The effect of normal saline resuscitation on vital organ blood flow in septic sheep

The REPERFUSE study protocol: The effects of vasopressor therapy on renal perfusion in patients with septic shock-A mechanistically focused randomised control trial

INTRODUCTION

Acute kidney injury (AKI) is a common complication of septic shock and together these conditions carry a high mortality risk. In septic patients who develop severe AKI, renal cortical perfusion is deficient despite normal macrovascular organ blood flow. This intra-renal perfusion abnormality may be amenable to pharmacological manipulation, which may offer mechanistic insight into the pathophysiology of septic AKI. The aim of the current study is to investigate the effects of vasopressin and angiotensin II on renal microcirculatory perfusion in a cohort of patients with septic shock.

METHODS AND ANALYSIS

In this single centre, mechanistically focussed, randomised controlled study, 45 patients with septic shock will be randomly allocated to either of the study vasopressors (vasopressin or angiotensin II) or standard therapy (norepinephrine). Infusions will be titrated to maintain a mean arterial pressure (MAP) target set by the attending clinician. Renal microcirculatory assessment will be performed for the cortex and medulla using contrast-enhanced ultrasound (CEUS) and urinary oxygen tension (pO2), respectively. Renal macrovascular flow will be assessed via renal artery ultrasound. Measurement of systemic macrovascular flow will be performed through transthoracic echocardiography (TTE) and microvascular flow via sublingual incident dark field (IDF) video microscopy. Measures will be taken at baseline, +1 and +24hrs following infusion of the study drug commencing. Blood and urine samples will also be collected at the measurement time points. Longitudinal data will be compared between groups and over time.

DISCUSSION

Vasopressors are integral to the management of patients with septic shock. This study aims to further understanding of the relationship between this therapy, renal perfusion and the development of AKI. In addition, using CEUS and urinary pO2, we hope to build a more complete picture of renal perfusion in septic shock by interrogation of the constituent parts of the kidney. Results will be published in peer-reviewed journals and presented at academic meetings.

TRIAL REGISTRATION

The REPERFUSE study was registered on Clinical Trials.gov (NCT06234592) on the 30th Jan 24.

Why physiology will continue to guide the choice between balanced crystalloids and normal saline: a systematic review and meta-analysis

BACKGROUND

Crystalloids are the most frequently prescribed drugs in intensive care medicine and emergency medicine. Thus, even small differences in outcome may have major implications, and therefore, the choice between balanced crystalloids versus normal saline continues to be debated. We examined to what extent the currently accrued information size from completed and ongoing trials on the subject allow intensivists and emergency physicians to choose the right fluid for their patients.

METHODS

Systematic review and meta-analysis with random effects inverse variance model. Published randomized controlled trials enrolling adult patients to compare balanced crystalloids versus normal saline in the setting of intensive care medicine or emergency medicine were included. The main outcome was mortality at the longest follow-up, and secondary outcomes were moderate to severe acute kidney injury (AKI) and initiation of renal replacement therapy (RRT). Trial sequential analyses (TSA) were performed, and risk of bias and overall quality of evidence were assessed. Additionally, previously published meta-analyses, trial sequential analyses and ongoing large trials were analysed for included studies, required information size calculations and the assumptions underlying those calculations.

RESULTS

Nine studies (n = 32,777) were included. Of those, eight had data available on mortality, seven on AKI and six on RRT. Meta-analysis showed no significant differences between balanced crystalloids versus normal saline for mortality (P = 0.33), the incidence of moderate to severe AKI (P = 0.37) or initiation of RRT (P = 0.29). Quality of evidence was low to very low. Analysis of previous meta-analyses and ongoing trials showed large differences in calculated required versus accrued information sizes and assumptions underlying those. TSA revealed the need for extremely large trials based on our realistic and clinically relevant assumptions on relative risk reduction and baseline mortality.

CONCLUSIONS

Our meta-analysis could not find significant differences between balanced crystalloids and normal saline on mortality at the longest follow-up, moderate to severe AKI or new RRT. Currently accrued information size is smaller, and the required information size is larger than previously anticipated. Therefore, completed and ongoing trials on the topic may fail to provide adequate guidance for choosing the right crystalloid. Thus, physiology will continue to play an important role for individualizing this choice.

Acute kidney injury from sepsis: current concepts, epidemiology, pathophysiology, prevention and treatment

Sepsis-associated acute kidney injury (S-AKI) is a frequent complication of the critically ill patient and is associated with unacceptable morbidity and mortality. Prevention of S-AKI is difficult because by the time patients seek medical attention, most have already developed acute kidney injury. Thus, early recognition is crucial to provide supportive treatment and limit further insults. Current diagnostic criteria for acute kidney injury has limited early detection; however, novel biomarkers of kidney stress and damage have been recently validated for risk prediction and early diagnosis of acute kidney injury in the setting of sepsis. Recent evidence shows that microvascular dysfunction, inflammation, and metabolic reprogramming are 3 fundamental mechanisms that may play a role in the development of S-AKI. However, more mechanistic studies are needed to better understand the convoluted pathophysiology of S-AKI and to translate these findings into potential treatment strategies and add to the promising pharmacologic approaches being developed and tested in clinical trials.

A Comparison of 4% Succinylated Gelatin Solution versus Normal Saline in Stable Normovolaemic Sheep: Global Haemodynamic, Regional Blood Flow and Oxygen Delivery Effects

The objective of this study was to compare the effects on regional blood flow and regional oxygen delivery of 4% succinylated gelatin solution (Gelofusine®, B. Braun) with those of normal saline. This was a randomised, controlled, crossover large animal study, which took place at the animal laboratory of university physiology institute. The subjects were seven merino cross-ewes.

We implanted flow probes around the aorta, coronary, renal and mesenteric arteries. We randomised animals to observation (control), normal saline (one litre over 15 minutes) or Gelofusine* (one litre over 15 minutes). We measured central haemodynamics, organ blood flows, arterial blood gases and haemoglobin every 30 minutes for 210 minutes.

Compared to control, both Gelofusine* and normal saline significantly and similarly increased mean arterial pressure, stroke volume, cardiac output and central venous pressure in the first hour (P <0.05). Such changes, however, were transient except for the increase in cardiac output seen with Gelofusine®. Normal saline significantly increased mesenteric blood flow in the first hour (P <0.05), while Gelofusine* caused a specific, sustained and progressive increase in renal blood flow and conductance (P <0.05). Both fluids increased urine output and creatinine clearance (P <0.05), but, due to haemodilution, both decreased renal oxygen delivery in the first hour (P <0.05).

Normal saline and Gelofusine® have transient, volume expansion-related systemic haemodynamic effects, which are greater for Gelofusine®. Saline had a more pronounced early effect on mesenteric blood flow, while Gelofusine* had a sustained and progressive greater effect on renal blood flow. The transient increase in urine output and creatinine clearance seen with both fluids occurred while renal oxygen delivery decreased.

Cardiac Index Changes With Fluid Bolus Therapy in Children With Sepsis-An Observational Study

OBJECTIVES

Fluid bolus therapy is the initial recommended treatment for acute circulatory failure in sepsis, yet it is unknown whether this has the intended effect of increasing cardiac index. We aimed to describe the effect of fluid bolus therapy on cardiac index in children with sepsis.

DESIGN

A prospective observational cohort study.

SETTING

The Emergency Department of The Royal Children's Hospital, Melbourne, VIC, Australia.

PATIENTS

A convenience sample of children meeting international consensus criteria for sepsis with acute circulatory failure.

INTERVENTION

Treating clinician decision to administer fluid bolus therapy.

MEASUREMENTS AND MAIN RESULTS

Transthoracic echocardiography was recorded immediately before, 5 minutes after, and 60 minutes after fluid bolus therapy. Cardiac index was calculated by a pediatric cardiologist blinded to the timing of the echocardiogram. Cardiac index was calculated for 49 fluid boluses in 41 children. The median change in cardiac index 5 minutes after a fluid bolus therapy was +18.0% (interquartile range, 8.6-28.1%) and after 60 minutes was -6.0% (interquartile range, -15.2% to 3.0%) relative to baseline. Thirty-one of 49 fluid boluses (63%) resulted in an increase in cardiac index of greater than 10% at 5 minutes, and these participants were considered fluid responsive. This was sustained in four of 31 (14%) at 60 minutes. No association between change in cardiac index at 5 or 60 minutes and age, baseline mean arterial blood pressure, fluid bolus volume, and prior volume of fluid bolus therapy was found on linear regression.

CONCLUSIONS

Fluid bolus therapy for pediatric sepsis is associated with a transient increase in cardiac index. Fluid responsiveness is variable and, when present, not sustained. The efficacy of fluid bolus therapy for achieving a sustained increase in cardiac index in children with sepsis is limited.

Fluid resuscitation for acute kidney injury: an empty promise

PURPOSE OF REVIEW

The past decade has seen more advances in our understanding of fluid therapy than the preceding decades combined. What was once thought to be a relatively benign panacea is increasingly being recognized as a potent pharmacological and physiological intervention that may pose as much harm as benefit.

RECENT FINDINGS

Recent studies have clearly indicated that the amount, type, and timing of fluid administration have profound effects on patient morbidity and outcomes. The practice of aggressive volume resuscitation for 'renal protection' and 'hemodynamic support' may in fact be contributing to end organ dysfunction. The practice of early goal-directed therapy for patients suffering from critical illness or undergoing surgery appears to offer no benefit over conventional therapy and may in fact be harmful. A new conceptual model for fluid resuscitation of critically ill patients has recently been developed and is explored here.

SUMMARY

The practice of giving more fluid early and often is being replaced with new conceptual models of fluid resuscitation that suggest fluid therapy be 'personalized' to individual patient pathophysiology.

Chloride Content of Fluids Used for Large-Volume Resuscitation Is Associated With Reduced Survival

OBJECTIVE

We sought to investigate if the chloride content of fluids used in resuscitation was associated with short- and long-term outcomes.

DESIGN

We identified patients who received large-volume fluid resuscitation, defined as greater than 60 mL/kg over a 24-hour period. Chloride load was determined for each patient based on the chloride ion concentration of the fluids they received during large-volume fluid resuscitation multiplied by the volume of fluids. We compared the development of hyperchloremic acidosis, acute kidney injury, and survival among those with higher and lower chloride loads.

SETTING

University Medical Center.

PATIENTS

Patients admitted to ICUs from 2000 to 2008.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Among 4,710 patients receiving large-volume fluid resuscitation, hyperchloremic acidosis was documented in 523 (11%). Crude rates of hyperchloremic acidosis, acute kidney injury, and hospital mortality all increased significantly as chloride load increased (p < 0.001). However, chloride load was no longer associated with hyperchloremic acidosis or acute kidney injury after controlling for total fluids, age, and baseline severity. Conversely, each 100 mEq increase in chloride load was associated with a 5.5% increase in the hazard of death even after controlling for total fluid volume, age, and severity (p = 0.0015) over 1 year.

CONCLUSIONS

Chloride load is associated with significant adverse effects on survival out to 1 year even after controlling for total fluid load, age, and baseline severity of illness. However, the relationship between chloride load and development of hyperchloremic acidosis or acute kidney injury is less clear, and further research is needed to elucidate the mechanisms underlying the adverse effects of chloride load on survival.

Impact of End-Stage Renal Disease and Acute Kidney Injury on ICU Outcomes in Patients With Sepsis

PURPOSE

To report the characteristics and outcomes of patients with sepsis in the intensive care unit (ICU) with end-stage renal disease (ESRD) and acute kidney injury (AKI) compared to patients with nonkidney injury (non-KI).

METHODS

Retrospective study of all patients with sepsis admitted to the ICU of a university hospital within a 12-month time period. Data were obtained from the University Health Consortium database and a chart review of the electronic medical records.

RESULTS

We identified 39 cases of ESRD, 106 cases of AKI, and 103 cases of non-KI. Intensive care unit mortality was 15.4% for ESRD, 30.2% for AKI, and 13.6% for non-KI ( P < .01). Hospital mortality was 20.5% for ESRD, 32.1% for AKI, and 13.6% for non-KI ( P < .01). Early AKI and late AKI had an ICU mortality of 24.4% versus 50% ( P <.01), hospital mortality of 26.8% versus 50% ( P = .03), ICU length of stay (LOS) of 3 and 6 days ( P = .04), and hospital LOS of 7 and 12.5 days ( P <.01), respectively.

CONCLUSION

Patients with sepsis having AKI have a higher mortality rate than those with ESRD and non-KI. Hospital and ICU mortality rates for patients with ESRD were similar to non-KI patients. Late AKI compared to early AKI had a higher mortality and longer LOS.

Fluid Overload

Most critically ill patients experience external or internal fluid shifts and hemodynamic instability. In response to these changes, intravenous fluids are frequently administered. However, rapid losses of administered fluids from circulation and the indirect link between the short-lived plasma volume expansion and end points frequently result in transient responses to fluid therapy. Therefore, fluid overload is a common finding in intensive care units. The authors consider the evidence of harm associated with fluid overload and the physiologic processes that lead to fluid accumulation in critical illness. The authors then consider methods to prevent fluid accumulation and/or manage its resolution.

A unified theory of sepsis-induced acute kidney injury: inflammation, microcirculatory dysfunction, bioenergetics, and the tubular cell adaptation to injury

Given that the leading clinical conditions associated with acute kidney injury (AKI), namely, sepsis, major surgery, heart failure, and hypovolemia, are all associated with shock, it is tempting to attribute all AKI to ischemia on the basis of macrohemodynamic changes. However, an increasing body of evidence has suggested that in many patients, AKI can occur in the absence of overt signs of global renal hypoperfusion. Indeed, sepsis-induced AKI can occur in the setting of normal or even increased renal blood flow. Accordingly, renal injury may not be entirely explained solely on the basis of the classic paradigm of hypoperfusion, and thus other mechanisms must come into play. Herein, we put forward a "unifying theory" to explain the interplay between inflammation and oxidative stress, microvascular dysfunction, and the adaptive response of the tubular epithelial cell to the septic insult. We propose that this response is mostly adaptive in origin, that it is driven by mitochondria, and that it ultimately results in and explains the clinical phenotype of sepsis-induced AKI.

Should chloride-rich crystalloids remain the mainstay of fluid resuscitation to prevent 'pre-renal' acute kidney injury?: con

The high chloride content of 0.9% saline leads to adverse pathophysiological effects in both animals and healthy human volunteers, changes not seen after balanced crystalloids. Small randomized trials confirm that the hyperchloremic acidosis induced by saline also occurs in patients, but no clinical outcome benefit was demonstrable when compared with balanced crystalloids, perhaps due to a type II error. A strong signal is emerging from recent large propensity-matched and cohort studies for the adverse effects that 0.9% saline has on the clinical outcome in surgical and critically ill patients when compared with balanced crystalloids. Major complications are the increased incidence of acute kidney injury and the need for renal replacement therapy, and that pathological hyperchloremia may increase postoperative mortality. However, there are no large-scale randomized trials comparing 0.9% saline with balanced crystalloids. Some balanced crystalloids are hypo-osmolar and may not be suitable for neurosurgical patients because of their propensity to cause brain edema. Saline may be the solution of choice used for the resuscitation of patients with alkalosis and hypochloremia. Nevertheless, there is evidence to suggest that balanced crystalloids cause less detriment to renal function than 0.9% saline, with perhaps better clinical outcome. Hence, we argue that chloride-rich crystalloids such as 0.9% saline should be replaced with balanced crystalloids as the mainstay of fluid resuscitation to prevent ‘pre-renal' acute kidney injury.

Fluid management for the prevention and attenuation of acute kidney injury

In patients with acute kidney injury (AKI), optimization of systemic haemodynamics is central to the clinical management. However, considerable debate exists regarding the efficacy, nature, extent and duration of fluid resuscitation, particularly when the patient has undergone major surgery or is in septic shock. Crucially, volume resuscitation might be required to maintain or restore cardiac output. However, resultant fluid accumulation and tissue oedema can substantially contribute to ongoing organ dysfunction and, particularly in patients developing AKI, serious clinical consequences. In this Review, we discuss the conflict between the desire to achieve adequate resuscitation of shock and the need to mitigate the harmful effects of fluid overload. In patients with AKI, limiting and resolving fluid overload might prompt earlier use of renal replacement therapy. However, rapid or early excessive fluid removal with diuretics or extracorporeal therapy might lead to hypovolaemia and recurrent renal injury. Optimal management might involve a period of guided fluid resuscitation, followed by management of an even fluid balance and, finally, an appropriate rate of fluid removal. To obtain best clinical outcomes, serial fluid status assessment and careful definition of cardiovascular and renal targets will be required during fluid resuscitation and removal.

A critique of fluid bolus resuscitation in severe sepsis

Resuscitation of septic patients by means of one or more fluid boluses is recommended by guidelines from multiple relevant organizations and as a component of surviving sepsis campaigns. The technique is considered a key and life-saving intervention during the initial treatment of severe sepsis in children and adults. Such recommendations, however, are only based on expert opinion and lack adequate experimental or controlled human evidence. Despite these limitations, fluid bolus therapy (20 to 40 ml/kg) is widely practiced and is currently considered a cornerstone of the management of sepsis. In this pointof-view critique, we will argue that such therapy has weak physiological support, has limited experimental support, and is at odds with emerging observational data in several subgroups of critically ill patients or those having major abdominal surgery. Finally, we will argue that this paradigm is now challenged by the findings of a large randomized controlled trial in septic children. In the present article, we contend that the concept of large fluid bolus resuscitation in sepsis needs to be investigated further.

Toward the optimal clinical use of the fraction excretion of solutes in oliguric azotemia

While the fractional excretion of solutes have long been considered excellent research tools to investigate tubular physiology, their clinical use has become common over the last 40 years in the diagnoses of many disorders; however, none have reached the clinical utility of the fractional excretion of sodium in the ability to distinguish pre-renal azotemia from acute tubular necrosis. Nevertheless, there are many drugs and medical conditions that interfere with that utility and recently other solutes, including urea, uric acid and lithium, have been recently investigated to improve the diagnostic ability in clinical situations where the fractional excretion of sodium is known to be unreliable. We review the tubular physiology of these solutes and show how the differences in tubular physiology might be exploited to develop a strategy for their optimal clinical use.

Fluid administration and the kidney

PURPOSE OF REVIEW

Intravenous fluids are widely administered in the ICU with the intention of preventing or ameliorating acute kidney injury (AKI). This review focuses on recent studies examining fluid administration and renal function in critical illness to critically examine conventional justifications for fluid administration.

RECENT FINDINGS

Early, targeted, resuscitation of inadequate cardiac output in shock may have a beneficial effect on organ function and patient outcome. However, experimental evidence suggests the relationship between fluid administration and an increase in renal oxygen delivery is weak, whereas any beneficial effects from fluid administration can be short lived. Conversely, evidence associating fluid overload and adverse outcomes is strengthening, whereas more restrictive fluid administration does not seem to predispose to clinically significant AKI in many situations. Furthermore, concerns persist that some colloid or high chloride concentration solutions may directly impair renal function independent of volume overload.

SUMMARY

Adequate volume resuscitation remains a cornerstone to the emergent treatment of critical illness. However, continued fluid administration and positive fluid balances have not been shown to improve renal outcomes and may worsen overall prognosis in AKI. Concerns about renal dysfunction should not deter clinicians from adopting more restrictive approaches to fluid administration.

Fluid balance and acute kidney injury

Intravenous fluids are widely administered to patients who have, or are at risk of, acute kidney injury (AKI). However, deleterious consequences of overzealous fluid therapy are increasingly being recognized. Salt and water overload can predispose to organ dysfunction, impaired wound healing and nosocomial infection, particularly in patients with AKI, in whom fluid challenges are frequent and excretion is impaired. In this Review article, we discuss how interstitial edema can further delay renal recovery and why conservative fluid strategies are now being advocated. Applying these strategies in critical illness is challenging. Although volume resuscitation is needed to restore cardiac output, it often leads to tissue edema, thereby contributing to ongoing organ dysfunction. Conservative strategies of fluid management mandate a switch towards neutral balance and then negative balance once hemodynamic stabilization is achieved. In patients with AKI, this strategy might require renal replacement therapy to be given earlier than when more-liberal fluid management is used. However, hypovolemia and renal hypoperfusion can occur in patients with AKI if excessive fluid removal is pursued with diuretics or extracorporeal therapy. Thus, accurate assessment of fluid status and careful definition of targets are needed at all stages to improve clinical outcomes. A conservative strategy of fluid management was recently tested and found to be effective in a large, randomized, controlled trial in patients with acute lung injury. Similar randomized, controlled studies in patients with AKI now seem justified.

Septic shock induces distinct changes in sympathetic nerve activity to the heart and kidney in conscious sheep

Sepsis and septic shock are the chief cause of death in intensive care units, with mortality rates between 30 and 70%. In a large animal model of septic shock, we have demonstrated hypotension, increased cardiac output, and tachycardia, together with renal vasodilatation and renal failure. The changes in cardiac sympathetic nerve activity (CSNA) that may contribute to the tachycardia have not been investigated, and the changes in renal SNA (RSNA) that may mediate the changes in renal blood flow and function are unclear. We therefore recorded CSNA and RSNA during septic shock in conscious sheep. Septic shock was induced by administration of Escherichia coli, which caused a delayed hypotension and an immediate, biphasic increase in heart rate (HR) associated with similar changes in CSNA. After E. coli, RSNA decreased for over 3 h, followed by a sustained increase (180%), whereas renal blood flow progressively increased and remained elevated. There was an initial diuresis, followed by oliguria and decreased creatinine clearance. There were differential changes in the range of the arterial baroreflex curves; it was depressed for HR, increased for CSNA, and unchanged for RSNA. Our findings, recording CSNA for the first time in septic shock, suggest that the increase in SNA to the heart is not driven solely by unloading of baroreceptors and that the increase has an important role to increase HR and cardiac output. There was little correlation between the changes in RSNA and renal blood flow, suggesting that the renal vasodilatation was mediated mainly by other mechanisms.

Early acute kidney injury and sepsis: a multicentre evaluation

Introduction

We conducted a study to evaluate the incidence, risk factors and outcomes associated with early acute kidney injury (AKI) in sepsis.

Methods

The study was a retrospective interrogation of prospectively collected data from the Australian New Zealand Intensive Care Society Adult Patient Database. Data were collected from 57 intensive care units (ICUs) across Australia. In total, 120,123 patients admitted to ICU for more than 24 hours from 1 January 2000 to 31 December 2005 were included in the analysis. The main outcome measures were clinical and laboratory data and outcomes.

Results

Of 120,123 patients admitted, 33,375 had a sepsis-related diagnosis (27.8%). Among septic patients, 14,039 (42.1%) had concomitant AKI (septic AKI). Sepsis accounted for 32.4% of all patients with AKI. For septic AKI stratified by RIFLE (risk of renal failure, injury to the kidney, failure of kidney function, loss of kidney function and end-stage kidney disease) category, 38.5% of patients belonged to the risk category, 38.8% to the injury category and 22.7% to the failure category. Septic AKI patients had greater acuity of illness (P < 0.0001), lower blood pressure (P < 0.0001), higher heart rates (P < 0.0001), worse pulmonary function measures by arterial oxygen tension/fraction of inspired oxygen ratio (P < 0.0001), greater acidaemia (P < 0.0001) and higher white cell counts (P < 0.0001) compared with patients with nonseptic AKI. Septic AKI was also associated with greater severity of AKI (RIFLE category injury or failure) compared with nonseptic AKI. Septic AKI was associated with a significantly higher crude and co-variate adjusted mortality in the ICU (19.8% versus 13.4%; odds ratio 1.60, 95% confidence interval 1.5 to 1.7; P < 0.001) and in hospital (29.7% versus 21.6%; odds ratio 1.53, 95% confidence interval 1.46 to 1.60; P < 0.001) compared with nonseptic AKI. Septic AKI was associated with higher ICU and hospital mortality across all strata of RIFLE categories. Septic AKI patients had longer durations of stay in both ICU and hospital across all strata of RIFLE categories.

Conclusion

Septic AKI is common during the first 24 hours after ICU admission. Patients with septic AKI are generally sicker, with a higher burden of illness, and have greater abnormalities in acute physiology compared with patients with nonseptic AKI. Moreover, septic AKI is independently associated with higher odds of death and longer duration of hospitalization.

The Effects of Normal and Hypertonic Saline on Regional Blood Flow and Oxygen Delivery

BACKGROUND

Boluses of crystalloids are frequently given to patients to optimize vital organ perfusion. However, their effect on regional blood flow and oxygen delivery in the normal mammalian circulation has not been studied. We compared the effects of normal or hypertonic (3%) saline or control on regional blood flow and oxygen delivery in normal animals.

METHODS

We conducted a randomized, controlled animal study in seven merino cross-ewes. We implanted chronic flow probes around aorta, coronary, renal, and mesenteric arteries. We randomized animals to three different interventions: observation (control), normal saline (1 L over 15 min), or 3% saline (300 mL over 15 min). We continuously measured central hemodynamics and organ blood flow for 210 min.

RESULTS

Both fluids increased heart rate, cardiac output, central venous pressure, peripheral conductance, coronary and mesenteric blood flow, and conductance in the first hour (P < 0.05). In the second and third hour, both maintained a greater cardiac output, total peripheral conductance, and mesenteric blood flow (P < 0.05) than control, but the difference decreased. In contrast, renal blood flow was unaffected and, because of hemodilution, renal oxygen delivery was decreased in the first hour (P < 0.05). Simultaneously, urine output and creatinine clearance increased (P < 0.05) in both groups. Finally, 3% saline significantly, but transiently, increased serum sodium and osmolarity.

CONCLUSIONS

Normal and hypertonic saline have similar systemic and regional hemodynamic effects. They also have no effect on renal blood flow and initially decrease renal oxygen delivery while increasing urine output.

Septic acute kidney injury in critically ill patients: clinical characteristics and outcomes

Sepsis is the most common cause of acute kidney injury (AKI) in critical illness, but there is limited information on septic AKI. A prospective, observational study of critically ill patients with septic and nonseptic AKI was performed from September 2000 to December 2001 at 54 hospitals in 23 countries. A total of 1753 patients were enrolled. Sepsis was considered the cause in 833 (47.5%); the predominant sources of sepsis were chest and abdominal (54.3%). Septic AKI was associated with greater aberrations in hemodynamics and laboratory parameters, greater severity of illness, and higher need for mechanical ventilation and vasoactive therapy. There was no difference in enrollment kidney function or in the proportion who received renal replacement therapy (RRT; 72 versus 71%; P = 0.83). Oliguria was more common in septic AKI (67 versus 57%; P < 0.001). Septic AKI had a higher in-hospital case-fatality rate compared with nonseptic AKI (70.2 versus 51.8%; P < 0.001). After adjustment for covariates, septic AKI remained associated with higher odds for death (1.48; 95% confidence interval 1.17 to 1.89; P = 0.001). Median (IQR) duration of hospital stay for survivors (37 [19 to 59] versus 21 [12 to 42] d; P < 0.0001) was longer for septic AKI. There was a trend to lower serum creatinine (106 [73 to 158] versus 121 [88 to 184] mumol/L; P = 0.01) and RRT dependence (9 versus 14%; P = 0.052) at hospital discharge for septic AKI. Patients with septic AKI were sicker and had a higher burden of illness and greater abnormalities in acute physiology. Patients with septic AKI had an increased risk for death and longer duration of hospitalization yet showed trends toward greater renal recovery and independence from RRT.

Fluid resuscitation and the septic kidney

Acute renal failure is a common complication of sepsis in the critically ill patient. Fluid resuscitation is considered a cornerstone for preservation of function in the septic kidney. This is generally based on the assumption that fluid therapy will restore and maintain adequate renal blood flow. This principle, however, has not yet been formally evaluated in humans. Thus, it remains unclear how fluid therapy may affect renal blood flow in septic acute renal failure. Further, there is new evidence to imply that the choice, timing and amount of fluid used for resuscitation in sepsis may have a direct impact on kidney function. Thus, in this editorial, we consider the relevant literature and more recent insights into the effect of fluid resuscitation on the septic kidney.