Arteriolar vasoconstrictive response: comparing the effects of arginine vasopressin and norepinephrine

Regulation of Skeletal Muscle Resistance Arteriolar Tone: Temporal Variability in Vascular Responses

INTRODUCTION

A full understanding of the integration of the mechanisms of vascular tone regulation requires an interrogation of the temporal behavior of arterioles across vasoactive challenges. Building on previous work, the purpose of the present study was to start to interrogate the temporal nature of arteriolar tone regulation with physiological stimuli.

METHODS

We determined the response rate of ex vivo proximal and in situ distal resistance arterioles when challenged by one-, two-, and three-parameter combinations of five major physiological stimuli (norepinephrine, intravascular pressure, oxygen, adenosine [metabolism], and intralumenal flow). Predictive machine learning models determined which factors were most influential in controlling the rate of arteriolar responses.

RESULTS

Results indicate that vascular response rate is dependent on the intensity of the stimulus used and can be severely hindered by altered environments, caused by application of secondary or tertiary stimuli. Advanced analytics suggest that adrenergic influences were dominant in predicting proximal arteriolar response rate compared to metabolic influences in distal arterioles.

CONCLUSION

These data suggest that the vascular response rate to physiologic stimuli can be strongly influenced by the local environment. Translating how these effects impact vascular networks is imperative for understanding how the microcirculation appropriately perfuses tissue across conditions.

Combining the vasoactive-inotropic score with lactate levels to predict mortality in post-cardiotomy patients supported with venoarterial extracorporeal membrane oxygenation

OBJECTIVES

Our goal was to determine the predictive role of the combined assessment of the vasoactive-inotropic score (VIS) and lactate levels for the prognosis of patients with postcardiotomy cardiogenic shock (PCS) requiring venoarterial extracorporeal membrane oxygenation (VA-ECMO).

METHODS

The data of adult patients with PCS requiring VA-ECMO between January 2015 and December 2018 at a tertiary hospital were analysed retrospectively. The incidence of in-hospital mortality and other clinical outcomes was analysed. The associations of the VIS and the lactate concentration and in-hospital mortality were assessed using logistic regression analysis.

RESULTS

A total of 222 patients were included and divided into 4 groups according to the cut-off points of the VIS (24.3) and the lactate level (6.85 mmol/L). The in-hospital mortality rates were 37.7%, 50.7%, 54.8% and 76.5% for the 4 groups (P < 0.001), and the rates of successful weaning off VA-ECMO were 73.9%, 69%, 61.3% and 39.2%, respectively (P = 0.001). Groups 1 and 2 exhibited significant differences compared to group 4 in both in-hospital mortality and weaning rates (P < 0.05). There was a statistically significant difference in the incidence of multiple organ dysfunction between group 1 and group 4 (P < 0.05). Groups 1, 2 and 3 demonstrated significantly improved cumulative 30-day survival compared with group 4 (log-rank test, P < 0.05). Logistic regression analysis revealed that age, a VIS > 24.3 and lactate levels > 6.85 mmol/L were independently predictive of in-hospital mortality.

CONCLUSIONS

Among patients with PCS requiring VA-ECMO, the initiation before reaching a VIS > 24.3 and lactate levels > 6.85 mmol/L was associated with improved in-hospital and 30-day outcomes, suggesting that the combined assessment of the VIS and lactate levels may be instructive for determining the initiation of VA-ECMO.

Assessment of cerebrovascular alterations induced by inflammatory response and oxidative-nitrative stress after traumatic intracranial hypertension and a potential mitigation strategy

The rapid perfusion of cerebral arteries leads to a significant increase in intracranial blood volume, exposing patients with traumatic brain injury to the risk of diffuse brain swelling or malignant brain herniation during decompressive craniectomy. The microcirculation and venous system are also involved in this process, but the precise mechanisms remain unclear. A physiological model of extremely high intracranial pressure was created in rats. This development triggered the TNF-α/NF-κB/iNOS axis in microglia, and released many inflammatory factors and reactive oxygen species/reactive nitrogen species, generating an excessive amount of peroxynitrite. Subsequently, the capillary wall cells especially pericytes exhibited severe degeneration and injury, the blood-brain barrier was disrupted, and a large number of blood cells were deposited within the microcirculation, resulting in a significant delay in the recovery of the microcirculation and venous blood flow compared to arterial flow, and this still persisted after decompressive craniectomy. Infliximab is a monoclonal antibody bound to TNF-α that effectively reduces the activity of TNF-α/NF-κB/iNOS axis. Treatment with Infliximab resulted in downregulation of inflammatory and oxidative-nitrative stress related factors, attenuation of capillary wall cells injury, and relative reduction of capillary hemostasis. These improved the delay in recovery of microcirculation and venous blood flow.

Effect of Norepinephrine on Peripheral Perfusion Index and Its Association With the Prognosis of Patients With Sepsis

Background: To evaluate whether the use of norepinephrine during the management of patients with sepsis affects the perfusion index (PI) and patient outcomes. Methods: We retrospectively studied patients with septic shock between January 2014 and December 2018 who had undergone Pulse index Continuous Cardiac Output-Plus cardiac output monitoring and received norepinephrine during the management. We collected data regarding basic clinical characteristics. Hemodynamic parameters, including lactate, PI, and norepinephrine dose at T0 and 24 h after Pulse index Continuous Cardiac Output catheterization (T24) were obtained. Results: The PI of the nonsurvivor group (n  =  44) was significantly lower than that of the survivor group (n  =  144) at T24, and the lactate level of the nonsurvivor group was significantly higher than that of the survivor group. The multiple logistic regression analysis suggested that the norepinephrine dose and PI were the most independent risk and protective factors, respectively, for intensive care unit mortality. The area under the curve for a poor prognosis was 0.847 (95% confidence interval, 0.782-0.912). The optimal cutoff value of the PI at T24 to predict intensive care unit mortality was 0.6, with a sensitivity of 77.1% and a specificity of 80%. Based on this optimal cutoff value, we divided patients into groups with PI ≥ 0.6 (n  =  125) and PI < 0.6 (n  =  59). The lactate level of the PI < 0.6 group was higher than that of the PI ≥ 0.6 group at T24. The PI < 0.6 group showed a significantly higher sublingual dose of norepinephrine indicators than the PI ≥ 0.6 group. The PI showed a strong negative correlation with norepinephrine dose (r  =  -0.344, P < .001) and lactate (r  =  -0.291, P < .001). Conclusions: A higher PI is a protective factor, and a higher dose of norepinephrine is a risk factor for the prognosis of critically ill patients with septic shock. A lower PI was associated with a higher dose of norepinephrine.

Predictors of hospital-acquired pressure injuries in patients with complete spinal cord injury: a retrospective case-control study

BACKGROUND

Despite current best practices, pressure injuries (PI) remain a devastating and prevalent hospital-acquired complication for patients with acute traumatic spinal cord injuries (SCIs). This study examined associations between risk factors for PI development in patients with complete SCI, such as norepinephrine dose and duration, and other demographic factors or lesion characteristics.

METHODS

This case-control study included adults with acute complete SCIs ASIA-A, who were admitted to a level-one trauma center between 2014-18. A retrospective review was implement using data on patient and injury characteristics, including age, gender, level of SCI (cervical vs. thoracic), Injury Severity Score (ISS), length of stay (LOS) and mortality; presence/absence of PI during their acute hospital stay; and treatment factors such as spinal surgery, mean arterial pressure (MAP) targets, and vasopressor treatment. Multivariable logistic regression evaluated associations with PI.

RESULTS

Eighty-two out of 103 eligible patients had complete data, and 30 (37%) developed PIs. Patient and injury characteristics, including age (Mean: 50.6; SD:21.3), location of SCI (48 cervical, 59%) and ISS (Mean 33.1; SD:11.8), did not differ between PI and non-PI groups. Logistic regression analysis revealed that male gender (OR:34.1; CI₉₅:2.3-506.5, p = 0.010) and increased LOS (log-transformed; OR:20.5, CI₉₅:2.8-149.9, p = 0.003) were associated with increased risk of PI. Having an order for a MAP > 80mmg (OR:0.05; CI₉₅:0.01-0.30, p = 0.001) was associated with a reduced risk of PI. There were no significant associations between PI and duration of norepinephrine treatment.

CONCLUSIONS

Norepinephrine treatment parameters were not associated with development of PI, suggesting that MAP targets should be a focus for future investigations for SCI management. Increasing LOS should highlight the need for high-risk PI prevention and vigilance.

Acute subdural haematoma exacerbates cerebral blood flow disorder and promotes the development of intraoperative brain bulge in patients with severe traumatic brain injury

BACKGROUND

Decompressive craniectomy (DC) is a routine procedure used for the treatment of severe traumatic brain injury (TBI) with concomitant acute subdural haematoma (SDH). However, certain patients are prone to developing malignant brain bulge during DC, which prolongs the operative time and worsens patient outcomes. Previous studies have shown that malignant intraoperative brain bulge (IOBB) may be associated with excessive arterial hyperaemia caused by cerebrovascular system disorders. Through a clinical retrospective analysis and prospective observations, we found that the cerebral blood flow of patients who possessed risk factors manifested high resistance and low flow velocity, which severely affected brain tissue perfusion and resulted in the occurrence of malignant IOBB. In the current literature, rat models of severe brain injury-associated brain bulge have rarely been reported.

METHODS

To gain an in-depth understanding of cerebrovascular changes and the cascade of responses related to brain bulge, we introduced acute SDH into the Marmarou model for the preparation of a rat model of high intracranial pressure (ICP) to simulate the pathological conditions experienced by patients with severe brain injury.

RESULTS

With the introduction of a 400-µL haematoma, significant dynamic changes occurred in ICP, mean arterial pressure, and relative blood perfusion rate of the cerebral cortical vessels. ICP increased to 56.9 ± 2.3 mmHg, mean arterial pressure showed reactive decrease, and the blood flow of cerebral cortical arteries and veins on the non-SDH-affected side decreased to < 10%. These changes could not fully recover even after DC. This resulted in generalised damage to the neurovascular unit and a lag effect to the venous blood reflux, which triggered malignant IOBB formation during DC.

CONCLUSION

An excessive increase in ICP causes cerebrovascular dysfunction and brings about a cascade of damage to brain tissue, which forms the basis for the development of diffuse brain swelling. The subsequent heterogeneous responses of the cerebral arteries and veins during craniotomy may be the main cause of primary IOBB. Clinicians should pay particular attention to the redistribution of CBF to various vessels when performing DC in patients with severe TBI.

The Role of Arginine-Vasopressin in Stroke and the Potential Use of Arginine-Vasopressin Type 1 Receptor Antagonists in Stroke Therapy: A Narrative Review

Stroke is a life-threatening condition in which accurate diagnoses and timely treatment are critical for successful neurological recovery. The current acute treatment strategies, particularly non-invasive interventions, are limited, thus urging the need for novel therapeutical targets. Arginine vasopressin (AVP) receptor antagonists are emerging as potential targets to treat edema formation and subsequent elevation in intracranial pressure, both significant causes of mortality in acute stroke. Here, we summarize the current knowledge on the mechanisms leading to AVP hyperexcretion in acute stroke and the subsequent secondary neuropathological responses. Furthermore, we discuss the work supporting the predictive value of measuring copeptin, a surrogate marker of AVP in stroke patients, followed by a review of the experimental evidence suggesting AVP receptor antagonists in stroke therapy. As we highlight throughout the narrative, critical gaps in the literature exist and indicate the need for further research to understand better AVP mechanisms in stroke. Likewise, there are advantages and limitations in using copeptin as a prognostic tool, and the translation of findings from experimental animal models to clinical settings has its challenges. Still, monitoring AVP levels and using AVP receptor antagonists as an add-on therapeutic intervention are potential promises in clinical applications to alleviate stroke neurological consequences.

Effects of mean arterial pressure target on mottling and arterial lactate normalization in patients with septic shock: a post hoc analysis of the SEPSISPAM randomized trial

Background

In patients with septic shock, the impact of the mean arterial pressure (MAP) target on the course of mottling remains uncertain. In this post hoc analysis of the SEPSISPAM trial, we investigated whether a low-MAP (65 to 70 mmHg) or a high-MAP target (80 to 85 mmHg) would affect the course of mottling and arterial lactate in patients with septic shock.

Methods

The presence of mottling was assessed every 2 h from 2 h after inclusion to catecholamine weaning. We compared mottling and lactate time course between the two MAP target groups. We evaluated the patient’s outcome according to the presence or absence of mottling.

Results

We included 747 patients, 374 were assigned to the low-MAP group and 373 to the high-MAP group. There was no difference in mottling and lactate evolution during the first 24 h between the two MAP groups. After adjustment for MAP and confounding factors, the presence of mottling ≥ 6 h during the first 24 h was associated with a significantly higher risk of death at day 28 and 90. Patients without mottling or with mottling < 6 h and lactate ≥ 2 mmol/L have a higher probability of survival than those with mottling ≥ 6 h and lactate < 2 mmol/L.

Conclusion

Compared with low MAP target, higher MAP target did not alter mottling and lactate course. Mottling lasting for more than 6 h was associated with higher mortality. Compared to arterial lactate, mottling duration appears to be a better marker of mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01053-1.

Cerebral Blood Flow Disorder in Acute Subdural Hematoma and Acute Intraoperative Brain Bulge

Context

Acute subdural hematoma (ASDH) has a high incidence and high mortality. During surgery for ASDH, brain tissue sometimes rapidly swells and protrudes into the bone window during or after removal of the hematoma. This phenomenon, known as acute intraoperative brain bulge, progresses rapidly and can cause ischemic necrosis of brain tissue or even mortality. The mechanism of this phenomenon remains unclear.

Objective

To investigate the changes in cerebral surface blood flow during ASDH and acute intraoperative brain bulge in rats.

Methods

Adult male Sprague–Dawley rats were selected to establish an ASDH model, and acute intraoperative brain bulge was induced by late-onset intracranial hematoma. The changes in cerebral surface blood flow during ASDH and acute intraoperative brain bulge were observed with a laser speckle imaging system, and intracranial pressure (ICP) was monitored.

Results

ICP in rats increased significantly after ASDH (P < 0.05). The blood perfusion rate (BPR) values of the superior sagittal sinus, collateral vein and artery decreased significantly in rats with subdural hematomas (P < 0.05). There was no significant difference between the preoperative and 90-min postoperative BPR values of rats. ICP was significantly increased in rats with acute intraoperative brain bulge (P < 0.05) and decreased significantly after the removal of delayed hematomas (P < 0.05). The BPR of the superior sagittal sinus, collateral vein and artery decreased significantly during brain bulge (P < 0.05). After the removal of delayed hematomas, BPR increased significantly, but it remained significantly different from the values measured before brain bulge (P < 0.05).

Conclusion

ASDH may cause not only high intracranial pressure but also cerebral blood circulation disorders. Brain bulge resulting from late-onset intracranial hematoma may aggravate these circulation disorders. If the cause of brain bulge in a given patient is late-onset intracranial hematoma, clinicians should promptly perform surgery to remove the hematoma and relieve circulation disorders, thus preventing more serious complications.

The Potential Role of Extracorporeal Cytokine Removal in Hemodynamic Stabilization in Hyperinflammatory Shock

Hemodynamic instability due to dysregulated host response is a life-threatening condition requiring vasopressors and vital organ support. Hemoadsorption with Cytosorb has proven to be effective in reducing cytokines and possibly in attenuating the devastating effects of the cytokine storm originating from the immune over-response to the initial insult. We reviewed the PubMed database to assess evidence of the impact of Cytosorb on norepinephrine needs in the critically ill. We further analyzed those studies including data on control cohorts in a comparative pooled analysis, defining a treatment effect as the standardized mean differences in relative reductions in vasopressor dosage at 24 h. The literature search returned 33 eligible studies. We found evidence of a significant reduction in norepinephrine requirement after treatment: median before, 0.55 (IQR: 0.39-0.90); after, 0.09 (0.00-0.25) μg/kg/min, p < 0.001. The pooled effect size at 24 h was large, though characterized by high heterogeneity. In light of the importance of a quick resolution of hemodynamic instability in the critically ill, further research is encouraged to enrich knowledge on the potentials of the therapy.

An Interaction Effect Analysis of Thermodilution-Guided Hemodynamic Optimization, Patient Condition, and Mortality after Successful Cardiopulmonary Resuscitation

Proper hemodynamic management is necessary among post-cardiac arrest patients to improve survival. We aimed to investigate the effects of PiCCO™-guided (pulse index contour cardiac output) hemodynamic management on mortality in post-resuscitation therapy. In this longitudinal analysis of 63 comatose patients after successful cardiopulmonary resuscitation cooled to 32–34 °C, 33 patients received PiCCO™, and 30 were not monitored with PiCCO™. Primary and secondary outcomes were 30 day and 1 year mortality. Kaplan–Meier curves and log-rank tests were used to assess differences in mortality among the groups. Interaction effects to disentangle the relationship between patient’s condition, PiCCO™ application, and mortality were assessed by means of Chi-square tests and logistic regression models. A 30 day mortality was significantly higher among PiCCO™ patients, while 1 year mortality was marginally higher. More severe patient condition per se was not the cause of higher mortality rate in the PiCCO™ group. Patients in better health conditions (without ST-elevation myocardial infarction, without cardiogenic shock, without intra-aortic balloon pump device, or without stroke in prior history) had worse outcomes with PiCCO™-guided therapy. Catecholamine administration worsened both 30 day and 1 year mortality among all patients. Our analysis showed that there was a complex interaction relationship between PiCCO™-guided therapy, patients’ condition, and 30 day mortality for most conditions.

Trauma, a Matter of the Heart-Molecular Mechanism of Post-Traumatic Cardiac Dysfunction

Trauma remains a leading global cause of mortality, particularly in the young population. In the United States, approximately 30,000 patients with blunt cardiac trauma were recorded annually. Cardiac damage is a predictor for poor outcome after multiple trauma, with a poor prognosis and prolonged in-hospitalization. Systemic elevation of cardiac troponins was correlated with survival, injury severity score, and catecholamine consumption of patients after multiple trauma. The clinical features of the so-called "commotio cordis" are dysrhythmias, including ventricular fibrillation and sudden cardiac arrest as well as wall motion disorders. In trauma patients with inappropriate hypotension and inadequate response to fluid resuscitation, cardiac injury should be considered. Therefore, a combination of echocardiography (ECG) measurements, echocardiography, and systemic appearance of cardiomyocyte damage markers such as troponin appears to be an appropriate diagnostic approach to detect cardiac dysfunction after trauma. However, the mechanisms of post-traumatic cardiac dysfunction are still actively being investigated. This review aims to discuss cardiac damage following trauma, focusing on mechanisms of post-traumatic cardiac dysfunction associated with inflammation and complement activation. Herein, a causal relationship of cardiac dysfunction to traumatic brain injury, blunt chest trauma, multiple trauma, burn injury, psychosocial stress, fracture, and hemorrhagic shock are illustrated and therapeutic options are discussed.

Minimizing catecholamines and optimizing perfusion

Catecholamines are used to increase cardiac output and blood pressure, aiming ultimately at restoring/improving tissue perfusion. While intuitive in its concept, this approach nevertheless implies to be effective that regional organ perfusion would increase in parallel to cardiac output or perfusion pressure and that the catecholamine does not have negative effects on the microcirculation. Inotropic agents may be considered in some conditions, but it requires prior optimization of cardiac preload. Alternative approaches would be either to minimize exposure to vasopressors, tolerating hypotension and trying to prioritize perfusion but this may be valid as long as perfusion of the organ is preserved, or to combine moderate doses of vasopressors to vasodilatory agents, especially if these are predominantly acting on the microcirculation. In this review, we will discuss the pros and cons of the use of catecholamines and alternative agents for improving tissue perfusion in septic shock.

Supra-plasma expanders: the future of treating blood loss and anemia without red cell transfusions?

Oxygen delivery capacity during profoundly anemic conditions depends on blood's oxygen-carrying capacity and cardiac output. Oxygen-carrying blood substitutes and blood transfusion augment oxygen-carrying capacity, but both have given rise to safety concerns, and their efficacy remains unresolved. Anemia decreases oxygen-carrying capacity and blood viscosity. Present studies show that correcting the decrease of blood viscosity by increasing plasma viscosity with newly developed plasma expanders significantly improves tissue perfusion. These new plasma expanders promote tissue perfusion, increasing oxygen delivery capacity without increasing blood oxygen-carrying capacity, thus treating the effects of anemia while avoiding the transfusion of blood.

Prolonged observation time reveals temporal fluctuations in the sublingual microcirculation in pigs given arginine vasopressin

Intravital videomicroscopy of sublingual microcirculation is used to monitor critically ill patients. Existing guidelines suggest averaging handheld video recordings of ∼20 s in duration from five areas. We assessed whether an extended observation time may provide additional information on the microcirculation. Pigs (n = 8) under general anesthesia were divided between two groups, one with manually held camera, in which microcirculation was assessed continuously for 1 min in five areas, and one with a fixed camera, in which the observation time was extended to 10 min in a single area. The microcirculation was challenged by infusing arginine vasopressin (AVP). In the fixed group, ischemic acute heart failure was induced by left coronary microembolization, and the AVP infusion was repeated. All recordings were divided into 20-s sequences, and the small-vessel microvascular flow index (MFI) was scored and averaged for each measurement point. When administering 0.003, 0.006, and 0.012 IU·kg(-1)·min(-1) of AVP, we observed that the small-vessel MFI in the fixed 10-min group was significantly reduced (2.03 ± 0.38, 0.98 ± 0.18, and 0.48 ± 0.11) compared with both the initial 20 s (2.77 ± 0.04, 2.06 ± 0.04, and 1.74 ± 0.06; P < 0.05) and the 1-min total (2.63 ± 0.09, 1.70 ± 0.07, and 1.33 ± 0.16; P < 0.05) in the handheld group. In acute heart failure, the cardiac output decreased to half of the preischemic values. Interestingly, the small-vessel MFI was more affected by the administration of 0.001 and 0.003 IU·kg(-1)·min(-1) of AVP in acute heart failure (1.62 ± 0.60 and 1.16 ± 0.38) compared with preischemic values (2.86 ± 0.09 and 2.03 ± 0.38; P < 0.05). In conclusion, a prolonged recording time reveals temporal heterogeneity that may impact the assessment of microcirculatory function.

Blood substitutes: evolution from noncarrying to oxygen- and gas-carrying fluids

The development of oxygen (O2)-carrying blood substitutes has evolved from the goal of replicating blood O2 transport properties to that of preserving microvascular and organ function, reducing the inherent or potential toxicity of the material used to carry O2, and treating pathologies initiated by anemia and hypoxia. Furthermore, the emphasis has shifted from blood replacement fluid to "O2 therapeutics" that restore tissue oxygenation to specific tissues regions. This review covers the different alternatives, potential and limitations of hemoglobin-based O2 carriers (HBOCs) and perfluorocarbon-based O2 carriers (PFCOCs), with emphasis on the physiologic conditions disturbed in the situation that they will be used. It describes how concepts learned from plasma expanders without O2-carrying capacity can be applied to maintain O2 delivery and summarizes the microvascular responses due to HBOCs and PFCOCs. This review also presents alternative applications of HBOCs and PFCOCs namely: 1) How HBOC O2 affinity can be engineered to target O2 delivery to hypoxic tissues; and 2) How the high gas solubility of PFCOCs provides new opportunities for carrying, dissolving, and delivering gases with biological activity. It is concluded that the development of current blood substitutes has amplified their applications horizon by devising therapeutic functions for O2 carriers requiring limited O2 delivery capacity restoration. Conversely, full, blood-like O2-carrying capacity reestablishment awaits the control of O2 carrier toxicity.

Classification of dermatological disorders in critical care patients: a prospective observational study

PURPOSE

The objective of this study was to identify dermatological disorders detected in the intensive care unit (ICU), to analyze their specific characteristics, and to define a useful classification for intensive care physicians.

MATERIALS AND METHODS

This was a prospective, observational study over a 3-year period (2006-2009) in a mixed ICU. This included all patients presenting with dermatological disorders that were detected at the time of ICU admission or developed along the ICU stay. We recorded the specific characteristics of the disorders and its evolution and treatment, which enabled us to classify the different observed conditions. As general variables, we analyzed demographic factors, the principal diagnosis, ICU procedures, the severity score (Acute Physiology and Chronic Health Evaluation II), length of stay, and mortality.

RESULTS

One hundred thirty-three patients showed at least one dermatological disorder (9.3%) and were classified into (1) preexisting dermatological disorders, (2) life-threatening dermatologic disorders, (3) systemic dermatological disorders, (4) infectious dermatological disorders, (5) reactive dermatological disorders, and (6) others.

CONCLUSIONS

Dermatological disorders are a frequent problem in the ICU, and their recognition is key to set up an appropriate care plan. We propose a classification and description of the different types of dermatological disorders that are most commonly found in ICUs.

The effect of vasopressin on choroidal blood flow, intraocular pressure, and orbital venous pressure in rabbits

PURPOSE

To investigate the effects of arginine-vasopressin (AVP) on intraocular pressure (IOP), orbital venous pressure (OVP), and choroidal blood flow (ChorBF) regulation in anesthetized rabbits.

METHODS

Mean arterial pressure (MAP), IOP, and OVP were measured by direct cannulation of the central ear artery, the vitreous, and the orbital venous sinus, respectively. Laser Doppler flowmetry was used to record ChorBF. To change the perfusion pressure (PP), MAP was manipulated mechanically with occluders around the aorta and vena cava. In the first group of animals (n = 11) the dose-response relationship was measured. In the second group of animals (n = 8) pressure-flow relationships were determined at baseline and in response to intravenous application of a low (0.08 ng/kg/min) and a high (1.33 ng/kg/min) infusion rate of AVP.

RESULTS

AVP caused a dose-dependent increase of MAP and choroidal vascular resistance (ChorR), whereas IOP, OVP, ChorBF, and heart rate (HR) were decreased. In contrast to the high infusion rate, the low infusion rate of AVP had no effect on baseline ChorBF. However, the pressure-flow relationship was shifted downward significantly by both infusion rates at PP below baseline.

CONCLUSIONS

AVP reduces IOP and OVP significantly and is a potent vasoconstrictor in the choroidal vascular bed. In the choroid, the effect of AVP is not only dose-dependent, but also PP-dependent, which is indicated by the reduced perfusion relative to control with low-dosed AVP at low PP.

Vasoactive hemoglobin solution improves survival in hemodilution followed by hemorrhagic shock

OBJECTIVE

To compare survival after exchange transfusion followed by hemorrhage using: 1) the vasoactive, oxygen-carrying, bovine hemoglobin-based blood substitute Oxyglobin (Biopure, 12.9 g hemoglobin/dL); and 2) the hydroxyethyl starch plasma expander Hextend (high molecular weight and low degree of substitution, 6%).

DESIGN

Comparison between treatments.

SETTING

Laboratory.

SUBJECTS

Awake hamster chamber window model.

INTERVENTIONS

Fifty percent blood volume exchange transfusion followed by a 60% hemorrhage over 1 hr, followed by 1 hr of observation. Measurement of blood gases, mean arterial blood pressure, functional capillary density, arteriolar and venular diameter, and Po2 tension distribution.

MEASUREMENTS AND MAIN RESULTS

Survival with Oxyglobin was 100% and only 50% for the Hextend group. Vasoconstriction was evident in the microcirculation. Mean arterial pressure was higher in the Oxyglobin group. Functional capillary density was significantly reduced, although to a lesser extent by Oxyglobin. There was no difference in microvascular Po2 distribution after 1 hr of shock between groups.

CONCLUSIONS

Higher mean arterial pressure during the initial stages of hemorrhage could be due to vasoconstriction in the Oxyglobin group as compared to the Hextend group. It is concluded that the pressor effect due to a vasoactive oxygen carrier may be beneficial in maintaining perfusion in conditions of severe hemodilution followed by hypovolemia.

The rate of O₂ loss from mesenteric arterioles is not unusually high

The O(2) disappearance curve (ODC) recorded in an arteriole after the rapid arrest of blood flow reflects the complex interaction among the dissociation of O(2) from hemoglobin, O(2) diffusivity, and rate of respiration in the vascular wall and surrounding tissue. In this study, the analysis of experimental ODCs allowed the estimation of parameters of O(2) transport and O(2) consumption in the microcirculation of the mesentery. We collected ODCs from rapidly arrested blood inside rat mesenteric arterioles using scanning phosphorescence quenching microscopy (PQM). The technique was used to prevent the artifact of accumulated O(2) photoconsumption in stationary media. The observed ODC signatures were close to linear, in contrast to the reported exponential decline of intra-arteriolar Po(2). The rate of Po(2) decrease was 0.43 mmHg/s in 20-μm-diameter arterioles. The duration of the ODC was 290 s, much longer than the 12.8 s reported by other investigators. The arterioles associated with lymphatic microvessels had a higher O(2) disappearance rate of 0.73 mmHg/s. The O(2) flux from arterioles, calculated from the average O(2) disappearance rate, was 0.21 nl O(2)·cm(-2)·s(-1), two orders of magnitude lower than reported in the literature. The physical upper limit of the O(2) consumption rate by the arteriolar wall, calculated from the condition that all O(2) is consumed by the wall, was 452 nl O(2)·cm(-3)·s(-1). From consideration of the microvascular tissue volume fraction in the rat mesentery of 6%, the estimated respiration rate of the vessel wall was ∼30 nl O(2)·cm(-3)·s(-1). This result was three orders of magnitude lower than the respiration rate in rat mesenteric arterioles reported by other investigators. Our results demonstrate that O(2) loss from mesenteric arterioles is small and that the O(2) consumption by the arteriolar wall is not unusually large.

The action of fish peptide Orpotrin analogs on microcirculation

In order to investigate the relationship between the primary structure of Orpotrin, a vasoactive peptide previously isolated from the freshwater stingray Potamotrygon gr. orbignyi, and its microcirculatory effects, three Orpotrin analogs were synthesized. The analogs have a truncated N-terminal with a His residue deletion and two substituted amino acid residues, where one Nle is substituted for one internal Lys residue and the third analog has a substitution of a Pro for an Ala (Orp-desH(1) , Orp-Nle and Orp-Pro/Ala, respectively). Only Orp-desH(1) could induce a lower vasoconstriction effect compared with the natural Orpotrin, indicating that besides the N-terminal, the positive charge of Lys and the Pro residues located at the center of the amino acid chain is crucial for this vasoconstriction effect. Importantly, the suggestions made with bioactive peptides were based on the molecular modeling and dynamics of peptides, the presence of key amino acids and shared activity in microcirculation, characterized by intravital microscopy. Moreover, this study has demonstrated that even subtle changes in the primary structure of Orpotrin alter the biological effects of this native peptide significantly, which could be of interest for biotechnological applications.

Impact of Modified Treatment in Echocardiographically Confirmed Pseudo-Pulseless Electrical Activity in Out-of-Hospital Cardiac Arrest Patients with Constant End-Tidal Carbon Dioxide Pressure during Compression Pauses

This study evaluated the ability of focused echocardiography (FE) and capnography to differentiate between pulseless electrical activity (PEA) and pseudo-PEA in out-of-hospital cardiac arrest, and the potential survival benefits with modified treatment. In PEA patients with stable end-tidal carbon dioxide pressure ( PetCO2) during the compression pause and concomitant FE showing cardiac kinetic activity, the compression pause was prolonged for 15 s and an additional 20 IU vasopressin was administered. If pulselessness persisted, compressions were continued. Fifteen of the 16 patients studied (94%) achieved restoration of spontaneous circulation (ROSC); eight patients (50%) attained a good neurological outcome (Cerebral Performance Category 1–2). In an historical PEA group with stable PetCO2 values ( n = 48), ROSC was achieved in 26 patients (54%); four patients (8%) attained Cerebral Performance Category 1–2. Echocardiographical verification of the pseudo-PEA state enabled additional vasopressor treatment and cessation of chest compressions, and was associated with significantly higher rates of ROSC, survival to discharge and good neurological outcome.

Microcirculatory assessment in daily clinical practice - not yet ready but not too far!

ABSTRACT Shock is characterized by an alteration in tissue perfusion that may lead to tissue hypoxia. Recent guidelines recommend aggressive and early resuscitation therapy, but mortality rate is still unacceptably high. Unfortunately, traditional clinical surrogates used to guide resuscitation therapy poorly correlate with microcirculatory blood flow, a key determinant of tissue perfusion. New techniques that directly assess microcirculatory perfusion at the bedside have emerged as a complement to traditional macrohemodynamic parameters. These techniques have been supported by several studies showing microcirculatory alterations in different clinical settings. In addition, these microcirculatory alterations are related with outcome and persist regardless of arterial pressure normalization, being a better predictor of organ dysfunction and mortality than global hemodynamic and laboratory parameters. These findings allowed the concept of “microcirculatory-goal directed therapy”, which is now in its preliminary phase, as the impact of many interventions still needs to be assessed. Finally, microcirculation assessment has also been explored in other medical fields such as perioperative, systemic arterial hypertension, heart failure, and hyperviscosity syndromes. In this review, we shortly present the characteristics of microcirculation and the main determinants of capillary blood flow, and we discuss advantages and limitations of some recently available techniques to evaluate microcirculation at the bedside, and how they could be useful for the general clinician in daily practice.

A treatment protocol including vasopressin and hydroxyethyl starch solution is associated with increased rate of return of spontaneous circulation in blunt trauma patients with pulseless electrical activity

BACKGROUND

Survival after cardiopulmonary resuscitation (CPR) using standard vasopressor therapy is disappointing. Vasopressin is a potent vasopressor that could become a useful therapeutic alternative in the treatment of cardiac arrest.

AIMS

The aim of this prehospital prospective cohort study was to assess the influence of treatment with vasopressin and hydroxyethyl starch solution (HHS) on outcome in resuscitated blunt trauma patients with pulseless electrical activity (PEA) cardiac arrest.

METHODS

Two treatment groups of resuscitated trauma patients in cardiac arrest were compared: in the epinephrine group patients received epinephrine 1 mg IV every 3 min only; in the vasopressin group patients first received hypertonic HHS and arginine vasopressin 40 units IV only or followed by epinephrine 1 mg every 3 min until cessation of CPR. Medical trauma care was provided according to advanced trauma life support (ATLS) guidelines.

RESULTS

The study included 31 patients and there were no significant demographic or clinical differences between the treatment groups. Significantly more circulatory restorations [11/13 (85%) vs 3/18 (17%); P < 0.01] and better 24-h survival rates [8/13 (62%) vs 2/18 (11%); P = 0.001] were observed in the vasopressin group. Average mean arterial pressure (100.4 +/- 11.4 mmHg vs 80.3 +/- 12.4 mmHg) and final end-tidal partial pressure of carbon dioxide (PETCO(2)) at admission (4.5 +/- 0.9 kPa vs 2.8 +/- 0.4 kPa) were also higher in the vasopressin group.

CONCLUSION

Our results suggest that victims of severe blunt trauma with PEA should be initially treated with vasopressin in combination with HHS volume resuscitation followed by standard resuscitation therapy and other procedures when appropriate. Vasopressin might be potentially lifesaving in blunt trauma cardiac arrest compared to standard treatment with epinephrine.

Expansion of microvascular networks in vivo by phthalimide neovascular factor 1 (PNF1)

Phthalimide neovascular factor (PNF1, formerly SC-3-149) is a potent stimulator of proangiogenic signaling pathways in endothelial cells. In this study, we evaluated the in vivo effects of sustained PNF1 release to promote ingrowth and expansion of microvascular networks surrounding biomaterial implants. The dorsal skinfold window chamber was used to evaluate the structural remodeling response of the local microvasculature. PNF1 was released from poly(lactic-co-glycolic acid) (PLAGA) films, and a transport model was utilized to predict PNF1 penetration into the surrounding tissue. PNF1 significantly expanded microvascular networks within a 2mm radius from implants after 3 and 7 days by increasing microvessel length density and lumenal diameter of local arterioles and venules. Staining of histological sections with CD11b showed enhanced recruitment of circulating white blood cells, including monocytes, which are critical for the process of vessel enlargement through arteriogenesis. As PNF1 has been shown to modulate MT1-MMP, a facilitator of CCL2 dependent leukocyte transmigration, aspects of window chamber experiments were repeated in CCR2(-/-) (CCL2 receptor) mouse chimeras to more fully explore the critical nature of monocyte recruitment on the therapeutic benefits of PNF1 function in vivo.

Microvascular experimental evidence on the relative significance of restoring oxygen carrying capacity vs. blood viscosity in shock resuscitation

The development of volume replacement fluids for resuscitation in hemorrhagic shock comprises oxygen carrying and non carrying fluids. Non oxygen carrying fluids or plasma expanders are used up to the transfusion trigger, and upon reaching this landmark either blood, and possibly in the near future oxygen carrying blood substitutes, are used. An experimental program in hemorrhagic shock using the hamster chamber window model allowed to compare the relative performance of most fluids proposed for shock resuscitation. This model allows investigating simultaneously the microcirculation and systemic reactions, in the awake condition, in a tissue isolated from the environment. Results from this program show that in general plasma expanders such as Ringer's lactate and dextran 70 kDa do not sufficiently restore blood viscosity upon reaching the transfusion trigger, causing microvascular collapse. This is in part restored by a blood transfusion, independently of the oxygen carrying capacity of red blood cells. These results lead to the proposal that effective blood substitutes must be designed to prevent microvascular collapse, manifested in the decrease of functional capillary density. Achievement of this goal, in combination with the increase of oxygen affinity, significantly postpones the need for a blood transfusion, and lowers the total requirement of restoration of intrinsic oxygen carrying capacity.

Effects of epinephrine and vasopressin on end-tidal carbon dioxide tension and mean arterial blood pressure in out-of-hospital cardiopulmonary resuscitation: an observational study

INTRODUCTION

Clinical data considering vasopressin as an equivalent option to epinephrine in cardiopulmonary resuscitation (CPR) are limited. The aim of this prehospital study was to assess whether the use of vasopressin during CPR contributes to higher end-tidal carbon dioxide and mean arterial blood pressure (MAP) levels and thus improves the survival rate and neurological outcome.

METHODS

Two treatment groups of resuscitated patients in cardiac arrest were compared: in the epinephrine group, patients received 1 mg of epinephrine intravenously every three minutes only; in the vasopressin/epinephrine group, patients received 40 units of arginine vasopressin intravenously only or followed by 1 mg of epinephrine every three minutes during CPR. Values of end-tidal carbon dioxide and MAP were recorded, and data were collected according to the Utstein style.

RESULTS

Five hundred and ninety-eight patients were included with no significant demographic or clinical differences between compared groups. Final end-tidal carbon dioxide values and average values of MAP in patients with restoration of pulse were significantly higher in the vasopressin/epinephrine group (p < 0.01). Initial (odds ratio [OR]: 18.65), average (OR: 2.86), and final (OR: 2.26) end-tidal carbon dioxide values as well as MAP at admission to the hospital (OR: 1.79) were associated with survival at 24 hours. Initial (OR: 1.61), average (OR: 1.47), and final (OR: 2.67) end-tidal carbon dioxide values as well as MAP (OR: 1.39) were associated with improved hospital discharge. In the vasopressin group, significantly more pulse restorations and a better rate of survival at 24 hours were observed (p < 0.05). Subgroup analysis of patients with initial asystole revealed a higher hospital discharge rate when vasopressin was used (p = 0.04). Neurological outcome in discharged patients was better in the vasopressin group (p = 0.04).

CONCLUSION

End-tidal carbon dioxide and MAP are strong prognostic factors for the outcome of out-of-hospital cardiac arrest. Resuscitated patients treated with vasopressin alone or followed by epinephrine have higher average and final end-tidal carbon dioxide values as well as a higher MAP on admission to the hospital than patients treated with epinephrine only. This combination vasopressor therapy improves restoration of spontaneous circulation, short-term survival, and neurological outcome. In the subgroup of patients with initial asystole, it improves the hospital discharge rate.

Endogenous and exogenous vasopressin in shock

PURPOSE OF REVIEW

Vasopressin is critical for blood pressure regulation when cardiovascular homeostasis is threatened and some patients with shock have inappropriately low levels of hormone in plasma. The present review focuses on recent work that addresses the role of endogenous vasopressin in the pathogenesis of shock and the potential therapeutic indications and secondary effects of exogenous hormone in patients with shock.

RECENT FINDINGS

Examples of types of shock resistant to catecholamine pressors in which exogenous vasopressin was effective in restoring arterial pressure continued to accumulate. Widespread determinations of plasma vasopressin in patients with shock suggest that endogenous vasopressin deficiency may be more frequent than previously thought. The generation of mice with deletion of vasopressin's V1a receptor highlighted the important role of the hormone on cardiovascular homeostasis.

SUMMARY

Vasopressin administration is very effective in restoring arterial pressure in many forms of shock and this appears to be due, at least in part, to deficiency of endogenous hormone. Generation of mice lacking vasopressin V1a receptor open new and exciting avenues of inquiry to clarify the role of the hormone in cardiovascular homeostasis.

Orpotrin: a novel vasoconstrictor peptide from the venom of the Brazilian stingray Potamotrygon gr. orbignyi

Characterization of the peptide content of venoms has a number of potential benefits for basic research, clinical diagnosis, development of new therapeutic agents, and production of antiserum. In order to analyze in detail the peptides and small proteins of crude samples, techniques such as chromatography and mass spectrometry have been employed. The present study describes the isolation, biochemical characterization, and sequence determination of a novel peptide, named Orpotrin from the venom of Potamotrygon gr. orbignyi. The natural peptide was shown to be effective in microcirculatory environment causing a strong vasoconstriction. The peptide was fully sequenced by de novo amino acid sequencing with mass spectrometry and identified as the novel peptide. Its amino acid sequence, HGGYKPTDK, aligns only with creatine kinase residues 97-105, but has no similarity to any bioactive peptide. Therefore, possible production of this peptide from creatine kinase by limited proteolysis is discussed. Taken together, the results indicate the usefulness of this single-step approach for low molecular mass compounds in complex samples such as venoms.

Arginine vasopressin versus norepinephrine: will the stronger one win the race?

In the current issue of Critical Care, Friesenecker and colleagues present a well-designed comparative study on the microvascular effects of arginine vasopressin (AVP) and norepinephrine (NE) in a physiological, unanesthetized hamster model. The authors clearly demonstrate that AVP, but not NE, has marked vasoconstrictive effects on large arterioles, whereas the impact on small arterioles is comparable for both vasopressors. However, it remains unclear if these results, per se, reflect a stronger vasopressive potential of AVP versus NE, as macrohemodynamic variables were not different between study groups. Since the authors did not investigate the effects of AVP and NE in vasodilatory shock states, the microcirculatory response in sepsis or systemic inflammatory response syndrome remains inconclusive. The same authors previously reported that AVP infusion in patients suffering from vasodilatory shock carries the risk for ischemic skin lesions. This in turn raises the question whether the quality of vasopressors should be judged by their potency.