Role of skeletal muscle Na+-K+ ATPase activity in increased lactate production in sub-acute sepsis

INTERPLAY BETWEEN BRAIN OXYGENATION AND THE DEVELOPMENT OF HYPOTHERMIA IN ENDOTOXIC SHOCK

ABSTRACT

There is evidence to suggest that the hypothermia observed in the most severe cases of systemic inflammation or sepsis is a regulated response with potential adaptive value, but the mechanisms involved are poorly understood. Here, we investigated the interplay between brain oxygenation (assessed by tissue P o2 ) and the development of hypothermia in unanesthetized rats challenged with a hypotension-inducing dose of bacterial LPS (1 mg/kg i.v.). At an ambient temperature of 22°C, oxygen consumption (V̇O 2 ) began to fall only a few minutes after the LPS injection, and this suppression in metabolic rate preceded the decrease in core temperature. No reduction in brain P o2 was observed prior to the development of the hypometabolic, hypothermic response, ruling out the possibility that brain hypoxia served as a trigger for hypothermia in this model. Brain P o2 was even increased. Such an improvement in brain oxygenation could reflect either an increased O 2 delivery or a decreased O 2 consumption. The former explanation seems unlikely because blood flow (cardiac output) was being progressively decreased during the recording period. On the other hand, the decrease in V̇O 2 usually preceded the rise in P o2 , and an inverse correlation between V̇O 2 and brain P o2 was consistently observed. These findings do not support the existence of a closed-loop feedback relationship between brain oxygenation and hypothermia in systemic inflammation. The data are consistent with a feedforward mechanism in which hypothermia is triggered (possibly by cryogenic inflammatory mediators) in anticipation of changes in brain oxygenation to prevent the development of tissue hypoxia.

The Association of the Lactate-Albumin Ratio With Mortality and Multiple Organ Dysfunction in PICU Patients

OBJECTIVES

To compare the relative associations of lactate, albumin, and the lactate-albumin ratio (LAR) measured early in disease course against mortality and prevalence of multiple organ dysfunction syndrome (MODS) in a general sample of critically ill pediatric patients.

DESIGN

Retrospective analysis of the Health Facts (Cerner Corporation, Kansas City, MO) national database.

SETTING

U.S. hospitals with PICUs.

PATIENTS

Children admitted to the ICU ( n = 648) from 2009 to 2018 who had lactate and albumin measured within 6 hours of admission.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 648 admissions were included, with an overall mortality rate of 10.8% ( n = 70) and a MODS prevalence of 29.3% ( n = 190). Compared with survivors, deaths had higher initial lactates (7.3 mmol/L [2.6-11.7 mmol/L] vs 1.9 mmol/L [1.2-3.1 mmol/L]; p < 0.01), lower initial albumins (3.3 g/dL [2.7-3.8 g/dL] vs 4.2 g/dL [3.7-4.7 g/dL]; p < 0.01), and higher LARs (2.2 [1.0-4.2] vs 0.5 [0.3-0.8]; p < 0.01), with similar trends in patients with MODS versus those without MODS. LAR demonstrated a higher odds ratio (OR) for death than initial lactate alone (2.34 [1.93-2.85] vs 1.29 [1.22-1.38]) and a higher OR for MODS than initial lactate alone (2.10 [1.73-2.56] vs 1.22 [1.16-1.29]). Area under the receiver operating characteristic (AUROC) curve of LAR for mortality was greater than initial lactate (0.86 vs 0.82; p < 0.01). The LAR AUROC for MODS was greater than the lactate AUROC (0.71 vs 0.66; p < 0.01). Trends of lactate, albumin, and LAR for mortality were consistent across several diagnostic subgroups (trauma, primary respiratory failure, toxicology), but not all.

CONCLUSIONS

LAR measured early in the course of critical illness is significantly associated with mortality and development of MODS when compared with initial lactate or initial albumin alone in critically ill pediatric patients.

Does severe hyperlactatemia during cardiopulmonary bypass predict a worse outcome?

INTRODUCTION

The aim of the current study was to evaluate the impact of increased blood lactate levels during cardiopulmonary bypass (CPB) on immediate results in patients who underwent open heart surgery.

MATERIALS AND METHODS

We performed a retrospective single-center study on 1290 patients. Adult cardiac surgical patients who underwent valve surgery, coronary artery bypass graft, combined procedure, adult congenital anomalies and aortic surgery were enrolled. Patients with associated comorbidities such as liver dysfunction, hemodynamic instability before surgery were excluded. Arterial blood lactate concentration was measured immediately after weaning from CPB and evaluated together with clinical data and outcomes including in hospital mortality. Patients were classified into 3 groups according to their peak arterial lactate level: group I [normal lactatemia, lactate ˂ 2 mmol/l (n = 749)], group II [mild hyperlactatemia, lactate 2-5 mmol/l (n = 489)], group III [severe hyperlactatemia, lactate ˃ 5 mmol/l (n = 52)].

RESULTS

When comparing outcomes across the 3 groups, severe hyperlactatemia was correlated with worse outcomes including higher in-hospital mortality, low output cardiac syndrome, postoperative renal insufficiency, myocardial infarction, red blood cell transfusion (RBC) transfusion, prolonged mechanical ventilation and longer intensive care unit (ICU) stay hours.

CONCLUSION

Blood lactate level above 5 mmol/l and more during CPB is associated with higher in-hospital mortality rate and postoperative complications. More attention must be given to correct the common abnormalities conditions inherent of CPB in order to conduct adequate tissue perfusion and reduce the risk of hyperlactatemia.

Growth Arrest-Specific Gene 6 Administration Ameliorates Sepsis-Induced Organ Damage in Mice and Reduces ROS Formation In Vitro

Sepsis is a widespread life-threatening disease, with a high mortality rate due to inflammation-induced multiorgan failure (MOF). Thus, new effective modulators of the immune response are urgently needed to ameliorate the outcome of septic patients. As growth arrest-specific gene 6 (Gas6)/Tyro3, Axl, MerTK (TAM) receptors signaling has shown immunomodulatory activity in sepsis, here we sought to determine whether Gas6 protein injection could mitigate MOF in a cecal slurry mouse model of sepsis. Mice, divided into different groups according to treatment-i.e., placebo (B), ampicillin (BA), Gas6 alone (BG), and ampicillin plus Gas6 (BAG)-were assessed for vitality, histopathology and cytokine expression profile as well as inducible nitric oxide synthase (iNOS), ALT and LDH levels. BAG-treated mice displayed milder kidney and lung damage and reduced levels of cytokine expression and iNOS in the lungs compared to BA-treated mice. Notably, BAG-treated mice showed lower LDH levels compared to controls. Lastly, BAG-treated cells of dendritic, endothelial or monocytic origin displayed reduced ROS formation and increased cell viability, with a marked upregulation of mitochondrial activity. Altogether, our findings indicate that combined treatment with Gas6 and antibiotics ameliorates sepsis-induced organ damage and reduces systemic LDH levels in mice, suggesting that Gas6 intravenous injection may be a viable therapeutic option in sepsis.

Demystifying Lactate in the Emergency Department

The role of lactic acid and its conjugate base, lactate, has evolved during the past decade in the care of patients in the emergency department (ED). A recent national sepsis quality measure has led to increased use of serum lactate in the ED, but many causes for hyperlactatemia exist outside of sepsis. We provide a review of the biology of lactate production and metabolism, the many causes of hyperlactatemia, and evidence on its use as a marker in prognosis and resuscitation. Additionally, we review the evolving role of lactate in sepsis care. We provide recommendations to aid lactate interpretation in the ED and highlight areas for future research.

Prognostic relevance of serum lactate kinetics in critically ill patients

PURPOSE

Changes of lactate concentration over time were reported to be associated with survival in septic patients. We aimed to evaluate delta-lactate (ΔLac) 24 h after admission (Δ24Lac) to an intensive care unit (ICU) in critically ill patients for short- and long-term prognostic relevance.

METHODS

In total, 26,285 lactate measurements of 2191 patients admitted to a German ICU were analyzed. Inclusion criterion was a lactate concentration at admission above 2.0 mmol/L. Maximum lactate concentrations of day 1 and day 2 were used to calculate Δ24Lac. Follow-up of patients was performed retrospectively. Association of Δ24Lac and both in-hospital and long-term mortality were investigated. An optimal cut-off was calculated by means of the Youden index.

RESULTS

Patients with lower Δ24Lac were of similar age, but clinically sicker. As continuous variable, higher Δ24Lac was associated with decreased in-hospital mortality (per 1% Δ24Lac; HR 0.987 95%CI 0.985-0.990; p < 0.001) and an optimal Δ24Lac cut-off was calculated at 19%. Δ24Lac ≤ 19% was associated with both increased in-hospital (15% vs 43%; OR 4.11; 95%CI 3.23-5.21; p < 0.001) and long-term mortality (HR 1.54 95%CI 1.28-1.87; p < 0.001), even after correction for APACHE II, need for catecholamines and intubation. We matched 256 patients with Δ24Lac ≤ 19% to case-controls > 19% corrected for APACHE II scores, baseline lactate level and sex: Δ24Lac ≤ 19% remained associated with lower in-hospital and long-term survival.

CONCLUSIONS

Lower Δ24Lac was robustly associated with adverse outcome in critically ill patients, even after correction for confounders. Δ24Lac might constitute an independent, easily available and important parameter for risk stratification in the critically ill.

The Lactate/Albumin Ratio: A Valuable Tool for Risk Stratification in Septic Patients Admitted to ICU

The lactate/albumin ratio has been reported to be associated with mortality in pediatric patients with sepsis. We aimed to evaluate the lactate/albumin ratio for its prognostic relevance in a larger collective of critically ill (adult) patients admitted to an intensive care unit (ICU). A total of 348 medical patients admitted to a German ICU for sepsis between 2004 and 2009 were included. Follow-up of patients was performed retrospectively between May 2013 and November 2013. The association of the lactate/albumin ratio (cut-off 0.15) and both in-hospital and post-discharge mortality was investigated. An optimal cut-off was calculated by means of Youden’s index. The lactate/albumin ratio was elevated in non-survivors (p < 0.001). Patients with an increased lactate/albumin ratio were of similar age, but clinically in a poorer condition and had more pronounced laboratory signs of multi-organ failure. An increased lactate/albumin ratio was associated with adverse in-hospital mortality. An optimal cut-off of 0.15 was calculated and was associated with adverse long-term outcome even after correction for APACHE2 and SAPS2. We matched 99 patients with a lactate/albumin ratio >0.15 to case-controls with a lactate/albumin ratio <0.15 corrected for APACHE2 scores: The group with a lactate/albumin ratio >0.15 evidenced adverse in-hospital outcome in a paired analysis with a difference of 27% (95%CI 10–43%; p < 0.01). Regarding long-term mortality, again, patients in the group with a lactate/albumin ratio >0.15 showed adverse outcomes (p < 0.001). An increased lactate/albumin ratio was significantly associated with an adverse outcome in critically ill patients admitted to an ICU, even after correction for confounders. The lactate/albumin ratio might constitute an independent, readily available, and important parameter for risk stratification in the critically ill.

Lactic Acidosis in Sepsis: It's Not All Anaerobic: Implications for Diagnosis and Management

Increased blood lactate concentration (hyperlactatemia) and lactic acidosis (hyperlactatemia and serum pH < 7.35) are common in patients with severe sepsis or septic shock and are associated with significant morbidity and mortality. In some patients, most of the lactate that is produced in shock states is due to inadequate oxygen delivery resulting in tissue hypoxia and causing anaerobic glycolysis. However, lactate formation during sepsis is not entirely related to tissue hypoxia or reversible by increasing oxygen delivery. In this review, we initially outline the metabolism of lactate and etiology of lactic acidosis; we then address the pathophysiology of lactic acidosis in sepsis. We discuss the clinical implications of serum lactate measurement in diagnosis, monitoring, and prognostication in acute and intensive care settings. Finally, we explore treatment of lactic acidosis and its impact on clinical outcome.

Lactate kinetics and mitochondrial respiration in skeletal muscle of healthy humans under influence of adrenaline

Plasma lactate is widely used as a biomarker in critical illness. The aims of the present study were to elucidate the usefulness of a three-compartment model for muscle lactate kinetics in humans and to characterize the response to an exogenous adrenaline challenge. Repeated blood samples from artery and femoral vein together with blood flow measurements and muscle biopsies were obtained from healthy male volunteers (n=8) at baseline and during an adrenaline infusion. Concentrations of lactate and enrichment of [13C]lactate were measured and kinetics calculated. Mitochondrial activity, glycogen concentration, oxygen uptake and CO2 release were assessed. The adrenaline challenge increased plasma lactate 4-fold as a result of a greater increase in the rate of appearance (R(a)) than the increase in the rate of disappearance (R(d)). Leg muscle net release of lactate increased 3.5-fold, whereas intramuscular production had a high variation but did not change. Mitochondrial state 3 respiration increased by 30%. Glycogen concentration, oxygen uptake and CO2 production remained unchanged. In conclusion a three-compartment model gives additional information to the two-compartment model but, due to its larger variation and invasive muscle biopsy, it is less likely to become a regularly used tool in clinical research. Hyperlactataemia in response to adrenergic stimuli was driven by an elevated lactate release from skeletal muscle most probably due to a redirection of a high intramuscular turnover rather than an increased production.

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Des-acyl-ghrelin (DAG) normalizes hyperlactacidemia and improves survival in a lethal rat model of burn trauma

Critical illness, including burn injury, results in elevated plasma lactate levels. Dysregulation of PI3K/Akt signaling has been shown to play a predominant role in the inactivation of skeletal muscle PDC and, hence, in hyperlactacidemia in rat models of sepsis and endotoxemia. This observation, and our previous finding that DAG can reverse burn-induced skeletal muscle proteolysis through the activation of PI3K/Akt pathway, led us to hypothesize that DAG may also attenuate hyperlactacidemia in burn injury. Our investigations revealed that burn injury significantly elevated both skeletal muscle lactate production and plasma lactate levels. Moreover, this was accompanied in skeletal muscle by a 5-7 fold increase in mRNA expression of pyruvate dehydrogenase kinases (PDK) 2 and 4, and a ∼30% reduction in PDC activity. DAG treatment of burn rats completely normalized not only the mRNA expression of the PDKs and PDC activity, but also hyperlactacidemia within 24h of burn injury. DAG also normalized epinephrine-induced lactate production by isolated skeletal muscles from normal rats. Moreover, DAG also improved survival in a lethal rat model of burn trauma. These findings with DAG may have clinical implications because chances of survival for critically ill patients are greatly improved if plasma lactate levels are normalized within 24h of injury.

Hypometabolism and hypothermia in the rat model of endotoxic shock: independence of circulatory hypoxia

We tested the hypothesis that development of hypothermia instead of fever in endotoxic shock is consequential to hypoxia. Endotoxic shock was induced by bacterial lipopolysaccharide (LPS, 500 μg kg(-1) i.v.) in rats at an ambient temperature of 22 °C. A β3-adrenergic agonist known to activate metabolic heat production, CL316,243, was employed to evaluate whether thermogenic capacity could be impaired by the fall in oxygen delivery (ḊO2) during endotoxic shock. This possibility was rejected as CL316,243 (0.15 mg kg(-1) i.v.) evoked similar rises in oxygen consumption (V̇O2) in the presence and absence of endotoxic shock. Next, to investigate whether a less severe form of circulatory hypoxia could be triggering hypothermia, the circulating volume of LPS-injected rats was expanded using 6% hetastarch with the intention of improving tissue perfusion and alleviating hypoxia. This intervention attenuated not only the fall in arterial pressure induced by LPS, but also the associated falls in V̇O2 and body temperature. These effects, however, occurred independently of hypoxia, as they were not accompanied by any detectable changes in NAD(+)/NADH ratios. Further experimentation revealed that even the earliest drops in cardiac output and ḊO2 during endotoxic shock did not precede the reduction in V̇O2 that brings about hypothermia. In fact, ḊO2 and V̇O2 fell in such a synchrony that the ḊO2/V̇O2 ratio remained unaffected. Only when hypothermia was prevented by exposure to a warm environment (30 °C) did an imbalance in the ḊO2/V̇O2 ratio become evident, and such an imbalance was associated with reductions in the renal and hypothalamic NAD(+)/NADH ratios. In conclusion, hypometabolism and hypothermia in endotoxic shock are not consequential to hypoxia but serve as a pre-emptive strategy to avoid hypoxia in this model.

Prognostic value of central venous oxygen saturation and blood lactate levels measured simultaneously in the same patients with severe systemic inflammatory response syndrome and severe sepsis

BACKGROUND

Blood lactate levels and central venous oxygen saturation (ScvO(2)) are known to be useful indicators of global tissue hypoxia. However, it is unclear whether ScvO(2) correlates with lactate levels when measured simultaneously and whether changes in ScvO(2) or lactate levels in serial measurements have prognostic value. We investigated the correlation between ScvO(2) and lactate levels measured simultaneously and their association with clinical outcomes.

METHODS

We performed a prospective observational study of patients with severe systemic inflammatory response syndrome (SIRS) and severe sepsis who were admitted to the medical intensive care unit. ScvO(2) and lactate levels were measured simultaneously at the time of study enrollment, every 6 h for 24 h, and then every 24 h until the goal was reached.

RESULTS

Twenty-five patients were enrolled in the study; 13 have died and 12 have survived. There was no correlation between lactate levels and ScvO(2). Neither lactate levels nor ScvO(2) at the time of admission differed between nonsurvivors and survivors. Normalization of lactate levels within 48 h was significantly associated with survival.

CONCLUSIONS

In patients with severe SIRS and severe sepsis, simultaneously measured ScvO(2) and lactate levels showed no correlation, and normalization of lactate levels within 48 h was a predictive factor for survival.

Epinephrine induces rapid deterioration in pulmonary oxygen exchange in intact, anesthetized rats: a flow and pulmonary capillary pressure-dependent phenomenon

BACKGROUND

Previous studies indicate epinephrine adversely affects arterial oxygenation when administered in a rat model of local anesthetic overdose. The authors tested whether epinephrine alone exerts similar effects in the intact animal.

METHODS

Anesthetized rats received a single intravenous injection of epinephrine (25, 50, or 100 mcg/kg); matched cohorts were pretreated with phentolamine (100 mcg/kg); n = 5 for each of the six treatment groups. Arterial pressure and blood gases were measured at baseline, 1 and 10 min after epinephrine administration. Pulmonary capillary pressures during epinephrine infusion with normal and increased flows were measured in an isolated lung preparation.

RESULTS

Epinephrine injection in the intact animal caused hypoxemia, hypercapnia, and acidosis at all doses. Arterial oxygen tension was reduced within 1 min of injection. Hyperlactatemia occurred by 10 min after 50 and 100 mcg/kg. Rate pressure product was decreased by 10 min after 100 mcg/kg epinephrine. Pretreatment with phentolamine attenuated these effects except at 100 mcg/kg epinephrine. In the isolated lung preparation, epinephrine in combination with increased pulmonary flow increased pulmonary capillary pressure and lung water.

CONCLUSIONS

Bolus injection of epinephrine in the intact, anesthetized rat impairs pulmonary oxygen exchange within 1 min of treatment. Effects were blunted by α-adrenergic receptor blockade. Edema occurred in the isolated lung above a threshold pulmonary capillary pressure when epinephrine treatment was coupled with an increase in pulmonary flow. These results potentially argue against using traditional doses of epinephrine for resuscitation, particularly in the anesthetized patient.

Increased Na+,K+-ATPase activity in the rat brain after meningitis induction by Streptococcus pneumoniae

Barichello T, Generoso JS, Cipriano AL, Casagrande R, Collodel A, Savi GD, Scherer EBS, Kolling J, Wyse ATS. Increase Na+,K+-ATPase activity in the rat brain after meningitis induction byStreptococcus pneumoniae.

Background: Pneumococcal meningitis is the most severe infection of the central nervous system with a mortality rate up to 20% and an adverse neurological result in up to 50% of survivors. A complicated series of interactions among the host immune response and oxidants seems to be responsible for meningitis associated brain dysfunctions. Na+,K+-ATPase is an essential enzyme responsible for generating and maintaining the membrane potential necessary for neural excitability, however, the Na+,K+-ATPase activity is altered in several illness;

Objective: The aim of this study is to evaluate the Na+,K+-ATPase activity in hippocampus and cortex of the rats submitted to pneumococcal meningitis.

Methods: Animals received 10 µl sterile saline as a placebo or an equivalent volume ofStreptococcus pneumoniaeto the concentration of 5 × 109cfu/ml and were killed at 24, 48, 72 and 96 h after meningitis induction. The brain structures, hippocampus and cortex, were immediately isolated on dry ice and stored at −80°C to analyse Na+,K+-ATPase activity.

Results: In the hippocampus, we verified the increase of Na+,K+-ATPase activity at 48, 72 and 96 h (p< 0.05) and in the cortex at 24 h (p< 0.05) after pneumococcal meningitis induction.

Conclusion: The Na+,K+-ATPase activity is under the control of a diversity of intracellular messengers that are able to modulate the function of the particular isozymes in a precise way. Furthermore, we verified that pneumococcal meningitis increased the Na+,K+-ATPase activity in hippocampus and cortex; this increase can be correlated with a compensatory mechanism in illness pathophysiology.

Protective effects of magnesium supplementation on metabolic energy derangements in lipopolysaccharide-induced cardiotoxicity in mice

Metabolic derangements and bioenergetic failure are major contributors to sepsis-induced multiple organ dysfunctions. Due to the well known role of magnesium (Mg) as a cofactor in many enzymatic reactions that involve energy creation and utilization, the present investigation was directed to estimate the cardioprotective effect of Mg supplementation in lipopolysaccharide (LPS)-induced metabolic energy changes in mice. Oral doses of Mg aspartate (20 or 40 mg/kg) were administered once daily for 7 day. Mice were then subjected to a single intraperitoneal injection of LPS (2 mg/kg). Plasma was separated 3 h after LPS injection for determination of creatine kinase-MB activity. Animals were then sacrificed and the hearts were separated for estimation of tissue thiobarbituric acid reactive substances, reduced glutathione, lactate, pyruvate, adenine nucleotides, creatine phosphate and cardiac Na(+),K(+)-ATPase activity. Finally, electron microscopic examination was performed to visualize the protective effects of Mg pretreatment on mitochondrial ultrastructure. In general, the higher dose of Mg was more effective than the lower dose in ameliorating creatine kinase-MB elevation and the state of oxidative stress, lactate accumulation, pyruvate reduction as well as preserving creatine phosphate, adenine nucleotides and Na(+),K(+)-ATPase activity. Moreover, the higher dose of Mg provided a significant cardioprotection against the mitochondrial ultrastructural changes. Mg therapy can afford a significant protection against metabolic energy derangements and mitochondrial ultrastructural changes induced by LPS cardiotoxicity in mice.

Critical care "normality": individualized versus protocolized care

Patients with critical illness are heterogeneous, with differing physiologic requirements over time. Goal-directed therapy in the emergency room demonstrates that protocolized care could result in improved outcomes. Subsequent studies have confirmed benefit with such a "bundle-based approach" in the emergency room and in preoperative and postoperative scenarios. However, this cannot be necessarily extrapolated to the medium-term and long-term care pathway of the critically ill patient. It is likely that the development of mitochondrial dysfunction could result in goal-directed types of approaches being detrimental. Equally, arterial pressure aims are likely to be considerably different as the patient's physiology moves toward "hibernation." The agents we utilize as sedative and pressor agents have considerable effects on immune function and the inflammatory profile, and should be considered as part of the total clinical picture. The role of gut failure in driving inflammation is considerable, and the drive to feed enterally, regardless of aspirate volume, may be detrimental in those with degrees of ileus, which is often a difficult diagnosis in the critically ill. The pathogenesis of liver dysfunction may be, at least in part, related to venous engorgement that will contribute toward portal hypertension and gut edema. This, in association with loss of the hepatosplanchnic buffer response, it is likely to contribute to venous pooling in the abdominal cavity, impaired venous return, and decreased central blood volumes. Therapies such as those used in "small-for-size syndrome" may have a role in the chronic stages of septic vascular failure.

Dexamethasone stimulates store-operated calcium entry and protein degradation in cultured L6 myotubes through a phospholipase A(2)-dependent mechanism

Muscle wasting in various catabolic conditions is at least in part regulated by glucocorticoids. Increased calcium levels have been reported in atrophying muscle. Mechanisms regulating calcium homeostasis in muscle wasting, in particular the role of glucocorticoids, are poorly understood. Here we tested the hypothesis that glucocorticoids increase intracellular calcium concentrations in skeletal muscle and stimulate store-operated calcium entry (SOCE) and that these effects of glucocorticoids may at least in part be responsible for glucocorticoid-induced protein degradation. Treatment of cultured myotubes with dexamethasone, a frequently used in vitro model of muscle wasting, resulted in increased intracellular calcium concentrations determined by fura-2 AM fluorescence measurements. When SOCE was measured by using calcium "add-back" to muscle cells after depletion of intracellular calcium stores, results showed that SOCE was increased 15-25% by dexamethasone and that this response to dexamethasone was inhibited by the store-operated calcium channel blocker BTP2. Dexamethasone treatment stimulated the activity of calcium-independent phospholipase A(2) (iPLA(2)), and dexamethasone-induced increase in SOCE was reduced by the iPLA(2) inhibitor bromoenol lactone (BEL). In additional experiments, treatment of myotubes with the store-operated calcium channel inhibitor gadolinium ion or BEL reduced dexamethasone-induced increase in protein degradation. Taken together, the results suggest that glucocorticoids increase calcium concentrations in myocytes and stimulate iPLA(2)-dependent SOCE and that glucocorticoid-induced muscle protein degradation may at least in part be regulated by increased iPLA(2) activity, SOCE, and cellular calcium levels.

Blood lactate monitoring in critically ill patients: a systematic health technology assessment

OBJECTIVE

To decide whether the use of blood lactate monitoring in critical care practice is appropriate. We performed a systematic health technology assessment as blood lactate monitoring has been implemented widely but its clinical value in critically ill patients has never been evaluated properly.

DATA SOURCE

PubMed, other databases, and citation review.

STUDY SELECTION

We searched for lactate combined with critically ill patients as the target patient population. Two reviewers independently selected studies based on relevance for the following questions: Does lactate measurement: 1) perform well in a laboratory setting? 2) provide information in a number of clinical situations? 3) relate to metabolic acidosis? 4) increase workers' confidence? 5) alter therapeutic decisions? 6) result in benefit to patients? 7) result in similar benefits in your own setting? 8) result in benefits which are worth the extra costs?

DATA EXTRACTION AND SYNTHESIS

We concluded that blood lactate measurement in critically ill patients: 1) is accurate in terms of measurement technique but adequate understanding of the (an)aerobic etiology is required for its correct interpretation; 2) provides not only diagnostic but also important prognostic information; 3) should be measured directly instead of estimated from other acid-base variables; 4) has an unknown effect on healthcare workers' confidence; 5) can alter therapeutic decisions; 6) could potentially improve patient outcome when combined with a treatment algorithm to optimize oxygen delivery, but this has only been shown indirectly; 7) is likely to have similar benefits in critical care settings worldwide; and 8) has an unknown cost-effectiveness.

CONCLUSIONS

The use of blood lactate monitoring has a place in risk-stratification in critically ill patients, but it is unknown whether the routine use of lactate as a resuscitation end point improves outcome. This warrants randomized controlled studies on the efficacy of lactate-directed therapy.

Metabolic acidosis in the critically ill: part 2. Causes and treatment

The correct identification of the cause, and ideally the individual acid, responsible for metabolic acidosis in the critically ill ensures rational management. In Part 2 of this review, we examine the elevated (corrected) anion gap acidoses (lactic, ketones, uraemic and toxin ingestion) and contrast them with nonelevated conditions (bicarbonate wasting, renal tubular acidoses and iatrogenic hyperchloraemia) using readily available base excess and anion gap techniques. The potentially erroneous interpretation of elevated lactate signifying cell ischaemia is highlighted. We provide diagnostic and therapeutic guidance when faced with a high anion gap acidosis, for example pyroglutamate, in the common clinical scenario 'I can't identify the acid--but I know it's there'. The evidence that metabolic acidosis affects outcomes and thus warrants correction is considered and we provide management guidance including extracorporeal removal and fomepizole therapy.

Persistent villi hypoperfusion explains intramucosal acidosis in sheep endotoxemia

OBJECTIVE

To test the hypothesis that persistent villi hypoperfusion explains intramucosal acidosis after endotoxemic shock resuscitation.

DESIGN

Controlled experimental study.

SETTING

University-based research laboratory.

SUBJECTS

A total of 14 anesthetized, mechanically ventilated sheep.

INTERVENTIONS

Sheep were randomly assigned to endotoxin (n = 7) or control groups (n = 7). The endotoxin group received 5 microg/kg endotoxin, followed by 4 microg x kg(-1) x hr(-1) for 150 mins. After 60 mins of shock, hydroxyethylstarch resuscitation was given to normalize oxygen transport for an additional 90 mins.

MEASUREMENTS AND MAIN RESULTS

Endotoxin infusion decreased mean arterial blood pressure, cardiac output, and superior mesenteric artery blood flow (96 +/- 10 vs. 51 +/- 20 mm Hg, 145 +/- 30 vs. 90 +/- 30 mL x min(-1) x kg(-1), and 643 +/- 203 vs. 317 +/- 93 mL x min(-1) x kg(-1), respectively; p < .05 vs. basal), whereas it increased intramucosal-arterial PCO2 (deltaPCO2) and arterial lactate (3 +/- 3 vs. 14 +/- 8 mm Hg, and 1.5 +/- 0.5 vs. 3.7 +/- 1.3 mmol/L; p < .05). Sublingual, and serosal and mucosal intestinal microvascular flow indexes, and the percentage of perfused ileal villi were reduced (3.0 +/- 0.1 vs. 2.3 +/- 0.4, 3.2 +/- 0.2 vs. 2.4 +/- 0.6, 3.0 +/- 0.0 vs. 2.0 +/- 0.2, and 98% +/- 3% vs. 76% +/- 10%; p < .05). Resuscitation normalized mean arterial blood pressure (92 +/- 13 mm Hg), cardiac output (165 +/- 32 mL x min(-1) x kg(-1)), superior mesenteric artery blood flow (683 +/- 192 mL x min(-1) x kg(-1)), and sublingual and serosal intestinal microvascular flow indexes (2.8 +/- 0.5 and 3.5 +/- 0.7). Nevertheless, deltaPCO2, lactate, mucosal intestinal microvascular flow indexes, and percentage of perfused ileal villi remained altered (10 +/- 6 mm Hg, 3.7 +/- 0.9 mmol/L, 2.3 +/- 0.4, and 78% +/- 11%; p < .05).

CONCLUSIONS

In this model of endotoxemia, fluid resuscitation corrected both serosal intestinal and sublingual microcirculation but was unable to restore intestinal mucosal perfusion. Intramucosal acidosis might be due to persistent villi hypoperfusion.

Glucose metabolism and catecholamines

Until now, catecholamines were the drugs of choice to treat hypotension during shock states. Catecholamines, however, also have marked metabolic effects, particularly on glucose metabolism, and the degree of this metabolic response is directly related to the beta2-adrenoceptor activity of the individual compound used. Under physiologic conditions, infusing catecholamine is associated with enhanced rates of aerobic glycolysis (resulting in adenosine triphosphate production), glucose release (both from glycogenolysis and gluconeogenesis), and inhibition of insulin-mediated glycogenesis. Consequently, hyperglycemia and hyperlactatemia are the hallmarks of this metabolic response. Under pathophysiologic conditions, the metabolic effects of catecholamines are less predictable because of changes in receptor affinity and density and in drug kinetics and the metabolic capacity of the major gluconeogenic organs, both resulting from the disease per se and the ongoing treatment. It is also well-established that shock states are characterized by a hypermetabolic condition with insulin resistance and increased oxygen demands, which coincide with both compromised tissue microcirculatory perfusion and mitochondrial dysfunction. This, in turn, causes impaired glucose utilization and may lead to inadequate glucose supply and, ultimately, metabolic failure. Based on the landmark studies on intensive insulin use, a crucial role is currently attributed to glucose homeostasis. This article reviews the effects of the various catecholamines on glucose utilization, both under physiologic conditions, as well as during shock states. Because, to date (to our knowledge), no patient data are available, results from relevant animal experiments are discussed. In addition, potential strategies are outlined to influence the catecholamine-induced effects on glucose homeostasis.

Fish oil after abdominal aorta aneurysm surgery

OBJECTIVE

Fish oil (FO) may attenuate the inflammatory response after major surgery such as abdominal aortic aneurysm (AAA) surgery. We aimed at evaluating the clinical impact and safety aspects of a FO containing parenteral nutrition (PN) after AAA surgery.

METHODS

Intervention consisted in 4 days of either standard (STD: Lipofundin medium-chain triglyceride (MCT): long-chain triglyceride (LCT)50%-MCT50%) or FO containing PN (FO: Lipoplus: LCT40%-MCT50%-FO10%). Energy target were set at 1.3 times the preoperative resting energy expenditure by indirect calorimetry. Blood sampling on days 0, 2, 3 and 4. Glucose turnover by the (2)H(2)-glucose method. Muscle microdialysis.

CLINICAL DATA

maximal daily T degrees, intensive care unit (ICU) and hospital stay.

RESULTS

Both solutions were clinically well tolerated, without any differences in laboratory safety parameters, inflammatory, metabolic data, or in organ failures. Plasma tocopherol increased similarly; with FO, docosahexaenoic and eicosapentaenoic acid increased significantly by day 4 versus baseline or STD. To increased postoperatively, with a trend to lower values in FO group (P=0.09). After FO, a trend toward shorter ICU stay (1.6+/-0.4 versus 2.3+/-0.4), and hospital stay (9.9+/-2.4 versus 11.3+/-2.7 days: P=0.19) was observed.

CONCLUSIONS

Both lipid emulsions were well tolerated. FO-PN enhanced the plasma n-3 polyunsaturated fatty acid content, and was associated with trends to lower body temperature and shorter length of stay.

The role of nitric oxide on contractile impairment during endotoxemia in rat diaphragm muscle

We examined the contribution of nitric oxide (NO) on the contractile impairment in diaphragm muscles of endotoxemic rats. Force-frequency relationship was depressed 24 h after lipopolysaccharide administration. 7-Nitroindazole, aminoguanidine and 1H-[1,2,4]Oxadiazole (4,3-a)quinoxalin-1-one (ODQ) partially restored the contractile impairment, Nomega-Nitro-L-Arginine (L-NNA) was ineffective. K+ contractions were reduced by 50% in endotoxemic muscles, 7-nitroindazole partially recovered, while aminoguanidine and L-NNA were ineffective. Verapamil reduced contractility to a greater extent in endotoxemic muscles. Caffeine and ryanodine contractions were augmented during endotoxemia without NOS contribution. L-NNA, 7-nitroindazole, ODQ and hemoglobin did not affect, but aminoguanidine completely restored partially inhibited neurotransmission by d-tubocurarine. Endotoxemia did not change membrane potentials and neurotransmitter release but slightly increased excitability. At this stage of endotoxemia, (1) constitutive NOS appears to be the dominant isoform, (2) NO does not have a major role on contractile dysfunction and (3) impairment could be explained by altered sensitivity of the voltage sensor. (4) NO does not substantially modulate neuromuscular transmission in normal and endotoxemic rats.

Epinephrine induces tissue perfusion deficit in porcine endotoxin shock: evaluation by regional CO(2) content gradients and lactate-to-pyruvate ratios

Epinephrine is widely used as a vasoconstrictor or inotrope in shock, although it may typically induce or augment lactic acidosis. Ongoing debate addresses the question of whether hyperlactatemia per se is a sign of tissue perfusion deficit or aerobic glycolysis. We wanted to test the hypothesis that epinephrine has selective detrimental effects on visceral perfusion and metabolism. We performed rigorous regional venous blood gas analyses as well as intraperitoneal microdialysis. We used a mathematical model to calculate regional arteriovenous CO(2) content gradients and estimated the magnitude of the Haldane effect in a porcine model of prolonged hypotensive shock induced by endotoxin infusion (mean arterial blood pressure < 60 mmHg). Subsequently, vasopressors (epinephrine or norepinephrine) were administered and adjusted to maintain systemic mean arterial pressure > 70 mmHg for 4 h. Epinephrine caused systemic hyperlactatemia and acidosis. Importantly, both systemic and regional venous lactate-to-pyruvate ratios increased. Epinephrine was associated with decreasing portal blood flow despite apparently maintained total splanchnic blood flow. Epinephrine increased gastric venous-to-arterial Pco(2) gradients and CO(2) content gradients with decreasing magnitude of the Haldane effect, and the regional gastric respiratory quotient remained higher after epinephrine as opposed to norepinephrine infusion. In addition, epinephrine induced intraperitoneal lactate and glycerol release. We did not observe these adverse hemodynamic or metabolic changes related to norepinephrine with the same arterial pressure goal. We conclude that high CO(2) content gradients with decreasing magnitude of the Haldane effect pinpoint the most pronounced perfusion deficiency to the gastric wall when epinephrine, as opposed to norepinephrine, is used in experimental endotoxin shock.

Practice parameters for hemodynamic support of sepsis in adult patients: 2004 update

OBJECTIVE

To provide the American College of Critical Care Medicine with updated guidelines for hemodynamic support of adult patients with sepsis.

DATA SOURCE

Publications relevant to hemodynamic support of septic patients were obtained from the medical literature, supplemented by the expertise and experience of members of an international task force convened from the membership of the Society of Critical Care Medicine.

STUDY SELECTION

Both human studies and relevant animal studies were considered.

DATA SYNTHESIS

The experts articles reviewed the literature and classified the strength of evidence of human studies according to study design and scientific value. Recommendations were drafted and graded levels based on an evidence-based rating system described in the text. The recommendations were debated, and the task force chairman modified the document until <10% of the experts disagreed with the recommendations.

CONCLUSIONS

An organized approach to the hemodynamic support of sepsis was formulated. The fundamental principle is that clinicians using hemodynamic therapies should define specific goals and end points, titrate therapies to those end points, and evaluate the results of their interventions on an ongoing basis by monitoring a combination of variables of global and regional perfusion. Using this approach, specific recommendations for fluid resuscitation, vasopressor therapy, and inotropic therapy of septic in adult patients were promulgated.