Plasma volume expansion by 0.9% NaCl during sepsis/systemic inflammatory response syndrome, after hemorrhage, and during a normal state

A novel Vascular Leak Index identifies sepsis patients with a higher risk for in-hospital death and fluid accumulation

PURPOSE

Sepsis is a leading cause of morbidity and mortality worldwide and is characterized by vascular leak. Treatment for sepsis, specifically intravenous fluids, may worsen deterioration in the context of vascular leak. We therefore sought to quantify vascular leak in sepsis patients to guide fluid resuscitation.

METHODS

We performed a retrospective cohort study of sepsis patients in four ICU databases in North America, Europe, and Asia. We developed an intuitive vascular leak index (VLI) and explored the relationship between VLI and in-hospital death and fluid balance using generalized additive models (GAM).

RESULTS

Using a GAM, we found that increased VLI is associated with an increased risk of in-hospital death. Patients with a VLI in the highest quartile (Q4), across the four datasets, had a 1.61-2.31 times increased odds of dying in the hospital compared to patients with a VLI in the lowest quartile (Q1). VLI Q2 and Q3 were also associated with increased odds of dying. The relationship between VLI, treated as a continuous variable, and in-hospital death and fluid balance was statistically significant in the three datasets with large sample sizes. Specifically, we observed that as VLI increased, there was increase in the risk for in-hospital death and 36-84 h fluid balance.

CONCLUSIONS

Our VLI identifies groups of patients who may be at higher risk for in-hospital death or for fluid accumulation. This relationship persisted in models developed to control for severity of illness and chronic comorbidities.

Intravenous Fluid Administration and the Coagulation System

Intravenous fluid administration in veterinary patients can alter coagulation function by several mechanisms. Both crystalloid and colloid fluids cause hemodilution, reducing platelet count and plasma coagulation protein concentrations. Hemodilution is associated with a hypercoagulable effect at low dilutions and a hypocoagulable effect at higher dilutions. Composition of crystalloid fluids likely has a minor effect, primarily dependent on fluid ion composition. Hypertonic crystalloids may also cause hypocoagulability. Colloids, both synthetic and natural, can cause hypocoagulability by several mechanisms beyond the effects of hemodilution. These include impaired platelet function, decreased plasma coagulation factor activity, impaired fibrin formation and crosslinking, and accelerated fibrinolysis. The vast majority of the veterinary literature investigates the hypocoagulable effects of hydroxyethyl starch-containing fluids using in vitro, experimental, and clinical studies. However, results are inconsistent, likely due to the varying doses and physicochemical properties of the specific fluid products across studies. In addition, some evidence exists for hypocoagulable effects of gelatin and albumin solutions. There is also evidence that these colloids increase the risk of clinical bleeding in people. Limitations of the veterinary evidence for the hypocoagulable effects of colloid fluids include a predominance of in vitro studies and in vivo studies using healthy subjects, which exclude the interaction of the effects of illness. Therefore, clinical relevance of these effects, especially for low-molecular-weight hydroxyethyl starch, is unknown. Firm recommendations about the most appropriate fluid to use in clinical scenarios cannot be made, although it is prudent to limit the dose of synthetic colloid in at-risk patients. Clinicians should closely monitor relevant coagulation assays and for evidence of hemorrhage in at-risk patients receiving any type of fluid therapy, especially in large volumes.

The Influence of Perioperative Fluid Therapy on N-terminal-pro-brain Natriuretic Peptide and the Association With Heart and Lung Complications in Patients Undergoing Colorectal Surgery: Secondary Results of a Clinical Randomized Assessor-blinded Multicenter Trial

OBJECTIVE

To investigate the influence of intravenous (iv) fluid volumes on the secretion of N-terminal-pro-brain natriuretic peptide (NT-Pro-BNP) in colorectal surgical patients and its association with cardiopulmonary complications (CPC). In addition, to examine if preoperative NT-Pro-BNP can predict the risk for postoperative CPC.

METHODS

Blood samples from patients enrolled in a previously published clinical randomized assessor-blinded multicenter trial were analyzed. Included were adult patients undergoing elective colorectal surgery with the American-Society-of-Anesthesiologists-scores of 1-3. Samples from 135 patients were available for analysis. Patients were allocated to either a restrictive (R-group) or a standard (S-group) iv-fluid regimen, commencing preoperatively and continuing until discharge. Blood was sampled every morning until the fourth postoperative day. The primary outcome for this study was NT-Pro-BNP changes and its association with fluid therapy and CPC.

RESULTS

The S-group received more iv-fluid than the R-group on the day-of-surgery [milliliter, median (range) 6485 (4401-10750) vs 3730 (2250-8510); P < 0.001] and on the first postoperative day. NT-Pro-BNP was elevated in the S-group compared with the R-group on all postoperative days [area under the curve: median (interquartile range) pg/mL: 3285 (1697-6179) vs 1290 (758-3719); P < 0.001 and in patients developing CPC vs no-CPC (area under the curve), median (interquartile range): 5196 (1823-9061) vs 1934 (831-5301); P = 0.005]. NT-pro-BNP increased with increasing fluid volumes all days (P < 0.003). Preoperative NT-Pro-BNP predicted CPC [odds ratio (confidence interval): 1.573 (0.973-2.541), P = 0.032; positive predictive value = 0.257, negative predictive value = 0.929].

CONCLUSIONS

NT-pro-BNP increases with iv-fluid volumes given to colorectal surgical patients, and the level of NT-Pro-BNP is associated with CPC. Preoperative NT-Pro-BNP is predictive for CPC, but the diagnostic value is low.Clinicaltrials.gov NCT03537989.

Physical Processes in Polymeric Filters Used for Dialysis

The key physical processes in polymeric filters used for the blood purification include transport across the capillary wall and the interaction of blood cells with the polymer membrane surface. Theoretical modeling of membrane transport is an important tool which provides researchers with a quantification of the complex phenomena involved in dialysis. In the paper, we present a dense review of the most successful theoretical approaches to the description of transport across the polymeric membrane wall as well as the cell⁻polymer surface interaction, and refer to the corresponding experimental methods while studying these phenomena in dialyzing filters.

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.

Effect of ringers acetate in different doses on plasma volume in rat models of hypovolemia

Background

Even though crystalloids are the first choice for fluid resuscitation in hemodynamically unstable patients, their potency as plasma volume expanders in hypovolemia of different etiologies is largely unknown. The objective of the study was to investigate dose–response curves of a crystalloid in hypovolemia induced by either sepsis or hemorrhagic shock.

Results

Rats were randomized to resuscitation with Ringers acetate at a dose 10, 30, 50, 75, or 100 ml/kg at 4 h after induction of sepsis by cecal ligation and puncture (CLP) or 2.5 h after a 30 ml/kg hemorrhage. Plasma volume (¹²⁵I–albumin) was the primary outcome. Plasma volume decreased by about 11.8 (IQR 9.9–14.5) ml/kg relative baseline after CLP and increased dose-dependently by at most 5.8 (IQR 3.3–7.0) ml/kg in the 100 ml/kg group at 15 min after resuscitation. In the hemorrhage group, the plasma volume increased by at most 13.8 (IQR 7.1–15.0) ml/kg in 100 ml/kg group. Blood volumes at baseline, calculated using hematocrit and plasma volumes, were 72.4 (IQR 68.2–79.5) ml/kg in sepsis group and 71.1 (IQR 69.1–74.7) ml/kg in hemorrhage group. At 15 min after resuscitation with a dose of 100 ml/kg blood volumes increased to 54.8 (IQR 52.5–57.7) ml/kg and ; 49.6 (IQR 45.3–56.4) ml/kg, in the sepsis and hemorrhage groups, respectively. Plasma volume expansion as the percentage of dose at 15 min was 5.9 (IQR 2.5–8.8)% and 14.5 (IQR 12.1–20.0)% in the sepsis and hemorrhage groups, respectively. At 60 min, average plasma volume as the percentage of dose had decreased to 2.9 (IQR ([−2.9] − 8.3)% (P = 0.006) in the sepsis group whereas no change was detected in the hemorrhage group. A dose-dependent decrease in the plasma oncotic pressure, which was more marked in sepsis, was detected at 60 min after resuscitation.

Conclusions

We conclude that the efficacy of Ringers acetate as a plasma volume expander is context dependent and that plasma volume expansion is lower than previously realized across a wide range of doses. Ringers acetate decreases plasma oncotic pressure in sepsis, in part, by mechanisms other than dilution.

Predicting the Need for Fluid Therapy-Does Fluid Responsiveness Work?

Fluid overdose can be harmful in critically ill patients. Since central venous pressure (CVP) is currently considered to be an inappropriate indicator of preload, much attention is being given to predicting fluid responsiveness, i.e., the response of stroke volume (SV) or cardiac output (CO) to fluid challenge. However, when fluid responsiveness was evaluated in critically ill patients, including sepsis, only 40–50% of the patients responded. Moreover, most fluid responders do not show significant hemodynamic improvement after fluid administration. In this review, we discuss why fluid responsiveness based on the Starling mechanism did not work well in the clinical setting.

According to the Starling mechanism, a patient whose SV/CO significantly increases after a fluid challenge is considered to be a fluid responder and judged to need fluid therapy. However, the currently recommended fluid challenge dose of crystalloid 250–500 mL has little effect on increasing blood volume and is not sufficient to increase the preload of the Starling curve. Especially in septic patients, due to their vascular hyperpermeability, increase in blood volume is even smaller. Furthermore, Infusion induced hemodilution is known to reduce blood viscosity and hematocrit, as a result, decreasing afterload. This indicates that the increased SV/CO after fluid challenge is caused not only by increased preload but also by decreased afterload. For these reasons, fluid responsiveness with small crystalloid challenge is questionable as a clinical indicator of fluid therapy.

Fluid resuscitation in human sepsis: Time to rewrite history?

Fluid resuscitation continues to be recommended as the first-line resuscitative therapy for all patients with severe sepsis and septic shock. The current acceptance of the therapy is based in part on long history and familiarity with its use in the resuscitation of other forms of shock, as well as on an incomplete and incorrect understanding of the pathophysiology of sepsis. Recently, the safety of intravenous fluids in patients with sepsis has been called into question with both prospective and observational data suggesting improved outcomes with less fluid or no fluid. The current evidence for the continued use of fluid resuscitation for sepsis remains contentious with no prospective evidence demonstrating benefit to fluid resuscitation as a therapy in isolation. This article reviews the historical and physiological rationale for the introduction of fluid resuscitation as treatment for sepsis and highlights a number of significant concerns based on current experimental and clinical evidence. The research agenda should focus on the development of hyperdynamic animal sepsis models which more closely mimic human sepsis and on experimental and clinical studies designed to evaluate minimal or no fluid strategies in the resuscitation phase of sepsis.

A rational approach to fluid therapy in sepsis

Aggressive fluid resuscitation to achieve a central venous pressure (CVP) greater than 8 mm Hg has been promoted as the standard of care, in the management of patients with severe sepsis and septic shock. However recent clinical trials have demonstrated that this approach does not improve the outcome of patients with severe sepsis and septic shock. Pathophysiologically, sepsis is characterized by vasoplegia with loss of arterial tone, venodilation with sequestration of blood in the unstressed blood compartment and changes in ventricular function with reduced compliance and reduced preload responsiveness. These data suggest that sepsis is primarily not a volume-depleted state and recent evidence demonstrates that most septic patients are poorly responsive to fluids. Furthermore, almost all of the administered fluid is sequestered in the tissues, resulting in severe oedema in vital organs and, thereby, increasing the risk of organ dysfunction. These data suggest that a physiologic, haemodynamically guided conservative approach to fluid therapy in patients with sepsis would be prudent and would likely reduce the morbidity and improve the outcome of this disease.

Response to fluid boluses in the fluid and catheter treatment trial

BACKGROUND

Recent emphasis has been placed on methods to predict fluid responsiveness, but the usefulness of using fluid boluses to increase cardiac index in critically ill patients with ineffective circulation or oliguria remains unclear.

METHODS

This retrospective analysis investigated hemodynamic responses of critically ill patients in the ARDS Network Fluid and Catheter Treatment Trial (FACTT) who were given protocol-based fluid boluses. Fluid responsiveness was defined as ≥ 15% increase in cardiac index after a 15 mL/kg fluid bolus.

RESULTS

A convenience sample of 127 critically ill patients enrolled in FACTT was analyzed for physiologic responses to 569 protocolized crystalloid or albumin boluses given for shock, low urine output (UOP), or low pulmonary artery occlusion pressure (PAOP). There were significant increases in mean central venous pressure (9.9 ± 4.5 to 11.1 ± 4.8 mm Hg, P < .0001) and mean PAOP (11.6 ± 3.6 to 13.3 ± 4.3 mm Hg, P < .0001) following fluid boluses. However, there were no significant changes in UOP, and there were clinically small changes in heart rate, mean arterial pressure, and cardiac index. Only 23% of fluid boluses led to a ≥ 15% change in cardiac index. There was no significant difference in the frequency of fluid responsiveness between boluses given for shock or oliguria vs boluses given only for low PAOP (24.0% vs 21.8%, P = .59). There were no significant differences in 90-day survival, need for hemodialysis, or return to unassisted breathing between patients defined as fluid responders and fluid nonresponders.

CONCLUSIONS

In this cohort of critically ill patients with ARDS who were previously resuscitated, the rate of fluid responsiveness was low, and fluid boluses only led to small hemodynamic changes.

A distributed two-pore model: theoretical implications and practical application to the glomerular sieving of Ficoll

In the present study, an extended two-pore theory is presented where the porous pathways are continuously distributed according to small- and large-pore mean radii and SDs. Experimental glomerular sieving data for Ficoll were analyzed using the model. In addition, several theoretical findings are presented along with analytic solutions to many of the equations used in distributed pore modeling. The results of the data analysis revealed a small-pore population in the glomerular capillary wall with a mean radius of 36.6 Å having a wide arithmetic SD of ∼5 Å and a large-pore radius of 98.6 Å with an even wider SD of ∼44 Å. The small-pore radius obtained in the analysis was close to that of human serum albumin (35.5 Å). By reanalyzing the data and setting the distribution spread of the model constant, we discovered that a narrow distribution is compensated by an increased mean pore radius and a decreased pore area-to-diffusion length ratio. The wide distribution of pore sizes obtained in the present analysis, even when considering electrostatic hindrance due to the negatively charged barrier, is inconsistent with the high selectivity to proteins typically characterizing the glomerular filtration barrier. We therefore hypothesize that a large portion of the variance in the distribution of pore sizes obtained is due to the molecular “flexibility” of Ficoll, implying that the true variance of the pore system is lower than that obtained using flexible probes. This would also, in part, explain the commonly noted discrepancy between the pore area-to-diffusion length ratio and the filtration coefficient.