A physicochemical approach to acid-base balance in critically ill trauma patients minimizes errors and reduces inappropriate plasma volume expansion. ACTA ACUST UNITED AC. 2009;66:1045-1051. [PMID: 19359913 DOI: 10.1097/ta.0b013e31819a04be]

The dose-dependent relationship between blood transfusions and infections after trauma: A population-based study

OBJECTIVE

The relationship between total transfusion volume and infection in the trauma patient remains unclear, especially at lower volumes of transfusion. We sought to quantify the cumulative, independent impact of transfusion within 24 hours of admission on the risk of infection in trauma patients.

METHODS

Using the Trauma Quality Improvement Program 2013 to 2016 database, we included all patients who received blood transfusions in the first 4 hours. Patients who were transferred or had incomplete/wrongly coded information on transfusion volume were excluded. Patients were divided into 20 cohorts based on the total blood product volume transfused in the first 24 hours. A composite infection variable (INF) was created, including surgical site infection, ventilator-associated pneumonia, urinary tract infection, central line associated blood stream infection, and sepsis. Univariate and stepwise multivariable logistic regression analyses were performed to study the relationship between blood transfusion and INF, controlling for demographics (e.g., age, sex), comorbidities (e.g., cirrhosis, diabetes, steroid use), severity of injury (e.g., vital signs on arrival, mechanism, Injury Severity Score), and operative and angiographic interventions.

RESULTS

Of 1,002,595 patients, 37,568 were included. The mean age was 42 ± 18.6 years, 74.6% were males, 68% had blunt trauma, and median Injury Severity Score was 25 [17-34]. Adjusting for all available confounders, odds of INF increased incrementally from 1.00 (reference, 0-2 units) to 1.23 (95% confidence interval, 1.11-1.37) for 4 units transfused to 4.89 (95% confidence interval, 2.72-8.80) for 40 units transfused. Each additional unit increased the odds of INF by 7.6%.

CONCLUSION

Transfusion of the bleeding trauma patient was associated with a dose-dependent increased risk of infectious complications. Trauma surgeons and anesthesiologists should resuscitate the trauma patient until prompt hemorrhage control while avoiding overtransfusion.

LEVEL OF EVIDENCE

Retrospective cohort study, Therapeutic IV.

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.

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.

Glutamine metabolism drives succinate accumulation in plasma and the lung during hemorrhagic shock

BACKGROUND

Metabolomic investigations have consistently reported succinate accumulation in plasma after critical injury. Succinate receptors have been identified on numerous tissues, and succinate has been directly implicated in postischemic inflammation, organ dysfunction, platelet activation, and the generation of reactive oxygen species, which may potentiate morbidity and mortality risk to patients. Metabolic flux (heavy-isotope labeling) studies demonstrate that glycolysis is not the primary source of increased plasma succinate during protracted shock. Glutamine is an alternative parent substrate for ATP generation during anaerobic conditions, a biochemical mechanism that ultimately supports cellular survival but produces succinate as a catabolite. We hypothesize that succinate accumulation during hemorrhagic shock is driven by glutaminolysis.

METHODS

Sprague-Dawley rats were subjected to hemorrhagic shock for 45 minutes (shock, n = 8) and compared with normotensive shams (sham, n = 8). At 15 minutes, animals received intravenous injection of C5-N2-glutamine solution (iLG). Blood, brain, heart, lung, and liver tissues were harvested at defined time points. Labeling distribution in samples was determined by ultrahigh-pressure liquid chromatography-mass spectrometry metabolomic analysis. Repeated-measures analysis of variance with Tukey comparison determined significance of relative fold change in metabolite level from baseline.

RESULTS

Hemorrhagic shock instigated succinate accumulation in plasma and lungs tissues (8.5- vs. 1.1-fold increase plasma succinate level from baseline, shock vs. sham, p = 0.001; 3.2-fold higher succinate level in lung tissue, shock vs. sham, p = 0.006). Metabolomic analysis identified labeled glutamine and labeled succinate in plasma (p = 0.002) and lung tissue (p = 0.013), confirming glutamine as the parent substrate. Kinetic analyses in shams showed constant total levels of all metabolites without significant change due to iLG.

CONCLUSION

Glutamine metabolism contributes to increased succinate concentration in plasma during hemorrhagic shock. The glutaminolytic pathway is implicated as a therapeutic target to prevent the contribution of succinate accumulation in plasma and the lung-to-postshock pathogenesis.

Anion gap corrected for albumin, phosphate and lactate is a good predictor of strong ion gap in critically ill patients: a nested cohort study

Objective

Corrected anion gap and strong ion gap are commonly used to estimate unmeasured anions. We evaluated the performance of the anion gap corrected for albumin, phosphate and lactate in predicting strong ion gap in a mixed population of critically ill patients. We hypothesized that anion gap corrected for albumin, phosphate and lactate would be a good predictor of strong ion gap, independent of the presence of metabolic acidosis. In addition, we evaluated the impact of strong ion gap at admission on hospital mortality.

Methods

We included 84 critically ill patients. Correlation and agreement between the anion gap corrected for albumin, phosphate and lactate and strong ion gap was evaluated by the Pearson correlation test, linear regression, a Bland-Altman plot and calculating interclass correlation coefficient. Two subgroup analyses were performed: one in patients with base-excess <-2mEq/L (low BE group - lBE) and the other in patients with base-excess >-2mEq/L (high BE group - hBE). A logistic regression was performed to evaluate the association between admission strong ion gap levels and hospital mortality.

Results

There was a very strong correlation and a good agreement between anion gap corrected for albumin, phosphate and lactate and strong ion gap in the general population (r²=0.94; bias 1.40; limits of agreement -0.75 to 3.57). Correlation was also high in the lBE group (r²=0.94) and in the hBE group (r²=0.92). High levels of strong ion gap were present in 66% of the whole population and 42% of the cases in the hBE group. Strong ion gap was not associated with hospital mortality by logistic regression.

Conclusion

Anion gap corrected for albumin, phosphate and lactate and strong ion gap have an excellent correlation. Unmeasured anions are frequently elevated in critically ill patients with normal base-excess. However, there was no association between unmeasured anions and hospital mortality.

Strong ion gap is associated with mortality in pediatric burn injuries

Severe burn injury produces significant tissue damage, resulting in metabolic acidosis. Current methods of acid-base evaluation are based on dependent variables that may not be accurate after burn injury. The strong ion method of acid-base evaluation is based on independent variables and may accurately predict outcomes in severely burn-injured patients. The authors hypothesize that an increased strong ion gap present on admission will be associated with mortality in severely burn-injured pediatric patients. A retrospective chart review was performed of burn-injured pediatric patients with a TBSA 20% or greater. Data collected included age, TBSA burn injury, mechanism of injury, survival, ventilator days, hospital length of stay, intensive care unit length of stay, and admission laboratory values. Apparent and effective strong ion difference (SIDa, SIDe) were calculated. The strong ion gap (SIG) was determined as the difference between SIDa and SIDe. A total of 48 patients were included in the study. Mean age (years) and TBSA were 7.9 ± 0.8 years and 56.8 ± 2.6%. Eleven patients (23%) died. Mean TBSA for survivors (54.2 ± 2.9%) did not significantly differ from that of nonsurvivors (65.7 ± 5.34%). Ten patients suffered inhalation injury, which was associated with an odds ratio of 10.1* for mortality. Mean SIDa was 44.2 ± 3.2 for the entire study population. Survivors had a significantly lower SIDa (36.6 ± 0.5) than nonsurvivors (59.7 ± 13*). Mean SIDe for all patients was (25 ± 0.7) and did not differ significantly between survivors (24.7 ± 0.7) and nonsurvivors (25.8 ± 2). SIG for nonsurvivors (33.91 ± 14*) was significantly higher than for survivors (14.9 ± 0.3). Controlling for both TBSA and inhalation injury, death was associated with both an increased SIDa (B = 19.3*) and SIG (B = 17.3*). SIG is increased in severely burn-injured pediatric patients, indicating the presence of metabolic acidosis. Furthermore, an increased SIG is significantly associated with mortality. (*P <.05.).

Has Stewart approach improved our ability to diagnose acid-base disorders in critically ill patients?

The Stewart approach-the application of basic physical-chemical principles of aqueous solutions to blood-is an appealing method for analyzing acid-base disorders. These principles mainly dictate that pH is determined by three independent variables, which change primarily and independently of one other. In blood plasma in vivo these variables are: (1) the PCO₂; (2) the strong ion difference (SID)-the difference between the sums of all the strong (i.e., fully dissociated, chemically nonreacting) cations and all the strong anions; and (3) the nonvolatile weak acids (A_tot). Accordingly, the pH and the bicarbonate levels (dependent variables) are only altered when one or more of the independent variables change. Moreover, the source of H⁺ is the dissociation of water to maintain electroneutrality when the independent variables are modified. The basic principles of the Stewart approach in blood, however, have been challenged in different ways. First, the presumed independent variables are actually interdependent as occurs in situations such as: (1) the Hamburger effect (a chloride shift when CO₂ is added to venous blood from the tissues); (2) the loss of Donnan equilibrium (a chloride shift from the interstitium to the intravascular compartment to balance the decrease of A_tot secondary to capillary leak; and (3) the compensatory response to a primary disturbance in either independent variable. Second, the concept of water dissociation in response to changes in SID is controversial and lacks experimental evidence. In addition, the Stewart approach is not better than the conventional method for understanding acid-base disorders such as hyperchloremic metabolic acidosis secondary to a chloride-rich-fluid load. Finally, several attempts were performed to demonstrate the clinical superiority of the Stewart approach. These studies, however, have severe methodological drawbacks. In contrast, the largest study on this issue indicated the interchangeability of the Stewart and conventional methods. Although the introduction of the Stewart approach was a new insight into acid-base physiology, the method has not significantly improved our ability to understand, diagnose, and treat acid-base alterations in critically ill patients.

Relationship between acid-base status and inflammation in the critically ill

Introduction

There is a complex interplay between changes in acid–base components and inflammation. This manuscript aims to explore associations between plasma cytokines and chemokines and acid–base status on admission to intensive care.

Methods

We conducted a prospective cohort study in a 13-bed ICU in a tertiary-care center in Brazil. 87 unselected patients admitted to the ICU during a 2-year period were included. We measured multiple inflammatory mediators in plasma using multiplex assays and evaluated the association between mediator concentrations and acid–base variables using a variety of statistical modeling approaches, including generalized linear models, multiadaptive regression splines and principal component analysis.

Results

We found a positive association between strong ion gap (SIG) and plasma concentrations of interleukin (IL)6, 8, 10 and tumor necrosis factor (TNF); whereas albumin was negatively associated with IL6, IL7, IL8, IL10, TNF and interferon (IFN)α. Apparent strong ion difference (SID_a) was negatively associated with IL10 and IL17. A principal component analysis including SAPS 3 indicated that the association between acid–base components and inflammatory status was largely independent of illness severity, with both increased SIG and decreased SID_a (both drivers of acidosis) associated with increased inflammation.

Conclusion

Acid–base variables (especially increased SIG, decreased albumin and decreased SID_a) on admission to ICU are associated with immunological activation. These findings should encourage new research into the effects of acid–base status on inflammation.

Severe metabolic or mixed acidemia on intensive care unit admission: incidence, prognosis and administration of buffer therapy. A prospective, multiple-center study

Introduction

In this study, we sought describe the incidence and outcomes of severe metabolic or mixed acidemia in critically ill patients as well as the use of sodium bicarbonate therapy to treat these illnesses.

Methods

We conducted a prospective, observational, multiple-center study. Consecutive patients who presented with severe acidemia, defined herein as plasma pH below 7.20, were screened. The incidence, sodium bicarbonate prescription and outcomes of either metabolic or mixed severe acidemia were analyzed.

Results

Among 2, 550 critically ill patients, 200 (8%) presented with severe acidemia, and 155 (6% of the total admissions) met the inclusion criteria. Almost all patients needed mechanical ventilation and vasopressors during their ICU stay, and 20% of them required renal replacement therapy within the first 24 hours of their ICU stay. Severe metabolic or mixed acidemia was associated with a mortality rate of 57% in the ICU. Delay of acidemia recovery as opposed to initial pH value was associated with increased mortality in the ICU. The type of acidemia did not influence the decision to administer sodium bicarbonate.

Conclusions

The incidence of severe metabolic or mixed acidemia in critically ill patients was 6% in the present study, and it was associated with a 57% mortality rate in the ICU. In contradistinction with the initial acid-base parameters, the rapidity of acidemia recovery was an independent risk factor for mortality. Sodium bicarbonate prescription was very heterogeneous between ICUs. Further studies assessing specific treatments may be of interest in this population.

Fluids, pH, ions and electrolytes

PURPOSE OF REVIEW

Significant attention has been recently focused on both maintenance fluid and resuscitation fluid use in critical care. Accordingly, a focused review of the properties of crystalloid and colloid fluids, their expected benefits, and potential deleterious side effects is appropriate and timely.

RECENT FINDINGS

Despite their ubiquitous use, well described side effects, and ability to be titrated to a physiologic endpoint, fluids are rarely considered in a fashion similar to other pharmacologic agents. Understanding their physical and chemical properties allows the clinician to understand, anticipate and deliberately harness their expected impact on acid-base balance. Expanded insights into the pathogenesis of common acid-base disorders may be gleaned from utilizing a physicochemical approach that allows the precise quantification of the ionic species that impact pH.

SUMMARY

This focused review further enables the clinician to appropriately investigate, modify, and optimize bedside clinical care related to fluid and acid-base management.