Mild hyperlactatemia in stable septic patients is due to impaired lactate clearance rather than overproduction

Lactate in veterinary critical care: pathophysiology and management

The measurement of blood lactate in people has proven to be a useful tool in the diagnosis, monitoring, and prognosis of a wide range of clinical syndromes. Its use in small animals is increasing, and several studies have been completed that demonstrate its potential role in critical care. This article summarizes the current state of knowledge regarding the physiology and pathophysiology of lactate production and lactic acidosis; current indications and the utility of measurement in a critical care setting are described; novel applications in the evaluation of cavitary effusions are highlighted; and a guide to the therapy of lactic acidosis is presented.

Acid-base disturbances in critically ill patients with cirrhosis

BACKGROUND/AIMS

The equilibrium of offsetting metabolic acid-base disorders in stable cirrhosis might be lost during episodes of hepatic decompensation, haemorrhage or sepsis. The purpose of this study was to determine whether the acid-base state is destabilized in critically ill patients with cirrhosis and whether this is associated with mortality.

PATIENTS AND METHOD

One-hundred and eighty-one consecutive patients with cirrhosis were investigated in a prospective observational cohort study on admission to a medical intensive care unit (ICU) of a university hospital. Arterial acid-base state was assessed according to the Gilfix methodology. Clinical data, ICU mortality and hospital mortality were recorded.

MAIN RESULTS

Patients had net metabolic acidosis owing to unmeasured anions and owing to hyperchloraemic, dilutional and lactic acidosis. Lactic acidosis, acidemia and acute renal failure on ICU admission were associated with increased mortality. Lactate and pH discriminated survivors from non-survivors. The presence of lactic acidosis could not always be recognized by customary acid-base parameters.

CONCLUSION

The stable equilibrium of acid-base disorders is lost when patients with cirrhosis become critically ill. Lactic acidosis and acidaemia are associated with increased ICU mortality caused by severe underlying organ dysfunction.

Substrate utilization in sepsis and multiple organ failure

Sepsis and multiple organ failure are characterized by an excessive release of inflammatory mediators and a marked stimulation of stress hormones. These in turn have profound effects on energy and substrate metabolism: energy expenditure is generally increased, and increased lipolysis and fat oxidation are observed. Net protein breakdown occurs and leads to accelerated wasting. Most of these effects can be produced in healthy humans by administration of bacterial endotoxin or by tumor necrosis factor-alpha. Hyperlactatemia is a hallmark of sepsis and critical illness, and its severity is related to mortality. An increased lactate production, possibly secondary to activation of Na-K adenosine 5'-triphosphatase and to muscle mitochondrial dysfunction, is involved. Lactate production by immune cells and wound tissue may also play a role. Long-chain, n-3 polyunsaturated fatty acids have anti-inflammatory effects that may be beneficial in sepsis. They also decrease the stimulation of stress hormones induced by bacterial endotoxin, possibly through an effect exerted at the level of the central nervous sytem. Their use in patients with sepsis does not lead to adverse metabolic effects.

Occult hypoperfusion and mortality in patients with suspected infection

OBJECTIVE

To determine, in the early stages of suspected clinically significant infection, the independent relationship of the presenting venous lactate level to 28-day in-hospital mortality.

DESIGN

Prospective, observational cohort study.

SETTING

Urban, university tertiary-care hospital.

PATIENTS

One thousand two hundred and eighty seven adults admitted through the emergency department who had clinically suspected infection and a lactate measurement.

MEASUREMENTS AND RESULTS

Seventy-three [5.7% (95% CI 4.4-6.9%)] patients died in the hospital within 28 days. Lactate level was strongly associated with 28-day in-hospital mortality in univariate analysis (p<0.0001). When stratified by blood pressure, lactate remained associated with mortality (p<0.0001). Normotensive patients with a lactate level >or=4.0 mmol/l had a mortality rate of 15.0% (6.0-24%). Patients with either septic shock or lactate >or=4.0 mmol/l had a mortality rate of 28.3% (21.3-35.3%), which was significantly higher than those who had neither [mortality of 2.5% (1.6-3.4%), p<0.0001. In a model controlling for age, blood pressure, malignancy, platelet count, and blood urea nitrogen level, lactate remained strongly associated with mortality. Patients with a lactate level of 2.5-4.0 mmol/l had adjusted odds of death of 2.2 (1.1-4.2); those with lactate >or=4.0 mmol/l had 7.1 (3.6-13.9) times the odds of death. The model had good discrimination (AUC=0.87) and was well calibrated.

CONCLUSIONS

In patients admitted with clinically suspected infection, the venous lactate level predicts 28-day in-hospital mortality independent of blood pressure and adds significant prognostic information to that provided by other clinical predictors.

Hemodynamic monitoring in shock and implications for management. International Consensus Conference, Paris, France, 27-28 April 2006

OBJECTIVE

Shock is a severe syndrome resulting in multiple organ dysfunction and a high mortality rate. The goal of this consensus statement is to provide recommendations regarding the monitoring and management of the critically ill patient with shock.

METHODS

An international consensus conference was held in April 2006 to develop recommendations for hemodynamic monitoring and implications for management of patients with shock. Evidence-based recommendations were developed, after conferring with experts and reviewing the pertinent literature, by a jury of 11 persons representing five critical care societies.

DATA SYNTHESIS

A total of 17 recommendations were developed to provide guidance to intensive care physicians monitoring and caring for the patient with shock. Topics addressed were as follows: (1) What are the epidemiologic and pathophysiologic features of shock in the ICU? (2) Should we monitor preload and fluid responsiveness in shock? (3) How and when should we monitor stroke volume or cardiac output in shock? (4) What markers of the regional and micro-circulation can be monitored, and how can cellular function be assessed in shock? (5) What is the evidence for using hemodynamic monitoring to direct therapy in shock? One of the most important recommendations was that hypotension is not required to define shock, and as a result, importance is assigned to the presence of inadequate tissue perfusion on physical examination. Given the current evidence, the only bio-marker recommended for diagnosis or staging of shock is blood lactate. The jury also recommended against the routine use of (1) the pulmonary artery catheter in shock and (2) static preload measurements used alone to predict fluid responsiveness.

CONCLUSIONS

This consensus statement provides 17 different recommendations pertaining to the monitoring and caring of patients with shock. There were some important questions that could not be fully addressed using an evidence-based approach, and areas needing further research were identified.

Metabolic effects of vasoactive agents

After adequate volume resuscitation, the mainstay of therapy in critically ill patients with shock is treatment with vasoactive substances to restore haemodynamics or to improve regional perfusion. These agents include adrenoceptor agonists with inotropic combined with either vasoconstricting or vasodilating effects, and predominantly vasodilating drugs such as prostacyclin and related compounds. However, vasoactive agents not only affect the cardiovascular system, but also have profound metabolic effects. The interdependence of vasoactive drugs with metabolism may be relevant regarding adequate oxygen and substrate delivery to cover actual organ needs. Therefore, the profiles of these metabolic effects have to be considered during their therapeutic administration.

The ArcA regulon and oxidative stress resistance in Haemophilus influenzae

Haemophilus influenzae transits between niches within the human host that are predicted to differ in oxygen levels. The ArcAB two-component signal transduction system controls gene expression in response to respiratory conditions of growth and has been implicated in bacterial pathogenesis, yet the mechanism is not understood. We undertook a genome-scale study to identify genes of the H. influenzae ArcA regulon. Deletion of arcA resulted in increased anaerobic expression of genes of the respiratory chain and of H. influenzae's partial tricarboxylic acid cycle, and decreased anaerobic expression levels of genes of polyamine metabolism, and iron sequestration. Deletion of arcA also conferred a susceptibility to transient exposure to hydrogen peroxide that was greater following anaerobic growth than after aerobic growth. Array data revealed that the dps gene, not previously assigned to the ArcA modulon in bacteria, exhibited decreased expression in the arcA mutant. Deletion of dps resulted in hydrogen peroxide sensitivity and complementation restored resistance, providing insight into the previously uncharacterized mechanism of arcA-mediated H(2)O(2) resistance. The results indicate a role for H. influenzae arcA and dps in pre-emptive defence against transitions from growth in low oxygen environments to aerobic exposure to hydrogen peroxide, an antibacterial oxidant produced by phagocytes during infection.

Lactate and shock state: the metabolic view

PURPOSE OF REVIEW

The conventional view in severe sepsis or septic shock is that most of the lactate that accumulates in the circulation is due to cellular hypoxia and the onset of anaerobic glycolysis. A number of papers have suggested that lactate formation during sepsis is not due to hypoxia. I discuss this hypothesis and outline the recent advances in the understanding of lactate metabolism in shock.

RECENT FINDINGS

Numerous experimental data have demonstrated that stimulation of aerobic glycolysis - that is, glycolysis not attributable to oxygen deficiency - and glycogenolysis occurs not only in resting, well-oxygenated skeletal muscles but also during experimental haemorrhagic shock and experimental sepsis, and is closely linked to stimulation of sarcolemmal Na+/K+ -ATPase under epinephrine stimulation. A human study of hyperkinetic septic shock demonstrated that skeletal muscle is a leading source of lactate production by exaggerated aerobic glycolysis through Na+/K+ -ATPase stimulation.

SUMMARY

There is increasing evidence that sepsis is accompanied by a hypermetabolic state, with enhanced glycolysis and hyperlactataemia. This should not be rigorously interpreted as an indication of hypoxia. It now appears, at least in the hyperkinetic state, that increased lactate production and concentration as a result of hypoxia are often the exception rather than the rule.

Prognostic implications of hyperlactatemia, multiple organ failure, and systemic inflammatory response syndrome in patients with acetaminophen-induced acute liver failure

OBJECTIVE

Hyperlactatemia has been suggested as a prognostic marker in acetaminophen-induced fulminant hepatic failure, and a modification of the King's College Hospital criteria to incorporate arterial lactate measurements has recently been proposed. The aims of the present study were to further evaluate arterial lactate as a prognostic marker in acetaminophen-induced fulminant hepatic failure and to analyze its relationship to known causes of hyperlactatemia such as multiple organ failure and inflammation.

DESIGN

Data were collected early after admission and again at the time of onset of grade 3-4 hepatic encephalopathy from acetaminophen-induced fulminant hepatic failure. Multiple organ failure and inflammatory response were assessed by the sequential organ failure assessment (SOFA) score and manifestation of the severe inflammatory response syndrome (SIRS), respectively.

SETTING

A specialized liver intensive care unit at a tertiary liver center.

PATIENTS

One hundred and one consecutive patients with acetaminophen-induced fulminant hepatic failure and grade 3-4 hepatic encephalopathy.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Arterial lactate was higher in nonsurvivors than in survivors both early after admission (9.8 +/- 6.5 mmol/L vs. 5.2 +/- 4.2 mmol/L, p = .00004) and at the time of onset of hepatic encephalopathy (6.9 +/- 5.6 mmol/L vs. 3.2 +/- 2.0 mmol/L, p < .00001). At both time points, arterial lactate significantly correlated with SOFA score and the number of SIRS components fulfilled. Applying the lactate modification of the King's College Hospital criteria increased their sensitivity but reduced their specificity to <50%.

CONCLUSIONS

The study confirmed arterial lactate as a prognostic marker in acetaminophen-induced fulminant hepatic failure. Arterial lactate correlated with SOFA score and with the number of SIRS components fulfilled. The lactate modification of the King's College Hospital criteria showed no obvious advantages over the existing selection criteria.

Lactate and glucose metabolism in severe sepsis and cardiogenic shock

OBJECTIVE

To evaluate the relative importance of increased lactate production as opposed to decreased utilization in hyperlactatemic patients, as well as their relation to glucose metabolism.

DESIGN

Prospective observational study.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

Seven patients with severe sepsis or septic shock, seven patients with cardiogenic shock, and seven healthy volunteers.

INTERVENTIONS

C-labeled sodium lactate was infused at 10 micromol/kg/min and then at 20 micromol/kg/min over 120 mins each. H-labeled glucose was infused throughout.

MEASUREMENTS AND MAIN RESULTS

Baseline arterial lactate was higher in septic (3.2 +/- 2.6) and cardiogenic shock patients (2.8 +/- 0.4) than in healthy volunteers (0.9 +/- 0.20 mmol/L, p < .05). Lactate clearance, computed using pharmacokinetic calculations, was similar in septic, cardiogenic shock, and controls, respectively: 10.8 +/- 5.4, 9.6 +/- 2.1, and 12.0 +/- 2.6 mL/kg/min. Endogenous lactate production was determined as the initial lactate concentration multiplied by lactate clearance. It was markedly enhanced in the patients (septic 26.2 +/- 10.5; cardiogenic shock 26.6 +/- 5.1) compared with controls (11.2 +/- 2.7 micromol/kg/min, p < .01). C-lactate oxidation (septic 54 +/- 25; cardiogenic shock 43 +/- 16; controls 65 +/- 15% of a lactate load of 10 micromol/kg/min) and transformation of C-lactate into C-glucose were not different (respectively, 15 +/- 15, 9 +/- 18, and 10 +/- 7%). Endogenous glucose production was markedly increased in the patients (septic 14.8 +/- 1.8; cardiogenic shock 15.0 +/- 1.5) compared with controls (7.2 +/- 1.1 micromol/kg/min, p < .01) and was not influenced by lactate infusion.

CONCLUSIONS

In patients suffering from septic or cardiogenic shock, hyperlactatemia was mainly related to increased production, whereas lactate clearance was similar to healthy subjects. Increased lactate production was concomitant to hyperglycemia and increased glucose turnover, suggesting that the latter substantially influences lactate metabolism during critical illness.

Clinical review: the meaning of acid-base abnormalities in the intensive care unit part I - epidemiology

Acid-base abnormalities are common in critically ill patients. Our ability to describe acid-base disorders must be precise. Small differences in corrections for anion gap, different types of analytical processes, and the basic approach used to diagnose acid-base aberrations can lead to markedly different interpretations and treatment strategies for the same disorder. By applying a quantitive acid-base approach, clinicians are able to account for small changes in ion distribution that may have gone unrecognized with traditional techniques of acid-base analysis. Outcome prediction based on the quantitative approach remains controversial. This is in part due to use of various technologies to measure acid-base variables, administration of fluid or medication that can alter acid-base results, and lack of standardized nomenclature. Without controlling for these factors it is difficult to appreciate the full effect that acid-base disorders have on patient outcomes, ultimately making results of outcome studies hard to compare.

EFFECTS OF DOPAMINE AND NOREPINEPHRINE ON SYSTEMIC AND HEPATOSPLANCHNIC HEMODYNAMICS, OXYGEN EXCHANGE, AND ENERGY BALANCE IN VASOPLEGIC SEPTIC PATIENTS

Dopamine is widely used to improve systemic and hepatosplanchnic hemodynamics and oxygenation during sepsis. However, some studies have suggest that norepinephrine may have beneficial effects on regional blood flow and metabolism, whereas dopamine might have deleterious effects related to redistribution of blood flow away from the intestinal mucosa or by decreasing directly the cell redox state. In 12 vasoplegic septic patients, we compared the effects of norepinephrine and dopamine on systemic and hepatosplanchnic hemodynamics, oxygenation, and energy metabolism. Catecholamines were administered in a crossover randomized order to maintain mean arterial pressure (MAP) at 80 mmHg. Hepatosplanchnic blood flow (Qspl) was determined using a continuous infusion of indocyanine green dye. Despite a similar MAP, the cardiac index was higher with dopamine than with norepinephrine (6.3 [5.3-7.3] vs. 4.3 [3.8-4.9] L.min.m) (P <0.001). Qspl was similar with both catecholamines, but the ratio of Qspl to cardiac output was significantly lower with dopamine (23.9% [17.5-33.5]) than with norepinephrine (33.5% [25.8-37]) (P <0.05). Although global O2 delivery and O2 consumption were higher with dopamine (782 [707-859] vs. 553 [512-629] mL.min.m, P <0.001 and 164 [134-192] vs. 128 [111-149] mL.min.m, P <0.001, respectively), hepatosplanchnic O2 delivery and consumption were not different. Hepatic lactate uptake was lower (0.47 [0.3-0.89] vs. 1.01 [0.69-1.34] mmol.min) (P <0.01), and hepatic venous lactate-to-pyruvate ratio was higher (15.3 [7.6-21.1] vs. 11.2 [6.6-15.1], P <0.05) with dopamine than with norepinephrine. In vasoplegic septic patients, maintaining mean arterial pressure, hepatosplanchnic hemodynamics, and oxygen exchange with dopamine requires a consequent increased cardiac output, which is responsible for an increased global oxygen demand when compared with norepinephrine. In addition, dopamine impairs the hepatic energy balance. Its position as a preferential treatment compared with norepinephrine in this context may therefore be questionable.

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.

THE HEPATOSPLANCHNIC CONTRIBUTION TO HYPERLACTATEMIA IN ENDOTOXIC SHOCK: EFFECTS OF TISSUE ISCHEMIA

We investigated the role of the hepatosplanchnic region in the hyperlactatemia observed during endotoxic shock. The study included 18 dogs anesthetized with pentobarbital and mechanically ventilated. After baseline measurements, including gut lactate production (GLP), liver lactate uptake (LLU), liver lactate extraction (LLE), and hepatosplanchnic lactate production (HSLP), each dog received 2 mg/kg of E. coli endotoxin. After a second set of measurements, cardiac tamponade was induced in 12 dogs (EDTX + Tamp) by repeated injections of normal saline into the pericardial sac to progressively reduce cardiac output and hepatic blood flow. The six remaining dogs served as septic controls (EDTX). From a net lactate consumer before endotoxin infusion, the gut became a lactate producer after the endotoxin infusion, with GLP increasing from -11.4 +/- 27.0 to 32.9 +/- 38.2 x 10(-3) mEq/min (P < 0.05). LLU increased from 48.1 +/- 26.2 to 86.6 +/- 45.2 x 10(-3) mEq/min (P < 0.05), so that LLE and HSLP did not change. In the EDTX + Tamp group, LLE became negative, and HSLP became positive only when hepatic oxygen delivery reached its critical value during cardiac tamponade. In the EDTX group, LLE remained positive and HSLP negative. In endotoxic shock, GLP is increased, but the liver can metabolize this additional load of lactate, so that the hepatosplanchnic area is not a major source of lactate unless the liver becomes profoundly hypoxic.

Lactic and hydrochloric acids induce different patterns of inflammatory response in LPS-stimulated RAW 264.7 cells

Metabolic acidosis frequently complicates sepsis and septic shock and may be deleterious to cellular function. Different types of metabolic acidosis (e.g., hyperchloremic and lactic acidosis) have been associated with different effects on the immune response, but direct comparative studies are lacking. Murine macrophage-like RAW 264.7 cells were cultured in complete medium with lactic acid or HCl to adjust the pH between 6.5 and 7.4 and then stimulated with LPS ( Escherichia coli 0111:B4; 10 ng/ml). Nitric oxide (NO), IL-6, and IL-10 levels were measured in the supernatants. RNA was extracted from the cell pellets, and RT-PCR was performed to amplify corresponding mediators. Gel shift assay was also performed to assess NF-κB DNA binding. Increasing concentrations of acid caused increasing acidification of the media. Trypan blue exclusion and lactate dehydrogenase release demonstrated that acidification did not reduce cell viability. HCl significantly increased LPS-induced NO release and NF-κB DNA binding at pH 7.0 but not at pH 6.5. IL-6 and IL-10 expression (RNA and protein) were reduced with HCl-induced acidification, but IL-10 was reduced much more than IL-6 at low pH. By contrast, lactic acid significantly decreased LPS-induced NO, IL-6, and IL-10 expression in a dose-dependent manner. Lactic acid also inhibited LPS-induced NF-κB DNA binding. Two common forms of metabolic acidosis (hyperchloremic and lactic acidosis) are associated with dramatically different patterns of immune response in LPS-stimulated RAW 264.7 cells. HCl is essentially proinflammatory as assessed by NO release, IL-6-to-IL-10 ratios, and NF-κB DNA binding. By contrast, lactic acidosis is anti-inflammatory.

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.

The roles of insulin and hyperglycemia in sepsis pathogenesis

Hyperglycemia is a risk marker of morbidity and mortality in acute critical illness, and insulin therapy seems to be beneficial in this patient group. Whether this is true for a population of sepsis patients, as such, has not been investigated in clinical trials, but evidence from in vitro studies and experimental sepsis suggests that this may be the case. The endocrinology of septic patients is characterized by a shift in the balance between insulin and its counter-regulatory hormones favoring the latter. This leads to prominent metabolic derangements composed of high release and low use of glucose, amino acids, and free fatty acids (FFA), resulting in increased blood levels of these substrates. Circulating, proinflammatory mediators further enhance this state of global catabolism. Increased levels of glucose and FFA have distinct effects on inflammatory signaling leading to additional release of proinflammatory mediators and endothelial and neutrophil dysfunction. Insulin has the inherent capability to counteract the metabolic changes observed in septic patients. Concomitantly, insulin therapy may act as a modulator of inflammatory pathways inhibiting the unspecific, inflammatory activation caused by metabolic substrates. Given these properties, insulin could conceivably be serving a dual purpose for the benefit of septic patients.

Anaemia and red blood cell transfusion in the critically ill patient

Anaemia is a common finding in critically ill patients. There are often multiple causes. Obvious causes include surgical bleeding and gastrointestinal haemorrhage but many patients have no overt bleeding episodes. Phlebotomy can be a significant source of blood loss. In addition, critically ill patients have impaired erythropoiesis as a consequence of blunted erythropoietin production and direct inhibitory effects of inflammatory cytokines. The ability of a patient to tolerate anaemia depends on their clinical condition and the presence of any significant co-morbidity; maintenance of circulating volume is of paramount importance. There is no universal transfusion trigger. Current guidelines for critically ill and perioperative patients advise that at Hb values <70 g/L red blood cell transfusion is strongly indicated and at Hb values >100 g/L transfusion is unjustified. For patients with Hb values in the range 70 to 100 g/L the transfusion trigger should be based on clinical indicators. Most stable critically ill patients can probably be managed with a Hb concentration between 70 and 90 g/L. Uncertainties exist concerning the most appropriate Hb concentration for patients with significant cardio-respiratory disease.

Assessment of adipose tissue metabolism by means of subcutaneous microdialysis in patients with sepsis or circulatory failure

To evaluate the role of adipose tissue in the metabolic stress response of critically ill patients, the release of glycerol and lactate by subcutaneous adipose tissue was assessed by means of microdialysis in patients with sepsis or circulatory failure and in healthy subjects. Patients with sepsis had lower plasma free fatty acid concentrations and non-significant elevations of plasma glycerol concentrations, but higher adipose-systemic glycerol concentrations gradients than healthy subjects or patients with circulatory failure, indicating a stimulation of subcutaneous adipose lipolysis. They also had a higher lipid oxidation. Lipid metabolism (adipose-systemic glycerol gradients, lipid oxidation) was not altered in patients with circulatory failure. These observations highlight major differences in lipolysis and lipid utilization between patients with sepsis and circulatory failure. Hyperlactataemia was present in both groups of patients, but the adipose-systemic lactate concentration gradient was not increased, indicating that lactate production by adipose tissue was not involved. This speaks against a role of adipose tissue in the development of hyperlactataemia in critically ill patients.

Metabolic alterations in sepsis and vasoactive drug-related metabolic effects

The main clinical characteristics of sepsis and septic shock are derangements of cardiocirculatory and respiratory function. Additionally, profound alterations in metabolic pathways occur leading to hypermetabolism, enhanced energy expenditure, and insulin resistance. The clinical hallmarks are hyperglycemia, hyperlactatemia, and enhanced protein catabolism. These metabolic alterations are even more pronounced during sepsis as a result of cytokine release and subsequent induction of inflammatory pathways. Increased oxygen demands from mitochondrial oxygen utilization and oxygen consumption related to oxygen radical formation may contribute to hypermetabolism. In addition, mitochondrial dysfunction with impaired cellular respiration may be present. Mainstay therapeutic interventions for hemodynamic stabilization are adequate volume resuscitation and vasoactive agents, which, however, have additional impact on metabolic activity. Therefore, beyond hemodynamic effects, specific drug-related metabolic alterations need to be considered for optimal treatment during sepsis. This review gives an overview of the typical metabolic alterations during sepsis and septic shock and highlights the impact of vasoactive therapy on metabolism.

Resolution and outcome of acute circulatory failure does not correlate with hemodynamics

INTRODUCTION

Hemodynamic goals in the treatment of acute circulatory failure (ACF) are controversial. In critical care, organ failures can be assessed using Sequential Organ Failure Assessment and its refinement, total maximal Sequential Organ Failure Assessment (TMS). We studied the associations between resolution of ACF and hemodynamics in the early (< 24 hours) phase of intensive care unit care and their relation to TMS and mortality.

PATIENTS AND METHODS

Eighty-three patients with ACF (defined as arterial lactate > 2 mmol/l and/or base deficit > 4) who had pulmonary artery catheters and stayed for longer than 24 hours in the intensive care unit were included. Hemodynamics, oxygen transport, vasoactive drugs and TMS scores were recorded. Normalisation of hyperlactatemia and metabolic acidosis in less than 24 hours after admission was defined as a positive response to hemodynamic resuscitation.

RESULTS

Fifty-two patients responded to resuscitation. Nonresponders had higher mortality than responders (52% versus 33%, P = 0.044). Hospital mortality was highest (63%) among nonresponders who received vasoactive drugs. The TMS scores of nonresponders (median [interquartile range], 12 9-16) were higher than the scores of responders (10 7-12, P = 0.019). Late accumulation of TMS scores was associated with increasing mortality, and if the TMS score increase occurred > 5 days after admission then the mortality was 77%. Responders had higher mean arterial pressure at 24 hours, but it was no different between survivors and nonsurvivors. No other hemodynamic and oxygen transport variables were associated with the success of resuscitation or with mortality.

CONCLUSIONS

Except for the mean arterial pressure at 24 hours, invasively derived hemodynamic and oxygen transport variables are not associated with the response to resuscitation or with mortality. Positive response to resuscitation in ACF is associated with less severe organ failures as judged by TMS scores. Late accumulation of the TMS score predicts poor outcome.

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.

Low exogenous lactate clearance as an early predictor of mortality in normolactatemic critically ill septic patients

OBJECTIVE

To evaluate the prognostic value of lactate clearance and lactate production in severely ill septic patients with normal or mildly elevated blood lactate concentration. DESIGN Prospective, observational study.

SETTING

Nineteen-bed mixed medicosurgical intensive care unit.

PATIENTS

Fifty-six patients with severe sepsis and blood lactate concentration <3 mmol/L.

MEASUREMENTS AND MAIN RESULTS

Lactate metabolism was evaluated in all patients. Lactate clearance was measured by modeling the change in arterial blood lactate over time induced by an infusion of 1 mmol/kg sodium lactate for 15 mins. Lactate production was calculated as the product of lactate clearance times the blood lactate concentration before the infusion. Outcome was taken to be mortality at 28 days after the beginning of the septic episode. A logistic regression model taking into account different risk factors was constructed. Among the 56 patients, 17 (30.3%) died before the 28th day. Basal blood lactate concentration was not different between survivors and nonsurvivors, whereas lactate clearance and production were higher in survivors (0.86 +/- 0.32 vs. 0.58 +/- 0.18 L/hr/kg, p < .005, and 1.19 +/- 0.63 vs. 0.89 +/- 0.24 mmol/hr/kg, p = .055, respectively). An increase in blood lactate 45 mins after the end of the lactate infusion (Deltalact-T60) > or = 0.6 mmol/L was predictive of 28-day mortality with 53% sensitivity and 90% specificity. Multivariate analysis showed that only three factors were independently and significantly correlated with 28-day mortality: presence of more than two organ failures (odds ratio, 27; p = .04), age >70 yrs (odds ratio, 5.7; p = .032), and Deltalact-T60 > or =0.6 mmol/L (odds ratio, 14.2; p = .042).

CONCLUSION

Low lactate clearance in severely ill septic patients with normal or mildly elevated blood lactate is predictive of poor outcome independently of other known risk factors such as age and number of organ failures.

Impaired mitochondrial function induced by serum from septic shock patients is attenuated by inhibition of nitric oxide synthase and poly(ADP-ribose) synthase

OBJECTIVE

The purpose of this study was to determine the role of nitric oxide and poly(ADP-ribose) synthase on impaired mitochondrial function in septic shock.

DESIGN

Human umbilical vein endothelial cells were incubated with serum from ten healthy controls, 20 patients with septic shock, and seven critically ill patients who were not septic. The experiment was repeated after pretreatment with 3-aminobenzamide, a poly(ADP-ribose) synthase inhibitor, or N(G)-methyl-L-arginine, a nonspecific nitric oxide synthase inhibitor.

MEASUREMENTS

Mitochondrial respiration was measured using a modified MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) assay.

SETTING

Research laboratory.

MAIN RESULT

Endothelial cell mitochondrial respiration was significantly depressed by septic serum and averaged 61% +/- 6% of control values (p <.05). Incubation with septic serum as compared with control serum also significantly decreased cellular adenosine triphosphate levels (6.7 +/- 1.2 nM vs. 13.5 +/- 1.9 nM, p<.01). The level of mitochondrial respiration in endothelial cells exposed to septic serum did not correlate with arterial lactate concentration but was correlated with both cardiac output (r(s) =.52, p<.05) and mixed venous oxygen saturation (r(s) =.61, p<.05). Pretreatment with N(G)-methyl-L-arginine significantly increased mitochondrial respiration in endothelial cells treated with septic serum from 63% +/- 6% of normal to 88% +/- 6% (p <.05) of normal values. Similarly, pretreatment with 3-aminobenzamide increased mitochondrial respiration in endothelial cells treated with septic serum from 64% +/- 6% to 100% +/- 4% (p <.01) of normal values. Endothelial cells incubated with serum from nonseptic critically ill patients did not demonstrate a significant decrease in mitochondrial respiration.

CONCLUSION

In vitro mitochondrial respiration was significantly depressed by septic serum. The addition of N(G)-methyl-L-arginine, a nitric oxide synthase inhibitor, and 3-aminobenzamide, a blocker of the poly(ADP-ribose) synthase pathway, significantly attenuated this suppression. These data suggest that nitric oxide and poly(ADP-ribose) synthase activation may play an important role in the inhibition of mitochondrial respiration in septic shock.

Endotoxin-induced hyperlactatemia results from decreased lactate clearance in hemodynamically stable rats

OBJECTIVE

To determine whether endotoxin-induced hyperlactatemia in hemodynamically stable animals is due to increased lactate production or decreased lactate clearance by measuring lactate turnover rate in the vascular compartment (LTRvc).

DESIGN

Prospective, controlled trial.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Male Sprague-Dawley rats weighing 275-425 g with chronic vascular catheters.

INTERVENTIONS

Chronically catheterized rats were treated with 6 microg/kg endotoxin or saline. LTRvc was determined from the specific activity of carbon-14 [14C]lactate in aortic blood during a constant infusion of [14C]lactate into the inferior vena cava. The role of the splanchnic organs in lipopolysaccharide-induced alterations in LTRvc was determined from the splanchnic first-pass clearance of [14C]lactate infused into the superior mesenteric artery and direct measurements of blood lactate concentration gradients across the splanchnic organs.

MEASUREMENTS AND MAIN RESULTS

Despite a 260% increase in lactate concentrations after lipopolysaccharide treatment, the specific activity of [14C]lactate and the LTRvc did not change, indicating that lipopolysaccharide-induced hyperlactatemia is caused by decreased lactate clearance from the vascular compartment rather than increased lactate flux into the vascular compartment. In contrast, lactate clearance by the splanchnic system was increased. The specific activity of [14C]lactate in aortic blood decreased 33% after lipopolysaccharide treatment when the [14C]lactate was infused into the superior mesenteric artery, indicating increased first-pass clearance of [14C]lactate by the splanchnic organs. Furthermore, the hepatic venous-aortic concentration gradient of lactate became increasingly negative after lipopolysaccharide treatment, indicating increased vascular extraction of lactate by the splanchnic system (0.07 +/- 0.07 micromol/mL vs. -0.34 +/- 0.14 micromol/mL).

CONCLUSIONS

Lipopolysaccharide-induced hyperlactatemia in hemodynamically stable rats is caused by a net decrease in lactate clearance from the vascular compartment despite the fact that the clearance of lactate by the splanchnic system remains intact.

Blood pH level modulates organ metabolism of lactate in septic shock in dogs

OBJECTIVE

Lactic acidosis is an important complication of septic shock. Alkali treatment such as sodium bicarbonate is often used to treat the low pH level that develops in sepsis. The effect of this treatment on lactate (Lac) clearance is not clear. In the present study, the objective was to examine whether blood pH level alters Lac metabolism in sepsis. Measurements were determined in a canine model of Escherichia coli sepsis after bolus infusion (5 mmol/kg) of either lactic acid (LA) or sodium lactate (NaL). In one preparation, Lac uptake by the splanchnic organs (SP), liver, lung, kidneys (Kid), and soft tissues of the lower extremity (SOL) was primarily determined, whereas in another preparation, Lac uptake by the head and neck region and lung was obtained.

METHODS

The dogs were studied while anesthetized and ventilated. After 4 hours of sepsis, either LA or NaL was given through a catheter positioned in the abdominal aorta in respective sepsis (SepLA, SepNaL) and nonsepsis groups (ConLA, ConNaL) (n approximately equal to 6 in each preparation). Catheters and flow probes were used to measure organ Lac uptake. Measurements were obtained at end infusion and at 15-minute intervals after infusion until 75 minutes after infusion.

RESULTS

Arterial clearance of Lac in the sepsis groups was slower as compared with the nonsepsis groups. In the liver, sepsis inhibited the uptake of LA as compared with the nonseptic group. In SP, both sepsis and pH affected Lac uptake in which an increase in uptake was found only after NaL infusion in the nonseptic group. In the head and neck region, Lac uptake was pH-level dependent and was found after LA infusion in the sepsis and nonsepsis groups. In the lung, Lac was produced after either LA or NaL infusion in all groups. Neither Kid nor SOL contributed to Lac uptake in any of the groups.

CONCLUSION

Lactate clearance was reduced in sepsis. Both effects of pH level and sepsis modulated the organ uptake of Lac in septic shock. Only a small amount of the total Lac infused could be accounted for by the organs measured in the present study. This suggests that additional organs may account for lactate removal in sepsis.

Blood lactate as an early predictor of outcome in paracetamol-induced acute liver failure: a cohort study

BACKGROUND

Although the King's College Hospital (KCH) selection criteria for emergency liver transplantation in paracetamol-induced acute liver failure are widely used, strategies to improve sensitivity and facilitate earlier transplantation are required. We investigated the use of arterial blood lactate measurement for the identification of transplantation candidates.

METHODS

In a single-centre study, we measured arterial blood lactate early (median 4 h) and after fluid resuscitation (median 12 h) in patients admitted to a tertiary-referral intensive-care unit. Threshold values that best identified individuals likely to die without transplantation were derived in a retrospective initial sample of 103 patients with paracetamol-induced acute liver failure and applied to a prospective validation sample of 107 patients. Predictive value and speed of identification were compared with those of KCH criteria.

FINDINGS

In the initial sample, median lactate was significantly higher in non-surviving patients than in survivors both in the early samples (8.5 [range 1.7--21.0] vs 1.4 [0.53--7.9] mmol/L, p<0.0001) and after fluid resuscitation (5.5 [1.3--18.6] vs 1.3 [0.26--3.2], p<0.0001). Applied to the validation sample, a threshold value of 3.5 mmol/L early after admission had sensitivity 67%, specificity 95%, positive likelihood ratio 13, and negative likelihood ratio 0.35; the corresponding values for a threshold of 3.0 mmol/L after fluid resuscitation were 76%, 97%, 30, and 0.24. Combined early and postresuscitation lactate concentrations had similar predictive ability to KCH criteria but identified non-surviving patients earlier (4 [3--13] vs 10 [3.5--19.5] h, p=0.01). Addition of postresuscitation lactate concentration to KCH criteria increased sensitivity from 76% to 91% and lowered negative likelihood ratio from 0.25 to 0.10.

INTERPRETATION

Arterial blood lactate measurement rapidly and accurately identifies patients who will die from paracetamol-induced acute liver failure. Its use could improve the speed and accuracy of selection of appropriate candidates for transplantation.

Lactate: A key metabolite in the intercellular metabolic interplay

Most physicians involved in intensive care consider lactate solely as a deleterious metabolite, responsible for high morbidity and bad prognosis in severe patients. For the physiologist, however, lactate is a key metabolite, alternatively produced or consumed. Many studies in the literature have infused animals or humans with exogenous lactate, demonstrating its safety and usefulness, but the bad reputation of lactate is still widespread. The metabolic meaning of glucose–lactate cycling exceeds its initial role described by Cori and Cori. According to recent works concerning lactate, it can be predicted that a new role as a therapeutic agent will arise for this metabolite.

Effect of three resuscitation procedures on respiratory and metabolic adaptation to extra uterine life in newborn calves

The purpose of this study was to evaluate the effects of three resuscitation procedures on respiratory and metabolic adaptation to extra-uterine life during the first 24 h after birth in healthy newborn calves. Twenty-four newborn calves were randomly grouped into four categories: six calves did not receive any specific resuscitation procedure and were considered as controls (C); six received pharyngeal and nasal suctioning immediately after birth by use of a hand-powered vacuum pump (SUC); six received five litres of cold water poured over their heads immediately after birth (CW) and six were housed in a calf pen with an infrared radiant heater for 24 h after birth (IR). Calves were examined at birth, 5, 15, 30, 45 and 60 min, 2, 3, 6, 12 and 24 h after birth and the following measurements were recorded: physical and clinical examination, arterial blood gas analysis, pulmonary function tests using the oesophageal balloon catheter technique, arterial and venous blood acid-base balance analysis, jugular venous blood sampling for determination of metabolic, haematological and passive immune transfer variables. SUC was accompanied by improved pulmonary function efficiency and by a less pronounced decrease in body temperature. The "head shaking movement" and the subsequent temporary increase in total pulmonary resistance as well as the greater lactic acidosis due to CW were accompanied by more efficient, but statistically non-significant, pulmonary gas exchanges. IR allowed maintenance of higher body temperature without requiring increased catabolism of energetic stores. IR also caused a change in breathing pattern which contributed to better distribution of the ventilation and to slightly improved gas exchange. The results indicate that use of SUC, CW and IR modified respiratory and metabolic adaptation during the first 24 h after birth without side-effects. These resuscitation procedures should be recommended for their specific indication, i.e. cleansing of fetal fluid from upper airways, hypothermal stimulation of breathing and prevention of heat losses.

Liver and intestinal lactate metabolism in patients with acute hepatic failure undergoing liver transplantation

OBJECTIVE

To determine the relative contribution of the gastrointestinal tract and the liver in lactate metabolism in patients with acute liver failure (ALF) and the effect of liver transplantation on this. We hypothesized that the liver and gut are net producers of lactate in ALF and that this is reversed after liver transplantation.

SETTING

A university-affiliated specialist liver transplant operating theater.

SUBJECTS

Eleven patients with ALF undergoing liver transplantation.

MEASUREMENTS AND INTERVENTIONS

After ethical approval, 11 patients with ALF listed for orthotopic hepatic transplantation were studied. Whole blood was analyzed for lactate concentration from radial artery (RA) catheter, portal vein (PV), and hepatic vein (HV) during the dissection phase and was repeated postreperfusion of the liver graft. Gradients across the gut and the liver were calculated to see if there was net production or consumption.

RESULTS

HV lactate was significantly higher than arterial (p =.028) in patients with ALF before liver transplantation, suggesting splanchnic production of lactate. Total splanchnic lactate gradient (HV-RA) is positive in ALF. Both the gut (PV-RA) and the liver (HV-PV) were net producers of lactate. After liver transplantation, hepatic venous lactate falls below arterial levels but not significantly. The gradient across the gut (PV-RA) remained positive, but the transhepatic gradient (HV-PV) became significantly negative, showing consumption by the graft (p =.021). The magnitude of lactate consumption after transplantation correlated positively with portal venous lactate concentration (p =.029) and inversely with graft cold ischemic time (p =.007).

CONCLUSION

The liver is a net producer of lactate in patients with ALF and an elevated whole blood lactate. After liver transplantation, the graft becomes a consumer of lactate as shown by the negative lactate gradient. The degree of consumption is dependent on portal venous lactate concentration and cold ischemic time.

A global approach to energy metabolism in an experimental model of sepsis

Disturbances in energy metabolism during sepsis are not clearly understood. The aim of the study was to globally assess the energy drive in septic rat myocytes, studying both glycolysis rates and mitochondrial maximal activities together, using recent in vitro techniques. Measurements were assessed before (H0) and 4 h after sepsis induction (H4). Hyperlactatemia was observed in all septic animals ([lactate] = 1.2 +/- 0.3 mmol/L at H0 versus 3.3 +/- 0.6 mmol/L at H4; p < 0.001). An enhanced glycolysis rate was observed in both aerobic ( J(A) = 7.2 +/- 0.9 at H0 versus 18.2 +/- 4.1 nmol glucose/min/g at H4; p < 0.05) and anaerobic ( J(B) = 7.5 +/- 1.2 at H0 versus 15.4 +/- 3.4 micromol glucose/min/g at H4; p < 0.05) fluxes, associated with a selective significant pyruvate-malate-dependent oxygen consumption rate decrease (V O(2)-PM = 0.144 +/- 0.008 at H0 versus 0.113 +/- 0.007 micromol O(2)/h/mg at H4; p < 0.05). This oxygen consumption decrease can be interpreted either as a complex I and/or a complex I-ubiquinone relation alteration. Our results are consistent with the hypothesis that an altered mitochondrial function during sepsis is responsible, at least in part, for hyperlactatemia, which is thus a consequence of an increased glycolysis rate.

An ultrafiltration catheter for monitoring of venous lactate and glucose around myocardial ischemia

Early detection of myocardial ischemia is of major importance in critical-care medicine. Changes of lactate or glucose levels in the cardial venous efflux may be useful parameters. We succeeded in integrating an ultrafiltration membrane in a cardiac catheter for continuous sampling. The ultrafiltrate was analyzed outside the body, resulting in a lag-time of about 24 min. Biosensors in a flow-injection analysis system were used for minute by minute sample analyses. The coronary sinus of pigs was catheterized to monitor the effects of 5, 15 or 45 min ischemia by coronary artery obstruction or myocardial stress by dobutamine infusion. A total of 27 h was monitored. The intravascular response time was 1.33+/-0.61 min (10-90%). Linear regression in vivo of blood and ultrafiltrate samples was 0.977 for lactate and 0.994 for glucose. Lactate levels rose 0.38+/-0.10 mM above baseline within 5 min after ischemia. Reperfusion was clearly marked by a promptly peaking lactate release (maximum 9.27 mM). Myocardial stress by dobutamine increased glucose but not lactate levels. Once, a wall effect was noted at the catheter tip. In vivo semi-continuous myocardial monitoring of absolute lactate and glucose concentrations was thus achieved by an ultrafiltration catheter. Ischemia and reperfusion can be detected very early by a lactate level rise. Further, development of the ultrafiltration catheter will be focused on the diagnostic potential of lactate monitoring for patients.

Gastrointestinal tract resuscitation in critically ill patients

Particular research interest is currently focusing on the resuscitation of the gastrointestinal tract, because the gut is regarded to be both the "canary of the body", i.e. a sentinel organ during situations of compromised oxygen or substrate supply, as well as the "motor of multiple organ failure". Several therapeutic strategies have recently been proposed for the resuscitation of this organ system, aimed primarily at the augmentation of blood flow and oxygenation but also integrating nutritional or metabolic support and antioxidant administration.

The hepatosplanchnic area is not a common source of lactate in patients with severe sepsis

OBJECTIVE

To investigate the role of the splanchnic region in the hyperlactatemia of septic patients.

DESIGN

Prospective, observational study.

SETTING

Thirty-one-bed mixed medicosurgical intensive care unit.

PATIENTS

Ninety invasively monitored and mechanically ventilated patients with severe sepsis.

MEASUREMENTS AND MAIN RESULTS

Splanchnic lactate balance was measured in all patients. Splanchnic blood flow was determined by using the primed continuous indocyanine green infusion technique in 69 patients. In 71 patients, gastric mucosal Pco2 and the Pco2 gap (the difference between gastric and arterial Pco2) also were determined by using gas tonometry with an automated gas analyzer. In each patient, arterial, mixed-venous, and hepatic venous blood samples were obtained to determine hemoglobin oxygen saturations and lactate concentrations. Arterial and hepatic venous lactate concentrations were determined in triplicate and were averaged, and the arterial hepatic venous difference in lactate and lactate consumption were calculated. The splanchnic region produced lactate in only six of the 90 patients. Mean arterial pressure, cardiac index, arterial lactate, hepatic venous oxygen saturation, and catecholamine use were similar in the six patients with splanchnic lactate production and in the 84 others. The arterial hepatic venous differences in lactate and splanchnic lactate consumption were related directly to arterial lactate concentrations (y = 0.073x + 0.209, r(2) =.06, p <.05, and y = 0.06x + 0.183, r(2) =.08, p <.05, respectively) but were not related to Pco2 gap, to the gradient between mixed-venous and hepatic venous oxygen saturations, or to bilirubin concentrations.

CONCLUSIONS

Splanchnic lactate release is uncommon in septic patients, even when hyperlactatemia is severe.

Glycolysis in the human muscle: a new approach

The flow response time theory allows the global assessment of a metabolic pathway. This study describes the first application of this concept to explore glycolysis on human skeletal muscle extracts. The muscle extract is used to convert glucose or glucose-6-phosphate into glycerol-phosphate through the first part of glycolysis. The functioning of the experimental model is assayed by a continuous recording of the reduced nicotinamide adenine dinucleotide decay in a spectrophotometer. This measurement method was applied to normal and pathologic human skeletal muscles. The aerobic (J(A)) and anaerobic (J(B)) fluxes and the time (t99) needed for the transition from J(A) to J(B) were measured under a wide clinical temperature range (30 degrees C to 40 degrees C). The two studied muscle types (gluteus maximus and tibialis anterior) have similar glycolytic flux values, with an identical functional modality. The thermal response of glycolysis is not linear, with a high thermal sensitivity in the hypothermic range (30 degrees C to 38 degrees C) and a thermal insensitivity in the hyperthermic range (37 degrees C to 40 degrees C). On the same type of muscle (tibialis anterior), a pathologic process can induce different variations in the glycolysis patterns, but further data are needed to clear this point. The flow response time concept allows an accurate assessment of glycolysis in the human skeletal muscle, whether normal or pathologic. This approach is interesting for evaluating the global influence of different stimulations on a metabolic pathway, such as temperature variation.

Validation and prognostic value of plasma lactate measurement in bovine respiratory disease

The purpose of this study was to evaluate the accuracy of a portable blood lactate analyser for bovine blood and to study the relevance of plasma lactate concentration in the prognosis of bovine pulmonary disorders. Measurements with the portable analyser were highly correlated (R = 0.94, P<0.0001) with the measurements of the reference method but significantly different (P<0.0001). The portable apparatus slightly overestimated plasma lactate concentration compared to the reference method (bias = + 0.412). Plasma lactate measurements on 109 calves suffering from acute bronchopneumonia showed increasing lactate concentrations with severity of the disease. A plasma lactate concentration higher than 3.6 mmol/L or 4 mmol/L, measured with the reference method and the portable analyser respectively, appeared to be a reliable prognostic indicator for mortality within 24 h. Consequently, this measurement could be very helpful to decrease economic losses in cases of bovine respiratory disease, by avoiding unnecessary treatment costs on cattle with poor prognosis.

Impaired hepatic extraction and increased splanchnic production contribute to lactic acidosis in canine sepsis

In septic shock, the extent to which lactic acidosis (LA) is a consequence of splanchnic lactate overproduction (SLP) or impaired hepatic lactate extraction (HLE) is not clear. We examined SLP and HLE in E. coli sepsis in dogs. We further determined the effects of vasopressor treatments, which included phenylephrine, dopamine, norepinephrine, and a combination of dobutamine and norepinephrine treatment, on SLP and HLE in respective groups. The animals were studied while anesthetized and ventilated. During sepsis, SLP increased as compared with presepsis (-0.017 versus 0.07 mmol/min, p < 0.05), but this increase could not be explained by reduced splanchnic oxygen delivery (SOD). During sepsis, HLE increased as compared with baseline (0.8 versus 8%, p < 0.05), but was significantly lower than that found during lactic acid loading in nonseptic dogs. None of the vasopressor treatments had a detrimental effect on SLP. These results indicate that LA in sepsis occurs secondary to an increase in splanchnic lactate production that is not related to reduced splanchnic oxygen delivery, as well as to a decrease in hepatic lactate extraction. Effects of different vasoactive agents did not alter either splanchnic lactate production or hepatic lactate extraction in this sepsis model.

Evolution of lactate/pyruvate and arterial ketone body ratios in the early course of catecholamine-treated septic shock

OBJECTIVES

To measure arterial lactate/pyruvate (L/P) and arterial ketone body ratios as reflection of cytoplasmic and mitochondrial redox state at different stages of catecholamine-treated septic shock and compare them with normal and pathologic values obtained in patients in shock who have decreased oxygen transport (cardiogenic shock), and to assess the relationship between the time course of lactate, L/P ratio, and mortality in septic shock.

DESIGN

Prospective, observational human study.

SETTING

A university intensive care unit.

PATIENTS

Sixty consecutive adult patients who developed septic shock and lactic acidosis requiring the administration of vasopressors. Twenty patients in the intensive care unit without shock, sepsis, and hypoxia and with normal lactate values and 10 patients with cardiogenic shock were also studied.

MEASUREMENTS

Hemodynamic measurements, arterial and mixed venous blood gases, arterial lactate and pyruvate concentrations, and arterial ketone body ratio were measured within 4 hrs after the introduction of catecholamine and 24 hrs later.

MAIN RESULTS

Fifteen patients (25%) died within the first 24 hrs of septic shock, and these early fatalities had a higher blood lactate (12.2+/-3 versus 4.6+/-1.3 mmol/L; p<.01) concentration and a higher L/P ratio (37+/-4 versus 20+/-1; p<.01) than those who died later. No difference was found for arterial ketone body ratio (0.41+/-0.1 versus 0.50+/-0.06). Forty-five patients survived >24 hrs including 25 survivors and 20 nonsurvivors. Although there was no difference between survivors and nonsurvivors in initial lactate concentration (4.1+/-0.4 and 4.6+/-0.3, respectively), L/P ratio (19+/-1 and 20+/-1, respectively), and arterial ketone body ratio (0.5+/-0.06 and 0.52+/-0.07, respectively), blood lactate and L/P ratio significantly decreased during the first 24 hrs in the survivors (2.8+/-0.4 and 14+/-1, respectively; p<.05). and were stable in the nonsurvivors (4+/-0.3 and 22+/-1, respectively) Although returning to normal values after 24 hrs in survivors and nonsurvivors, arterial ketone body ratio was higher in survivors (1.72+/-0.17 versus 1.09+/-0.15; p<.05). Lactate and L/P ratio were closely correlated (r2 = .8, p<.0001). In the cardiogenic shock group, lactate concentration was 4+/-1 mmol/L, L/P ratio was 40+/-6, and arterial ketone body ratio was 0.2+/-0.05. The mortality rate was 60%.

CONCLUSIONS

The main result of the present study is that hemodynamically unstable patients with sepsis needing catecholamine therapy had a lactic acidosis with an elevated L/P ratio and a decreased arterial ketone body ratio, suggesting a decrease in cytoplasmic and mitochondrial redox state. The duration of lactic acidosis is associated with the development of multiple organ failure and death.

Hyperlactatemia and pulmonary lactate production in patients with fulminant hepatic failure

STUDY OBJECTIVES

To determine whether the lungs of patients with fulminant hepatic failure release lactate, and if so, whether this release relates to systemic lactate concentration or acid base status. Another objective was to examine the accuracy of lactate flux calculations in critically ill patients.

DESIGN

Prospective observational study.

SETTING

The ICU of a major teaching hospital.

PATIENTS

Twelve patients with fulminant hepatic failure; 30 other critically ill patients in whom a pulmonary artery catheter was in place.

INTERVENTIONS

None.

MEASUREMENT AND RESULTS

The precision of whole-blood lactate measurements was assessed in 30 patients with critical illnesses of variable etiology who had a wide range of arterial lactate concentrations. The reliability of lactate measurements decreased with increasing lactate concentration. In each patient with liver failure, pulmonary lactate flux was calculated on three occasions using the Fick principle. Arterial blood lactate concentration was consistently higher than venous concentrations, indicating lactate release by the lungs (mean difference, 0.15 mmol/L; 95% confidence interval, 0.09 to 0.21; p<0.001). Mean pulmonary lactate production for the 12 patients was 83 mmol/h (range, 22 to 210 mmol/h). No patient had significant acute lung injury. Correlations were found among the arterial lactate concentration and both the arteriovenous (AV) lactate difference (p<0.025) and pulmonary lactate production (p<0.05), but not with acid-base status or cardiac output. The reliability of individual AV lactate difference calculations and pulmonary lactate flux calculations was poor.

CONCLUSION

The lungs release lactate in patients with fulminant hepatic failure at a rate proportional to the degree of systemic hyperlactatemia. However, the measurement errors associated with pulmonary lactate flux calculations using the Fick principle are large, so individual measurements should be interpreted with caution.