Effects of acetate on energy metabolism and function in the isolated perfused rat heart

Metabolic Considerations in Direct Procurement and Perfusion Protocols with DCD Heart Transplantation

Heart transplantation with donation after circulatory death (DCD) provides excellent patient outcomes and increases donor heart availability. However, unlike conventional grafts obtained through donation after brain death, DCD cardiac grafts are not only exposed to warm, unprotected ischemia, but also to a potentially damaging pre-ischemic phase after withdrawal of life-sustaining therapy (WLST). In this review, we aim to bring together knowledge about changes in cardiac energy metabolism and its regulation that occur in DCD donors during WLST, circulatory arrest, and following the onset of warm ischemia. Acute metabolic, hemodynamic, and biochemical changes in the DCD donor expose hearts to high circulating catecholamines, hypoxia, and warm ischemia, all of which can negatively impact the heart. Further metabolic changes and cellular damage occur with reperfusion. The altered energy substrate availability prior to organ procurement likely plays an important role in graft quality and post-ischemic cardiac recovery. These aspects should, therefore, be considered in clinical protocols, as well as in pre-clinical DCD models. Notably, interventions prior to graft procurement are limited for ethical reasons in DCD donors; thus, it is important to understand these mechanisms to optimize conditions during initial reperfusion in concert with graft evaluation and re-evaluation for the purpose of tailoring and adjusting therapies and ensuring optimal graft quality for transplantation.

Acetate suppresses myocardial contraction via the short-chain fatty acid receptor GPR43

The heart has high energy requirements, with an estimated 40%-60% of myocardial ATP production derived from the oxidation of fatty acids under physiological conditions. However, the effect of short-chain fatty acids on myocardial contraction remains controversial, warranting further research. The present study sought to investigate the effects and mechanisms of acetate, a short-chain fatty acid, on myocardial contraction in rat ventricular myocytes. Echocardiography and Langendorff heart perfusion were used to evaluate cardiac function. Cell shortening and calcium transient were measured in isolated cardiomyocytes. The patch-clamp method determined the action potential and L-type Ca²⁺ current in cardiomyocytes. Moreover, the expression of GPR43, a type of short-chain fatty acid receptors in cardiomyocytes was examined by immunofluorescent staining and Western blot. We demonstrated that acetate transiently reduced left ventricular developmental pressure in isolated Langendorff heart perfusion model, with no effect on stroke volume and cardiac output in vivo. In addition, acetate transiently and reversibly inhibited cardiomyocyte contraction and calcium transient. Acetate did not affect the action potential and L-type Ca²⁺ currents in cardiomyocytes. As a short-chain fatty acid receptor, GPR43 was expressed in rat cardiomyocytes. Furthermore, the GPR43 antagonist GLPG0974 prevented the acetate-induced inhibitory effect on myocardial contraction. We conclude that acetate transiently inhibits contraction via the short-chain fatty acid receptor GPR43 in cardiomyocytes.

Acetate- versus lactate-buffered crystalloid solutions: A systematic review with meta-analysis and trial sequential analysis

OBJECTIVE

There is a widespread use of buffered crystalloid solutions in clinical practice. However, guidelines do not distinguish between specific types of buffered solutions and clinical equipoise exists. We aimed to assess the desirable and undesirable effects of acetate- versus lactate-buffered solutions in hospitalised patients.

METHODS

We conducted a systematic review with meta-analysis and trial sequential analysis of randomised clinical trials assessing the use of acetate- versus lactate-buffered solutions for intravenous administration in hospitalised adults and children. The primary outcome was all-cause short-term mortality. We adhered to our published protocol, the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement, the Cochrane Handbook and the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methodology.

RESULTS

We included five RCTs enrolling 390 patients. We found no statistically significant difference in short-term mortality (random effects, risk ratio [RR] 0.29; 95% confidence interval [CI] 0.06-1.51, p = .14, I2  = 0%) or hospital length of stay (LOS) (random effects, mean difference [MD]-1.31, 95% CI -3.66 to 1.05, p = .28, I2  = 0%) between acetate- versus lactate-buffered solutions. The quality of evidence was very low. Data regarding intensive care unit LOS were reported by three trials and duration of vasopressor treatment by one trial; none of these data allowed for pooling in meta-analyses. No trials reported data on long-term mortality, health-related quality of life, adverse events, duration of mechanical ventilation or renal replacement therapy.

CONCLUSION

In this systematic review, we found very low quantity and quality of evidence on the use of acetate- versus lactate-buffered solutions in hospitalised patients.

The Efficacy and Safety of Sodium Bicarbonate Ringer's Solution in Critically Ill Patients: A Retrospective Cohort Study

Background: Sodium bicarbonate Ringer’s solution has been widely used in clinical practice in recent years. There are few clinical studies on the efficacy and safety of this fluid among critically ill patients until now.

Method: This retrospective cohort study included critically ill adult patients in the intensive care unit (ICU) of Tongji Hospital from 1 January 2019 to 31 December 2020. By reviewing exclusively the use of either sodium bicarbonate Ringer’s solution or saline for resuscitation or maintenance, the patients were included into two groups, respectively. The primary outcome was the major adverse kidney event within 30 days (MAKE30), including death, new receipt of renal replacement therapy, or persistent renal dysfunction. Safety outcomes were focused on arterial blood gas and plasma biochemical alterations, which might potentially be induced by the administration of bicarbonate Ringer’s solution.

Result: A total of 662 patients were included in the cohort. Compared to the saline group, the bicarbonate Ringer’s group had a significantly lower rate of the new receipt of renal replacement therapy [adjusted odds ratio (OR) = 0.591, 95% confidence interval (CI), 0.406 to 0.861; p = 0.006]. There was no significant difference between the two groups in 30-day mortality, final creatinine level ≥200% of baseline, and major adverse kidney event within 30 days. In subgroup analysis, the incidence of MAKE30 was higher in the bicarbonate Ringer’s group than that of the saline group among patients with cardiovascular disease. The patients in the bicarbonate Ringer’s group had a longer length of intensive care unit stay than patients in the saline group, but their new renal replacement therapy days were shorter. No major alterations were found in arterial blood gas and plasma biochemical during the follow-up period.

Conclusion: Compared to saline, sodium bicarbonate Ringer’s solution exhibited a potential renal function protective effect while causing no major alterations in arterial blood gas and plasma biochemistry. However, the application in patients with cardiovascular disease diagnosis at ICU admission should be cautious.

Noninvasive assessment of myocardial energy metabolism and dynamics using in vivo deuterium MRS imaging

PURPOSE

The assessment of cellular energy metabolism is crucial for understanding myocardial physiopathology. Here, we conducted a pilot study to develop an alternative imaging approach for the assessment of myocardial energy metabolism.

METHODS

We developed a deuterium MRSI method to noninvasively monitor the accumulation of deuterated downstream metabolites and deuterated water in rat hearts infused with deuterated glucose or acetate substrate on a 16.4 Tesla animal scanner.

RESULTS

We found that the deuterated water accumulation rate and isotopic turnover rate of deuterated glutamate/glutamine via the tricarboxylic acid cycle and exchange in rat hearts were much higher when infused with acetate compared to that with glucose, demonstrating the myocardium substrate preference for acetate over glucose.

CONCLUSION

We demonstrated the feasibility of deuterium MRSI for noninvasive imaging and assessment of myocardial energy metabolism in vivo. Although the strong signal and large dynamics of myocardial deuterated water may provide a sensitive imaging biomarker, quantifying the metabolic rates still poses a challenge due to the confounding effects of blood recirculation, perfusion, and multiple deuterated water production pathways. In contrast, the deuterated glutamate/glutamine signal and change should directly reflect the metabolic activity of the myocardial tricarboxylic acid cycle, which can be used to study the metabolic shift in substance preference between acetate and glucose in the diseased state. Deuterium MRSI is noninvasive and robust and may have the potential to assess myocardial energy metabolism in human patients.

The role of diet-derived short-chain fatty acids in regulating cardiac pressure overload

Heart failure (HF) is one of the leading causes of mortality and morbidity in the modern world whose increasing prevalence is associated with "Western" diet and sedentary lifestyles. Of particular concern is the increasing burden of HF with preserved ejection fraction (HFpEF) that involves complex pathophysiology and is difficult to treat. Pressure overload caused by hypertension (HTN) is the predominant driver of cardiac injury, left ventricular hypertrophy, and fibrosis that progresses to diastolic dysfunction and ultimately HFpEF. Although pharmacological control of blood pressure may affect the degree of pressure overload, such therapies are largely ineffective in established HFpEF, and there is a need to modulate the festering inflammatory and fibrotic response to injury to halt and perhaps reverse pathology. An emerging literature indicates potentially important links between the gut microbiota, dietary soluble fiber, and microbiota-derived metabolites that modulate blood pressure and the immune response. In particular, high-fiber diets demonstrate protective properties in systemic hypertension and left-sided cardiac pathology, and this action is closely associated with short-chain fatty acid (SCFA)-producing bacteria. Mechanisms underlying the beneficial action of SCFAs in immunity and the systemic circulation could potentially be applied to the treatment of hypertension and the cardiac damage it causes. In this review, we discuss the potential beneficial effects of SCFAs, with an emphasis on mechanisms that are involved in cardiac responses to pressure overload.

Production of highly polarized [1-13 C]acetate by rapid decarboxylation of [2-13 C]pyruvate - application to hyperpolarized cardiac spectroscopy and imaging

PURPOSE

The objective of the present work was to develop and implement an efficient approach to hyperpolarize [1-¹³ C]acetate and apply it to in vivo cardiac spectroscopy and imaging.

METHODS

Rapid hydrogen peroxide induced decarboxylation was used to convert hyperpolarized [2-¹³ C]pyruvate into highly polarized [1-¹³ C]acetate employing an additional step following rapid dissolution of [2-¹³ C]pyruvate in a home-built multi-sample dissolution dynamic nuclear polarization system. Phantom dissolution experiments were conducted to determine optimal parameters of the decarboxylation reaction, retaining polarization and T₁ of [1-¹³ C]acetate. In vivo feasibility of detecting [1-¹³ C]acetate metabolism is demonstrated using slice-selective spectroscopy and multi-echo imaging of [1-¹³ C]acetate and [1-¹³ C]acetylcarnitine in the healthy rat heart.

RESULTS

The first in vivo signal was observed ~23 s after dissolution. At the corresponding time point in the phantom experiments, 97.9 ± 0.4% of [2-¹³ C]pyruvate were converted into [1-¹³ C]acetate by the decarboxylation reaction. T₁ and polarization of [1-¹³ C]acetate was determined to be 29.7 ± 1.9% and a 47.7 ± 0.5 s. Polarization levels of [2-¹³ C]pyruvate and [1-¹³ C]acetate were not significantly different after transfer to the scanner. In vivo, [1-¹³ C]acetate and [1-¹³ C]acetylcarnitine could be detected using spectroscopy and imaging.

CONCLUSION

Decarboxylation of hyperpolarized [2-¹³ C]pyruvate enables the efficient production of highly polarized [1-¹³ C]acetate that is applicable to study short-chain fatty acid metabolism in the in vivo heart.

Plasma-Lyte 148 vs. Hartmann's solution for cardiopulmonary bypass pump prime: a prospective double-blind randomized trial

BACKGROUND

The mechanisms of acid-base changes during cardiopulmonary bypass (CPB) remain unclear. We tested the hypothesis that, when used as CPB pump prime solutions, Plasma-Lyte 148 (PL) and Hartmann's solution (HS) have differential mechanisms of action in their contribution to acid-base changes.

METHODS

We performed a prospective, double-blind, randomized trial in adult patients undergoing elective cardiac surgery with CPB. Participants received a CPB prime solution of 2000 mL, with either PL or HS. The primary endpoint was the standard base excess (SBE) value measured at 60 minutes after full CPB flows (SBE60min). Secondary outcomes included changes in SBE, pH, chloride, sodium, lactate, gluconate, acetate, strong ion difference and strong ion gap at two (T2min), five (T5min), ten (T10min), thirty (T30min) and sixty (T60min) minutes on CPB. The primary outcome was measured using a two-tailed Welch's t-test. Repeated measures ANOVA was used to test for differences between time points.

RESULTS

Twenty-five participants were randomized to PL and 25 to HS. Baseline characteristics, EURO and APACHE scores, biochemistry, hematology and volumes of cardioplegia were similar. Mean (SD) SBE at T60min was -1.3 (1.4) in the PL group and -0.1 (2.7) in the HS group; p=0.55. No significant differences in SBE between the groups was observed during the first 60 minutes (p=0.48). During CPB, there was hyperacetatemia and hypergluconatemia in the PL group and hyperlactatemia and hyperchloremia in the HS group. No significant difference between the groups in plasma bicarbonate levels and total weak acid levels were found. Complications and intensive care unit and hospital length of stays were similar.

CONCLUSIONS

During CPB, PL and HS did not cause a significant metabolic acidosis. There was hyperacetatemia and hypergluconatemia with PL and hyperchloremia and hyperlactatemia with HS. These physiochemical effects appear clinically innocuous.

Microbe-mitochondrion crosstalk and health: An emerging paradigm

Human mitochondria are descendants of microbes and altered mitochondrial function has been implicated in processes ranging from ageing to diabetes. Recent work has highlighted the importance of gut microbial communities in human health and disease. While the spotlight has been on the influence of such communities on the human immune system and the extraction of calories from otherwise indigestible food, an important but less investigated link between the microbes and mitochondria remains unexplored. Microbial metabolites including short chain fatty acids as well as other molecules such as pyrroloquinoline quinone, fermentation gases, and modified fatty acids influence mitochondrial function. This review focuses on the known direct and indirect effects of microbes upon mitochondria and speculates regarding additional links for which there is circumstantial evidence. Overall, while there is compelling evidence that a microbiota-mitochondria link exists, explicit and holistic mechanistic studies are warranted to advance this nascent field.

Plasma-Lyte 148: A clinical review

AIM

To outline the physiochemical properties and specific clinical uses of Plasma-Lyte 148 as choice of solution for fluid intervention in critical illness, surgery and perioperative medicine.

METHODS

We performed an electronic literature search from Medline and PubMed (via Ovid), anesthesia and pharmacology textbooks, and online sources including studies that compared Plasma-Lyte 148 to other crystalloid solutions. The following keywords were used: “surgery”, “anaesthesia”, “anesthesia”, “anesthesiology”, “anaesthesiology”, “fluids”, “fluid therapy”, “crystalloid”, “saline”, “plasma-Lyte”, “plasmalyte”, “hartmann’s”, “ringers”“acetate”, “gluconate”, “malate”, “lactate”. All relevant articles were accessed in full. We summarized the data and reported the data in tables and text.

RESULTS

We retrieved 104 articles relevant to the choice of Plasma-Lyte 148 for fluid intervention in critical illness, surgery and perioperative medicine. We analyzed the data and reported the results in tables and text.

CONCLUSION

Plasma-Lyte 148 is an isotonic, buffered intravenous crystalloid solution with a physiochemical composition that closely reflects human plasma. Emerging data supports the use of buffered crystalloid solutions in preference to saline in improving physicochemical outcomes. Further large randomized controlled trials assessing the comparative effectiveness of Plasma-Lyte 148 and other crystalloid solutions in measuring clinically important outcomes such as morbidity and mortality are needed.

Crystalloid fluid therapy

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency medicine 2016. Other selected articles can be found online at http://www.biomedcentral.com/collections/annualupdate2016. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Acetate transiently inhibits myocardial contraction by increasing mitochondrial calcium uptake

Background

There is a close relationship between cardiovascular disease and cardiac energy metabolism, and we have previously demonstrated that palmitate inhibits myocyte contraction by increasing K_v channel activity and decreasing the action potential duration. Glucose and long chain fatty acids are the major fuel sources supporting cardiac function; however, cardiac myocytes can utilize a variety of substrates for energy generation, and previous studies demonstrate the acetate is rapidly taken up and oxidized by the heart. In this study, we tested the effects of acetate on contractile function of isolated mouse ventricular myocytes.

Results

Acute exposure of myocytes to 10 mM sodium acetate caused a marked, but transient, decrease in systolic sarcomere shortening (1.49 ± 0.20% vs. 5.58 ± 0.49% in control), accompanied by a significant increase in diastolic sarcomere length (1.81 ± 0.01 μm vs. 1.77 ± 0.01 μm in control), with a near linear dose response in the 1–10 mM range. Unlike palmitate, acetate caused no change in action potential duration; however, acetate markedly increased mitochondrial Ca²⁺ uptake. Moreover, pretreatment of cells with the mitochondrial Ca²⁺ uptake blocker, Ru-360 (10 μM), markedly suppressed the effect of acetate on contraction.

Conclusions

Lehninger and others have previously demonstrated that the anions of weak aliphatic acids such as acetate stimulate Ca²⁺ uptake in isolated mitochondria. Here we show that this effect of acetate appears to extend to isolated cardiac myocytes where it transiently modulates cell contraction.

Vasopressin and prevention of hypotension during hemodialysis

CONTEXT

The occurrence of intradialytic hypotension (IDH) during hemodialysis (HD) continues to be a main problem in patients with ESRD (end-stage kidney disease). It also negatively affects health-related quality of life. We aimed to determine vasopressin effect in decreasing IDH.

EVIDENCE ACQUISITION

We reviewed clinical and experimental literature in a variety of sources, including PubMed, Current Content, Scopus, Embase, and Iranmedex regarding the possible effect of vasopressin administration in prevention of hypotension during HD to clarify its mechanism, efficacy, and safety.

RESULTS

Although arginine vasopressin is widely recognized for its anti-diuretic properties, it is also a well-recognized vasoconstrictor. It has been shown that the vasopressin release (as it would normally be expected) does not increase in the majority of HD patients with recurrent dialysis hypotension. In addition, it has also been reported that vasopressin secretion (due to the osmotic stimulation) is the most important mechanism in blood pressure control in ESRD patients receiving hypertonic solution for IDH. Therefore, it is suggested that vasopressin administration may improve hemodynamic stability among ESRD patients during HD. There are few clinical trials about this issue, suggesting that administration of exogenous vasopressin may be significantly associated with a decreased incidence of IDH as well as cardiovascular stability in ESRD patients in need of volume removal during HD.

CONCLUSIONS

Vasopressin insufficiency may have an important role in the pathogenesis of hemodynamic instability during HD and administration of exogenous vasopressin is significantly associated with a lower incidence of IDH.

The ideal crystalloid - what is 'balanced'?

PURPOSE OF REVIEW

This review explores the contemporary definition of the term 'balanced crystalloid' and outlines optimal design features and their underlying rationale.

RECENT FINDINGS

Crystalloid interstitial expansion is unavoidable, but also occurs with colloids when there is endothelial glycocalyx dysfunction. Reduced chloride exposure may lessen kidney dysfunction and injury with a possible mortality benefit. Exact balance from an acid-base perspective is achieved with a crystalloid strong ion difference of 24 mEq/l. This can be done simply by replacing 24 mEq/l of chloride in 0.9% sodium chloride with bicarbonate or organic anion bicarbonate substitutes. Potassium, calcium and magnesium additives are probably unnecessary. Large volumes of mildly hypotonic crystalloids such as lactated Ringer's solution reduce extracellular tonicity in volunteers and increase intracranial pressure in nonbrain-injured experimental animals. A total cation concentration of 154 mmol/l with accompanying anions provides isotonicity. Of the commercial crystalloids, Ringer's acetate solution is close to balanced from both acid-base and tonicity perspectives, and there is little current evidence of acetate toxicity in the context of volume loading, in contrast to renal replacement.

SUMMARY

The case for balanced crystalloids is growing but unproven. A large randomized controlled trial of balanced crystalloids versus 0.9% sodium chloride is the next step.

Effects of Intravascular Volume Replacement on Lung and Kidney Function and Damage in Nonseptic Experimental Lung Injury

Background:

Intravascular volume replacement is often required in the presence of increased pulmonary capillary leakage, for example in patients with volutrauma with major hemorrhage. In the present study, the effects of Ringer’s acetate (RA), gelatin-polysuccinate (GEL), and a modern hydroxyethyl starch (HES, 6% 130/0.42) on lung and kidney function and damage were compared in a two-hit model of acute lung injury. The authors hypothesized that GEL and HES, compared to RA: (1) reduced lung histological damage, (2) impaired kidney morphology and function.

Methods:

Acute lung injury was induced in 30 anesthetized pigs by tidal volumes approximately 40 ml/kg, after saline lung lavage. Protective ventilation was initiated and approximately≈25% of estimated blood volume was drawn. Animals were randomly assigned to receive RA, GEL, or HES (n = 10/group) aimed at approximately 90% of intrathoracic blood volume before blood drainage.

Results:

Fluid volumes were higher with RA (2,250 ± 764 ml) than GEL (704 ± 159 ml) and HES (837 ± 82 ml) (P < 0.05). Compared to RA, HES reduced diffuse alveolar damage overall, and GEL in nondependent zones only. GEL and HES yielded lower wet-to-dry ratios compared to RA (6.5 ± 0.5 and 6.5 ± 0.6 vs. 7.9 ± 0.9, respectively, P < 0.05). HES and RA resulted in less kidney damage than GEL, but kidney function did not differ significantly among groups. Compared to GEL, HES yielded lower lung elastance (55 ± 12 vs. 45 ± 13 cm H2O/l, P < 0.05) and intra-abdominal pressure (15 ± 5 vs. 11 ± 4 cm 14;H2O, P < 0.05).

Conclusions:

In this model of acute lung injury, intravascular volume expansion after major hemorrhage with HES yielded less lung damage than RA and less kidney damage than GEL.

Effects of acetate-free citrate dialysate on glycoxidation and lipid peroxidation products in hemodialysis patients

Background/Aims

Previous studies have shown the presence of high levels of glycoxidation and lipid peroxidation products in association with atherosclerosis in patients with end-stage kidney disease. Acetates are commonly used buffer for correcting metabolic acidosis in hemodialysis (HD) patients. Since the toxic effects of acetates are well established, acetate-free citrate dialysate (AFD) has become available in Japan. The objective of the present study was to evaluate the suppressive effects of AFD on oxidative stress in maintenance HD patients by measuring plasma pentosidine and malondialdehyde-modified low-density lipoprotein (MDA-LDL) levels as markers for glycoxidation and lipid peroxidation products.

Methods

Plasma pentosidine, MDA-LDL and other laboratory parameters were examined on maintenance HD at the Juntendo University Hospital before and after switching to AFD.

Results

MDA-LDL levels divided by LDL cholesterol were significantly lower than those before switching to AFD. Furthermore, levels of plasma pentosidine were lower than those before switching to AFD. Stepwise multiple regression analysis revealed that the percent change of the calcium-phosphorus product in the nondiabetic group and that of phosphorus in the diabetic group were predictive variables for the percent change of MDA-LDL/LDL, whereas the percent change of log high-sensitive C-reactive protein and that of systolic blood pressure in the nondiabetic group and that of diastolic blood pressure in the diabetic group were predictive variables for the percent change of plasma pentosidine.

Conclusions

It appears that AFD decreases glycoxidation and lipid peroxidation products when compared with acid citrate dextrose in HD patients. The reduction of oxidative stress by AFD during HD may have possible beneficial effects on atherosclerosis through calcium-phosphorus metabolism and blood pressure.

Plasma acetate, gluconate and interleukin-6 profiles during and after cardiopulmonary bypass: a comparison of Plasma-Lyte 148 with a bicarbonate-balanced solution

INTRODUCTION

As even small concentrations of acetate in the plasma result in pro-inflammatory and cardiotoxic effects, it has been removed from renal replacement fluids. However, Plasma-Lyte 148 (Plasma-Lyte), an electrolyte replacement solution containing acetate plus gluconate is a common circuit prime for cardio-pulmonary bypass (CPB). No published data exist on the peak plasma acetate and gluconate concentrations resulting from the use of Plasma-Lyte 148 during CPB.

METHODS

Thirty adult patients were systematically allocated 1:1 to CPB prime with either bicarbonate-balanced fluid (24 mmol/L bicarbonate) or Plasma-Lyte 148. Arterial blood acetate, gluconate and interleukin-6 (IL-6) levels were measured immediately before CPB (T1), three minutes after CPB commencement (T2), immediately before CPB separation (T3), and four hours post separation (T4).

RESULTS

Acetate concentrations (normal 0.04 to 0.07 mmol/L) became markedly elevated at T2, where the Plasma-Lyte group (median 3.69, range (2.46 to 8.55)) exceeded the bicarbonate group (0.16 (0.02 to 3.49), P < 0.0005). At T3, levels had declined but the differential pattern remained apparent (Plasma-Lyte 0.35 (0.00 to 1.84) versus bicarbonate 0.17 (0.00 to 0.81)). Normal circulating acetate concentrations were not restored until T4. Similar gluconate concentration profiles and inter-group differences were seen, with a slower T3 decay. IL-6 increased across CPB, peaking at T4, with no clear difference between groups.

CONCLUSIONS

Use of acetate containing prime solutions result in supraphysiological plasma concentrations of acetate. The use of acetate-free prime fluid in CPB significantly reduced but did not eliminate large acetate surges in cardiac surgical patients. Complete elimination of acetate surges would require the use of acetate free bolus fluids and cardioplegia solutions.

TRIAL REGISTRATION

Australia and New Zealand Clinical Trials Register (ANZCTR): ACTRN12610000267055.

Controversies and Issues in Hemodiafiltration Therapy

Hemodiafiltration appears to be the most effective technique of renal replacement therapy but several drawbacks are not counterbalanced by significant advantages. Although optimal transfer for both small and middle molecules can be achieved, there is no difference in mortality risk between HDF and HD patients. The infusion of a large amount of dialysate containing residual acetate of 2-7 mmol/l could lead to impaired cardiac contractile functions and carbonyl stress whereas loss of amino acids and water-soluble vitamins along with high UF rate could lead to malnutrition. Moreover, as substitution fluid is prepared on-line, contaminated fluid could be inadvertently infused to patients. Stringent maintenance rules are required for the production of sterile and non-pyrogenic dialysis solutions. Finally, daily hemodialysis could be the most promising mode of renal replacement therapy since it leads to a more stable 'milieu interieur' than other techniques whatever the mode of solutes removal when performed three times a week.

Effect of Bicarbonated Ringer's Solution on the Acid-base Balance in Patients Undergoing Abdominal Aortic Aneurysm Repair

AIM

The present study was designed to assess whether prophylactic use of bicarbonated Ringer's solution ameliorates metabolic acidosis in patients undergoing aortic surgery.

METHODS

Twenty patients undergoing elective infrarenal aortic aneurysm repair were randomly assigned to receive either bicarbonated Ringer's solution or acetated Ringer's solution. The pH, PaCO(2), and base excess (BE) were measured before surgical incision (T0), 5 min before reperfusion (T1), 5 min after reperfusion (T2), and 30 min after reperfusion (T3). Data were compared between the two groups.

RESULTS

Both pH and BE initially showed a slight decrease in both groups during clamping. After unclamping of the aorta, an additional decrease in pH was observed in both groups (T0 to T2, and T3). There were no significant differences in pH between the groups throughout the study period.

CONCLUSIONS

Aortic cross-clamping leads to the development of metabolic acidosis, with a decrease in pH and BE. The effect of administration of bicarbonated infusion fluid during elective abdominal aortic surgery had not significant compared with that of acetated Ringer's solution with respect to acid-base homeostasis.

Study of plasma exchange for liver failure: beneficial and harmful effects

Plasma exchange (PE) is often performed in combination with hemodialysis (HD) or hemodiafiltration. However, most methods were developed for the treatment of renal failure, so various problems may arise during treatment of liver failure (LF). In this study, we investigated the impact of PE alone and in combination with HD, and we assessed the complications of using PE + HD for the treatment of LF. After the exchange of 1 L of fresh frozen plasma (FFP), we measured serum electrolytes, HCO(3) (-), citrate, and acetate at 3 points in the circuit: A) the plasma separator inflow; B) after mixing of FFP/the dialyzer inflow; and C) the dialyzer outflow. Serum levels of human hepatocyte growth factor (HGF), acetate, and citrate were also measured before and after PE + HD. The levels of K(+), Ca(++), HCO(3) (-), and acetate were significantly decreased, and citrate was increased, between A and B. K(+) and citrate were decreased, while Ca(++), HCO(3) (-), and acetate showed an increase between B and C. Comparison of A with C revealed insufficient correction of the Ca(++) and citrate levels by HD. After PE + HD, serum levels of acetate and citrate were increased, while HGF was decreased. We concluded that i) when PE is performed, HD is also necessary for correction, but achieves insufficient correction of Ca(++) and citrate, ii) PE is non-selective and not only removes toxins but also beneficial substances such as HGF, iii) accumulation of acetate occurred, even with bicarbonate dialysate, since it also contains acetate for acidification.

Approach to intradialytic hypotension in intensive care unit patients with acute renal failure

The increasing prevalence of acute renal failure (ARF) patients with hemodynamic intolerance of intermittent hemodialysis (HD), generally because of septic vasoparesis or severe cardiac dysfunction, has led to the development of several strategies to improve the delivery of renal replacement therapy (RRT) in ARF patients. Intradialytic hypotension (IDH) is caused by the interaction of dialysis-dependent and dialysis-independent factors. Dialysis-dependent factors include the prescriptions for fluid removal, solute removal, and dialysate components such as sodium, buffer, and calcium. Dialysis-independent factors include hemodynamic compromise caused by hypovolemic, cardiogenic, vasodilatory, and mixed mechanisms. We propose an approach to the prevention and management of IDH in critically ill ARF patients, which minimizes hypovolemic, cardiogenic, and vasodilatory insults by optimizing fluid removal, cardiac function, and vascular contractility.

Isolated four-chamber working swine heart model

BACKGROUND

Isolated heart models separate cardiac characteristics from systemic characteristics with subsequent findings used in cardiac research, including responses to pharmacologic, mechanical, and electrical components. The model objective was to develop the ability to represent in situ physiologic cardiac function ex vivo.

METHODS

Swine hearts were chosen over rat or guinea pig models due to their notably greater anatomical and physiologic similarities to humans. An in vitro apparatus was designed to work all four chambers under simulated in situ physiologic conditions. Using standard cardiac surgical techniques, 12 porcine hearts (mean weight 331 +/- 18 g) were explanted into the apparatus. Preload and afterload resistances simulated in situ input and output physiologic conditions. Hemodynamic characterizations, including cardiac output, max +/- dP/dt, and heart rate, were used to determine in situ function leading to explantation (prethoracic operation, postmedial sternotomy, and postperidectomy) and during in vitro function (t = 0, 60, 120, and 240 minutes).

RESULTS

In vitro performance decayed with time, with statistical differences from base line (t = 0) function at t = 240 minutes (p > 0.05).

CONCLUSIONS

An isolation and in vitro explantation protocol has been improved to aid in the study of isolated cardiac responses, and to determine cardiac hemodynamic function during open chest operation, transplantation, and in vitro reanimation with a crystalloid perfusate. The resulting model offers similar working physiologic function, with real-time imaging capabilities. The resulting model is advantageous in representing human cardiac function with regard to anatomic and physiologic functions, and can account for atrial and ventricular interactions.