A comparison of prognostic significance of strong ion gap (SIG) with other acid-base markers in the critically ill: a cohort study

Acid-Base Analysis in the Operating Room: A Bedside Stewart Approach

The bedside Stewart approach to acid–base disorders is a simple, pragmatic tool that can assist anesthesiologists in analyzing and managing acid–base changes in the operating room, particularly metabolic acidosis.

Prognostic Significance of the Strong Ion Gap in Patients in Medical and Surgical Intensive Care Units

Background This study aimed to analyze acid-base imbalance by assessing the arterial blood gas (ABG) samples of the medical and surgical intensive care unit (ICU) patients by the Stewart approach and demonstrate the advantages of this method in delineating the acid-base status in cases where Henderson-Hasselbalch, anion gap, and base excess cannot optimally depict the imbalance and create recognition in the clinicians in this regard.  Methodology Adult (i.e., age > 18 years) patients admitted to the ICU of our institution during a one-year study period were included in this study. The patients were divided into two groups based on the indication of admission to the ICU as medical or surgical. The ABG, sodium, potassium, calcium, magnesium, phosphate, chloride, albumin, lactate, hemoglobin, hematocrit, leukocyte, blood urea nitrogen, and creatinine values determined during the first 24-hour period were used for calculating the Acute Physiologic Assessment and Chronic Health Evaluation (APACHE II), strong ion difference apparent (SIDa), and SID effective (SIDe) scores, which were subsequently compared between the groups.  Results Overall, 220 (110 medical and 110 surgical) patients were included. The mean patient age was 63.56 ± 18.08 years. The mean APACHE II scores were 21.99 and 19.63 in the medical and surgical groups, respectively. Overall, 110 patients died, while 110 were referred to the regular patient floor. The mean APACHE II score of the patients who died was 28.3, and the latter group had a mean APACHE II score of 13.57. There was a significant difference between the surgical and medical patient groups regarding mean values of APACHE II, SIDa, and SIDe scores. Also, the differences were significant between the patients who died and were discharged. There was a significant difference between the patients who died and were discharged regarding the strong ion gap (SIG); however, the medical and surgical patient groups were not different concerning the SIG values.  Conclusions We conclude that SIDa, SIDe, and SIG can be used in medical and surgical ICU patients to predict prognosis.

Unmeasured Organic Anions as Predictors of Clinical Outcomes in Lactic Acidosis due to Sepsis

Background and Objectives: In lactic acidosis, lactate can only explain 30% of the variance in the anion gap (AG), and the elevated AG not explained by lactate is due to unmeasured organic anions (UOAs). Some studies using less precise surrogates for UOA have suggested that UOA may predict clinical outcomes better than lactate. The aim of this study was to determine whether UOA predicts clinical outcomes better than lactate levels. Design, Setting, Participants, & Measurements: This was a retrospective cohort study of adult ICU patients with sepsis. Baseline AG and albumin measurements were obtained. An albumin-corrected delta AG was calculated. UOAs were estimated using the formula: Delta AG - serum lactate. A multivariate logistic regression model with its respective ROC curve was constructed to explore the relationship between in-hospital mortality, UOA, and lactate. Results: 526 patients were included. In the combined model examining both lactate and UOA, the odds ratio (OR) [95% CI] for predicting ICU length of stay (LOS) was 1.050 [1.029-1.072] and 1.022 [1.009-1.035], respectively; the OR [95% CI] for predicting in-hospital mortality was 1.224 [1.104-1.358] and 0.997 [0.943-1.054], respectively. The ROC curve for in-hospital mortality demonstrated that the Area Under the Curve (AUC) for lactate, UOA, and combined lactate and UOA was 0.7726, 0.7486, and 0.7732, respectively. The AUC for combined lactate and UOA were not statistically significantly higher than the AUC for lactate alone (P .9193). Conclusions: As expected, serum lactate predicted both ICU LOS and in-hospital mortality. UOA did predict ICU LOS, although the reason for this association is not known. UOA did not predict in-hospital mortality based on the OR and the ROC curve's AUC, contrary to some previous studies. However, our study used a more precise quantitative estimate of UOA, including the use of baseline albumin-corrected AG. Prior studies attempting to identify UOA have identified Krebs cycle intermediates including citrate and isocitrate, suggesting that in our study these anions associated with the Krebs cycle contributed to the UOA.

Insights into Hemodynamic Features of Survivors and the Deceased with Acute Brain Injury: A Step Forward Tailored Treatment

BACKGROUND

Pulmonary artery catheters are widely used for hemodynamical monitoring in critically ill patients. Acute brain injury is among the severe conditions treated in an intensive care unit. The advanced monitoring of hemodynamical parameters, fluid balance and adequate administered treatment based on those values are components of goal-directed therapy.

METHODS

A prospective observational study included adult patients who were hospitalized in the ICU due to acute bran injury, excluding brain oedema after cardiac arrest. Each patient had PAC inserted and hemodynamic data were collected during the first 3 days of the ICU stay every 6 h. Patients were divided into two groups based on the endpoint: the survivors and the deceased.

RESULTS

Length of stay in hospital differed between patiens. All patients, regardless of their outcome, had noradrenaline administered. The initial values of PAP differed between the groups (p = 0.05). There were positive correlations noticed between noradrenaline dose, CVP and fluid balance when compared to PCWP in a group of survivors and a positive correlation in the fluid balance when compared to PAP and PVRI. Lactate serum concentrations presented a correlation with the dose of noradrenaline in both groups.

CONCLUSIONS

Upon acute brain injury, values of PVRI and PAP increase. This is corelated with fluid load and worsened by an excessive fluid treatment in the case of an inconsiderate approach for stabilizing the patient hemodynamically. PAC may present limited advantages in terms of PAP and PVRI control during the treatment.

Effect of systemic inflammatory response syndrome on thrombocytogram, acute phase proteins, electrolytes, acid-base indices and cytokine expression in naturally canine parvovirus infected dogs

Systemic inflammatory response syndrome (SIRS) in canine parvoviral enteritis (CPVE) is associated with high mortality in young puppies. Changes in acute phase response, thrombocytogram, inflammatory cytokine profiles, and disturbances in electrolyte and acid-base homeostasis are thought to have a significant impact on the development of SIRS. However, the mechanisms causing these perturbations have not been well described in CPVE puppies, especially with SIRS. The purpose of this study was to assess the changes of electrolytes, acid-base indices using strong ion model, acute phase proteins and thrombocytogram in blood and expressions of inflammatory cytokines in blood mononuclear cells of CPVE puppies with or without SIRS at admission. Additionally, the positive predictive value (PPV) and cut-off value with specificity and sensitivity of the biomarkers were determined by receiver operating characteristic (ROC) curve analysis to predict the development of SIRS in CPVE puppies at admission. A case-controlled, prospective and observational study was conducted on fifteen SIRS-positive CPVE, twenty-one SIRS-negative CPVE and six healthy puppies. Our data showed marked hyponatremia, hypokalemia, hypoalbuminemia and hypoproteinemia, decreased A_Tot-albumin and A_{Tot-total protein} and increased mean platelet volume (MPV), platelet distribution width (PDW) and C-reactive protein (CRP) concentration and up-regulation of TNF-α, IL-8 and IL-10 expressions in SIRS-positive CPVE puppies as compared to SIRS-negative CPVE puppies at admission. Based on sensitivity, specificity and AUC from ROC curve analysis and PPV, the CRP concentration in serum at a cut-off value of 141.9 mg/L and TLC of blood at a cut-off value of 3.355 × 10³/μL were identified as potential prognostic biomarkers followed by A_{Tot-total protein} and total protein at a cut-off value of 11.80 and 4.72 g/dL, respectively to predict the development of SIRS in CPVE puppies at admission. In conclusion, the findings of the current study will help the canine practitioners to institute the time-sensitive and need based interventions to disrupt progression along the continuum of shock and multi-organ dysfunction syndrome in CPVE puppies that develop SIRS at admission.

Admission Lactate Concentration, Base Excess, and Alactic Base Excess Predict the 28-Day Inward Mortality in Shock Patients

Base excess (BE) and lactate concentration may predict mortality in critically ill patients. However, the predictive values of alactic BE (aBE; the sum of BE and lactate), or a combination of BE and lactate are unknown. The study aimed to investigate whether BE, lactate, and aBE measured on admission to ICU may predict the 28-day mortality for patients undergoing any form of shock. In 143 consecutive adults, arterial BE, lactate, and aBE were measured upon ICU admission. Receiver Operating Curve (ROC) characteristics and Cox proportional hazard regression models (adjusted to age, gender, forms of shock, and presence of severe renal failure) were then used to investigate any association between these parameters and 28-day mortality. aBE < −3.63 mmol/L was found to be associated with a hazard ratio of 3.19 (HR; 95% confidence interval (CI): 1.62−6.27) for mortality. Risk of death was higher for BE < −9.5 mmol/L (HR: 4.22; 95% CI: 2.21−8.05), particularly at lactate concentrations > 4.5 mmol/L (HR: 4.62; 95% CI: 2.56−8.33). A 15.71% mortality rate was found for the combined condition of BE > cut-off and lactate < cut-off. When BE was below but lactate above their respective cut-offs, the mortality rate increased to 78.91%. The Cox regression model demonstrated that the predictive values of BE and lactate were mutually independent and additive. The 28-day mortality in shock patients admitted to ICU can be predicted by aBE, but BE and lactate deliver greater prognostic value, particularly when combined. The clinical value of our findings deserves further prospective evaluation.

Association between delta anion gap and hospital mortality for patients in cardiothoracic surgery recovery unit: a retrospective cohort study

Backgrounds

High level of anion gap (AG) was associated with organic acidosis. This study aimed to explore the relationship between delta AG (ΔAG = AG_max − AG_min) during first 3 days after intensive care unit (ICU) admission and hospital mortality for patients admitted in the cardiothoracic surgery recovery unit (CSRU).

Methods

In this retrospective cohort study, we identified patients from the open access database called Multiparameter Intelligent Monitoring in Intensive Care III (MIMIC III). A logistic regression model was established to predict hospital mortality by adjusting confounding factors using a stepwise backward elimination method. We conducted receiver operating characteristic (ROC) curves to compare the diagnostic performance of acid–base variables. Cox regression model and Kaplan Meier curve were applied to predict patients’ 90-day overall survival (OS).

Results

A total of 2,860 patients were identified. ΔAG was an independent predictive factor of hospital mortality (OR = 1.24 per 1 mEq/L increase, 95% CI: 1.11–1.39, p < 0.001). The area under curve (AUC) values of ΔAG suggested a good diagnostic accuracy (AUC = 0.769). We established the following formula to estimate patients’ hospital mortality: Logit(P) = − 15.69 + 0.21ΔAG + 0.13age-0.21BE + 2.69AKF. After calculating Youden index, patients with ΔAG ≥ 7 was considered at high risk (OR = 4.23, 95% CI: 1.22–14.63, p = 0.023). Kaplan Meier curve demonstrated that patients with ΔAG ≥ 7 had a poorer 90-day OS (Adjusted HR = 3.20, 95% CI: 1.81–5.65, p < 0.001).

Conclusion

ΔAG is a prognostic factor of hospital mortality and 90-day OS. More prospective studies are needed to verify and update our findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12893-022-01625-9.

The Effect of the Non-compressed Oxygen Therapy and Hyperbaric Oxygenation in Combination With Standardized Drug Therapy on the Blood Acid-Base State Biomarkers in Alcohol Withdrawal Syndrome, an Experimental Study

In alcohol withdrawal syndrome (AWS), pathophysiological mechanisms cover acid-base disturbances that affect the clinical picture of this state. An earlier study found that oxygen therapy methods in combination with pharmacotherapy improved the cognitive state in persons suffering from AWS. As impairments in the acid-base state influence the general health, timely and effective correction of these acid-base disturbances could result in a potential improvement in the treatment of the alcohol withdrawal symptoms. Therefore, the aim of this study was to evaluate the effectiveness of non-compressed oxygen therapy (NOT) and hyperbaric oxygenation (HBO) in combination with standard drug therapy (SDT), based on the dynamics of the acid-base state (ABS) in blood during AWS. HBO is the use of oxygen under pressure, whereas NOT uses oxygen without pressure. A comparative assessment of the acid-base state biomarkers was made in 160 patients with a moderate alcohol withdrawal state (3 groups), namely, in patients who underwent SDT only (control group/CG; n = 42) and two comparison groups who underwent SDT in combination with NOT (SG1 group; n = 56) and HBO (SG2 group; n = 62). The use of both oxygen therapy methods (i.e., NOT and HBO) in combination with SDT corrected the ABS in a shorter time and more effectively, which was due to the better restoration of the carbonate buffer system. Although we did not find proof that novel oxygen-related therapeutic procedures such as NOT and HBO in combination with SDT improved the alcohol withdrawal symptoms, it helped with the faster restoration of the acid-base state.

Association Between Anion Gap and Mortality in Critically Ill Patients with Cardiogenic Shock

Background

No epidemiological study has determined the association between the anion gap (AG) and all-cause mortality in critically ill patients with cardiogenic shock (CS). This study was conducted to clarify the relationship between the AG and mortality in CS.

Methods

We extracted clinical data from the public database, MIMIC-III V1.4, by using a generalized additive model to identify the nonlinear relationship between the AG and the 30-day mortality in 1248 intensive care unit patients. Cox proportional hazard models were used to assess the association between the AG and the 30-day, 90-day, and 365-day mortality in CS.

Results

The AG and 30-day all-cause mortality showed a nonlinear relationship, indicated by a J-shaped curve. In the multivariate analysis, after adjusting for potential confounders, a high AG was associated with an increased risk of 30-day, 90-day, and 365-day all-cause mortality in patients with CS compared with patients who had low AG (hazard ratio [95% confidence interval] 1.62 [1.14-2.30]; 1.35 [1.04-1.84]; and 1.38 [1.03-1.84], respectively). Similar results were shown in Model I (adjusted for age, sex and ethnicity) and in Model II (fully adjusting for age, ethnicity, sex, acute kidney injury stage, CHF, renal disease, stroke, malignancy, respiratory failure, pneumonia, sodium, potassium, chloride, BUN, PT, WBC, pH, creatinine, albumin, glucose, bicarbonate, vasopressor use, diastolic blood pressure, respiration rate, temperature, the Elixhauser Comorbidity Index, SOFA score and SAPSII score).

Conclusion

The relationship between the AG and 30-day all-cause mortality followed a J-shaped curve. Higher AG was associated with an increased risk of 30-day, 90-day, and 365-day all-cause mortality in critically ill patients with CS.

Association between ion shift index and prognosis in severe trauma patients without isolated head injury

INTRODUCTION

This study aimed to investigate the ion shift index (ISI) as a prognostic factor of severe trauma. We hypothesized that the initial ISI measured in the emergency department (ED) is associated with discharge survival in severe non-isolated head injury (IHI) patients.

MATERIALS AND METHODS

This retrospective observational study included severe trauma patients with available medical records from January 2017 to December 2018 but excluded those with IHI. Logistic regression analysis was conducted to identify the risk factors for mortality in non-IHI patients, and adjustments were performed for relevant covariates. An area under the receiver operating characteristics curve (AUROC) analysis was performed to examine the primary outcome of our study, which was mortality at hospital discharge in severe non-IHI trauma patients.

RESULTS

Of the 483 severe non-IHI trauma patients included in the study, 86 patients (17.8 %) died. The multiple logistic regression analysis demonstrated ISI (odds ratio [OR], 2.300; 95% CI, 1.183-4.470) was significantly associated with mortality in the non-IHI group. Additionally, trauma and injury severity score (TRISS; OR, 0.538; 95% CI, 0.447-0.649), lactate (OR, 1.410; 95% CI, 1.252-1.588), creatinine (OR, 1.554; 95% CI, 1.221-1.979), and activated partial thromboplastin time (aPTT; OR, 1.050; 95% CI, 1.021-1.080) were independently associated with mortality at hospital discharge. The AUROC values for TRISS, lactate, aPTT, creatinine, and ISI were as follows: 0.892 (95% CI, 0.861-0.918), 0.838 (95% CI, 0.803-0.870), 0.754 (95% CI, 0.712-0.792), 0.650 (95% CI, 0.606-0.693), and 0.848 (95% CI, 0.813-0.879), respectively. The AUROC for the multiple logistic regression model with ISI was 0.942 (95% CI, 0.917-0.962). In a model in which TRISS was omitted, the addition of ISI to other predictors significantly improved the AUROC to 0.900 (95% CI, 0.869-0.925) (p=0.039).

CONCLUSION

The initial ISI in the ED after trauma was associated with mortality in severe non-IHI trauma patients. In conjunction with other prognostic indicators, it could be used as an early prognostic marker, particularly if TRISS is unavailable.

Impact of Acid-Base Status on Mortality in Patients with Acute Pesticide Poisoning

We investigated clinical impacts of various acid-base approaches (physiologic, base excess (BE)-based, and physicochemical) on mortality in patients with acute pesticide intoxication and mutual intercorrelated effects using principal component analysis (PCA). This retrospective study included patients admitted from January 2015 to December 2019 because of pesticide intoxication. We compared parameters assessing the acid-base status between two groups, survivors and non-survivors. Associations between parameters and 30-days mortality were investigated. A total of 797 patients were analyzed. In non-survivors, pH, bicarbonate concentration (HCO₃⁻), total concentration of carbon dioxide (tCO₂), BE, and effective strong ion difference (SIDe) were lower and apparent strong ion difference (SIDa), strong ion gap (SIG), total concentration of weak acids, and corrected anion gap (corAG) were higher than in survivors. In the multivariable logistic analysis, BE, corAG, SIDa, and SIDe were associated with mortality. PCA identified four principal components related to mortality. SIDe, HCO₃⁻, tCO₂, BE, SIG, and corAG were loaded to principal component 1 (PC1), referred as total buffer bases to receive and handle generated acids. PC1 was an important factor in predicting mortality irrespective of the pesticide category. PC3, loaded mainly with pCO₂, suggested respiratory components of the acid-base system. PC3 was associated with 30-days mortality, especially in organophosphate or carbamate poisoning. Our study showed that acid-base abnormalities were associated with mortality in patients with acute pesticide poisoning. We reduced these variables into four PCs, resembling the physicochemical approach, revealed that PCs representing total buffer bases and respiratory components played an important role in acute pesticide poisoning.

Association of Chloride Ion and Sodium-Chloride Difference With Acute Kidney Injury and Mortality in Critically Ill Patients

Objectives

Derangements of chloride ion concentration ([Cl^-]) have been shown to be associated with acute kidney injury and other adverse outcomes. For a physicochemical approach, however, chloride ion concentration should be considered with sodium ion concentration. This study aimed to examine the association of chloride ion concentration and the main strong ion difference (difference between sodium ion concentration and chloride ion concentration) during the first 24 hours after admission into ICU with the development of acute kidney injury and mortality.

Design

Retrospective analyses using the eICU Collaborative Research Database.

Setting

ICUs in 208 hospitals across the United States between 2014 and 2015.

Patients

Critically ill patients who were admitted into the ICU.

Interventions

None.

Measurements and Main Results

A total of 34,801 patients records were analyzed. A multivariable logistic regression analysis for the development of acute kidney injury within 7 days of ICU admission shows that, compared with main strong iron difference 32-34 mEq/as a reference, there were significantly high odds for the development of acute kidney injury in nearly all groups with main strong iron difference more than 34 mEq/L (main strong iron difference = 34-36 mEq/L, odds ratio = 1.17, p = 0.02; main strong iron difference = 38-40 mEq/L, odds ratio = 1.40, p < 0.001; main strong iron difference = 40-42 mEq/L, odds ratio = 1.46, p = 0.001; main strong iron difference > 42 mEq/L, odds ratio = 1.56, p < 0.001). With chloride ion concentration 104-106 mEq/L as a reference, the odds for acute kidney injury were significantly higher only in chloride ion concentration less than or equal to 94 mEq/L and chloride ion concentration 98-100 mEq/L groups. Analyses conducted using inverse probability weighting showed significantly greater odds for ICU mortality in all groups with main strong iron difference greater than 34mEq/L other than the 36-38mEq/L group, as well as in the less than 26-mEq/L group.

Conclusions

Main strong iron difference measured on ICU presentation to the ICU predicts acute kidney injury within 7 days, with low and, in particular, high values representing increased risk. The association between the chloride levels and acute kidney injury is statistically insignificant in models incorporating main strong iron difference, suggesting main strong iron difference is a better predictive marker than chloride on ICU admission.

Non-linear association between arterial oxygen tension and survival after out-of-hospital cardiac arrest: A multicentre observational study

BACKGROUND

Studies to identify safe oxygenation targets after out-of-hospital cardiac arrest (OHCA) have often assumed a linear relationship between arterial oxygen tension (PaO₂) and survival, or have dichotomised PaO₂ at a supra-physiological level. We hypothesised that abnormalities in mean PaO₂ (both high and low) would be associated with decreased survival after OHCA.

METHODS

We conducted a retrospective multicentre cohort study of adult OHCA patients who received mechanical ventilation on admission to the intensive care unit (ICU). The potential non-linear relationship between the mean PaO₂ within the first 24 -hs of ICU admission and survival to hospital discharge (STHD) was assessed by a four-knot restricted cubic spline function with adjustment for potential confounders.

RESULTS

3764 arterial blood gas results were available for 491 patients in the first 24-hs of ICU admission. The relationship between mean PaO₂ over the first 24-hs and STHD was an inverted U-shape, with highest survival for those with a mean PaO₂ between 100 and 180 mmHg (reference category) compared to a mean PaO₂ of <100 mmHg (adjusted odds ratio [aOR] 0.50 95% confidence interval [CI] 0.30, 0.84), or >180 mmHg (aOR 0.41, 95% CI 0.18, 0.92). Mean PaO₂ within 24 -hs was the third most important predictor and explained 9.1% of the variability in STHD.

CONCLUSION

The mean PaO₂ within the first 24-hs after admission for OHCA has a non-linear association with the highest STHD seen between 100 and 180 mmHg. Randomised controlled trials are now needed to validate the optimal oxygenation targets in mechanically ventilated OHCA patients.

Arterial blood gas as a prognostic indicator in patients with sepsis

Abnormal arterial blood gas (ABG) among patients with sepsis is an important prognostic indicator. All-cause mortality was the highest among patients with respiratory acidosis (4/9 = 44.4%), followed by those having metabolic acidosis (3/8 = 37.5%). Median length of hospital and intensive care unit stay was 15.75 days and 6.25 days for those with abnormal ABG and 11 and 3.5 days among those with normal ABG. Median health-care expenditure at the time of discharge or death of the patient was the highest in patients with respiratory acidosis ($14,473) and least in patients with normal ABG ($3,384) (average expenditure among patients with abnormal ABG was [$10,059]).

Metabolic Acidosis in Critically Ill Cirrhotic Patients with Acute Kidney Injury

Background and Aims: The metabolic acid-base disorders have a high incidence of acute kidney injury (AKI) in critically ill cirrhotic patients (CICPs). The aims of our study were to ascertain the composition of metabolic acidosis of CICPs with AKI and explore its relationship with hospital mortality. Methods: Three-hundred and eighty consecutive CICPs with AKI were eligible for the cohort study. Demographic, clinical and laboratory parameters were recorded and arterial acid-base state was analyzed by the Stewart and Gilfix methodology. Results: Net metabolic acidosis, lactic acidosis, acidosis owing to unmeasured anions, acidemia, and dilutional acidosis were less frequent in the non-survival group compared to the survival group of CICPs. The presence of acidemia, acidosis owing to unmeasured anions, and lactic acidosis were independently associated with increased risk of intensive care unit 30-day mortality, with hazard ratios of 2.11 (95% confidence interval (CI): 1.43-3.12), 3.38 (95% CI: 2.36-4.84), and 2.16 (95% CI: 1.47-3.35), respectively. After full adjustment for confounders, the relationship between acidosis owing to unmeasured anions with hospital mortality was still significant, with hazard ratio of 2.29 (95% CI: 1.22-4.30). Furthermore, arterial lactate concentration in combination with chronic liver failure-sequential organ failure assessment and BE_UMA had the strongest ability to differentiate 30-day mortality (area under the receiver operating characteristic curve: 0.79, 95% CI: 0.74-0.83). Conclusions: CICPs with AKI exhibit a complex metabolic acidosis during intensive care unit admission. Lactic acidosis and BE_UMA, novel markers of acid-base disorders, show promise in predicting mortality rate of CICPs with AKI.

Traditional approach versus Stewart approach for acid-base disorders: Inconsistent evidence

Purpose

The traditional approach and the Stewart approach have been developed for evaluating acid-base phenomena. While some experts have suggested that the two approaches are essentially identical, clinical researches have still been conducted on the superiority of one approach over the other one. In this review, we summarize the concepts of each approach and investigate the reasons of the discrepancy, based on current evidence from the literature search.

Methods

In the literature search, we completed a database search and reviewed articles comparing the Stewart approach with the traditional, bicarbonate-centered approach to November 2016.

Results

Our literature review included 17 relevant articles, 5 of which compared their diagnostic abilities, 9 articles compared their prognostic performances, and 3 articles compared both diagnostic abilities and prognostic performances. These articles show a discrepancy over the abilities to detect acid-base disturbances and to predict patients' outcomes. There are many limitations that could yield this discrepancy, including differences in calculation of the variables, technological differences or errors in measuring variables, incongruences of reference value, normal range of the variables, differences in studied populations, and confounders of prognostic strength such as lactate.

Conclusion

In conclusion, despite the proposed equivalence between the traditional approach and the Stewart approach, our literature search shows inconsistent results on the comparison between the two approaches for diagnostic and prognostic performance. We found crucial limitations in those studies, which could lead to the reasons of the discrepancy.

Can base excess and anion gap predict lactate level in diagnosis of septic shock?

Background

Lactate measurement is the key component in septic shock identification and resuscitation. However, point-of-care lactate testing is not widely used due to the lack of access to nearby test equipment. Biomarkers such as serum lactate, anion gap (AG), and base excess (BE) are used in determining shock in patients with seemingly normal vital signs.

Purpose

We aimed to determine if these biomarkers can be used interchangeably in patients with septic shock in the emergency setting.

Patients and methods

A prospective observational cohort study was undertaken at a tertiary hospital in southern Thailand. Baseline point-of-care BE, AG, and serum lactate were recorded in all patients presenting with septic shock at the emergency department. Overall correlations including area under the receiver operating characteristic curve (AUROC) for both BE and AG to predict serum lactate level were calculated.

Results

One hundred and fifteen patients were enrolled. Pearson correlation of serum lactate to BE was −0.59 (r² = 0.35; 95% confidence interval [CI], −0.69 to −0.44; P < 0.001) and BE to AG was −0.67 (r² = 0.49; 95% CI, −0.76 to −0.55; P < 0.001), and serum lactate to AG was 0.64 (r² = 0.41; 95% CI, 0.52 to 0.74; P < 0.001). A cut-off point of 15.8 for AG identified a lactate level ≥2 mmol/L (sensitivity, 71.4%; specificity, 80.7%; and AUROC, 0.76), and the best cut-off value to predict a lactate level ≥4 mmol/L was 18.5 (sensitivity, 64.2%; specificity, 85.5%; and AUROC 0.78).

Conclusion

In patients with septic shock, lactate and AG showed a strong correlation with each other, whereas lactate and BE showed a moderate correlation with each other. Thus, these biomarkers can be used interchangeably to help determine septic shock earlier in patients.

Relationship of at Admission Lactate, Unmeasured Anions, and Chloride to the Outcome of Critically Ill Patients

OBJECTIVES

To investigate the association between the concentration of the causative anions responsible for the main types of metabolic acidosis and the outcome.

DESIGN

Prospective observational study.

SETTING

Teaching ICU.

PATIENTS

All patients admitted from January 2006 to December 2014.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Four thousand nine hundred one patients were admitted throughout the study period; 1,609 met criteria for metabolic acidosis and 145 had normal acid-base values. The association between at admission lactate, unmeasured anions, and chloride concentration with outcome was assessed by multivariate analysis in the whole cohort and in patients with metabolic acidosis. We also compared the mortality of patients with lactic, unmeasured anions, and hyperchloremic metabolic acidosis with that of patients without acid-base disorders. In the whole population, increased lactate and unmeasured anions were independently associated with increased mortality, even after adjusting for potential confounders (odds ratio [95% CI], 1.14 (1.08-1.20); p < 0.0001 and 1.04 (1.02-1.06); p < 0.0001, respectively). In patients with metabolic acidosis, the results were similar. Patients with lactic and unmeasured anions acidosis, but not those with hyperchloremic acidosis, had an increased mortality compared to patients without alterations (17.7%, 12.7%, 4.9%, and 5.8%, respectively; p < 0.05).

CONCLUSIONS

In this large cohort of critically ill patients, increased concentrations of lactate and unmeasured anions, but not chloride, were associated with increased mortality. In addition, increased unmeasured anions were the leading cause of metabolic acidosis.

Metabolic acidosis and the role of unmeasured anions in critical illness and injury

Acid-base disorders are frequently present in critically ill patients. Metabolic acidosis is associated with increased mortality, but it is unclear whether as a marker of the severity of the disease process or as a direct effector. The understanding of the metabolic component of acid-base derangements has evolved over time, and several theories and models for precise quantification and interpretation have been postulated during the last century. Unmeasured anions are the footprints of dissociated fixed acids and may be responsible for a significant component of metabolic acidosis. Their nature, origin, and prognostic value are incompletely understood. This review provides a historical overview of how the understanding of the metabolic component of acid-base disorders has evolved over time and describes the theoretical models and their corresponding tools applicable to clinical practice, with an emphasis on the role of unmeasured anions in general and several specific settings.

Effect of Intravenously Administered Crystalloid Solutions on Acid-Base Balance in Domestic Animals

Intravenous fluid therapy can alter plasma acid-base balance. The Stewart approach to acid-base balance is uniquely suited to identify and quantify the effects of the cationic and anionic constituents of crystalloid solutions on plasma pH. The plasma strong ion difference (SID) and weak acid concentrations are similar to those of the administered fluid, more so at higher administration rates and with larger volumes. A crystalloid's in vivo effects on plasma pH are described by 3 general rules: SID > [HCO3-] increases plasma pH (alkalosis); SID < [HCO3-] decreases plasma pH (alkalosis); and SID = [HCO3-] yields no change in plasma pH. The in vitro pH of commercially prepared crystalloid solutions has little to no effect on plasma pH because of their low titratable acidity. Appreciation of IV fluid composition and an understanding of basic physicochemical principles provide therapeutically valuable insights about how and why fluid therapy can produce and correct alterations of plasma acid-base equilibrium. The ideal balanced crystalloid should (1) contain species-specific concentrations of key electrolytes (Na+ , Cl- , K+ , Ca++ , Mg++ ), particularly Na+ and Cl- ; (2) maintain or normalize acid-base balance (provide an appropriate SID); and (3) be isosmotic and isotonic (not induce inappropriate fluid shifts) with normal plasma.

Effect of non-linearity of a predictor on the shape and magnitude of its receiver-operating-characteristic curve in predicting a binary outcome

Area under a receiver-operating-characteristic (AUROC) curve is widely used in medicine to summarize the ability of a continuous predictive marker to predict a binary outcome. This study illustrated how a U-shaped or inverted U-shaped continuous predictor would affect the shape and magnitude of its AUROC curve in predicting a binary outcome by comparing the ROC curves of the worst first 24-hour arterial pH values of 9549 consecutive critically ill patients in predicting hospital mortality before and after centering the predictor by its mean or median. A simulation dataset with an inverted U-shaped predictor was used to assess how this would affect the shape and magnitude of the AUROC curve. An asymmetrical U-shaped relationship between pH and hospital mortality, resulting in an inverse-sigmoidal ROC curve, was observed. The AUROC substantially increased after centering the predictor by its mean (0.611 vs 0.722, difference = 0.111, 95% confidence interval [CI] 0.087–0.135), and was further improved after centering by its median (0.611 vs 0.745, difference = 0.133, 95%CI 0.110–0.157). A sigmoidal-shaped ROC curve was observed for an inverted U-shaped predictor. In summary, a non-linear predictor can result in a biphasic-shaped ROC curve; and centering the predictor can reduce its bias towards null predictive ability.

Combining quick Sequential Organ Failure Assessment with plasma lactate concentration is comparable to standard Sequential Organ Failure Assessment score in predicting mortality of patients with and without suspected infection

PURPOSE

We sought to determine whether quick Sequential Organ Failure Assessment (qSOFA) score can be used to predict mortality of patients without suspected infection.

MATERIALS AND METHODS

Using prospectively collected data within the first hour of intensive care unit admission, the predictive ability of qSOFA was compared with the Simplified Acute Physiology Score III, Admission Mortality Prediction Model III, Acute Physiology and Chronic Health Evaluation II model, and standard (full-version) SOFA score using area under the receiver operating characteristic (AUROC) curve and Brier score.

RESULTS

Of the 2322 patients included, 279 (12.0%) died after intensive care unit admission. The qSOFA score had a modest ability to predict mortality of all critically ill patients (AUROC, 0.672; 95% confidence interval [CI], 0.638-0.707; Brier score 0.099) including the noninfected patients (AUROC, 0.685; 95% CI, 0.637-0.732; Brier score 0.081). The overall predictive ability and calibration of the qSOFA was comparable to other prognostic scores. Combining qSOFA score with lactate concentrations further enhanced its predictive ability (AUROC, 0.730; 95% CI, 0.694-0.765; Brier score 0.097), comparable to the standard SOFA score.

CONCLUSIONS

The qSOFA score had a modest ability to predict mortality of both septic and nonseptic patients; combining qSOFA with plasma lactate had a predictive ability comparable to the standard SOFA score.

Unmeasured anions and mortality in critically ill patients in 2016

The presence of acid-base disturbances, especially metabolic acidosis may negatively affect the outcome of critically ill patients. Lactic acidosis is the most frequent etiology and has largest impact on the prognosis. Since lactate measurement might not have always been available at bedside, it had been regarded as one of the unmeasured anions. Therefore, anion gap and strong ion gap has been used to as a surrogate of lactate concentration. From this perspective, the relationship between either anion gap or strong ion gap and mortality has been explored. Then, lactate became routinely measurable at bedside and the direct comparison between directly measured lactate and these surrogate parameters can be possible. Currently available evidence suggests that directly measured lactate has larger prognostic ability for mortality than albumin-corrected anion gap and strong ion gap without lactate. In this commentary, the rationale and possible clinical implications of these findings are discussed.