Lactic acidosis in sepsis: Another commentary*

Cardiogenic Shock: Reflections at the Crossroad Between Perfusion, Tissue Hypoxia, and Mitochondrial Function

Cardiogenic shock is classically defined by systemic hypotension with evidence of hypoperfusion and end organ dysfunction. In modern practice, however, these metrics often incompletely describe cardiogenic shock because patients present with more advanced cardiovascular disease and greater degrees of multiorgan dysfunction. Understanding how perfusion, congestion, and end organ dysfunction contribute to hypoxia at the cellular level are central to the diagnosis and management of cardiogenic shock. Although, in clinical practice, increased lactate level is often equated with hypoxia, several other factors might contribute to an elevated lactate level including mitochondrial dysfunction, impaired hepatic and renal clearance, as well as epinephrine use. To this end, we present the evidence underlying the value of lactate to pyruvate ratio as a potential discriminator of cellular hypoxia. We will then discuss the physiological implications of hypoxia and congestion on hepatic, intestinal, and renal physiology. Organ-specific susceptibility to hypoxia is presented in the context of their functional architecture. We discuss how the concepts of contractile reserve, fluid responsiveness, tissue oxygenation, and cardiopulmonary interactions can help personalize the management of cardiogenic shock. Finally, we highlight the limitations of using lactate for tailoring therapy in cardiogenic shock.

Clinical use of plasma lactate concentration. Part 1: Physiology, pathophysiology, and measurement

OBJECTIVE

To review the current literature with respect to the physiology, pathophysiology, and measurement of lactate.

DATA SOURCES

Data were sourced from veterinary and human clinical trials, retrospective studies, experimental studies, and review articles. Articles were retrieved without date restrictions and were sourced primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection.

HUMAN AND VETERINARY DATA SYNTHESIS

Lactate is an important energy storage molecule, the production of which preserves cellular energy production and mitigates the acidosis from ATP hydrolysis. Although the most common cause of hyperlactatemia is inadequate tissue oxygen delivery, hyperlactatemia can, and does occur in the face of apparently adequate oxygen supply. At a cellular level, the pathogenesis of hyperlactatemia varies widely depending on the underlying cause. Microcirculatory dysfunction, mitochondrial dysfunction, and epinephrine-mediated stimulation of Na⁺ -K⁺ -ATPase pumps are likely important contributors to hyperlactatemia in critically ill patients. Ultimately, hyperlactatemia is a marker of altered cellular bioenergetics.

CONCLUSION

The etiology of hyperlactatemia is complex and multifactorial. Understanding the relevant pathophysiology is helpful when characterizing hyperlactatemia in clinical patients.

Shock Management for Cardio-surgical ICU Patients - The Golden Hours

Postoperative shock following cardiac surgery is a serious condition with a high morbidity and mortality. There are four types of shock: cardiogenic, hypovolemic, obstructive and distributive and these can occur alone or in combination. Early identification of the underlying diseases and understanding of the mechanisms at play are key for successful management of shock. Prompt resuscitation measures are necessary to reverse the shock state and avoid permanent organ dysfunction or death. In this review, the authors focus on the management during the first 6 hours of shock (the 'golden hours'). They discuss how to optimise preload, vascular tone, contractility, heart rate and oxygen delivery. The review incorporates the findings of recent trials on early goal-directed therapy and includes practical recommendations in areas in which the evidence is scare or controversial. While the review focuses on cardio-surgical patients, the suggested treatment algorithms might be usefully expanded to other critically ill patients with shock arising from other causes.

Comparison of lactate values obtained from different sites and their clinical significance in patients with severe sepsis

CONTEXT AND OBJECTIVE

The ideal site for lactate collection has not been clearly established. This study aimed to evaluate associations between lactate levels in arterial blood (Lart), peripheral venous blood (Lper) and central venous blood (Lcen) in patients with severe sepsis or septic shock.

DESIGN AND SETTING

Cross-sectional analytical study in an tertiary university hospital.

METHOD

Samples from patients with a central venous catheter and from healthy volunteers (control group) were collected. Blood was drawn simultaneously for measurements of Lart, Lper and Lcen, and the first sample was collected less than 24 hours after the onset of organ dysfunction. The results were analyzed using Pearson correlation, Bland-Altman and McNemar tests.

RESULTS

A total of 238 samples were collected from 32 patients. The correlation results were r = 0.79 (P < 0.0001) for Lart/Lper and r = 0.84 (P < 0.0001) for Lart/Lcen. Bland-Altman showed large limits of agreement: -3.2 ± 4.9 (-12.8 to 6.4) and -0.8 ± 5.9 (-12.5 to 10.8), for Lper and Lcen respectively. In the control group, there was greater correlation (r = 0.9009, P = 0.0004) and agreement: -0.7 ± 1.2 (-3.1 to 1.7). Regarding clinical intervention, there was good agreement between Lart/Lcen (96.3%; three disagreements), with worst results for Lart/Lper (87.0%) with 10 cases of disagreement (P = 0.04). In eight patients (80.0%) Lper was higher than Lart.

CONCLUSION

Lcen, and not Lper, can replace Lart with good correlation and clinical agreement. Lper tends to overestimate Lart, thus leading to unnecessary therapeutic interventions.

Anion gap, anion gap corrected for albumin, base deficit and unmeasured anions in critically ill patients: implications on the assessment of metabolic acidosis and the diagnosis of hyperlactatemia

Background

Base deficit (BD), anion gap (AG), and albumin corrected anion gap (ACAG) are used by clinicians to assess the presence or absence of hyperlactatemia (HL). We set out to determine if these tools can diagnose the presence of HL using cotemporaneous samples.

Methods

We conducted a chart review of ICU patients who had cotemporaneous arterial blood gas, serum chemistry, serum albumin (Alb) and lactate(Lac) levels measured from the same sample. We assessed the capacity of AG, BD, and ACAG to diagnose HL and severe hyperlactatemia (SHL). HL was defined as Lac > 2.5 mmol/L. SHL was defined as a Lac of > 4.0 mmol/L.

Results

From 143 patients we identified 497 series of lab values that met our study criteria. Mean age was 62.2 ± 15.7 years. Mean Lac was 2.11 ± 2.6 mmol/L, mean AG was 9.0 ± 5.1, mean ACAG was 14.1 ± 3.8, mean BD was 1.50 ± 5.4. The area under the curve for the ROC for BD, AG, and ACAG to diagnose HL were 0.79, 0.70, and 0.72, respectively.

Conclusion

AG and BD failed to reliably detect the presence of clinically significant hyperlactatemia. Under idealized conditions, ACAG has the capacity to rule out the presence of hyperlactatemia. Lac levels should be obtained routinely in all patients admitted to the ICU in whom the possibility of shock/hypoperfusion is being considered. If an AG assessment is required in the ICU, it must be corrected for albumin for there to be sufficient diagnostic utility.

Anion gap, anion gap corrected for albumin, and base deficit fail to accurately diagnose clinically significant hyperlactatemia in critically ill patients

Anion gap, anion gap corrected for serum albumin, and base deficit are often used as surrogates for measuring serum lactate. None of these surrogates is postulated to predict hyperlactatemia in the critically ill. We prospectively collected data from September 2004 through August 2005 for 1381 consecutive admissions. Patients with renal disease, ketoacidosis, or toxic ingestion were excluded. Anion gap, anion gap corrected for albumin, and base deficit were calculated for all patients. We identified 286 patients who met our inclusion or exclusion criteria. The receiver-operating characteristic area under the curve for the prediction of hyperlactatemia for anion gap, anion gap corrected for albumin, and base deficit were 0.55, 0.57, and 0.64, respectively. Anion gap, anion gap corrected for albumin, and base deficit do not predict the presence or absence of clinically significant hyperlactatemia. Serum lactate should be measured in all critically ill adults in whom hypoperfusion is suspected.

Understanding the role of inflammatory cytokines in malaria and related diseases

It is now broadly accepted for infectious disease in general that it is not the invading organism, but the body's unbridled response to it--the "cytokine storm"--that causes illness and pathology. Nevertheless, many researchers still regard the harmful effects of falciparum malaria as being governed by oligaemic hypoxia arising from parasitised erythrocytes obstructing blood flow through vulnerable organs, particularly the brain, and we summarise why these notions are no longer tenable. In our view, this harmful sequestration is readily accommodated within the cytokine storm perspective as one of its secondary effects. We approach these issues by examining aspects of malaria, sepsis and influenza in parallel, and discuss the insights that comparisons of the literature can provide on the validity of possible anti-disease therapies.

The molecular basis of paediatric malarial disease

Severe falciparum malaria is an acute systemic disease that can affect multiple organs, including those in which few parasites are found. The acute disease bears many similarities both clinically and, potentially, mechanistically, to the systemic diseases caused by bacteria, rickettsia, and viruses. Traditionally the morbidity and mortality associated with severe malarial disease has been explained in terms of mechanical obstruction to vascular flow by adherence to endothelium (termed sequestration) of erythrocytes containing mature-stage parasites. However, over the past few decades an alternative ‘cytokine theory of disease’ has also evolved, where malarial pathology is explained in terms of a balance between the pro- and anti-inflammatory cytokines. The final common pathway for this pro-inflammatory imbalance is believed to be a limitation in the supply and mitochondrial utilisation of energy to cells. Different patterns of ensuing energy depletion (both temporal and spatial) throughout the cells in the body present as different clinical syndromes. This chapter draws attention to the over-arching position that inflammatory cytokines are beginning to occupy in the pathogenesis of acute malaria and other acute infections. The influence of inflammatory cytokines on cellular function offers a molecular framework to explain the multiple clinical syndromes that are observed during acute malarial illness, and provides a fresh avenue of investigation for adjunct therapies to ameliorate the malarial disease process.

Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficiency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease.