Low-dose vasopressin increases glomerular filtration rate, but impairs renal oxygenation in post-cardiac surgery patients

Focus on oliguria during renal replacement therapy

Oliguria is a clinical symptom characterized by decreased urine output, which can occur at any stage of acute kidney injury and also during renal replacement therapy. In some cases, oliguria may resolve with adjustment of blood purification dose or fluid management, while in others, it may suggest a need for further evaluation and intervention. It is important to determine the underlying cause of oliguria during renal replacement therapy and to develop an appropriate treatment plan. This review looks into the mechanisms of urine production to investigate the mechanism of oliguria during renal replacement therapy from two aspects: diminished glomerular filtration rate and tubular abnormalities. The above conditions all implying a renal oxygen supply-demand imbalance, which is the signal of worsening kidney injury. It also proposes a viable clinical pathway for the treatment and management of patients with acute kidney injury receiving renal replacement therapy.

Is mild dehydration a risk for progression of childhood chronic kidney disease?

Children with chronic kidney disease (CKD) can have an inherent vulnerability to dehydration. Younger children are unable to freely access water, and CKD aetiology and stage can associate with reduced kidney concentrating capacity, which can also impact risk. This article aims to review the risk factors and consequences of mild dehydration and underhydration in CKD, with a particular focus on evidence for risk of CKD progression. We discuss that assessment of dehydration in the CKD population is more challenging than in the healthy population, thus complicating the definition of adequate hydration and clinical research in this field. We review pathophysiologic studies that suggest mild dehydration and underhydration may cause hyperfiltration injury and impact renal function, with arginine vasopressin as a key mediator. Randomised controlled trials in adults have not shown an impact of improved hydration in CKD outcomes, but more vulnerable populations with baseline low fluid intake or poor kidney concentrating capacity need to be studied. There is little published data on the frequency of dehydration, and risk of complications, acute or chronic, in children with CKD. Despite conflicting evidence and the need for more research, we propose that paediatric CKD management should routinely include an assessment of individual dehydration risk along with a treatment plan, and we provide a framework that could be used in outpatient settings.

Hypohydration induced by prolonged cycling in the heat increases biomarkers of renal injury in males

PURPOSE

Recent studies have shown that hypohydration can increase renal injury. However, the contribution of hypohydration to the extent of renal injury is often confounded by exercise induced muscle damage. Therefore, the aim of the present study was to investigate the effect of manipulating hydration status during moderate-intensity cycling in the heat on biomarkers of renal injury.

METHODS

Following familiarisation, fourteen active males (age: 21 [20-22] y; BMI: 22.1 ± 1.9 kg/m2; V ˙ O2peak: 55 ± 9 mL/kg/min) completed two experimental trials, in a randomised cross-over design. Experimental trials consisted of up to 120 min of intermittent cycling (~ 50% Wpeak) in the heat (~ 35 °C, ~ 50% relative humidity). During exercise, subjects consumed either a water volume equal to 100% body mass losses (EU) or minimal water (HYP; 75-100 mL) to induce ~ 3% body mass loss. Blood and urine samples were collected at baseline, 30 min post-exercise and 24 h post-baseline, with an additional urine sample collected immediately post-exercise.

RESULTS

Thirty minutes post-exercise, body mass and plasma volume were lower in HYP than EU (P < 0.001), whereas serum and urine osmolality (P < 0.001), osmolality-corrected urinary kidney injury molecule-1 concentrations (HYP: 2.74 [1.87-5.44] ng/mOsm, EU: 1.15 [0.84-2.37] ng/mOsm; P = 0.024), and percentage change in osmolality-corrected urinary neutrophil gelatinase-associated lipocalin concentrations (HYP: 61 [17-141] %, EU: 7.1 [- 4 to 24] %; P = 0.033) were greater in HYP than EU.

CONCLUSION

Hypohydration produced by cycling in the heat increased renal tubular injury, compared to maintaining euhydration with water ingestion.

Incorporating intraoperative blood pressure time-series variables to assist in prediction of acute kidney injury after type a acute aortic dissection repair: an interpretable machine learning model

BACKGROUND

Acute kidney injury (AKI) is a common and serious complication after the repair of Type A acute aortic dissection (TA-AAD). However, previous models have failed to account for the impact of blood pressure fluctuations on predictive performance. This study aims to develop machine learning (ML) models combined with intraoperative medicine and blood pressure time-series data to improve the accuracy of early prediction for postoperative AKI risk.

METHODS

Indicators reflecting the duration and depth of hypotension were obtained by analyzing continuous mean arterial pressure (MAP) monitored intraoperatively with multiple thresholds (<65, 60, 55, 50) set in the study. The predictive features were selected by logistic regression and the least absolute shrinkage and selection operator (LASSO), and 4 ML models were built based on the above features. The performance of the models was evaluated by area under receiver operating characteristic curve (AUROC), calibration curve and decision curve analysis (DCA). Shapley additive interpretation (SHAP) was used to explain the prediction models.

RESULTS

Among the indicators reflecting intraoperative hypotension, 65 mmHg showed a statistically superior difference to other thresholds in patients with or without AKI (p < .001). Among 4 models, the extreme gradient boosting (XGBoost) model demonstrated the highest AUROC: 0.800 (95% 0.683-0.917) and sensitivity: 0.717 in the testing set and was verified the best-performing model. The SHAP summary plot indicated that intraoperative urine output, cumulative time of mean arterial pressure lower than 65 mmHg outside cardiopulmonary bypass (OUT_CPB_MAP_65 time), autologous blood transfusion, and smoking were the top 4 features that contributed to the prediction model.

CONCLUSION

With the introduction of intraoperative blood pressure time-series variables, we have developed an interpretable XGBoost model that successfully achieve high accuracy in predicting the risk of AKI after TA-AAD repair, which might aid in the perioperative management of high-risk patients, particularly for intraoperative hemodynamic regulation.

Atrial natriuretic peptide in the prevention of acute renal dysfunction after heart transplantation-a randomized placebo-controlled double-blind trial

BACKGROUND

Acute kidney injury (AKI) and renal dysfunction after heart transplantation are common and serious complications. Atrial natriuretic peptide (ANP) has been shown to increase glomerular filtration rate (GFR) and exert renoprotective effects when used for the prevention/treatment of AKI in cardiac surgery. We tested the hypothesis that intraoperative and postoperative administration of ANP could prevent a postoperative decrease in renal function early after heart transplantation.

METHODS

Seventy patients were randomized to receive either ANP (50 ng/kg/min) (n = 33) or placebo (n = 37) starting after induction of anesthesia and continued for 4 days after heart transplantation or until treatment with dialysis was started. The primary end-point of the present study was measured GFR (mGFR) at day 4, assessed by plasma clearance of a renal filtration marker. Also, the incidence of postoperative AKI and dialysis were assessed.

RESULTS

Median (IQR) mGFR at day 4 postoperatively was 60.0 (57.0) and 50.1 (36.3) ml/min/1.72 m2 for the placebo and ANP groups, respectively (p = .705). During ongoing ANP infusion, the need for dialysis was 21.6% and 9.1% for the placebo and ANP groups, respectively (p = .197). The incidences of AKI for the placebo and the ANP groups were 76.5% and 63.6%, respectively (p = .616). The incidences of AKI stage 1 were 32.4% and 21.2% for the placebo and ANP groups, respectively (p = .420) and for AKI stage 2 or 3, 37.8% and 42.4%, respectively (p = .808).

CONCLUSION

The study failed to detect that ANP infusion attenuates renal dysfunction or decreases the incidence of AKI after heart transplantation.

Low-Dose vasopressin and renal perfusion in pediatric cardiac surgery

Background

Congenital heart surgeries are associated with post-bypass renal and cardiac dysfunctions. The use of low-dose vasopressin has been found to be beneficial in adult cardiac surgeries.

Objective

To assess the hemodynamic and renal effects of patients undergoing on-pump pediatric cardiac surgery under general anesthesia (GA) with low-dose vasopressin infusion.

Design

Prospective randomized controlled study.

Setting

Operation room and ICU, tertiary care teaching hospital.

Patients

Fifty-five pediatric cardiac patients undergoing repair for congenital heart diseases (CHD).

Interventions

Low-dose vasopressin infusion in the study group and placebo in the control group.

Measurements and Main Results

Renal near-infrared spectroscopy (NIRS), serum NGAL, and inflammatory mediators-IL6 and IL8 along with other renal and hemodynamic parameters in the perioperative period were recorded. Diastolic blood pressure (DBP) and cardiac index were significantly higher in the vasopressin group. Inflammatory markers were significantly high in the immediate postoperative period in all patients which later stabilized in the next 48 h but showed similar trends in both groups. Low-dose vasopressin infusion did not improve either renal perfusion or function. The duration of mechanical ventilation and length of hospital stay, the incidence of AKI development, and transfusion requirements were marginally lower in the vasopressin group, although not significant.

Conclusion

Low-dose vasopressin infusion improved hemodynamics and showed a decreased incidence of complications. However, it failed to show any benefit of renal function and overall outcome in pediatric cardiac surgery.

Youth versus adult-onset type 2 diabetic kidney disease: Insights into currently known structural differences and the potential underlying mechanisms

Type 2 diabetes (T2D) is a global health pandemic with significant humanitarian, economic, and societal implications, particularly for youth and young adults who are experiencing an exponential rise in incident disease. Youth-onset T2D has a more aggressive phenotype than adult-onset T2D, and this translates to important differences in rates of progression of diabetic kidney disease (DKD). We hypothesize that youth-onset DKD due to T2D may exhibit morphometric, metabolic, and molecular characteristics that are distinct from adult-onset T2D and develop secondary to inherent differences in renal energy expenditure and substrate metabolism, resulting in a central metabolic imbalance. Kidney structural changes that are evident at the onset of puberty also serve to exacerbate the organ’s baseline high rates of energy expenditure. Additionally, the physiologic state of insulin resistance seen during puberty increases the risk for kidney disease and is exacerbated by both concurrent diabetes and obesity. A metabolic mismatch in renal energetics may represent a novel target for pharmacologic intervention, both for prevention and treatment of DKD. Further investigation into the underlying molecular mechanisms resulting in DKD in youth-onset T2D using metabolomics and RNA sequencing of kidney tissue obtained at biopsy is necessary to expand our understanding of early DKD and potential targets for therapeutic intervention. Furthermore, large-scale clinical trials evaluating the duration of kidney protective effects of pharmacologic interventions that target a metabolic mismatch in kidney energy expenditure are needed to help mitigate the risk of DKD in youth-onset T2D.

Hypohydration produced by high-intensity intermittent running increases biomarkers of renal injury in males

Purpose

Whilst there is evidence to suggest that hypohydration caused by physical work in the heat increases renal injury, whether this is the case during exercise in temperate conditions remains unknown. This study investigated the effect of manipulating hydration status during high-intensity intermittent running on biomarkers of renal injury.

Methods

After familiarisation, 14 males (age: 33 ± 7 years; V̇O_2peak: 57.1 ± 8.6 ml/kg/min; mean ± SD) completed 2 trials in a randomised cross-over design, each involving 6, 15 min blocks of shuttle running (modified Loughborough Intermittent Shuttle Test protocol) in temperate conditions (22.3 ± 1.0 °C; 47.9 ± 12.9% relative humidity). During exercise, subjects consumed either a volume of water equal to 90% of sweat losses (EU) or 75 mL water (HYP). Body mass, blood and urine samples were taken pre-exercise (baseline/pre), 30 min post-exercise (post) and 24 h post-baseline (24 h).

Results

Post-exercise, body mass loss, serum osmolality and urine osmolality were greater in HYP than EU (P ≤ 0.024). Osmolality-corrected urinary kidney injury molecule-1 (uKIM-1) concentrations were increased post-exercise (P ≤ 0.048), with greater concentrations in HYP than EU (HYP: 2.76 [1.72–4.65] ng/mOsm; EU: 1.94 [1.1–2.54] ng/mOsm; P = 0.003; median [interquartile range]). Osmolality-corrected urinary neutrophil gelatinase-associated lipocalin (uNGAL) concentrations were increased post-exercise (P < 0.001), but there was no trial by time interaction effect (P = 0.073).

Conclusion

These results suggest that hypohydration produced by high-intensity intermittent running increases renal injury, compared to when euhydration is maintained, and that the site of this increased renal injury is at the proximal tubules.

Effects of atrial natriuretic peptide on renal function during cardiopulmonary bypass: a randomized pig model

OBJECTIVES

Acute kidney injury is a well-known complication after cardiac surgery and cardiopulmonary bypass (CPB). In this experimental animal study, we evaluated the effects of atrial natriuretic peptide (ANP) on renal function, perfusion, oxygenation and tubular injury during CPB.

METHODS

Twenty pigs were blindly randomized to continuous infusion of either ANP (50 ng/kg/min) or placebo before, during and after CPB. Renal blood flow as well as cortical and medullary perfusion was measured. Blood was repeatedly sampled from the renal vein. Glomerular filtration rate was measured by infusion clearance of 51Cr-EDTA.

RESULTS

Glomerular filtration rate was higher (P < 0.001), whereas renal blood flow or renal oxygen delivery was not affected by ANP during CPB. Renal oxygen consumption did not differ between groups during CPB, whereas renal oxygen extraction was higher in the ANP group (P = 0.03). Urine flow and sodium excretion were higher in the ANP group during CPB. Blood flow in the renal medulla, but not in the cortex, dropped during CPB, an effect that was not seen in the animals that received ANP.

CONCLUSIONS

ANP improved renal function during CPB. Despite impaired renal oxygenation, ANP did not cause tubular injury, suggesting a renoprotective effect of ANP during CPB. Also, CPB induced a selectively reduced blood flow in the renal medulla, an effect that was counteracted by ANP.

Effects of levosimendan on renal blood flow and glomerular filtration in patients with acute kidney injury after cardiac surgery: a double blind, randomized placebo-controlled study

BACKGROUND

Acute kidney injury (AKI) is a common and serious complication after cardiac surgery, and current strategies aimed at treating AKI have proven ineffective. Levosimendan, an inodilatating agent, has been shown to increase renal blood flow and glomerular filtration rate in uncomplicated postoperative patients and in patients with the cardiorenal syndrome. We hypothesized that levosimendan through its specific effects on renal vasculature, a preferential vasodilating effect on preglomerular resistance vessels, could improve renal function in AKI-patients with who did not have clinical indication for inotropic support.

METHODS

In this single-center, double-blind, randomized controlled study, adult patients with postoperative AKI within 2 days after cardiac surgery, who were hemodynamically stable with a central venous oxygen saturation (ScvO₂) ≥ 60% without inotropic support were eligible for inclusion. After randomization, study drug infusions, levosimendan (n = 16) or placebo (n = 13) were given for 5 h. A bolus infusion of levosimendan (12 µg/kg), were given for 30 min followed by 0.1 µg/kg/min for 5 h. Renal blood flow and glomerular filtration rate were measured using infusion clearance of para-aminohippuric acid and a filtration marker, respectively. As a safety issue, norepinephrine was administered to maintain mean arterial pressure between 70-80 mmHg. Intra-group differences were tested by Mann-Whitney U-tests, and a linear mixed model was used to test time and group interaction.

RESULTS

Twenty-nine patients completed the study. At inclusion, the mean serum creatinine was higher in the patients randomized to levosimendan (148 ± 29 vs 127 ± 22 µmol/L, p = 0.030), and the estimated GFR was lower (46 ± 12 vs 57 ± 11 ml/min/1.73 m², p = 0.025). Levosimendan induced a significantly (p = 0.011) more pronounced increase in renal blood flow (15%) compared placebo (3%) and a more pronounced decrease in renal vascular resistance (- 18% vs. - 4%, respectively, p = 0.043). There was a trend for a minor increase in glomerular filtration rate with levosimendan (4.5%, p = 0.079), which did differ significantly from the placebo group (p = 0.440). The mean norepinephrine dose was increased by 82% in the levosimedan group and decreased by 29% in the placebo group (p = 0.012).

CONCLUSIONS

In hemodynamically stable patients with AKI after cardiac surgery, levosimendan increases renal blood flow through renal vasodilatation. Trial registration NCT02531724, prospectly registered on 08/20/2015. https://clinicaltrials.gov/ct2/show/NCT02531724?cond=AKI&cntry=SE&age=1&draw=2&rank=1.

Effects of Exercise on Acute Kidney Injury Biomarkers and the Potential Influence of Fluid Intake

Acute kidney injury (AKI) incidence (diagnosed by changes in serum creatinine [Cr]) following prolonged endurance events has been reported to be anywhere from 4 to 85%, and hypohydration may contribute to this. Whilst an increase in serum Cr indicates impaired kidney function, this might be influenced by muscle damage. Therefore, the use of other AKI biomarkers which can detect renal tubular injury may be more appropriate. The long-term consequences of AKI are not well understood, but there are some potential concerns of an increased subsequent risk of chronic kidney disease (CKD). Therefore, this brief review explores the effects of exercise training/competition on novel AKI biomarkers and the potential influence of fluid intake. The increase in novel AKI biomarkers following prolonged endurance events suggests renal tubular injury. This is likely due to the long duration and relatively high exercise intensity, producing increased sympathetic tone, body temperature, hypohydration, and muscle damage. Whilst muscle damage appears to be an important factor in the pathophysiology of exercise-associated AKI, it may require coexisting hypohydration. Fluid intake seems to play a role in exercise-associated AKI, as maintaining euhydration with water ingestion during simulated physical work in the heat appears to attenuate rises in AKI biomarkers. The composition of fluid intake may also be important, as high-fructose drinks have been shown to exacerbate AKI biomarkers. However, it is yet to be seen if these findings are applicable to athletes performing strenuous exercise in a temperate environment. Additionally, further work should examine the effects of repeated bouts of strenuous exercise on novel AKI biomarkers.

Renal Hemodynamics, Function, and Oxygenation in Critically Ill Patients and after Major Surgery

This review outlines the available data from the work of our group on renal hemodynamics, function, and oxygenation in patients who are critically ill with acute renal dysfunction, such as those with postoperative AKI, those in early clinical septic shock, in patients undergoing cardiac surgery with cardiopulmonary bypass, or in patients undergoing liver transplantation. We also provide information on renal hemodynamics, function, and oxygenation in patients with chronic renal impairment due to congestive heart failure. This review will argue that, for all of these groups of patients, the common denominator is that renal oxygenation is impaired due to a lower renal oxygen delivery or a pronounced increase in renal oxygen consumption.

Vasopressin associated with renal vascular resistance in adults with longstanding type 1 diabetes with and without diabetic kidney disease

OBJECTIVE

Arginine vasopressin (AVP) and its surrogate, copeptin, have been implicated in diabetic kidney disease (DKD) pathogenesis, which develops in a subset of people with longstanding type 1 diabetes, but not in others (DKD Resistors). We hypothesized that patients with DKD would exhibit higher copeptin concentrations vs. DKD Resistors.

METHODS

Participants with type 1 diabetes (n = 62, duration ≥50 years) were stratified into 42 DKD Resistors and 20 with DKD (eGFR ≤60 mL/min/1.73m² or ≥30 mg/day urine albumin), and age/sex-matched controls (HC, n = 74) were included. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were calculated by inulin and p-aminohippurate clearance before and after angiotensin II (ang II) infusion. Renal vascular resistance (RVR) was calculated as mean arterial pressure/renal blood flow. Plasma copeptin, renin, aldosterone, neutrophil gelatinase-associated lipocalin (NGAL), and urea concentrations were measured, along with 24-h urine volume.

RESULTS

DKD resistors had lower copeptin (95% CI: 4.0 [3.4-4.8] pmol/l) compared to DKD (5.8 [4.5-7.6] pmol/l, p = 0.02) and HC (4.8 [4.1-5.5] pmol/l, p = 0.01) adjusting for age, sex and HbA1c. In type 1 diabetes, higher copeptin correlated with lower GFR (r: -0.32, p = 0.01) and higher renin concentration (r: 0.40, p = 0.002) after multivariable adjustments. These relationships were not evident in HC. Copeptin inversely associated with RVR change following exogenous ang II only in participants with type 1 diabetes (β ± SE: -6.9 ± 3.4, p = 0.04).

CONCLUSIONS

In longstanding type 1 diabetes, copeptin was associated with intrarenal renin-angiotensin-aldosterone system (RAAS) activation and renal hemodynamic function, suggesting interplay between AVP and RAAS in DKD pathogenesis.

Immunopathophysiology of trauma-related acute kidney injury

Physical trauma can affect any individual and is globally accountable for more than one in every ten deaths. Although direct severe kidney trauma is relatively infrequent, extrarenal tissue trauma frequently results in the development of acute kidney injury (AKI). Various causes, including haemorrhagic shock, rhabdomyolysis, use of nephrotoxic drugs and infectious complications, can trigger and exacerbate trauma-related AKI (TRAKI), particularly in the presence of pre-existing or trauma-specific risk factors. Injured, hypoxic and ischaemic tissues expose the organism to damage-associated and pathogen-associated molecular patterns, and oxidative stress, all of which initiate a complex immunopathophysiological response that results in macrocirculatory and microcirculatory disturbances in the kidney, and functional impairment. The simultaneous activation of components of innate immunity, including leukocytes, coagulation factors and complement proteins, drives kidney inflammation, glomerular and tubular damage, and breakdown of the blood-urine barrier. This immune response is also an integral part of the intense post-trauma crosstalk between the kidneys, the nervous system and other organs, which aggravates multi-organ dysfunction. Necessary lifesaving procedures used in trauma management might have ambivalent effects as they stabilize injured tissue and organs while simultaneously exacerbating kidney injury. Consequently, only a small number of pathophysiological and immunomodulatory therapeutic targets for TRAKI prevention have been proposed and evaluated.

Role of sodium-glucose cotransporter 2 inhibition to mitigate diabetic kidney disease risk in type 1 diabetes

Diabetic kidney disease (DKD) is a common complication of type 1 diabetes (T1D) and a major risk factor for premature death from cardiovascular disease (CVD). Current treatments, such as control of hyperglycaemia and hypertension, are beneficial, but only partially protect against DKD. Finding new, safe and effective therapies to halt nephropathy progression has proven to be challenging. Sodium-glucose cotransporter 2 (SGLT2) inhibitors have demonstrated, in addition to glycaemic lowering, impressive protection against DKD and CVD progression in people with type 2 diabetes. Although these beneficial cardiorenal effects may also apply to people with T1D, supporting data are lacking. Furthermore, the increased rates of euglycaemic diabetic ketoacidosis may limit the use of this class in people with T1D. In this review we highlight the pathophysiology of DKD in T1D and the unmet need that exists. We further detail the beneficial and adverse effects of SGLT2 inhibitors based on their mechanism of action. Finally, we balance the effects in people with T1D and indicate future lines of research.

Vasoplegia after cardiopulmonary bypass: A narrative review of pathophysiology and emerging targeted therapies

Cardiovascular disease remains the leading cause of death in the United States, and cardiopulmonary bypass is a cornerstone in the surgical management of many related disease states. Pathophysiologic changes associated both with extracorporeal circulation and shock can beget a syndrome of low systemic vascular resistance paired with relatively preserved cardiac output, termed vasoplegia. While increased vasopressor requirements accompany vasoplegia, related pathophysiologic mechanisms may also lead to true catecholamine resistance, which is associated with further heightened mortality. The introduction of a second non-catecholamine vasopressor, angiotensin II, and non-specific nitric oxide scavengers offers potential means by which to manage this challenging phenomenon. This narrative review addresses both the definition, risk factors, and pathophysiology of vasoplegia and potential therapeutic interventions.

Pathophysiological Mechanisms by which Heat Stress Potentially Induces Kidney Inflammation and Chronic Kidney Disease in Sugarcane Workers

BACKGROUND

Chronic kidney disease of non-traditional origin (CKDnt) is common among Mesoamerican sugarcane workers. Recurrent heat stress and dehydration is a leading hypothesis. Evidence indicate a key role of inflammation.

METHODS

Starting in sports and heat pathophysiology literature, we develop a theoretical framework of how strenuous work in heat could induce kidney inflammation. We describe the release of pro-inflammatory substances from a leaky gut and/or injured muscle, alone or in combination with tubular fructose and uric acid, aggravation by reduced renal blood flow and increased tubular metabolic demands. Then, we analyze longitudinal data from >800 sugarcane cutters followed across harvest and review the CKDnt literature to assess empirical support of the theoretical framework.

RESULTS

Inflammation (CRP elevation and fever) and hyperuricemia was tightly linked to kidney injury. Rehydrating with sugary liquids and NSAID intake increased the risk of kidney injury, whereas electrolyte solution consumption was protective. Hypokalemia and hypomagnesemia were associated with kidney injury.

DISCUSSION

Heat stress, muscle injury, reduced renal blood flow and fructose metabolism may induce kidney inflammation, the successful resolution of which may be impaired by daily repeating pro-inflammatory triggers. We outline further descriptive, experimental and intervention studies addressing the factors identified in this study.

Differential effects of inotropes and inodilators on renal function in acute cardiac care

Pathological interplay between the heart and kidneys is widely encountered in heart failure (HF) and is linked to worse prognosis and quality of life. Inotropes, along with diuretics and vasodilators, are a core medical response to HF but decompensated patients who need inotropic support often present with an acute worsening of renal function. The impact of inotropes on renal function is thus potentially an important influence on the choice of therapy. There is currently relatively little objective data available to guide the selection of inotrope therapy but recent direct observations on the effects of levosimendan and milrinone on glomerular filtration favour levosimendan. Other lines of evidence indicate that in acute decompensated HF levosimendan has an immediate renoprotective effect by increasing renal blood flow through preferential vasodilation of the renal afferent arterioles and increases in glomerular filtration rate: potential for renal medullary ischaemia is avoided by an offsetting increase in renal oxygen delivery. These indications of a putative reno-protective action of levosimendan support the view that this calcium-sensitizing inodilator may be preferable to dobutamine or other adrenergic inotropes in some settings by virtue of its renal effects. Additional large studies will be required, however, to clarify the renal effects of levosimendan in this and other relevant clinical situations, such as cardiac surgery.

The role of renal hypoxia in the pathogenesis of diabetic kidney disease: a promising target for newer renoprotective agents including SGLT2 inhibitors?

Diabetic kidney disease is the most common cause of end-stage kidney disease and poses a major global health problem. Finding new, safe, and effective strategies to halt this disease has proven to be challenging. In part that is because the underlying mechanisms are complex and not fully understood. However, in recent years, evidence has accumulated suggesting that chronic hypoxia may be the primary pathophysiological pathway driving diabetic kidney disease and chronic kidney disease of other etiologies and was called the chronic hypoxia hypothesis. Hypoxia is the result of a mismatch between oxygen delivery and oxygen demand. The primary determinant of oxygen delivery is renal perfusion (blood flow per tissue mass), whereas the main driver of oxygen demand is active sodium reabsorption. Diabetes mellitus is thought to compromise the oxygen balance by impairing oxygen delivery owing to hyperglycemia-associated microvascular damage and exacerbate oxygen demand owing to increased sodium reabsorption as a result of sodium-glucose cotransporter upregulation and glomerular hyperfiltration. The resultant hypoxic injury creates a vicious cycle of capillary damage, inflammation, deposition of the extracellular matrix, and, ultimately, fibrosis and nephron loss. This review will frame the role of chronic hypoxia in the pathogenesis of diabetic kidney disease and its prospect as a promising therapeutic target. We will outline the cellular mechanisms of hypoxia and evidence for renal hypoxia in animal and human studies. In addition, we will highlight the promise of newer imaging modalities including blood oxygenation level-dependent magnetic resonance imaging and discuss salutary interventions such as sodium-glucose cotransporter 2 inhibition that (may) protect the kidney through amelioration of renal hypoxia.

The New Biology of Diabetic Kidney Disease-Mechanisms and Therapeutic Implications

Diabetic kidney disease remains the most common cause of end-stage kidney disease in the world. Despite reductions in incidence rates of myocardial infarction and stroke in people with diabetes over the past 3 decades, the risk of diabetic kidney disease has remained unchanged, and may even be increasing in younger individuals afflicted with this disease. Accordingly, changes in public health policy have to be implemented to address the root causes of diabetic kidney disease, including the rise of obesity and diabetes, in addition to the use of safe and effective pharmacological agents to prevent cardiorenal complications in people with diabetes. The aim of this article is to review the mechanisms of pathogenesis and therapies that are either in clinical practice or that are emerging in clinical development programs for potential use to treat diabetic kidney disease.

Bariatric surgery and kidney disease outcomes in severely obese youth

Bariatric surgery, an emerging treatment for severely obese youth with and without T2D, provides marked improvement in insulin resistance, beta-cell function, and central adiposity. Further, preliminary data suggest that bariatric surgery also results in significant improvement in markers of obesity-related nephropathy and DKD, beyond that which can be achieved with current medical interventions. Yet, the mechanisms whereby bariatric surgery attenuates kidney disease remain unclear. This review summarizes the data on the effects of bariatric surgery on obesity-related nephropathy and DKD in youth with and without T2D, in addition to potential mechanisms underlying the nephroprotective effects of weight loss surgery and how these may differ in Roux-en-Y gastric bypass vs. vertical sleeve gastrectomy. Finally, we discuss potential future non-surgical therapies to mitigate kidney disease.

Effects of milrinone on renal perfusion, filtration and oxygenation in patients with acute heart failure and low cardiac output early after cardiac surgery

PURPOSE

Early postoperative heart failure is common after cardiac surgery, and inotrope treatment may impact renal perfusion and oxygenation. We aimed to study the renal effects of the inodilator milrinone when used for the treatment of heart failure after weaning from cardiopulmonary bypass (CPB).

MATERIAL AND METHODS

In 26 patients undergoing cardiac surgery with CPB, we used renal vein catheterization to prospectively measure renal blood flow (RBF), glomerular filtration rate (GFR), and renal oxygenation. Patients who developed acute heart failure and low cardiac output (cardiac index <2.1 L/min/m²) at 30 min after weaning from CPB (n = 7) were given milrinone, and the remaining patients (n = 19) served as controls. Additional measurements were made at 60 min after CPB.

RESULTS

In patients with acute postoperative heart failure, before receiving milrinone, renal blood flow was lower (-33%, p < .05) while renal oxygen extraction was higher (41%, p < .05) compared to the control group. Milrinone increased cardiac index (21%, p < .001), RBF (36%, p < .01) and renal oxygen delivery (35%, p < .01), with no significant change in GFR and oxygen consumption compared to the control group.

CONCLUSIONS

In patients with acute heart failure after weaning from CPB, the milrinone-induced increase in cardiac output was accompanied by improved renal oxygenation.

TRIAL REGISTRATION

ClinicalTrials.gov; identifier NCT02405195, date of registration; March 27, 2015, and NCT02549066, date of registration; 9 September 2015.

SGLT2 inhibition increases serum copeptin in young adults with type 1 diabetes

AIMS

Copeptin, a surrogate of vasopressin, is elevated in type 1 diabetes (T1D) and predicts kidney disease and cardiovascular mortality. Given the cardiorenal protective effects of SGLT2 inhibition (SGLT2i), our aim was to examine: 1) the relationship between serum copeptin, metabolic, renal and systemic hemodynamic parameters in adults with T1D; and 2) serum copeptin after SGLT2i with empagliflozin.

MATERIALS AND METHODS

In this post-hoc, exploratory analysis, serum copeptin, glomerular filtration rate (GFR_Inulin), effective renal plasma flow (ERPF_PAH), plasma renin angiotensin aldosterone system markers, HbA_1c, 24-hour urine volume and sodium excretion were measured in 40 participants with T1D (24.3±5.1 years) during eu- and hyperglycaemia before and after 8 weeks of 25mg of daily empagliflozin.

RESULTS

Higher baseline copeptin correlated with higher HbA_1c, lower 24-hour urine volume and sodium excretion, after correcting for age, sex, systolic blood pressure, and HbA_1c. Copeptin concentrations increased in response to empagliflozin under euglycaemia (4.1±2.1 to 5.1±2.8pmol/L, P=0.0053) and hyperglycaemia (3.3±1.4 to 5.6±2.8pmol/L, P<0.0001). The rise in copeptin in response to empagliflozin correlated with change in 24-hour urine volume, but was independent of changes in fractional excretion of sodium and haematocrit.

CONCLUSIONS

Elevated serum copeptin was associated with worse glycaemic control and lower diuresis and natriuresis. SGLT2i increased serum copeptin in adults with T1D, and the rise correlated with change in diuresis, but not natriuresis and hemo-concentration. Further work is required to evaluate the clinical implications of elevated copeptin with SGLT2i, including whether it is simply a marker of diuresis or may contribute to cardiorenal disease long-term.

Elevated copeptin, arterial stiffness, and elevated albumin excretion in adolescents with type 1 diabetes

OBJECTIVE

We sought to evaluate copeptin concentrations in adolescents with and without type 1 diabetes (T1D) and examine the associations between copeptin and measures of arterial stiffness and kidney dysfunction.

RESEARCH DESIGN AND METHODS

This analysis included 169 adolescents with T1D (12-19 years of age, 59% girls, mean HbA1c 9.0 ± 1.5% and diabetes duration of 8.6 ± 2.9 years), in addition to 61 controls without T1D. Arterial stiffness including carotid-femoral pulse wave velocity (CF-PWV), carotid-radial PWV (CR-PWV), augmentation index normalized to heart rate of 75 bpm (AIx@HR75), and brachial artery distensibility (BAD). Serum copeptin, urinary albumin-to-creatinine ratio (UACR), and estimated glomerular filtration rate (eGFR) by serum creatinine and cystatin C were also assessed.

RESULTS

Compared to controls, adolescents with T1D had higher median (Q1-Q3) copeptin (7.5 [5.2-11.3] vs 6.4 [4.8-8.3] pmol/L, P = .01), mean ± SD eGFR (121 ± 23 vs 112 ± 16 mL/min/1.73m² , P = .002) and lower BAD (7.1 ± 1.3 vs 7.2 ± 1.2%, P = .02). Adolescents with T1D in the in high tertile copeptin group (>9.1 pmol/L) had higher AIx@HR75 (10.7 ± 1.2 vs 5 ± 1.2, P = .001), CR-PWV (5.30 ± 1.0 vs 5.18 ± 1.0 m/s, P = .04), and UACR (12 ± 1 vs 8 ± 1 mg/g, P = .025) compared to those in low tertile (<5.8 pmol/L) after adjusting for age, sex, and eGFR. Copeptin inversely associated with CF-PWV independent of age, sex, eGFR, SBP, and HbA1c in T1D adolescents.

CONCLUSIONS

Our data demonstrate that elevated copeptin was associated with worse arterial stiffness in adolescents with T1D. These findings suggest that copeptin could improve CVD risk stratification in adolescents with T1D.

Renal effects of norepinephrine-induced variations in mean arterial pressure after liver transplantation: A randomized cross-over trial

BACKGROUND

Acute kidney injury is commonly seen after liver transplantation. The optimal perioperative target mean arterial pressure (MAP) for renal filtration, perfusion and oxygenation in liver recipients is not known. The effects of norepinephrine-induced changes in MAP on renal blood flow (RBF), oxygen delivery (RDO₂ ), glomerular filtration rate (GFR) and renal oxygenation (=renal oxygen extraction, RO₂ Ex) were therefore studied early after liver transplantation.

METHODS

Ten patients with an intra- and post-operative vasopressor-dependent systemic vasodilation were studied early after liver transplantation during sedation and mechanical ventilation. To achieve target MAP levels of 60, 75 and 90 mm Hg, the norepinephrine infusion rate was randomly and sequentially titrated. At each target MAP, data on cardiac index (CI), RBF and GFR were obtained by transpulmonary thermodilution (PiCCO), the renal vein thermodilution technique and renal extraction of chromium ethylenediaminetetraaceticacid (⁵¹ Cr-EDTA), respectively. Renal oxygen consumption (RVO₂ ) and extraction (RO₂ Ex) were calculated according to standard formulas.

RESULTS

At a target MAP of 75 mm Hg, CI (13%), RBF (18%), RDO₂ (24%), GFR (31%) and RVO₂ (20%) were higher while RO₂ Ex was unchanged compared to a target MAP of 60 mm Hg. Increasing MAP from 75 up to 90 mm Hg increased RVR by 38% but had no further effects on CI, RBF, RDO₂ or GFR.

CONCLUSIONS

In patients undergoing liver transplantation, RBF and GFR are pressure-dependent at MAP levels below 75 mm Hg. Our results suggest that MAP should probably be targeted to approximately 75 mm Hg for optimal perioperative renal filtration, perfusion and oxygenation in patients undergoing liver transplantation.

Differential Effects of Levosimendan and Dobutamine on Glomerular Filtration Rate in Patients With Heart Failure and Renal Impairment:A Randomized Double-Blind Controlled Trial

Background The management of the cardiorenal syndrome in advanced heart failure is challenging, and the role of inotropic drugs has not been fully defined. Our aim was to compare the renal effects of levosimendan versus dobutamine in patients with heart failure and renal impairment. Methods and Results In a randomized double-blind study, we assigned patients with chronic heart failure (left ventricular ejection fraction <40%) and impaired renal function (glomerular filtration rate <80 mL/min per 1.73 m2) to receive either levosimendan (loading dose 12 μg/kg+0.1 μg/kg per minute) or dobutamine (7.5  μg/kg per minute) for 75 minutes. A pulmonary artery catheter was used for measurements of systemic hemodynamics, and a renal vein catheter was used to measure renal plasma flow by the infusion clearance technique for PAH (para-aminohippurate) corrected by renal extraction of PAH . Filtration fraction was measured by renal extraction of chromium ethylenediamine tetraacetic acid. A total of 32 patients completed the study. Following treatment, the levosimendan and dobutamine groups displayed similar increases in renal blood flow (22% and 26%, respectively) with no significant differences between groups. Glomerular filtration rate increased by 22% in the levosimendan group but remained unchanged in the dobutamine group ( P=0.012). Filtration fraction was not affected by levosimendan but decreased by 17% with dobutamine ( P=0.045). Conclusions In patients with chronic heart failure and renal impairment, levosimendan increases glomerular filtration rate to a greater extent than dobutamine and thus may be the preferred inotropic agent for treating patients with the cardiorenal syndrome. Clinical Trial Registration URL: https://www.clinicaltrials.gov . Unique identifier: NCT 02133105.

Vasopressin and nitroglycerin decrease portal and hepatic venous pressure and hepato-splanchnic blood flow

BACKGROUND

Various methods are used to reduce venous blood pressure in the hepato-splanchnic circulation, and hence minimise blood loss during liver surgery. Previous studies show that combination of vasopressin and nitroglycerin reduces portal pressure and flow in patients with portal hypertension, and in this study we investigated this combination in patients with normal portal pressure.

METHOD

In all, 13 patients were studied. Measurements were made twice to confirm baseline (C1 and BL), during vasopressin infusion 4.8 U/h (V), and during vasopressin infusion combined with nitroglycerin infusion (V + N). Portal venous pressure (PVP), hepatic venous pressure (HVP), central haemodynamics and arterial and venous blood gases were obtained at each measuring point, and portal (splanchnic) and hepato-splanchnic blood flow changes were calculated.

RESULTS

Vasopressin alone did not affect PVP, whereas HVP increased slightly. In combination with nitroglycerin, PVP decreased from 10.1 ± 1.6 to 8.9 ± 1.3 mmHg (P < 0.0001), and HVP decreased from 7.9 ± 1.9 to 6.2 ± 1.3 mmHg (P = 0.001). Vasopressin reduced portal blood flow by 47 ± 19% and hepatic venous flow by 11 ± 18%, respectively. Addition of nitroglycerin further reduced portal- and hepatic flow by 55 ± 13% and 30 ± 13%, respectively. Vasopressin alone had minor effects on central haemodynamics, whereas addition of nitroglycerin reduced cardiac index (3.2 ± 0.7 to 2.7 ± 0.5; P < 0.0001). The arterial-portal vein lactate gradient was unaffected.

CONCLUSION

The combination of vasopressin and nitroglycerin decreases portal pressure and hepato-splanchnic blood flow, and could be a potential treatment to reduce bleeding in liver resection surgery.

Renal haemodynamics and oxygenation during and after cardiac surgery and cardiopulmonary bypass

Acute kidney injury (AKI) is a common complication following cardiac surgery performed on cardiopulmonary bypass (CPB) and has important implications for prognosis. The aetiology of cardiac surgery-associated AKI is complex, but renal hypoxia, particularly in the medulla, is thought to play at least some role. There is strong evidence from studies in experimental animals, clinical observations and computational models that medullary ischaemia and hypoxia occur during CPB. There are no validated methods to monitor or improve renal oxygenation during CPB, and thus possibly decrease the risk of AKI. Attempts to reduce the incidence of AKI by early transfusion to ameliorate intra-operative anaemia, refinement of protocols for cooling and rewarming on bypass, optimization of pump flow and arterial pressure, or the use of pulsatile flow, have not been successful to date. This may in part reflect the complexity of renal oxygenation, which may limit the effectiveness of individual interventions. We propose a multi-disciplinary pathway for translation comprising three components. Firstly, large-animal models of CPB to continuously monitor both whole kidney and regional kidney perfusion and oxygenation. Secondly, computational models to obtain information that can be used to interpret the data and develop rational interventions. Thirdly, clinically feasible non-invasive methods to continuously monitor renal oxygenation in the operating theatre and to identify patients at risk of AKI. In this review, we outline the recent progress on each of these fronts.

Prevention of acute kidney injury and protection of renal function in the intensive care unit: update 2017 : Expert opinion of the Working Group on Prevention, AKI section, European Society of Intensive Care Medicine

BACKGROUND

Acute kidney injury (AKI) in the intensive care unit is associated with significant mortality and morbidity.

OBJECTIVES

To determine and update previous recommendations for the prevention of AKI, specifically the role of fluids, diuretics, inotropes, vasopressors/vasodilators, hormonal and nutritional interventions, sedatives, statins, remote ischaemic preconditioning and care bundles.

METHOD

A systematic search of the literature was performed for studies published between 1966 and March 2017 using these potential protective strategies in adult patients at risk of AKI. The following clinical conditions were considered: major surgery, critical illness, sepsis, shock, exposure to potentially nephrotoxic drugs and radiocontrast. Clinical endpoints included incidence or grade of AKI, the need for renal replacement therapy and mortality. Studies were graded according to the international GRADE system.

RESULTS

We formulated 12 recommendations, 13 suggestions and seven best practice statements. The few strong recommendations with high-level evidence are mostly against the intervention in question (starches, low-dose dopamine, statins in cardiac surgery). Strong recommendations with lower-level evidence include controlled fluid resuscitation with crystalloids, avoiding fluid overload, titration of norepinephrine to a target MAP of 65-70 mmHg (unless chronic hypertension) and not using diuretics or levosimendan for kidney protection solely.

CONCLUSION

The results of recent randomised controlled trials have allowed the formulation of new recommendations and/or increase the strength of previous recommendations. On the other hand, in many domains the available evidence remains insufficient, resulting from the limited quality of the clinical trials and the poor reporting of kidney outcomes.

Blood pressure deficits in acute kidney injury: not all about the mean arterial pressure?

Acute kidney injury (AKI) is associated with increased morbidity and mortality. Although there are many causes of AKI, it is known that patients undergoing high-risk surgery are known to be at significant risk. Although much effort has centred on the minimum arterial pressure needed to maintain renal perfusion, this tends to be based on relatively crude measures such as the mean arterial pressure (MAP), which is widely used as an index for the optimal blood pressure. The rationale behind maintaining MAP is to provide adequate organ perfusion, although this is difficult to assess other than by applying crude end-points. Recent studies have examined the progression of AKI as defined by the KDIGO criteria in terms of time-weighted average values for premorbid and within-ICU haemodynamic pressure-related parameters. Although principally performed on patients who had undergone cardiovascular surgery and who were on vasopressor support, some interesting results were obtained suggesting that crude MAP may not be an adequate target in AKI. In patients with AKI progression, greater observed deficits in mean perfusion pressure, diastolic arterial perfusion, and diastolic perfusion pressures were observed. This study may highlight potential modifiable risk factors for the prevention of progression of AKI, and hopefully translate into improved outcomes.

Renal function and oxygenation are impaired early after liver transplantation despite hyperdynamic systemic circulation

Background

Acute kidney injury (AKI) occurs frequently after liver transplantation and is associated with the development of chronic kidney disease and increased mortality. There is a lack of data on renal blood flow (RBF), oxygen consumption, glomerular filtration rate (GFR) and renal oxygenation, i.e. the renal oxygen supply/demand relationship, early after liver transplantation. Increased insight into the renal pathophysiology after liver transplantation is needed to improve the prevention and treatment of postoperative AKI. We have therefore studied renal hemodynamics, function and oxygenation early after liver transplantation in humans.

Methods

Systemic hemodynamic and renal variables were measured during two 30-min periods in liver transplant recipients (n = 12) and post-cardiac surgery patients (controls, n = 73). RBF and GFR were measured by the renal vein retrograde thermodilution technique and by renal extraction of Cr-EDTA (= filtration fraction), respectively. Renal oxygenation was estimated from the renal oxygen extraction.

Results

In the liver transplant group, GFR decreased by 40% (p < 0.05), compared to the preoperative value. Cardiac index and systemic vascular resistance index were 65% higher (p < 0.001) and 36% lower (p < 0.001), respectively, in the liver transplant recipients compared to the control group. GFR was 27% (p < 0.05) and filtration fraction 40% (p < 0.01) lower in the liver transplant group. Renal vascular resistance was 15% lower (p < 0.05) and RBF was 18% higher (p < 0.05) in liver transplant recipients, but the ratio between RBF and cardiac index was 27% lower (p < 0.001) among the liver-transplanted patients compared to the control group. Renal oxygen consumption and extraction were both higher in the liver transplants, 44% (p < 0.01) and 24% (p < 0.05) respectively.

Conclusions

Despite the hyperdynamic systemic circulation and renal vasodilation, there is a severe decline in renal function directly after liver transplantation. This decline is accompanied by an impaired renal oxygenation, as the pronounced elevation of renal oxygen consumption is not met by a proportional increase in renal oxygen delivery. This information may provide new insights into renal pathophysiology as a basis for future strategies to prevent/treat AKI after liver transplantation.

Trial registration

ClinicalTrials.gov, NCT02455115. Registered on 23 April 2015.

Effects of Cardiopulmonary Bypass on Renal Perfusion, Filtration, and Oxygenation in Patients Undergoing Cardiac Surgery

Background

Acute kidney injury is a common complication after cardiac surgery with cardiopulmonary bypass. The authors evaluated the effects of normothermic cardiopulmonary bypass on renal blood flow, glomerular filtration rate, renal oxygen consumption, and renal oxygen supply/demand relationship, i.e., renal oxygenation (primary outcome) in patients undergoing cardiac surgery.

Methods

Eighteen patients with a normal preoperative serum creatinine undergoing cardiac surgery procedures with normothermic cardiopulmonary bypass (2.5 l · min−1 · m−2) were included after informed consent. Systemic and renal hemodynamic variables were measured by pulmonary artery and renal vein catheters before, during, and after cardiopulmonary bypass. Arterial and renal vein blood samples were taken for measurements of renal oxygen delivery and consumption. Renal oxygenation was estimated from the renal oxygen extraction. Urinary N-acetyl-β-d-glucosaminidase was measured before, during, and after cardiopulmonary bypass.

Results

Cardiopulmonary bypass induced a renal vasoconstriction and redistribution of blood flow away from the kidneys, which in combination with hemodilution decreased renal oxygen delivery by 20%, while glomerular filtration rate and renal oxygen consumption were unchanged. Thus, renal oxygen extraction increased by 39 to 45%, indicating a renal oxygen supply/demand mismatch during cardiopulmonary bypass. After weaning from cardiopulmonary bypass, renal oxygenation was further impaired due to hemodilution and an increase in renal oxygen consumption, accompanied by a seven-fold increase in the urinary N-acetyl-β-d-glucosaminidase/creatinine ratio.

Conclusions

Cardiopulmonary bypass impairs renal oxygenation due to renal vasoconstriction and hemodilution during and after cardiopulmonary bypass, accompanied by increased release of a tubular injury marker.

Vasopressin-induced changes in splanchnic blood flow and hepatic and portal venous pressures in liver resection

BACKGROUND

To minimize blood loss during hepatic surgery, various methods are used to reduce pressure and flow within the hepato-splanchnic circulation. In this study, the effect of low- to moderate doses of vasopressin, a potent splanchnic vasoconstrictor, on changes in portal and hepatic venous pressures and splanchnic and hepato-splanchnic blood flows were assessed in elective liver resection surgery.

METHODS

Twelve patients were studied. Cardiac output (CO), stroke volume (SV), mean arterial (MAP), central venous (CVP), portal venous (PVP) and hepatic venous pressures (HVP) were measured, intraoperatively, at baseline and during vasopressin infusion at two infusion rates (2.4 and 4.8 U/h). From arterial and venous blood gases, the portal (splanchnic) and hepato-splanchnic blood flow changes were calculated, using Fick's equation.

RESULTS

CO, SV, MAP and CVP increased slightly, but significantly, while systemic vascular resistance and heart rate remained unchanged at the highest infusion rate of vasopressin. PVP was not affected by vasopressin, while HVP increased slightly. Vasopressin infusion at 2.4 and 4.8 U/h reduced portal blood flow (-26% and -37%, respectively) and to a lesser extent hepato-splanchnic blood flow (-9% and -14%, respectively). The arterial-portal vein lactate gradient was not significantly affected by vasopressin. Postoperative serum creatinine was not affected by vasopressin.

CONCLUSION

Short-term low to moderate infusion rates of vasopressin induced a splanchnic vasoconstriction without metabolic signs of splanchnic hypoperfusion or subsequent renal impairment. Vasopressin caused a centralization of blood volume and increased cardiac output. Vasopressin does not lower portal or hepatic venous pressures in this clinical setting.

Variable responses of regional renal oxygenation and perfusion to vasoactive agents in awake sheep

Vasoactive agents are used in critical care to optimize circulatory function, but their effects on renal tissue oxygenation in the absence of anesthesia remain largely unknown. Therefore, we assessed the effects of multiple vasoactive agents on regional kidney oxygenation in awake sheep. Sheep were surgically instrumented with pulmonary and renal artery flow probes, and combination fiber-optic probes, in the renal cortex and medulla, comprising a fluorescence optode to measure tissue Po2 and a laser-Doppler probe to assess tissue perfusion. Carotid arterial and renal venous cannulas enabled measurement of arterial pressure and total renal oxygen delivery and consumption. Norepinephrine (0.1 or 0.8 μg·kg−1·min−1) dose-dependently reduced cortical and medullary laser Doppler flux (LDF) and Po2 without significantly altering renal blood flow (RBF), or renal oxygen delivery or consumption. Angiotensin II (9.8 ± 2.1 μg/h) reduced RBF by 21%, renal oxygen delivery by 28%, oxygen consumption by 18%, and medullary Po2 by 38%, but did not significantly alter cortical Po2 or cortical or medullary LDF. Arginine vasopressin (3.3 ± 0.5 μg/h) caused similar decreases in RBF and renal oxygen delivery, but did not significantly alter renal oxygen consumption or cortical or medullary LDF or Po2. Captopril had no observable effects on cortical or medullary LDF or Po2, at a dose that increased renal oxygen delivery by 24%, but did not significantly alter renal oxygen consumption. We conclude that vasoactive agents have diverse effects on regional kidney oxygenation in awake sheep that are not predictable from their effects on LDF, RBF, or total renal oxygen delivery and consumption.

Hypotensive resuscitation in combination with arginine vasopressin may prolong the hypotensive resuscitation time in uncontrolled hemorrhagic shock rats

BACKGROUND

The optimal resuscitation strategy for traumatic hemorrhagic shock is not completely determined. The objective of the present study was to investigate whether hypotensive resuscitation in combination with arginine vasopressin (AVP) can prolong the hypotensive resuscitation time by minimizing blood loss and stabilizing hemodynamics for uncontrolled hemorrhagic shock.

METHODS

With an established rat model of uncontrolled hemorrhagic shock, we compared the beneficial effects of hypotensive resuscitation in combination with AVP to maintain blood pressure at 50 mm Hg for 3 hours to hypotensive resuscitation alone on animal survival, blood loss, and vital organ functions.

RESULTS

Hypotensive resuscitation in combination with AVP maintenance for 3 hours significantly reduced total blood loss and fluid requirement during hypotensive resuscitation period and significantly improved the survival of shock rats as compared with hypotensive resuscitation alone. Among the four concentrations of AVP, 5 × 10 U/mL had the best effect: it significantly improved hemodynamics and increased cardiac function, oxygen delivery, as well as hepatic blood flow and hepatic function in the shock rats. However, renal blood flow in the hypotensive resuscitation + AVP group was lower than that in the hypotensive resuscitation alone group.

CONCLUSION

Hypotensive resuscitation in combination with early application of AVP could prolong the tolerance time of hypotensive resuscitation and "buy" longer safe prehospital transport time by reducing blood loss and stabilizing hemodynamics. This strategy may be a promising strategy for the early management of trauma patients with active bleeding.

Basal renal O2 consumption and the efficiency of O2 utilization for Na+ reabsorption

We examined how the presence of a fixed level of basal renal O2 consumption (Vo2(basal); O2 used for processes independent of Na(+) transport) confounds the utility of the ratio of Na(+) reabsorption (TNa(+)) to total renal Vo2 (Vo2(total)) as an index of the efficiency of O2 utilization for TNa(+). We performed a systematic review and additional experiments in anesthetized rabbits to obtain the best possible estimate of the fractional contribution of Vo2(basal) to Vo2(total) under physiological conditions (basal percent renal Vo2). Estimates of basal percent renal Vo2 from 24 studies varied from 0% to 81.5%. Basal percent renal Vo2 varied with the fractional excretion of Na(+) (FENa(+)) in the 14 studies in which FENa(+) was measured under control conditions. Linear regression analysis predicted a basal percent renal Vo2 of 12.7-16.5% when FENa(+) = 1% (r(2) = 0.48, P = 0.001). Experimentally induced changes in TNa(+) altered TNa(+)/Vo2(total) in a manner consistent with theoretical predictions. We conclude that, because Vo2(basal) represents a significant proportion of Vo2(total), TNa(+)/Vo2(total) can change markedly when TNa(+) itself changes. Therefore, caution should be taken when TNa(+)/Vo2(total) is interpreted as a measure of the efficiency of O2 utilization for TNa(+), particularly under experimental conditions where TNa(+) or Vo2(total) changes.

Effects of levosimendan on glomerular filtration rate, renal blood flow, and renal oxygenation after cardiac surgery with cardiopulmonary bypass: a randomized placebo-controlled study

OBJECTIVES

Acute kidney injury develops in a large proportion of patients after cardiac surgery because of the low cardiac output syndrome. The inodilator levosimendan increases cardiac output after cardiac surgery with cardiopulmonary bypass, but a detailed analysis of its effects on renal perfusion, glomerular filtration, and renal oxygenation in this group of patients is lacking. We therefore evaluated the effects of levosimendan on renal blood flow, glomerular filtration rate, renal oxygen consumption, and renal oxygen demand/supply relationship, i.e., renal oxygen extraction, early after cardiac surgery with cardiopulmonary bypass.

DESIGN

Prospective, placebo-controlled, and randomized trial.

SETTING

Cardiothoracic ICU of a tertiary center.

PATIENTS

Postcardiac surgery patients (n=30).

INTERVENTIONS

The patients were randomized to receive levosimendan, 0.1 µg/kg/min after a loading dose of 12 µg/kg (n=15), or placebo (n=15).

MEASUREMENTS AND MAIN RESULTS

The experimental procedure started 4-6 hours after surgery in the ICU during propofol sedation and mechanical ventilation. Systemic hemodynamic were evaluated by a pulmonary artery thermodilution catheter. Renal blood flow and glomerular filtration rate were measured by the renal vein retrograde thermodilution technique and by renal extraction of Cr-EDTA, respectively. Central venous pressure was kept constant by colloid/crystalloid infusion. Compared to placebo, levosimendan increased cardiac index (22%), stroke volume index (15%), and heart rate (7%) and decreased systemic vascular resistance index (21%), whereas mean arterial pressure was not affected. Levosimendan induced significant increases in renal blood flow (12%, p<0.05) and glomerular filtration rate (21%, p<0.05), decreased renal vascular resistance (18%, p<0.05) but caused no significant changes in filtration fraction, renal oxygen consumption, or renal oxygen extraction, compared to placebo.

CONCLUSIONS

After cardiac surgery with cardiopulmonary bypass, levosimendan induces a vasodilation, preferentially of preglomerular resistance vessels, increasing both renal blood flow and glomerular filtration rate without jeopardizing renal oxygenation. Due to its pharmacodynamic profile, levosimendan might be an interesting alternative for treatment of postoperative heart failure complicated by acute kidney injury in postcardiac surgery patients.

Renal oxygenation and haemodynamics in acute kidney injury and chronic kidney disease

Acute kidney injury (AKI) is a major burden on health systems and may arise from multiple initiating insults, including ischaemia-reperfusion injury, cardiovascular surgery, radiocontrast administration and sepsis. Similarly, the incidence and prevalence of chronic kidney disease (CKD) continues to increase, with significant morbidity and mortality. Moreover, an increasing number of AKI patients survive to develop CKD and end-stage renal disease. Although the mechanisms for the development of AKI and progression to CKD remain poorly understood, initial impairment of oxygen balance likely constitutes a common pathway, causing renal tissue hypoxia and ATP starvation that, in turn, induce extracellular matrix production, collagen deposition and fibrosis. Thus, possible future strategies for one or both conditions may involve dopamine, loop diuretics, atrial natriuretic peptide and inhibitors of inducible nitric oxide synthase, substances that target kidney oxygen consumption and regulators of renal oxygenation, such as nitric oxide and heme oxygenase-1.