Oncotic Properties Research Articles

A randomized-controlled trial comparing 20% albumin to plasmalyte in patients with cirrhosis and sepsis-induced hypotension [ALPS trial

The choice of resuscitation fluid in patients with cirrhosis and sepsis-induced hypotension is unclear. 5% albumin was superior to normal saline in the FRISC study. We compared the efficacy and safety of 20% albumin, which has greater oncotic properties, to plasmalyte in reversing sepsis-induced hypotension. Critically ill patients with cirrhosis underwent open-label randomization to receive either 20% albumin (0.5-1.0g/kg over 3 hours; n= 50) or plasmalyte (30ml/kg over 3 hours, n= 50). The primary endpoint of the study was the attainment of mean arterial pressure (MAP) above 65mmHg at 3 hours. Baseline characteristics were comparable in albumin and plasmalyte groups; arterial lactate (6.16±3.18mmol/L vs. 6.38±4.77mmol/L; p= 0.78), MAP (51.4±6.52mmHg vs. 49.9±4.45mmHg; p= 0.17) and SOFA score (10.8±2.96 vs. 11.1±4.2; p= 0.68), respectively. Most patients were alcoholics (39%) and had pneumonia (40%). In the intention-to-treat analysis, albumin was superior to plasmalyte in achieving the primary endpoint (62% vs. 22%; p <0.001). A faster decline in arterial lactate (p= 0.03), a reduced need for dialysis (48% vs. 62%; p= 0.16), and a longer time to initiation of dialysis (in hours) (68.13±47.79 vs. 99.7± 63.4; p= 0.06) were seen with albumin. However, the 28-day mortality rate was not different (58% vs. 62%, p= 0.57) and treatment had to be discontinued in 11 (22%) patients in the albumin group due to adverse effects compared to no discontinuations in the plasmalyte group. In patients with cirrhosis and sepsis-induced hypotension, 20% albumin leads to a faster improvement in hemodynamics and lactate clearance than plasmalyte, while 28-day survival was similar. However, patients on 20% albumin need to be closely monitored as it was more often associated with pulmonary complications. NCT02721238. The current randomized-controlled trial performed in critically ill patients with cirrhosis and sepsis-induced hypotension highlights that 20% albumin restores arterial pressure more quickly but causes more pulmonary complications than plasmalyte. The impact on renal functions was also modest. These effects did not result in improvement in survival at 28 days. Plasmalyte is safer and well-tolerated and can be considered for volume resuscitation in patients with cirrhosis and sepsis-induced hypotension.

Structure and Functions of Human Serum Albumin in Normal Conditions and in Patients with Liver Cirrhosis

The aim: to highlight the main points of albumin synthesis, posttranslational modifications and functions in normal conditions and in patients with liver cirrhosis.Key points. Albumin is the most abundant protein in blood plasma. Along with oncotic properties, albumin performs transport, antioxidant, immunomodulatory and endothelioprotective functions. Serum albumin in patient with liver cirrhosis undergoes modifications, leading to functional impairment. Human serum albumin is a compaund of human mercaptalbumin with cysteine residues having a reducing ability, and oxidized human non-mercaptalbumin. The proportion of irreversibly oxidized non-mercaptalbumin-2 with impaired functional activity increases in liver cirrhosis.Conclusion. The conformational structure of the albumin molecule plays an important role in maintaining its non-oncotic functions. Non-oncotic functions depend on albumin conformation. Further investigation of albumin conformation and albumin functions in patients with hepatic insufficiency can serve as an additional criterion for assessing the severity of cirrhosis and predictor of complications may become an additional criterion to new clinical applications and treatment strategies of liver failure.

From the Editor’s Desk…

From the Editor’s Desk…

Albumin Substitution in Decompensated Liver Cirrhosis: Don't Forget Zinc.

Decompensated liver cirrhosis has a dismal prognosis, with patients surviving on average for 2–4 years after the first diagnosis of ascites. Albumin is an important tool in the therapy of cirrhotic ascites. By virtue of its oncotic properties, it reduces the risk of cardiovascular dysfunction after paracentesis. Treatment with albumin also counteracts the development of hepatorenal syndrome and spontaneous bacterial peritonitis. More recently, the positive impact of long-term albumin supplementation in liver disease, based on its pleiotropic non-oncotic activities, has been recognized. These include transport of endo- and exogenous substances, anti-inflammatory, antioxidant and immunomodulatory activities, and stabilizing effects on the endothelium. Besides the growing recognition that effective albumin therapy requires adjustment of the plasma level to normal physiological values, the search for substances with adjuvant activities is becoming increasingly important. More than 75% of patients with decompensated liver cirrhosis do not only present with hypoalbuminemia but also with zinc deficiency. There is a close relationship between albumin and the essential trace element zinc. First and foremost, albumin is the main carrier of zinc in plasma, and is hence critical for systemic distribution of zinc. In this review, we discuss important functions of albumin in the context of metabolic, immunological, oxidative, transport, and distribution processes, alongside crucial functions and effects of zinc and their mutual dependencies. In particular, we focus on the major role of chronic inflammatory processes in pathogenesis and progression of liver cirrhosis and how albumin therapy and zinc supplementation may affect these processes.

Intravenous Albumin for Mitigating Hypotension and Augmenting Ultrafiltration during Kidney Replacement Therapy.

Among its many functions, owing to its oversized effect on colloid oncotic pressure, intravascular albumin helps preserve the effective circulatory volume. Hypoalbuminemia is common in hospitalized patients and is found especially frequently in patients who require KRT either for AKI or as maintenance hemodialysis. In such patients, hypoalbuminemia is strongly associated with morbidity, intradialytic hypotension, and mortality. Intravenous albumin may be administered in an effort to prevent or treat hypotension or to augment fluid removal, but this practice is controversial. Theoretically, intravenous albumin administration might prevent or treat hypotension by promoting plasma refilling in response to ultrafiltration. However, clinical trials have demonstrated that albumin administration is not nearly as effective a volume expander as might be assumed according to its oncotic properties. Although intravenous albumin is generally considered to be safe, it is also very expensive. In addition, there are potential risks to using it to prevent or treat intradialytic hypotension. Some recent studies have suggested that hyperoncotic albumin solutions may precipitate or worsen AKI in patients with sepsis or shock; however, the overall evidence supporting this effect is weak. In this review, we explore the theoretical benefits and risks of using intravenous albumin to mitigate intradialytic hypotension and/or enhance ultrafiltration and summarize the current evidence relating to this practice. This includes studies relevant to its use in patients on maintenance hemodialysis and critically ill patients with AKI who require KRT in the intensive care unit. Despite evidence of its frequent use and high costs, at present, there are minimal data that support the routine use of intravenous albumin during KRT. As such, adequately powered trials to evaluate the efficacy of intravenous albumin in this setting are clearly needed.

Effects of Sanguinate on Systemic and Microcirculatory Variables in a Model of Prolonged Hemorrhagic Shock

Hemorrhage and its complications are the leading cause of preventable death from trauma in young adults, especially in remote locations. To address this, deliverable, shelf-stable resuscitants that provide therapeutic benefits throughout the time course of hemorrhagic shock and the progressive ischemic injury it produces are needed. SANGUINATE is a novel bovine PEGylated carboxyhemoglobin-based oxygen carrier, which has desirable oxygen-carrying and oncotic properties as well as a CO moiety to maintain microvascular perfusion. To compare the crystalloid (Lactated Ringer's Solution; LRS), and the colloid (Hextend) standards of care with SANGUINATE in a post "golden hour" resuscitation model. Rats underwent a controlled, stepwise blood withdrawal (45% by volume), were maintained in untreated hemorrhagic shock state for >60 min, resuscitated with a 20% bolus of one of the three test solutions, and observed till demise. Parameters of tissue oxygenation (PISFO2), arteriolar diameters, and mean arterial pressure (MAP) were collected. SANGUINATE-treated animals survived significantly longer than those treated with Hextend and LRS. SANGUINATE also significantly increased tissue PISFO2 2 h after resuscitation, whereas LRS and Hextend did not. SANGUINATE also produced a significantly higher MAP, which was hypotensive compared to baseline, that endured until demise. Resuscitation with SANGUINATE after prolonged hemorrhagic shock improves survival, MAP, and PISFO2 compared with standard of care plasma expanders. Since the pathologies of hemorrhagic shock and the associated systemic ischemia are progressive, preclinical studies of this nature are essential to determine efficacy of new resuscitants across the range of possible times to treatment.

Human albumin solution for patients with cirrhosis and acute on chronic liver failure: Beyond simple volume expansion.

To provide an overview of the properties of human serum albumin (HSA), and to review the evidence for the use of human albumin solution (HAS) in critical illness, sepsis and cirrhosis. A MEDLINE search was performed using the terms "human albumin", "critical illness", "sepsis" and "cirrhosis". The references of retrieved articles were reviewed manually. Studies published between 1980 and 2014 were selected based on quality criteria. Data extraction was performed by all authors. HSA is the main plasma protein contributing greatly to its oncotic pressure. HSA demonstrates important binding properties for endogenous and exogenous toxins, drugs and drug metabolites that account for its anti-oxidant and anti-inflammatory properties. In disease states, hypoalbuminaemia is secondary to decreased HSA production, increased loss or transcapillary leakage into the interstitial space. HSA function can be also altered in disease with reduced albumin binding capacity and increased production of modified isoforms. HAS has been used as volume expander in critical illness, but received criticism due to cost and concerns regarding safety. More recent studies confirmed the safety of HAS, but failed to show any survival benefit compared to the cheaper crystalloid fluids, therefore limiting its use. On the contrary, in cirrhosis there is robust data to support the efficacy of HAS for the prevention of circulatory dysfunction post-large volume paracentesis and in the context of spontaneous bacterial peritonitis, and for the treatment of hepato-renal syndrome and hypervolaemic hyponatraemia. It is likely that not only the oncotic properties of HAS are beneficial in cirrhosis, but also its functional properties, as HAS replaces the dysfunctional HSA. The role of HAS as the resuscitation fluid of choice in critically ill patients with cirrhosis, beyond the established indications for HAS use, should be addressed in future studies.

Developmental toxicity in rats of a hemoglobin-based oxygen carrier results from impeded function of the inverted visceral yolk sac.

HBOC-201 is a bovine-derived, cross-linked, and stabilized hemoglobin (250kDa) in physiological saline. Daily intravenous infusions of HBOC (1.95, 3.90, or 5.85g/kg/day) during gestational days (GDs) 6-18 in Sprague-Dawley rats caused fetal mortality, reduced birth weight, and malformations. Subsequent single-day infusions (5.85g/kg/day) showed that developmental toxicity was limited to GDs 7-9 when histiotrophic nutrition via the inverted visceral yolk sac (invVYS) is essential. Histiotrophic nutrition is receptor-mediated endocytosis of bulk maternal proteins and subsequent lysosomal degradation providing amino acids and other nutrients for embryonic growth. Controls for protein content, oncotic properties, and hemoglobin content indicated that toxicity was due to hemoglobin. Rat whole embryo cultures verified HBOC interference with invVYS transport capacity and resultant deficient embryonic nutrition. These mechanisms of action are not expected to impact human development based on differences in VYS morphology and function, although a complete understanding of early human embryonic nutrition is lacking.

Hepatology Highlights

Hepatology Highlights

Immunomodulatory and antioxidant function of albumin stabilises the endothelium and improves survival in a rodent model of chronic liver failure

Liver failure is characterized by endothelial dysfunction, which results in hemodynamic disturbances leading to renal failure. Albumin infusion improves hemodynamics and prevents renal dysfunction in advance liver failure. These effects are only partly explained by the oncotic properties of albumin. This study was designed to test the hypothesis that albumin exerts its beneficial effects by stabilising endothelial function. In vivo: systemic hemodynamics, renal function, markers of endothelial dysfunction (ADMA) and inflammation were studied in analbuminaemic and Sprague-Dawley rats, 6-weeks after sham/bile duct ligation surgery. In vitro: human umbilical vein endothelial cells were stimulated with LPS with or without albumin. We studied protein expression and gene expression of adhesion molecules, intracellular reactive oxygen species, and cell stress markers. Compared to controls, analbuminaemic rats had significantly greater hemodynamic deterioration after bile duct ligation, resulting in worse renal function and shorter survival. This was associated with significantly greater plasma renin activity, worse endothelial function, and disturbed inflammatory response. In vitro studies showed that albumin was actively taken up by endothelial cells. Incubation of albumin pre-treated endothelial cells with LPS was associated with significantly less activation compared with untreated cells, decreased intracellular reactive oxygen species, and markers of cell stress. These results show, for the first time, that absence of albumin is characterised by worse systemic hemodynamics, renal function and higher mortality in a rodent model of chronic liver failure and illustrates the important non-oncotic properties of albumin in protecting against endothelial dysfunction.

Albumin Regeneration for Extracorporeal Liver Support Using Prometheus: A Step in the Right Direction

Albumin Regeneration for Extracorporeal Liver Support Using Prometheus: A Step in the Right Direction

Vasoactive Properties of Keratin-Derived Compounds

Keratin proteins have been utilized as biomaterials for decades, and are currently under investigation for a variety of tissue regeneration and trauma applications. It has been suggested that certain keratins may have the capacity to act as a colloid in fluid resuscitation applications, providing viscosity and oncotic properties that may be beneficial during acute ischemic events. Oxidized keratin derivatives, also known as keratoses, show good blood and cardiovascular compatibility and thus are the subject of this study. The effects of keratose compounds will be assessed using a topload i.v. infusion model and observation of changes in the microvasculature of the cremaster muscle of rats. Keratose resuscitation fluid (KRF) administration resulted in significant vasodilation in the cremaster muscle. This effect was blocked with pretreatment of l-NA to inhibit NO. Another keratin fraction, alpha-keratose, which is the primary viscosic compound, was not found to induce vasodilation. The apparent mechanism of vasodilation was found to be NO-mediated and isolated to a particular purified fraction, the KAP.

Resuscitation with hyperoncotic colloids in the intensive care unit

Sir, Artificial colloids display nephrotoxicity, and the pathophysiological mechanisms are of considerable clinical interest [1]. In a cohort study report, Schortgen and collaborators [2] pose the question whether ‘‘highoncotic forces rather than the chemical nature of fluids have a deleterious effect on renal function’’. Unfortunately, the question is left unanswered. The study population of 1,013 intensive care unit patients was divided into four groups according to whether they received (1) crystalloids only, (2) hypo-oncotic colloids (gelatins and/or 4% albumin) with or without crystalloids, (3) artificial hyperoncotic colloids with or without crystalloids or hypo-oncotic colloids, or (4) hyperoncotic 20–25% albumin with or without crystalloids or other colloids. Dextrans and/or hydroxyethyl starches (HES) were placed in the hyperoncotic artificial colloid category. This classification scheme of itself already makes the study uninterpretable. The in vitro colloid osmotic pressure (COP) of human plasma is approximately 28 mmHg, and resuscitation fluids of comparable in vitro COP expand the intravascular space by roughly 100% of the administered volume. Such fluids are iso-oncotic. Concentration is a powerful determinant of oncotic properties. All 6% HES solutions, regardless of molecular weight and substitution, are essentially isooncotic, whereas 10% HES with an in vitro COP of 80 mmHg is hyperoncotic [3]. Therefore, the designated artificial hyperoncotic colloid group evidently received an unspecified mixture of isoand hyperoncotic fluid. Oncotic forces in vivo will also heavily depend on the volumes and properties of co-administered fluids. There was no accounting for concomitant crystalloid used in the three colloid groups or of other colloids with different oncotic properties in the two hyperoncotic colloid groups. Crucially, the plasma COP after fluid infusion was not measured. Consequently, the actual oncotic forces at work in patients remained totally undefined. Further confounding interpretation was clear bias in fluid selection. Hyperoncotic colloids were reserved for the sickest patients, as evidenced by significantly greater organ dysfunction, high-dose vasopressor use and need for mechanical ventilation at study entry. Multivariate adjustment and propensity scores were applied, but these methods cannot correct for unmeasured variables, and numerous known independent risk factors for acute renal failure (ARF) were not evaluated in this study. Indeed randomized trial evidence makes plain that the attempts to adjust for bias were unsuccessful. Thus, Schortgen et al. observed poorer renal function and increased mortality in the hyperoncotic albumin group. In contrast, in a recent metaanalysis of 25 randomized clinical trials evaluating hyperoncotic albumin for volume expansion among 1,485 total patients, there was no evidence of renal injury due to hyperoncotic albumin and no effect on survival (relative risk 0.95; 95% confidence interval 0.78–1.17) [4]. Available evidence shows that the type of fluid can govern renal effects irrespective of oncotic properties per se. For example, in randomized trials both isoand hyperoncotic HES solutions have increased the incidence of ARF in patients with severe sepsis or septic shock [5]. Conversely, in model system studies and clinical trials albumin solutions, including hyperoncotic albumin, have displayed renoprotective activity [1, 4]. Further mechanistic studies are needed to define more precisely the effects of colloids on the kidney.

Phase III Trials Required to Resolve Clinical Equipoise over Optimal Fluid Management in Children with Severe Malaria

There is a consensus among paediatricians that outcome of children presenting with life-threatening infections, irrespective of the infecting pathogen, can be improved by timely recognition and prompt intervention to correct disordered physiology using simple approaches to resuscitation [1–3]. These approaches include the provision of oxygen and the correction of fluid, electrolyte, and glucose deficits [4,5]. Indeed, studies have shown that most of the recent gains in survival of children with severe infections have come through the application of this approach by non-specialists during the initial hours of management [6,7]. Correction of hypotension and volume depletion through fluid administration is a fundamental component of resuscitation in most critically ill children [8,9], but its role in severe malaria remains uncertain and thus represents one of the most important theoretical gaps in our understanding of supportive treatments in this condition. Many children with severe malaria have signs of cardiovascular compromise or compensated shock on presentation to hospital and a smaller proportion are hypotensive [10]. One of the major unresolved aspects of management is whether volume expansion should be undertaken in children displaying signs of compensated shock, as is recommended in other paediatric disorders. Intravascular volume depletion (hypovolaemic shock) results in impaired cardiovascular function and inadequate tissue and organ perfusion, and would usually be corrected rapidly. Simple dehydration, predominantly affecting the intracellular compartment, can be safely corrected gradually. The choice of the optimum fluid for resuscitation is also unclear. Colloidal solutions, although more costly, are less likely to precipitate cerebral and pulmonary oedema due to their oncotic properties. Recognising the importance of adequate fluid management to the outcome of the critically ill child, the group at Kilifi has conducted a staged series of studies over the last 15 years to address each of these questions. In a collaboration that included specialists in paediatric intensive care, neurology, and clinical trials, the group demonstrated the importance, prognostic implications [11], and clinical correlates of metabolic acidosis in children with severe malaria [12] and provided clear evidence of intravascular hypovolaemia by using standard methods for studying critical illness [13]. We have undertaken two randomised trials to assess the safety of and response to volume expansion, and to determine whether colloid replacement offers any advantage over crystalloid replacement [13,14]. We hypothesised that administration of colloids such as human albumin solution with volume expansion would help to retain fluid in the intravascular compartment and may also improve endothelial function. In each of these trials we observed that albumin administration was associated with a lower mortality than saline. Although this data suggested the need for a large clinical trial of albumin, in view of the cost of albumin we thought that cheaper synthetic colloids should be assessed before embarking on a phase III trial. The intention in the small phase II trial, recently published in PLoS Clinical Trials [15], was to provide sufficient physiological data on succinylated gelatin to inform the design of the next phase, rather than to establish statistical superiority of one colloid over the other. For this purpose the trial was most instructive. Again we observed the same benefits of albumin: only one child who received albumin died, out of a group of participants that included children treated as emergencies who were subsequently found to be ineligible for the trial. The results for Gelofusine, however, were not encouraging. The combined findings that death, severe allergic reaction, and acute neurological events were more common in the Gelofusine group suggested that albumin, rather than a cheaper substitute, should be taken forward into the next phase. This was supported by the analysis of the combined data from three trials, including 238 children receiving volume expansion. While this small phase II study was not powered to prove that Gelofusine was superior to saline or albumin, the results suggest that Gelofusine is unlikely to offer any advantage over the cheaper saline solution. Given the continued controversy over the use of resuscitation fluids in the management of severe malaria, we suggest that this can only be resolved through a definitive clinical trial. Woodrow and Planche [16] have chosen a different interpretation. The evidence presented from two studies conducted in Gabon, one which assessed volume depletion in only 12 survivors [17] and the other larger study conducted in less critically unwell children [18], supports a position of equipoise—the basis which usually prompts the need for a definitive clinical trial.

Preclinical biology of recombinant human hemoglobin, rHb1.1.

Historically, the development of hemoglobin based oxygen carriers, HBOCs, were confounded by issues related to activation of the complement cascade and other inflammatory processes, renal toxicity, and significant systemic vasoconstriction. However, with shortages in the blood supply, the risk of infectious agent contamination, and delays associated with complete crossmatch as well as transfusion reactions, HBOC development has assumed greater importance. A successful HBOC in addition to having favorable oxygen binding parameters and colloid oncotic properties, must also have a low toxicity profile, be nonimmunogenic, have positive rheologic properties, and have an adequate in vivo half life. In addition, it must also be stable in vivo and not undergo significant oxidation to methemoglobin or release heme or iron in the vasculature. The preclinical studies which have been designed and executed to address these requirements for recombinant human hemoglobin rHb1.1 serve as the focus of this review. Recombinant Hb1.1 represents the first HBOC to enter clinical trials as a recombinant product in distinction to other HBOCs which are derived from bovine or outdated human blood. While currently in phase II clinical trials, the preclinical biology which has increased our understanding of this molecule are the subject of this review.

Pulmonary Vascular Filtration of Starch-Based Macromolecules: Effects on Lung Fluid Balance

Background: Pulmonary edema is a complication of critical care fluid management that may be restricted by the use of oncotically effective resuscitation fluids. Potentially beneficial oncotic properties of starch-based plasma volume expanders such as hetastarch (Het), pentafraction (Pen), and Dextran-70 (Dex) may be compromised by their broad range of molecular masses, some of which are small enough to filter from the circulation. Leakage of these molecules into the pulmonary interstitium may limit their oncotic effectiveness and enhance fluid filtration. We measured the filtration of these three resuscitation solutions into lung lymph to evaluate their oncotic contribution to pulmonary edema formation. Materials and Methods: Unanesthetized euvolemic adult sheep, prepared with chronic lung lymph fistulae, underwent plasma volume expansion with Het (n= 6), Pen (n= 6), or Dex (n= 6 ) (6%, 35 ml/kg/90 min). Oncotic effectiveness was determined by measuring plasma and lymph oncotic pressures and the oncotic pressures contributed by each starch. Pulmonary hydrostatic pressures and lung lymph flows (QL) were also measured. Results are expressed as means ± SEM. Comparisons were made by two-factor analysis of variance. Results: Dex contributed 9.0 ± 0.9 mmHg to the plasma oncotic pressure, significantly more than Het and Pen (5.3 ± 0.6, 6.5 ± 0.6 mmHg, respectively). However, Dex filtration also contributed 6.1 ± 0.5 mmHg to the lymph oncotic pressure, compared to 3.1 ± 0.3 and 4.7 ± 0.5 mmHg for Het and Pen, respectively (P≤ 0.05). Dex, Het, and Pen raisedQLover baseline by 7.7 ± 1.5, 4.3 ± 1.0, and 3.2 ± 0.7 ml/30 min, respectively (P≤ 0.05). Dex increasedQLsignificantly more than Het or Pen. Conclusions: Pen and Het demonstrated greater oncotic effectiveness because of restricted plasma-to-lymph macromolecular filtration and limited transvascular fluid flux. By comparison, Dex filtered rapidly and increased transvascular fluid filtration. Pen appears to possess filtration properties that optimize critical care fluid management compared to currently available colloid solutions such as Het and Dex.

Protein concentrations have little effect on reabsorption of fluid from isolated rat lungs

A study was conducted to determine whether differences in the concentrations of large molecules between the air space and perfusate solutions altered the rates at which fluid was reabsorbed from isolated fluid-filled perfused rat lungs. Four groups of experiments were conducted: 1) 5 g/dl albumin in the air spaces and perfusate, 2) 15 g/dl albumin in the air space and 5 g/dl albumin in the perfusate, 3) 5 g/dl albumin in the air space and 15 g/dl albumin in the perfusate, and 4) a mixture of 5 g/dl albumin and 7 g/dl Dextran 70 in the air spaces and 5 g/dl albumin in the perfusate. Fluid reabsorption was determined by following the concentration of albumin labeled with Evans blue (T-1824) in the air space and perfusate compartments. Because leakage of protein between the air space and perfusate compartments is very slow, increases in T-1824 concentrations in the air spaces indicated loss of fluid from this compartment, whereas decreases in these concentrations in the perfusate compartment provided evidence of fluid transport into the vasculature. Approximately 30% of the air space fluid was reabsorbed in a 2-h period, and virtually all of this fluid reached the perfusate compartment. Despite oncotic differences that ranged from -65 to 65 Torr, variations in air space or perfusate albumin concentrations did not have a significant effect on this process. A 30% decrease in fluid reabsorption was observed when dextran was in the air space solution, but this decrease did not appear to be due to the oncotic properties of this solution because albumin did not have a measurable effect on reabsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydroxyethyl Starch Pretreatment in Bacteremic Sheep

Live bacteria were infused in a chronic ovine lung lymph model to determine if a preceding infusion of the colloid, hydroxyethyl starch (HES), exaggerated the cardiopulmonary dysfunction or impaired removal of bacteria by macrophages in the pulmonary circulation. HES was infused (3 mL/kg/hr; n = 6) from 24 to 12 hr before the bacteria and decreased plasma protein content and increased pulmonary lymph to plasma protein concentration because of its oncotic properties. Ringer's lactate (2 mL/kg/hr) was given after stopping HES and also to the control group (n = 6). Infusion of live Ps. aeruginosa (2.5 x 10(8) Ps./min for approximately 30 min) induced equivalent pulmonary hypertension, increased pulmonary microvascular permeability, and cardiovascular depression in the two groups. The removal of bacteria in the lungs was not affected, indicating that this measurement of the function of the mononuclear phagocytic system was not impaired by the preceding HES.

Hypothermic preservation of hepatocytes: I. Role of cell swelling

Hepatocytes from isolated rat livers were hypothermically incubated (5 °C) in an oxygenated environment with continuous shaking (to simulate organ perfusion preservation). The incubation solution was either a tissue culture medium (L-15), an organ preservation perfusate (UW gluconate), or a simple cold-storage solution used for organ preservation (UW lactobionate). Hepatocyte viability was assessed from the release of lactate dehydrogenase (LDH) into the incubation medium. Cell swelling (due to the uptake of water) was also measured. Within 24 hr, hepatocytes hypothermically stored in each of the three incubation solutions became swollen (30 to 40% water gain) and lost a significant amount of LDH (as much as 60%). The addition of polyethylene glycol (PEG; relative molecular mass 8000; 5 g%) to the solutions suppressed cell swelling and allowed the incubated hepatocytes to remain relatively well preserved (30% LDH release) for as long as 120 hr. Adding either dextran (relative molecular mass 10,000 to 78,000; 5 g%) or saccharides (100 mmol/liter) instead of PEG neither prevented cell swelling nor prevented the cells from dying. The results of this study suggest (i) there is a direct correlation ( r = 0.873) between hypothermia-induced cell swelling and cell death (i.e., the suppression of cell swelling prevents cell death); (ii) the mechanism by which PEG prevents cell swelling (and thus maintains cell viability) is not related to the osmotic or oncotic properties of the molecule but instead is apparently related to some unknown interaction between PEG and the cell, an interaction that provides stability during hypothermie incubation; and (iii) hypothermia-induced cell swelling must be prevented if isolated hepatocytes are to be used as a model for studying the mechanism by which cell damage occurs during hypothermic organ preservation. By eliminating cell death due to cell swelling, the biochemical mechanisms of cell death can be studied.

Pathophysiological aspects of blood-brain barrier disturbances in experimental brain tumors and brain abscesses.

Experimental tumors and abscesses were produced by intrahemispheric inoculation of a blastomatous glial cell clone and of staphylococcus aureus, respectively. In both models severe vasogenic brain edema developed. The site of the barrier lesion was identified by systemic application of Evans blue or peroxidase, and the spread of edema by immunoautoradiographic localisation of extravasated serum proteins. In both experimental conditions, serum proteins accumulated diffusely in the white matter of the ipsilateral hemisphere, although the barrier lesion was strictly confined to the pathological focus. Water content of the edematous white matter in the vicinity of tumors and abscesses increased from 69.1 to 80.6 and 82.3 ml/100g w.w., respectively. This increase was associated with a volume-dependent decrease of flow, a parallel increase of sodium and an increase of extravasated serum proteins. The latter was determined by a newly developed immunochemical approach with appropriate corrections for the intravascular fraction of total serum protein content. The calculated concentration of sodium in edema fluid of tumors and abscesses amounted to 132 and 129 ueq/ml, respectively. The concentration of serum proteins was 8.7 and 6.4 mg/ml, respectively. Protein content of edema fluid, in consequence was less than 10% of blood serum. This suggests that fluid accumulation in vasogenic edema cannot be explained by the oncotic properties of extravasated proteins alone.