Lactic acidosis

Severe hyperlactatemia in unselected surgical patients: retrospective analysis of prognostic outcome factors

Background

Etiology of hyperlactatemia in ICU patients is heterogeneous—septic, cardiogenic or hemorrhagic shock seem to be predominant reasons. Multiple studies show hyperlactatemia as an independent predictor for ICU mortality. Only limited data exists about the etiology of hyperlactatemia and lactate clearance and their influence on mortality. The goal of this single-center retrospective study, was to evaluate the effect of severe hyperlactatemia and reduced lactate clearance rate on the outcome of unselected ICU surgical patients.

Methods

Overall, 239 surgical patients with severe hyperlactatemia (> 10 mmol/L) who were treated in the surgical ICU at the University Medical Center Freiburg between June 2011 and August 2017, were included in this study. The cause of the hyperlactatemia as well as the postoperative course and the patient morbidity and mortality were retrospectively analyzed. Lactate clearance was calculated by comparing lactate level 12 h after first measurement of > 10 mmol/L.

Results

The overall mortality rate in our cohort was 82.4%. Severe hyperlactatemia was associated with death in the ICU (p < 0.001). The main etiologic factor was sepsis (51.9%), followed by mesenteric ischemia (15.1%), hemorrhagic shock (13.8%) and liver failure (9.6%). Higher lactate levels at ICU admission were associated with increased mortality (p < 0.001). Lactate clearance after 12 h was found to predict ICU mortality (ANOVA p < 0.001) with an overall clearance of under 50% within 12 h. The median percentage of clearance was 60.3% within 12 h for the survivor and 29.1% for the non-survivor group (p < 0.001).

Conclusion

Lactate levels appropriately reflect disease severity and are associated with short-term mortality in critically ill patients. The main etiologic factor for surgical patients is sepsis. When elevated lactate levels persist more than 12 h, survival chances are low and the benefit of continued maximum therapy should be evaluated.

Comprehensive Analysis of 13C6 Glucose Fate in the Hypoxia-Tolerant Blind Mole Rat Skin Fibroblasts

The bioenergetics of the vast majority of terrestrial mammals evolved to consuming glucose (Glc) for energy production under regular atmosphere (about 21% oxygen). However, some vertebrate species, such as aquatic turtles, seals, naked mole rat, and blind mole rat, Spalax, have adjusted their homeostasis to continuous function under severe hypoxic environment. The exploration of hypoxia-tolerant species metabolic strategies provides a better understanding of the adaptation to hypoxia. In this study, we compared Glc homeostasis in primary Spalax and rat skin cells under normoxic and hypoxic conditions. We used the targeted-metabolomics approach, utilizing liquid chromatography and mass spectrometry (LC-MS) to track the fate of heavy Glc carbons (¹³C₆ Glc), as well as other methodologies to assist the interpretation of the metabolic landscape, such as bioenergetics profiling, Western blotting, and gene expression analysis. The metabolic profile was recorded under steady-state (after 24 h) of the experiment. Glc-originated carbons were unequally distributed between the cytosolic and mitochondrial domains in Spalax cells compared to the rat. The cytosolic domain is dominant apparently due to the hypoxia-inducible factor-1 alpha (HIF-1α) mastering, since its level is higher under normoxia and hypoxia in Spalax cells. Consumed Glc in Spalax cells is utilized for the pentose phosphate pathway maintaining the NADPH pool, and is finally harbored as glutathione (GSH) and UDP-GlcNAc. The cytosolic domain in Spalax cells works in the semi-uncoupled mode that limits the consumed Glc-derived carbons flux to the tricarboxylic acid (TCA) cycle and reduces pyruvate delivery; however, it maintains the NAD⁺ pool via lactate dehydrogenase upregulation. Both normoxic and hypoxic mitochondrial homeostasis of Glc-originated carbons in Spalax are characterized by their massive cataplerotic flux along with the axis αKG→Glu→Pro→hydroxyproline (HPro). The product of collagen degradation, HPro, as well as free Pro are apparently involved in the bioenergetics of Spalax under both normoxia and hypoxia. The upregulation of 2-hydroxyglutarate production detected in Spalax cells may be involved in modulating the levels of HIF-1α. Collectively, these data suggest that Spalax cells utilize similar metabolic frame for both normoxia and hypoxia, where glucose metabolism is switched from oxidative pathways (conversion of pyruvate to Acetyl-CoA and further TCA cycle processes) to (i) pentose phosphate pathway, (ii) lactate production, and (iii) cataplerotic pathways leading to hexosamine, GSH, and HPro production.

Regional venous-arterial CO2 to arterial-venous O2 content difference ratio in experimental circulatory shock and hypoxia

Background

Venous–arterial carbon dioxide (CO₂) to arterial–venous oxygen (O₂) content difference ratio (Cv-aCO₂/Ca-vO₂) > 1 is supposed to be both sensitive and specific for anaerobic metabolism. What regional hemodynamic and metabolic parameters determine the ratio has not been clarified.

Objectives

To address determinants of systemic and renal, spleen, gut and liver Cv-aCO₂/Ca-vO₂.

Methods

Post hoc analysis of original data from published experimental studies aimed to address effects of different fluid resuscitation strategies on oxygen transport, lactate metabolism and organ dysfunction in fecal peritonitis and endotoxin infusion, and from animals in cardiac tamponade or hypoxic hypoxia. Systemic and regional hemodynamics, blood flow, lactate uptake, carbon dioxide and oxygen-derived variables were determined. Generalized estimating equations (GEE) were fit to assess contributors to systemic and regional Cv-aCO₂/Ca-vO₂.

Results

Median (range) of pooled systemic Cv-aCO₂/Ca-vO₂ in 64 pigs was 1.02 (0.02 to 3.84). While parameters reflecting regional lactate exchange were variably associated with the respective regional Cv-aCO₂/Ca-vO₂ ratios, only regional ratios were independently correlated with systemic ratio: renal Cv-aCO₂ /Ca-vO₂ (β = 0.148, 95% CI 0.062 to 0.234; p = 0.001), spleen Cv-aCO₂/Ca-vO₂ (β = 0.065, 95% CI 0.002 to 0.127; p = 0.042), gut Cv-aCO₂/Ca-vO₂ (β = 0.117, 95% CI 0.025 to 0.209; p = 0.013), liver Cv-aCO₂/Ca-vO₂ (β = − 0.159, 95% CI − 0.297 to − 0.022; p = 0.023), hepatosplanchnic Cv-aCO₂/Ca-vO₂ (β = 0.495, 95% CI 0.205 to 0.786; p = 0.001).

Conclusion

In a mixed set of animals in different shock forms or during hypoxic injury, hepatosplanchnic Cv-aCO₂/Ca-vO₂ ratio had the strongest independent association with systemic Cv-aCO₂/Ca-vO₂, while no independent association was demonstrated for lactate or hemodynamic variables.

Pre-Hospital Lactatemia Predicts 30-Day Mortality in Patients with Septic Shock-Preliminary Results from the LAPHSUS Study

Background: Assessment of disease severity in patients with septic shock (SS) is crucial in determining optimal level of care. In both pre- and in-hospital settings, the clinical picture alone is not sufficient for assessing disease severity and outcomes. Because blood lactate level is included in the clinical criteria of SS it should be considered to improve the assessment of its severity. This study aims to investigate the relationship between pre-hospital blood lactate level and 30-day mortality in patients with SS. Methods: From 15 April 2017 to 15 April 2019, patients with SS requiring pre-hospital Mobile Intensive Care Unit intervention (MICU) were prospectively included in the LAPHSUS study, an observational, non-randomized controlled study. Pre-hospital blood lactate levels were measured at the time of first contact between the patients and the MICU. Results: Among the 183 patients with septic shock requiring action by the MICU drawn at random from LAPHSUS study patients, six (3%) were lost to follow-up on the 30th day and thus 177 (97%) were analyzed for blood lactate levels (mean age 70 ± 14 years). Pulmonary, urinary and digestive infections were probably the cause of the SS in respectively 58%, 21% and 11% of the cases. The 30-day overall mortality was 32%. Mean pre-hospital lactatemia was significantly different between patients who died and those who survived (respectively 7.1 ± 4.0 mmol/L vs. 5.9 ± 3.5 mmol/L, p < 10⁻³). Using Cox regression analysis adjusted for potential confounders we showed that a pre-hospital blood lactate level ≥ 4 mmol/L significantly predicted 30-day mortality in patients with SS (adjusted hazard ratio = 2.37, 95%CI (1.01–5.57), p = 0.04). Conclusion: In this study, we showed that pre-hospital lactatemia predicts 30-day mortality in patients with septic shock handled by the MICU. Further studies will be needed to evaluate if pre-hospital lactatemia alone or combined with clinical scores could affect the triage decision-making process for those patients.

The Association of Hypophosphatemia With Resistant Lactic Acidosis in Critical Care Illness

Critically ill patients are known to have a variety of electrolyte abnormalities. Lactic acidosis can frequently be seen secondary to shock states and is usually treated with aggressive volume resuscitation. Interestingly, hypophosphatemia is a potential cause of resistant lactic acidosis, which may not be as commonly identified or considered. We present a case of a 42-year-old man admitted twice over a span of 6 months with an elevated lactate level that did not resolve with volume resuscitation. It was ultimately determined that his lactic acidosis was due to hypophosphatemia after ruling out other potential causes. Phosphate replacement therapy resulted in the normalization of his lactate. In the literature, multiple theories have indicated the association of hypophosphatemia with lactic acidosis though no prior cases exist supporting a direct relationship. In this case, we set forth to evaluate the complicated relationship between all of these factors and to highlight the importance of early detection and treatment of hypophosphatemia, which may be beneficial in treating lactic acidosis.

Molecular and cellular mechanisms for zoledronic acid-loaded magnesium-strontium alloys to inhibit giant cell tumors of bone

Giant Cell Tumors of Bone (GCTB) are benign but aggressive and metastatic tumors. Surgical removal cannot eradicate GCTB due to the subsequent recurrence and osteolysis. Here we developed Zoledronic acid (ZA)-loaded magnesium-strontium (Mg-Sr) alloys that can inhibit GCTB and studied the molecular and cellular mechanisms of such inhibition. We first formed a calcium phosphate (CaP) coating on the Mg-1.5 wt%Sr implants by coprecipitation and then loaded ZA on the CaP coating. We examined the response of GCTB cells to the ZA-loaded alloys. At the cellular level, the alloys not only induced apoptosis and oxidative stress of GCTB cells, and suppressed their resultant pre-osteoclast recruitment, but also inhibited their migration. At the molecular level, the alloys could significantly activate the mitochondrial pathway and inhibit the NF-κB pathway in the GCTB cells. These collectively enable the ZA-loaded alloys to suppress GCTB cell growth and osteolysis, and thus improve our understanding of the materials-induced tumor inhibition. Our study shows that ZA-loaded alloys could be a potential implant in repairing the bone defects after tumor removal in GCTB therapy.

STATEMENT OF SIGNIFICANCE

In clinics, giant cell tumors of bone (GCTB) are removed by surgery. However, the resultant defects in bone still contain aggressive and metastatic GCTB cells that can recruit osteoclasts to damage bone, leading to new GCTB tumor growth and bone damage after tumor surgery. Hence, it is of high demand in developing a material that can not only fill the bone defects as an implant but also inhibit GCTB in the defect area as a therapeutic agent. More importantly, the molecular and cellular mechanism by which such a material inhibits GCTB growth has never been explored. To solve these two problems, we prepared a new biomaterial, the Mg-Sr alloys that were first coated with calcium phosphate and then loaded with a tumor-inhibiting molecule (Zoledronic acid, ZA). Then, by using a variety of molecular and cellular biological assays, we studied how the ZA-loaded alloys induced the death of GCTB cells (derived from patients) and inhibited their growth at the molecular and cellular level. At the cellular level, our results showed that ZA-loaded Mg-Sr alloys not only induced apoptosis and oxidative stress of GCTB cells, and suppressed their induced pre-osteoclast recruitment, but also inhibited their migration. At the molecular level, our data showed that ZA released from the ZA-loaded Mg-Sr alloys could significantly activate the mitochondrial pathway and inhibit the NF-κB pathway in the GCTB cells. Both mechanisms collectively induced GCTB cell death and inhibited GCTB cell growth. This work showed how a biomaterial inhibit tumor growth at the molecular and cellular level, increasing our understanding in the fundamental principle of materials-induced cancer therapy. This work will be interesting to readers in the fields of metallic materials, inorganic materials, biomaterials and cancer therapy.

Recent advances in bedside microcirculation assessment in critically ill patients

Parameters related to macrocirculation, such as the mean arterial pressure, central venous pressure, cardiac output, mixed venous saturation and central oxygen saturation, are commonly used in the hemodynamic assessment of critically ill patients. However, several studies have shown that there is a dissociation between these parameters and the state of microcirculation in this group of patients. Techniques that allow direct viewing of the microcirculation are not completely disseminated, nor are they incorporated into the clinical management of patients in shock. The numerous techniques developed for microcirculation assessment include clinical assessment (e.g., peripheral perfusion index and temperature gradient), laser Doppler flowmetry, tissue oxygen assessment electrodes, videomicroscopy (orthogonal polarization spectral imaging, sidestream dark field imaging or incident dark field illumination) and near infrared spectroscopy. In the near future, the monitoring and optimization of tissue perfusion by direct viewing and microcirculation assessment may become a goal to be achieved in the hemodynamic resuscitation of critically ill patients.

Use of stepwise lactate kinetics-oriented hemodynamic therapy could improve the clinical outcomes of patients with sepsis-associated hyperlactatemia

Background

Setting lactate kinetics at >30% might improve the clinical outcomes of patients with sepsis-associated hyperlactatemia. The aim of this study was to explore the outcome benefits of stepwise lactate kinetics vs central venous oxygen saturation (ScvO₂)-oriented hemodynamic therapy at 6 h as the protocol goal during early resuscitation.

Methods

The relevant parameters and adverse events after different targets in 360 randomly assigned patients with sepsis-associated hyperlactatemia were recorded and compared.

Results

Heart rate (HR) at 48 h in the ScvO₂ group was higher than in the lactate kinetics group (105 ± 19 bpm vs 99 ± 20 bpm, P = 0.040). The liquid balance at 4 h, 12 h, and 24 h in the lactate kinetics group was larger than in the ScvO₂ group (1535 (1271–1778) ml vs 826 (631–1219) ml, P < 0.001; 1688 (1173–1923) ml vs 1277 (962 − 1588) ml, P <0.001; and 1510 (904–2087) ml vs 1236 (740–1808) ml, P = 0.005), respectively. Mortality was higher in the ScvO₂ group (27.9% vs 18.3%, P = 0.033), but there was no significant difference between the two groups in the length of stay in the ICU or mechanical ventilation. In terms of new onset organ dysfunction, there was a significant difference between the two groups in total bilirubin at 48 h and 72 h. Based on the 60-day survival curves, there was significantly more mortality in the ScvO₂ group than in the lactate kinetics group (X² = 4.133, P = 0.042). In addition, fewer adverse events occurred in the lactate kinetics group.

Conclusions

Stepwise lactate kinetics-oriented hemodynamic therapy can reduce mortality in patients with sepsis-associated hyperlactatemia compared with ScvO₂-oriented therapy.

Trial registration

National Institutes of Health Clinical Trials Registry, NCT02566460. Registered on 26 September 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1617-1) contains supplementary material, which is available to authorized users.

The value of blood lactate kinetics in critically ill patients: a systematic review

BACKGROUND

The time course of blood lactate levels could be helpful to assess a patient's response to therapy. Although the focus of published studies has been largely on septic patients, many other studies have reported serial blood lactate levels in different groups of acutely ill patients.

METHODS

We performed a systematic search of PubMed, Science Direct, and Embase until the end of February 2016 plus reference lists of relevant publications. We selected all observational and interventional studies that evaluated the capacity of serial blood lactate concentrations to predict outcome. There was no restriction based on language. We excluded studies in pediatric populations, experimental studies, and studies that did not report changes in lactate values or all-cause mortality rates. We separated studies according to the type of patients included. We collected data on the number of patients, timing of lactate measurements, minimum lactate level needed for inclusion if present, and suggested time interval for predictive use.

RESULTS

A total of 96 studies met our criteria: 14 in general ICU populations, five in general surgical ICU populations, five in patients post cardiac surgery, 14 in trauma patients, 39 in patients with sepsis, four in patients with cardiogenic shock, eight in patients after cardiac arrest, three in patients with respiratory failure, and four in other conditions. A decrease in lactate levels over time was consistently associated with lower mortality rates in all subgroups of patients. Most studies reported changes over 6, 12 or 24 hrs, fewer used shorter time intervals. Lactate kinetics did not appear very different in patients with sepsis and other types of patients. A few studies suggested that therapy could be guided by these measurements.

CONCLUSIONS

The observation of a better outcome associated with decreasing blood lactate concentrations was consistent throughout the clinical studies, and was not limited to septic patients. In all groups, the changes are relatively slow, so that lactate measurements every 1-2 hrs are probably sufficient in most acute conditions. The value of lactate kinetics appears to be valid regardless of the initial value.