Bicarbonate-based haemofiltration in the management of acute renal failure with lactic acidosis

Intraoperative Renal Replacement Therapy: Practical Information for Anesthesiologists

Previous publications regarding perioperative renal replacement therapy (RRT) have focused on the general care of the RRT-dependent patient and provided a broad overview of the various RRT modalities. The goal of this review article is to provide anesthesiologists with specific practical information regarding the possible intraoperative advantages and limitations of each modality, mandatory equipment to institute intraoperative therapy, and background knowledge necessary to communicate effectively with nephrologists and/or support staff regarding the intraoperative RRT goals.

A simple risk score for prediction of sepsis associated-acute kidney injury in critically ill patients

BACKGROUND

Sepsis is common and frequently fatal condition in critically ill patients and is a major cause of acute kidney injury (AKI). In this retrospective study, we sought to develop a comprehensive risk score model of sepsis associated-AKI (SA-AKI).

METHODS

A total of 2617 patients were randomly assigned to a development (1554 patients) and a validation group (777 patients). The risk score model for SA-AKI was developed with multivariate regression analysis in development group and the model was further evaluated on validation group.

RESULTS

We identified 16 independent predictors of SA-AKI in development group (age ≥ 60 years, hypertension/coronary heart disease, diabetes, chronic kidney disease, heart failure, chronic obstructive pulmonary disease, acute severe pancreatitis, hypotension, hypoproteinemia, lactic acidosis, the length of stay in intensive care unit(ICU), 60 g/L<hemoglobin < 90 g/L, hemoglobin ≤ 60 g/L, and ≥ 2 failed organs. This model had excellent performance characteristics in validation cohort(c statistic 0.857, 95% CI 0.839-0.874).

CONCLUSION

The novel risk score model for SA-AKI in ICU can identify patients at high risk to develop AKI. Application of this model could help clinicians to stratify patients for primary prevention, surveillance and early therapeutic intervention to improve care and prognosis of sepsis patients in ICU.

Perioperative Management of Lactic Acidosis in End-Stage Liver Disease Patient

Lactic acidosis (LA) in end-stage liver disease (ESLD) patients has been recognized as one of the most complicated clinical problems and is associated with increased morbidity and mortality. Multiple-organ failure, associated with advanced stages of cirrhosis, exacerbates dysfunction of numerous parts of lactate metabolism cycle, which manifests as increased lactate production and impaired clearance, leading to severe LA-induced acidemia. These problems become especially prominent in ESLD patients, that undergo partial hepatectomy and, particularly, liver transplantation. Perioperative management of LA and associated severe acidemia is an inseparable part of anesthesia, post-operative and critical care for this category of patients, presenting a wide variety of challenges. In this review, lactic acidosis applied pathophysiology, clinical implications for ESLD patients, diagnosis, role of intraoperative factors, such as anesthesia and surgery-related, vasoactive agents impact, and also current treatment options and modalities have been discussed.

Continuous Renal Replacement Therapy for the Management of Acid-Base and Electrolyte Imbalances in Acute Kidney Injury

Continuous renal replacement therapy (CRRT) is used to manage electrolyte and acid-base imbalances in critically ill patients with acute kidney injury. Although a standard solution and prescription is acceptable in most clinical circumstances, specific disorders may require a tailored approach such as adjusting fluid composition, regulating CRRT dose, and using separate intravenous infusions to mitigate and correct these disturbances. Errors in fluid prescription, compounding, or delivery can be rapidly fatal. This article provides an overview of the principles of acid-base and electrolyte management using CRRT.

Lactic Acidosis in a Patient with Type 2 Diabetes Mellitus

Lactic acidosis occurs when lactate production exceeds its metabolism. There are many possible causes of lactic acidosis, and in any given patient, several causes may coexist. This Attending Rounds presents a case in point. Metformin's role in the pathogenesis of lactic acidosis in patients with diabetes mellitus is complex, as the present case illustrates. The treatment of lactic acidosis is controversial, except for the imperative to remedy its underlying cause. The use of sodium bicarbonate to treat the often alarming metabolic derangements may be quite efficacious in that regard but is of questionable benefit to patients. Renal replacement therapies (RRTs) have particular appeal in this setting for a variety of reasons, but their effect on clinical outcomes is untested.

Lactate clearance and metabolic aspects of continuous high-volume hemofiltration

Lactic acidosis is associated with high morbidity and mortality in hospitalized patients. Treatment of lactic acidosis is targeted on correcting the underlying causes and optimizing adequate oxygen delivery to the tissues. Even though evidence is lacking, continuous renal replacement therapy (CRRT) and dialysis have been advocated as treatments for lactic acidosis. We report a 28-year-old Caucasian male with a history of hemophagocytic lymphohistiocytosis who presented with septic shock, severe lactic acidosis and multiple organ failure. Metabolic acidosis was corrected after bicarbonate therapy and CRRT with a hemofiltration rate of 7 L/h (58 mL/kg/h). Lactate clearance was calculated to be 79 mL/min. Compared with reported rates of lactate overproduction in septic shock, the rate of lactate clearance is quite small. Our case suggests that CRRT with high-volume hemofiltration is not effective for severe lactic acidosis. Lactic acidosis alone should not be considered as a nonrenal indication for CRRT.

The effect of bicarbonate administration via continuous venovenous hemofiltration on acid-base parameters in ventilated patients

Background. Acute kidney injury (AKI) and metabolic acidosis are common in the intensive care unit. The effect of bicarbonate administration on acid-base parameters is unclear in those receiving continuous venovenous hemofiltration (CVVH) and mechanical ventilatory support. Methods. Metabolic and ventilatory parameters were prospectively examined in 19 ventilated subjects for up to 96 hours following CVVH initiation for AKI at an academic tertiary care center. Mixed linear regression modeling was performed to measure changes in pH, partial pressure of carbon dioxide (pCO₂), serum bicarbonate, and base excess over time. Results. During the 96-hour study period, pCO₂ levels remained stable overall (initial pCO₂ 42.0 ± 14.6 versus end-study pCO₂ 43.8 ± 16.1 mmHg; P = 0.13 for interaction with time), for those with initial pCO₂ ≤40 mmHg (31.3 ± 5.7 versus 35.0 ± 4.8; P = 0.06) and for those with initial pCO₂ >40 mmHg (52.7 ± 12.8 versus 53.4 ± 19.2; P = 0.57). pCO₂ decreased during the immediate hours following CVVH initiation (42.0 ± 14.6 versus 37.3 ± 12.6 mmHg), though this change was nonsignificant (P = 0.052). Conclusions. We did not detect a significant increase in pCO₂ in response to the administration of bicarbonate via CVVH in a ventilated population. Additional studies of larger populations are needed to confirm this finding.

Severe lactic acidosis in critically ill patients with acute kidney injury treated with renal replacement therapy

PURPOSE

Severe lactic acidosis (SLA) is frequent in intensive care unit (ICU) patients with acute kidney injury (AKI) treated with renal replacement therapy (RRT). The aim of the study is to describe the epidemiology of SLA in this setting.

MATERIALS AND METHODS

An observational single-center cohort analysis was performed on AKI patients treated with RRT. At initiation of RRT, SLA patients (serum lactate concentration>5 mmol/L and pH<7.35) were compared with non-SLA patients.

RESULTS

Of the 454 patients dialyzed during the study period, 342 patients matched inclusion criteria (116 with and 226 patients without SLA). In SLA patients, lactate stabilized/decreased in 69.7% at 4 hours (P=.001) and in 81.8% during the period of 4 to 24 hours (P<.001) after initiation of RRT. Mortality during this 24-hour period was 31.0%. Intensive care unit mortality was 83.6% compared with 47.3% in non-SLA patients. Initial lactate concentration was not related to ICU mortality in SLA patients.

CONCLUSIONS

Severe lactic acidosis was frequent in AKI patients treated with RRT. Severe lactic acidosis patients were more severely ill and had higher mortality compared with patients without. During the first 24 hours of RRT, a correction of lactate concentration and acidosis was observed. In SLA patients, lactate concentration at initiation of RRT was not able to discriminate between survivors and nonsurvivors.

Early acid-base and blood pressure effects of continuous renal replacement therapy intensity in patients with metabolic acidosis

PURPOSE

In acute kidney injury patients, metabolic acidosis is common. Its severity, duration, and associated changes in mean arterial pressure (MAP) and vasopressor therapy may be affected by the intensity of continuous renal replacement therapy (CRRT). We aimed to compare key aspects of acidosis and MAP and vasopressor therapy in patients treated with two different CRRT intensities.

METHODS

We studied a nested cohort of 115 patients from two tertiary intensive care units (ICUs) within a large multicenter randomized controlled trial treated with lower intensity (LI) or higher intensity (HI) CRRT.

RESULTS

Levels of metabolic acidosis at randomization were similar [base excess (BE) of -8 ± 8 vs. -8 ± 7 mEq/l; p = 0.76]. Speed of BE correction did not differ between the two groups. However, the HI group had a greater increase in MAP from baseline to 24 h (7 ± 3 vs. 0 ± 3 mmHg; p < 0.01) and a greater decrease in norepinephrine dose (from 12.5 to 3.5 vs. 5 to 2.5 μg/min; p < 0.05). The correlation (r) coefficients between absolute change in MAP and norepinephrine (NE) dose versus change in BE were 0.05 and -0.37, respectively.

CONCLUSIONS

Overall, LI and HI CRRT have similar acid-base effects in patients with acidosis. However, HI was associated with greater improvements in MAP and vasopressor requirements (clinical trial no. NCT00221013).

Clinical review: timing of renal replacement therapy

Acute kidney injury is common in intensive care patients and continuous renal replacement therapy is the preferred treatment for this in most centres. Although these techniques have been adopted internationally, there remains significant variation with regard to their clinical application. This is particularly pertinent when one considers that the fundamental questions regarding any treatment, such as initiation, dose and length of treatment, remain a source of debate and have not as yet all been fully answered. In this narrative review we consider the timing of renal replacement therapy, highlighting the relative paucity of high quality data regarding this fundamental question. We examine the role of the usual biochemical criteria as well as conventional clinical indications for commencing renal replacement therapy together with the application of recent classification systems, namely RIFLE and AKIN. We discuss the potential role of biomarkers for acute kidney injury as predictors for the need for renal support and discuss commencing therapy for indications other than acute kidney injury.

Do bicarbonate-based solutions for continuous renal replacement therapy offer better control of metabolic acidosis than lactate-containing fluids?

INTRODUCTION

Evidence that bicarbonate haemofiltration and dialysate fluids are superior to lactate in patients with acute kidney injury treated by continuous renal replacement therapy (CRRT) remains controversial.

METHODS

We prospectively audited acid-base during the first 48 h of CRRT in 62 patients, using bicarbonate and lactate fluids.

RESULTS

Baseline lactate was greater in the bicarbonate group (4.76 ± 0.77 vs. 2.92 ± 0.5 mmol/l, p < 0.01), but pH, bicarbonate, chloride and base excess were similar. Lactate fell significantly in the bicarbonate group to 2.88 ± 0.3 mmol/l at 24 h and 2.39 ± 0.2 mmol/l at 48 h, but not in the lactate group. Base excess improved more with bicarbonate, median increase in the first 24 h was 51.6% (29.1-96.9) versus 18.5% (-5 to 55) with lactate and 74.2% (38.5-123) versus 36.1% (-3.6 to 68), p < 0.05 at 48 h. However, there were no significant differences in bicarbonate, chloride, pH, blood pressure and vasopressor requirements. 13.3% of patients were switched from lactate to bicarbonate fluids due to failure to correct acidosis. Subgroup analysis of 19 patients with liver failure showed similar results.

CONCLUSION

Bicarbonate fluids led to a more rapid fall in lactate and greater improvement in base excess during CRRT, but not overall control of acidosis.

Continuous renal replacement therapy: cause and treatment of electrolyte complications

Continuous renal replacement therapy (CRRT) has become the modality of choice for critically ill patients. Although often hemodynamically better tolerated than intermittent dialysis, the continuous nature of this therapy may cause significant electrolyte complications. These complications commonly result from removal of electrolytes from the body without adequate replacement or because of the use of trisodium citrate as the anticoagulant. Both hypophosphatemia and hypokalemia frequently complicate prolonged treatment. These complications can be avoided by adding these electrolytes to the dialysate or replacement fluid. The use of citrate, especially if this anticoagulant is not used routinely following established protocols, can also result in several electrolyte abnormalities. Because citrate works by chelating calcium, hypo- and hypercalcemia occur because of under- or overreplacement of calcium. Because citrate is a base equivalent, if the bicarbonate concentration of the dialysate or replacement fluid is not decreased, a metabolic alkalosis may develop. Less commonly, in patients with severe liver dysfunction who cannot metabolize citrate back to bicarbonate, a metabolic acidosis may develop. Although CRRT may cause electrolyte complication it also can be the treatment of choice for the correction of certain electrolyte complications. In patients with acute or chronic renal failure who present with significant dysnatremias, intermittent hemodialysis may cause overly rapid correction of the serum sodium with serious neurologic sequelae. The ability to manipulate the sodium concentration of the dialysate or replacement fluid and the more sustained nature of the treatment allows for a slower correction thus avoiding complications.

Lactic acidosis: from sour milk to septic shock

Lactic acidosis is frequently encountered in the intensive care unit. It occurs when there is an imbalance between production and clearance of lactate. Although lactic acidosis is often associated with a high anion gap and is generally defined as a lactate level >5 mmol/L and a serum pH <7.35, the presence of hypoalbuminemia may mask the anion gap and concomitant alkalosis may raise the pH. The causes of lactic acidosis are traditionally divided into impaired tissue oxygenation (Type A) and disorders in which tissue oxygenation is maintained (Type B). Lactate level is often used as a prognostic indicator and may be predictive of a favorable outcome if it normalizes within 48 hours. The routine measurement of serum lactate, however, should not determine therapeutic interventions. Unfortunately, treatment options remain limited and should be aimed at discontinuation of any offending drugs, treatment of the underlying pathology, and maintenance of organ perfusion. The mainstay of therapy of lactic acidosis remains prevention.

Circulating anions usually associated with the Krebs cycle in patients with metabolic acidosis

Introduction

Acute metabolic acidosis of non-renal origin is usually a result of either lactic or ketoacidosis, both of which are associated with a high anion gap. There is increasing recognition, however, of a group of acidotic patients who have a large anion gap that is not explained by either keto- or lactic acidosis nor, in most cases, is inappropriate fluid resuscitation or ingestion of exogenous agents the cause.

Methods

Plasma ultrafiltrate from patients with diabetic ketoacidosis, lactic acidosis, acidosis of unknown cause, normal anion gap metabolic acidosis, or acidosis as a result of base loss were examined enzymatically for the presence of low molecular weight anions including citrate, isocitrate, α-ketoglutarate, succinate, malate and d-lactate. The results obtained from the study groups were compared with those obtained from control plasma from normal volunteers.

Results

In five patients with lactic acidosis, a significant increase in isocitrate (0.71 ± 0.35 mEq l^-1), α-ketoglutarate (0.55 ± 0.35 mEq l^-1), malate (0.59 ± 0.27 mEq l^-1), and d-lactate (0.40 ± 0.51 mEq l^-1) was observed. In 13 patients with diabetic ketoacidosis, significant increases in isocitrate (0.42 ± 0.35 mEq l^-1), α-ketoglutarate (0.41 ± 0.16 mEq l^-1), malate (0.23 ± 0.18 mEq l^-1) and d-lactate (0.16 ± 0.07 mEq l^-1) were seen. Neither citrate nor succinate levels were increased. Similar findings were also observed in a further five patients with high anion gap acidosis of unknown origin with increases in isocitrate (0.95 ± 0.88 mEq l^-1), α-ketoglutarate (0.65 ± 0.20 mEq l^-1), succinate (0.34 ± 0.13 mEq l^-1), malate (0.49 ± 0.19 mEq l^-1) and d-lactate (0.18 ± 0.14 mEq l^-1) being observed but not in citrate concentration. In five patients with a normal anion gap acidosis, no increases were observed except a modest rise in d-lactate (0.17 ± 0.14 mEq l^-1).

Conclusion

The levels of certain low molecular weight anions usually associated with intermediary metabolism were found to be significantly elevated in the plasma ultrafiltrate obtained from patients with metabolic acidosis. Our results suggest that these hitherto unmeasured anions may significantly contribute to the generation of the anion gap in patients with lactic acidosis and acidosis of unknown aetiology and may be underestimated in diabetic ketoacidosis. These anions are not significantly elevated in patients with normal anion gap acidosis.

Management of severe malaria: interventions and controversies

This article emphasizes that for many controversial reasons, severe malaria in travelers differs from that seen in endemic areas. There is no controversy, however, that malaria in individuals living in endemic areas should retain research priority. Some of the questions raised might never be amenable to randomized controlled trials, either because of ethical or logistical restraints. A possibly indulgent wish list of outcome (mortality) studies using currently known treatment modalities, however, includes the loading dose of quinine, vigorous fluid replacement, ET, the artemisinins, mannitol, and N-acetylcysteine in the treatment of severe malaria. There may clearly be many more. The treatment of severe malaria remains a challenge to those with an interest in managing life-threatening disease with complex and fascinating pathophysiology. As challenging as the studies listed previously may seem, however, priority must inevitably be given to research on how one can prevent and treat mild disease in the first place.

The treatment of complicated and severe malaria

All cases of falciparum malaria are potentially severe and life threatening, especially when managed inappropriately. A major reason for progression from mild through complicated to severe disease is missed or delayed diagnosis. Once diagnosed, the priority for treatment of complicated and severe disease is the parenteral administration of adequate, safe doses of an appropriate antimalarial, in the setting of the highest possible level of clinical care (i.e. usually an intensive care unit). Supportive management of complications such as coma, convulsions, metabolic acidosis, hypoglycaemia, fluid and electrolyte disturbances, renal failure, secondary infections, bleeding disorders and anaemia is also important. The most recent advance in antimalarial chemotherapy has been the use of artemisinin derivatives especially intravenous artesunate, which may well revolutionize the management of severe disease. Outside antimalarial therapy, mechanical ventilation and renal replacement have also played an important role in reducing mortality of this life-threatening condition.

Adjunctive therapies in sepsis: An evidence-based review

OBJECTIVE

In 2003, critical care and infectious disease experts representing 11 international organizations developed management guidelines for adjunctive therapies in sepsis that would be of practical use for the bedside clinician, under the auspices of the Surviving Sepsis Campaign, an international effort to increase awareness and to improve outcome in severe sepsis.

DESIGN

The process included a modified Delphi method, a consensus conference, several subsequent smaller meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee.

METHODS

The modified Delphi methodology used for grading recommendations built on a 2001 publication sponsored by the International Sepsis Forum. We undertook a systematic review of the literature graded along five levels to create recommendation grades from A to E, with A being the highest grade. Pediatric considerations to contrast adult and pediatric management are in the article by Parker et al. on p. S591.

CONCLUSION

Glycemic control (maintenance of glucose <150 mg/dL) is recommended. The beneficial effect of glycemic control appears to be related control of glucose and not the administration of insulin. Glycemic control should be combined with a nutritional protocol. The dialysis dose is important in sepsis-induced acute renal failure. Continuous hemofiltration offers easier management of fluid balance in hemodynamically unstable septic patients but in the absence of hemodynamic instability is equivalent to intermittent hemodialysis. It is uncertain whether high-volume hemofiltration improves prognosis in sepsis. Bicarbonate therapy is not recommended for the purpose of improving hemodynamics or reducing vasopressor requirements in the presence of lactic academia and pH >7.15.

Effect of bicarbonate and lactate buffer on glucose and lactate metabolism during hemodiafiltration in patients with multiple organ failure

OBJECTIVE

To compare the effects of sodium bicarbonate and lactate for continuous veno-venous hemodiafiltration (CVVHDF) in critically ill patients.

DESIGN AND SETTINGS

Prospective crossed-over controlled trial in the surgical and medical ICUs of a university hospital.

PATIENTS

Eight patients with multiple organ dysfunction syndrome (MODS) requiring CVVHDF.

INTERVENTION

Each patient received the two buffers in a randomized sequence over two consecutive days.

MEASUREMENTS AND RESULTS

The following variables were determined: acid-base parameters, lactate production and utilization ((13)C lactate infusion), glucose turnover (6,6(2)H(2)-glucose), gas exchange (indirect calorimetry). No side effect was observed during lactate administration. Baseline arterial acid-base variables were equal with the two buffers. Arterial lactate (2.9 versus 1.5 mmol/l), glycemia (+18%) and glucose turnover (+23%) were higher in the lactate period. Bicarbonate and glucose losses in CVVHDF were substantial, but not lactate elimination. Infusing (13)C lactate increased plasma lactate levels equally with the two buffers. Lactate clearance (7.8+/-0.8 vs 7.5+/-0.8 ml/kg per min in the bicarbonate and lactate periods) and endogenous production rates (14.0+/-2.6 vs 13.6+/-2.6 mmol/kg per min) were similar. (13)C lactate was used as a metabolic substrate, as shown by (13)CO(2) excretion. Glycemia and metabolic rate increased significantly and similarly during the two periods during lactate infusion.

CONCLUSION

Lactate was rapidly cleared from the blood of critically ill patients without acute liver failure requiring CVVHDF, being transformed into glucose or oxidized. Lactate did not exert undesirable effects, except moderate hyperglycemia, and achieved comparable effects on acid-base balance to bicarbonate.

Treatment of metabolic acidosis

Metabolic acidosis is characterized by a decrease of the blood pH associated with a decrease in the bicarbonate concentration. This may be secondary to a decrease in the strong ion difference or to an increase in the weak acids concentration, mainly the inorganic phosphorus. From a conceptual point of view, two types of nontoxic metabolic acidosis must be differentiated: the mineral metabolic acidosis that reveals the presence of an excess of nonmetabolizable anions, and the organic metabolic acidosis that reveals an excess of metabolizable anions. Significance and consequences of these two types of acidosis are radically different. Mineral acidosis is not caused by a failure in the energy metabolic pathways, and its treatment is mainly symptomatic by correcting the blood pH (alkali therapy) or accelerating the elimination of excessive mineral anions (renal replacement therapy). On the other hand, organic acidosis gives evidence that a severe underlying metabolic distress is in process. No reliable argument exists to prove that this acidosis is harmful under these conditions in humans. Experimental data even show that hypoxic cells are able to survive only if the medium is kept acidic. The management of an acute organic metabolic acidosis is therefore primarily based on the cause of the acidosis, and no scientific argument exists to justify the correction of the acid-base imbalance in this context.

Impact of continuous veno-venous hemofiltration on acid-base balance

BACKGROUND

Continuous veno-venous hemofiltration (CVVH) appears to have a significant and variable impact on acid-base balance. However, the pathogenesis of these acid-base effects remains poorly understood. The aim of this study was to understand the nature of acid-base changes in critically ill patients with acute renal failure during continuous veno-venous hemofiltration by applying quantitative methods of biophysical analysis (Stewart-Figge methodology).

METHODS

We studied forty patients with ARF receiving CVVH in the intensive care unit. We retrieved the biochemical data from computerized records and conducted quantitative biophysical analysis. We measured serum Na+, K+, Mg2+, Cl-, HCO3-, phosphate, ionized Ca2+, albumin, lactate and arterial blood gases and calculated the following Stewart-Figge variables: Strong Ion Difference apparent (SIDa), Strong Ion Difference Effective (SIDe) and Strong Ion Gap (SIG).

RESULTS

Before treatment, patients had mild acidemia (pH: 7.31) secondary to metabolic acidosis (bicarbonate: 19.8 mmol/L and base excess: -5.9 mEq/L). This acidosis was due to increased unmeasured anions (SIG: 12.3 mEq/L), hyperphosphatemia (1.86 mmol/L) and hyperlactatemia (2.08 mmol/L). It was attenuated by the alkalinizing effect of hypoalbuminemia (22.5 g/L). After commencing CVVH, the acidemia was corrected within 24 hours (pH 7.31 vs 7.41, p<0.0001). This correction was associated with a decreased strong ion gap (SIG) (12.3 vs. 8.8 mEq/L, p<0.0001), phosphate concentration (1.86 vs. 1.49 mmol/L, p<0.0001) and serum chloride concentration (102 vs. 98.5 mmol/L, p<0.0001). After 3 days of CVVH, however, patients developed alkalemia (pH: 7.46) secondary to metabolic alkalosis (bicarbonate: 29.8 mmol/L, base excess: 6.7 mEq/L). This alkalemia appeared secondary to a further decrease in SIG to 6.7 mEq/L (p<0.0001) and a further decrease in serum phosphate to 0.77 mmol/L (p<0.0001) in the setting of persistent hypoalbuminemia (21.0 g/L; p=0.56).

CONCLUSIONS

CVVH corrects metabolic acidosis in acute renal failure patients through its effect on unmeasured anions, phosphate and chloride. Such correction coupled with the effect of hypoalbuminemia, results in the development of a metabolic alkalosis after 72 hours of treatment.

The Acute Dialysis Quality Initiative--part VII: fluid composition and management in CRRT

Fluid composition and management are important parts of continuous renal replacement therapy (CRRT). Most commercially available CRRT solutions are able to reestablish electrolyte homeostasis provided some phosphate supplementation is given. Supraphysiologic glucose concentrations should be avoided. Predilution fluid replacement allows higher ultrafiltration rates and can be considered as an adjunct to the anticoagulation regimen. Lactate is an effective buffer in most CRRT patients. Bicarbonate is preferred in patients with lactic acidosis and/or liver failure. When citrate is used as anticoagulant, frequent monitoring of pH is required. The clinical consequences of CRRT-induced decreases of body temperature are not clear. Substitution fluid should be sterile, but the bacteriologic requirements for CRRT dialysate are less clear. There is no consensus on the optimal parameters to monitor fluid management. Integrated balancing systems have theoretical advantages over adaptive use of intravenous fluid pumps. Although there is evidence that volume overload is associated with adverse outcome, there is no evidence that fluid removal per se improves outcome in critically ill patients with or without acute renal failure.

Hemofiltration and peritoneal dialysis in infection-associated acute renal failure in Vietnam

BACKGROUND

In some parts of the world, peritoneal dialysis is widely used for renal replacement in acute renal failure. In resource-rich countries, it has been supplanted in recent years by hemodialysis and, most recently, by hemofiltration and associated techniques. The relative efficacy of peritoneal dialysis and hemofiltration is not known.

METHODS

We conducted an open, randomized comparison of pumped venovenous hemofiltration and peritoneal dialysis in patients with infection-associated acute renal failure in an infectious-disease referral hospital in Vietnam.

RESULTS

Seventy adult patients with severe falciparum malaria (48 patients) or sepsis (22 patients) were enrolled; 34 were assigned to hemofiltration and 36 to peritoneal dialysis. The mortality rate was 47 percent (17 patients) in the group assigned to peritoneal dialysis, as compared with 15 percent (5 patients) in the group assigned to hemofiltration (P=0.005). The rates of resolution of acidosis and of decline in the serum creatinine concentration in the group assigned to hemofiltration were more than twice those in the group assigned to peritoneal dialysis (P<0.005), and renal-replacement therapy was required for a significantly shorter period. In a multivariate analysis, the odds ratio for death was 5.1 (95 percent confidence interval, 1.6 to 16) and that for a need for future dialysis was 4.7 (95 percent confidence interval, 1.3 to 17) in the group assigned to peritoneal dialysis. The cost of hemofiltration per survivor was less than half that of peritoneal dialysis, and the cost per life saved was less than one third.

CONCLUSIONS

Hemofiltration is superior to peritoneal dialysis in the treatment of infection-associated acute renal failure.

Bench-to-bedside review: lactate and the kidney

The native kidney has a major role in lactate metabolism. The renal cortex appears to be the major lactate-consuming organ in the body after the liver. Under conditions of exogenous hyperlactatemia, the kidney is responsible for the removal of 25-30% of all infused lactate. Most of such removal is through lactate metabolism rather than excretion, although under conditions of marked hyperlactatemia such excretion can account for approximately 10-12% of renal lactate disposal. Indeed, nephrectomy results in an approximately 30% decrease in exogenous lactate removal. Importantly and differently from the liver, however, the kidney's ability to remove lactate is increased by acidosis. While acidosis inhibits hepatic lactate metabolism, it increases lactate uptake and utilization via gluconeogenesis by stimulating the activity of phospho-enolpyruvate carboxykinase. The kidney remains an effective lactate-removing organ even during endotoxemic shock. The artificial kidney also has a profound effect on lactate balance. If lactate-buffered fluids are used in patients who require continuous hemofiltration and who have pretreatment hyperlactatemia, the serum lactate levels can significantly increase. In some cases, this increase can result in an exacerbation of metabolic acidosis. If bicarbonate-buffered replacement fluids are used, a significant correction of the acidosis or acidemia can also be achieved. The clinician needs to be aware of these renal effects on lactate levels to understand the pathogenesis of hyperlactatemia in critically ill patients, and to avoid misinterpretations and unnecessary or inappropriate diagnostic or therapeutic activities.

The bradykinin response and early hypotension at the introduction of continuous renal replacement therapy in the intensive care unit

We assessed the relationship of certain clinical variables (including bradykinin [BK] release and dialysis membrane) to initial mean arterial pressure (MAP) reduction in 47 patients requiring continuous renal replacement therapy (CRRT) in an intensive care unit. The pretreatment MAP was 84 +/- 14 mm Hg for the group as a whole. The initial MAP reduction was 11.5 (7-20) mm Hg, occurring 4 to 8 min after connection. MAP reduction was 9 (6-15) mm Hg with polyacryonitrile (PAN) membranes versus 14 (5-19) mm Hg with polysulfone (PS) (not significant). There were positive correlations between MAP reduction and BK concentration at 3 (BK3; r = 0.58, p < 0.01) and 6 (BK6; r = 0.67, p < 0.001) min with PAN but not with PS. A greater reduction in MAP was seen in patients who were not receiving inotropic support (Mann-Whitney test, p < 0.01). BK3 and BK6 values for the PAN and PS groups were not significantly different. However, BK concentrations greater than 1,000 pg/ml were only seen with PAN (6 patients, MAP reduction 27 [17-31] mm Hg). There were positive (albumin) and negative (age; acute physiology, age, and chronic health evaluation score; C-reactive protein [CRP]; calcium) correlations with BK3/BK6 in the PAN and PS groups, some of which (albumin, CRP) reached statistical significance. In summary, MAP reduction at the start of CRRT correlates with BK concentration. The similarity of response with PAN and PS suggests an importance for other clinical factors. In this study, hemodynamic instability was more likely in patients with evidence of a less severe inflammatory or septic illness.

Use of base in the treatment of severe acidemic states

Severe acidemia (blood pH < 7.1 to 7.2) suppresses myocardial contractility, predisposes to cardiac arrhythmias, causes venoconstriction, and can decrease total peripheral vascular resistance and blood pressure, reduce hepatic blood flow, and impair oxygen delivery. These alterations in organ function can contribute to increased morbidity and mortality. Although it seemed logical to administer sodium bicarbonate to attenuate acidemia and therefore lessen the impact on cardiac function, the routine use of bicarbonate in the treatment of the most common causes of severe acidemia, diabetic ketoacidosis, lactic acidosis, and cardiac arrest, has been an issue of great controversy. Studies of animals and patients with these disorders have reported conflicting data on the benefits of bicarbonate, showing both beneficial and detrimental effects. Alternative alkalinizing agents, tris-hydroxymethyl aminomethane and Carbicarb, have shown some promise in studies of animals and humans, and reevaluation of these buffers in the treatment of severe acidemic states seems warranted. The potential value of base therapy in the treatment of severe acidemia remains an important issue, and further studies are required to determine which patients should be administered base therapy and what base should be used.

The value of blood lactate measurements in ICU: an evaluation of the role in the management of patients on haemofiltration

In response to clinical demand some point-of-care analysers now provide blood lactate measurements, but recently concern has been expressed about the value and interpretation of these measurements. We undertook this study to evaluate blood lactate measurements in patients with acute renal failure undergoing haemofiltration (HF) with lactate replacement fluid. At baseline, 27 patients had base deficits of >5 mmol/l and 14 (52%) had blood lactates of >3.5 mmol/l. Lactate 'tolerance' was monitored by peak changes in these parameters during the procedure. There was a worsening of base deficit in only three of the patients in whom lactate rises exceeded 10 mmol/l with one survivor. Twelve patients with rises of blood lactate greater than 5 mmol/l improved their base deficit (+1 to +17) with eight (67%) survivors. Of the remaining 12 patients with improved base deficit (+2 to +20), 10 (83%) survived. Lactate tolerance was compromised in patients with co-incidental liver disease, those on inotropic support, and in patients with initial blood lactate measurements of >10 mmol/l and large base deficits. The data suggest that blood lactate and simultaneous acid-base response measurements during HF help to assign correct buffer replacement and should be performed on all patients.

Lactic Acidosis Update for Critical Care Clinicians

Abstract. Lactic acidosis is a broad-anion gap metabolic acidosis caused by lactic acid overproduction or underutilization. The quantitative dimensions of these two mechanisms commonly differ by 1 order of magnitude. Overproduction of lactic acid, also termed type A lactic acidosis, occurs when the body must regenerate ATP without oxygen (tissue hypoxia). Circulatory, pulmonary, or hemoglobin transfer disorders are commonly responsible. Overproduction of lactate also occurs with cyanide poisoning or certain malignancies. Underutilization involves removal of lactic acid by oxidation or conversion to glucose. Liver disease, inhibition of gluconeogenesis, pyruvate dehydrogenase (thiamine) deficiency, and uncoupling of oxidative phosphorylation are the most common causes. The kidneys also contribute to lactate removal. Concerns have been raised regarding the role of metformin in the production of lactic acidosis, on the basis of individual case reports. The risk appears to be considerably less than with phenformin and involves patients with underlying severe renal and cardiac dysfunction. Drugs used to treat lactic acidosis can aggravate the condition. NaHCO3 increases lactate production. Treatment of type A lactic acidosis is particularly unsatisfactory. NaHCO3 is of little value. Carbicarb is a mixture of Na2CO3 and NaHCO3 that buffers similarly to NaHCO3 but without net generation of CO2. The results from animal studies are promising; however, clinical trials are sparse. Dichloroacetate stimulates pyruvate dehydrogenase and improves laboratory values, but unfortunately not survival rates, among patients with lactic acidosis. Hemofiltration has been advocated for the treatment of lactic acidosis, on the basis of anecdotal experiences. However, kinetic studies of lactate removal do not suggest that removal can counteract lactate production in any meaningful way. The ideal treatment is to stop acid production by treating the underlying disorder.

Effects of lactate-buffered and lactate-free dialysate in CAVHD patients with and without liver dysfunction

BACKGROUND

Continuous modalities of renal replacement deplete patients of bicarbonate, which is traditionally replaced indirectly by lactate in dialysate or replacement fluids. We have compared a new lactate-free dialysate (unbuffered dialysate with separate bicarbonate replacement of dialytic bicarbonate loss) with standard lactate-buffered dialysate in terms of acid-base control, lactate accumulation, and hemodynamic stability in patients undergoing continuous renal replacement therapy in an intensive care unit.

METHODS

A nonrandomized crossover cohort study involving 54 patients with multi-organ failure (of whom 19 had significant hepatic dysfunction) was performed. All patients completed 24-hour continuous hemodiafiltration against both lactate-buffered and lactate-free dialysate. Arterial pH, blood gases, bicarbonate, and lactate, venous sodium, blood pressure, and inotrope requirements were measured before and at six hourly intervals during the first 24 hours of dialysis against each dialysate.

RESULTS

Lactate-free dialysate provided more rapid control of acidosis than lactate buffered with less total administration of buffer than that given during the lactate-buffered period (total mmol bicarbonate vs. total mmol lactate + bicarbonate). Lactate accumulation was slight in both periods, but was higher during lactate-buffered continuous venovenous hemodiafiltration (CVVHD). The mean arterial pressure rose during lactate-free dialysis with decreased inotrope doses and fell during lactate-buffered dialysis with increased inotrope requirement. Results in patients with liver dysfunction were not significantly different from those without it.

CONCLUSIONS

Over the time scale of 24 hours, lactate derived from continuous dialysis circuits is efficiently cleared from the blood of most patients with multi-organ failure, but with less effect on systemic acidosis than is produced by equivalent amounts of bicarbonate.

Non-renal indications for continuous renal replacement therapy

While there is clear support for the use of continuous renal replacement therapy (CRRT) in critically ill acute renal failure patients, there are other illnesses without renal involvement where CRRT might be of value. These include sepsis and other inflammatory syndromes such as acute respiratory distress syndrome (ARDS) and cardiopulmonary bypass where removal of inflammatory mediators by hemofiltration is hypothesized to improve outcome. Adsorption appears to be the predominant mechanism of mediator elimination. However, the observed hemodynamic improvement can, at least partially, be attributed to a reduction of body temperature or to fluid removal, and the evidence for a clinically important removal of proinflammatory cytokines remains limited. Continuous and therefore smooth fluid removal may improve organ function in ARDS, after surgery with cardiopulmonary bypass, and in patients with refractory congestive heart failure. Continuous removal of endogenous toxins, eventually combined with intermittent hemodialysis, is probably beneficial in inborn errors of metabolism, severe lactic acidosis, or tumor lysis syndrome.