive with correction of the predisposing event and better control of the underlying medical condition. Complications include esophageal perforation, mediastinitis, stricture formation and death.Figure 1: Blackening of the distal esophagus, which classically stops at the GE junction.

Assessment of low-flow, low-gradient aortic stenosis: multimodality imaging is the key to success.

In patients with aortic stenosis (AS), a low-flow state may occur with reduced LV ejection fraction (LVEF) (i.e., classic low flow) or with preserved LVEF (i.e., paradoxical low flow) and it is often associated with low gradient because the gradient is highly flow-dependent. Low-flow, low-gradient (LF-LG) AS is a frequent clinical entity generally associated with worse outcomes. A multimodality imaging approach, including comprehensive resting echocardiography, dobutamine stress echocardiography (DSE), and multidetector computed tomography (MDCT), is the key to successful management of patients with LF-LG AS, who represent a highly challenging subset from both a diagnostic and a therapeutic standpoint. DSE and quantification of aortic valve calcification by MDCT provide important information that is crucial to differentiate true-severe from pseudo-severe AS and therefore select the most appropriate therapy (i.e., AVR vs. medical). The assessment of LV flow reserve by DSE is useful to stratify the operative risk and guide decision making between surgical and transcatheter AVR. Other imaging biomarkers, such as the global LV longitudinal strain measured during DSE or the amount of myocardial fibrosis assessed by cardiac magnetic resonance imaging, may provide incremental information for risk stratification and therapeutic management in LF-LG AS, but additional studies are needed to validate and refine these emerging biomarkers further.