Diagnosis of metabolic acid-base disturbances in critically ill patients

Comparison of the effects of normal saline versus Plasmalyte on acid-base balance during living donor kidney transplantation using the Stewart and base excess methods

BACKGROUND

Ischemia-reperfusion injury is an inevitable consequence of kidney transplantation, leading to metabolic acidosis. This study compared the effects of normal saline (NS) and Plasmalyte on acid-base balance and electrolytes during living donor kidney transplantation using the Stewart and base excess (BE) methods.

METHODS

Patients were randomized to an NS group (n = 30) or a Plasmalyte group (n = 30). Arterial blood samples were collected for acid-base analysis after induction of anesthesia (T0), prior to clamping the iliac vein (T1), 10 minutes after reperfusion of the donated kidney (T2), and at the end of surgery (T3). In addition serum creatinine and 24-hour urine output were recorded on postoperative days 1,2, and 7. Over the first postoperative 7 days we recorded episodes of graft failure requiring dialysis.

RESULTS

Compared with the Plasmalyte group, the NS group showed significantly lower values of pH, BE, and effective strong ion differences during the postreperfusion period (T2 and T3). Chloride-related values (chloride [Cl(-)], free-water corrected Cl(-), BEcl) were significantly higher at T1, T2, and T3, indicating hyperchloremic rather than dilutional metabolic acidosis. Early postoperative graft functions in terms of serum creatinine, urine output, and graft failure requiring dialysis were not significantly different between the groups.

CONCLUSIONS

Both NS and Plamalyte can be used safely during uncomplicated living donor kidney transplantation. However, Plasmalyte more stably maintains acid-base and electrolyte balance compared with NS especially during the postreperfusion period.

Physicochemical evaluation of acid-base disorders after liver transplantation and the contribution from administered fluids

OBJECTIVES

To analyze the mechanism of acid-base disorders in liver transplant recipients and to examine the relationship between these disorders and the fluids administered during surgery.

METHODS

This prospective study in a university-affiliated hospital intensive care unit (ICU) included 52 patients admitted to the ICU from December 2009 to January 2011. We examined the contributions of inorganic ion differences, lactate, unmeasured anions, phosphate, and albumin to metabolic acidosis. In addition to laboratory variables, we collected demographic and clinical data.

RESULTS

Metabolic acidosis (standard base excess ≤ -2.0 mmol/L) was identified in 37 (71.2%) patients during the immediate postoperative period. The inorganic ion difference was the main determinant of acidosis, accounting for -6.17 mEq/L of acidifying effect. The acidemia was attenuated mainly by the alkalinizing effect of albumin reduction, which contributed +6.03 mEq/L. There was an inverse proportional relationship between the quantity of saline solution used during surgery and the inorganic ion difference during the immediate postoperative period.

CONCLUSIONS

Hyperchloremia is the primary contributor to metabolic acidosis in liver transplant recipients. Possibly the use of chloride-rich solutions increases the incidence of this disorder.

Point-of-care testing on admission to the intensive care unit: lactate and glucose independently predict mortality

BACKGROUND

The aim of the study was to retrospectively investigate whether parameters of routine point-of-care testing (POCT) predict hospital mortality in critically ill surgical patients on admission to the intensive care unit (ICU).

METHODS

Arterial blood analyses of 1551 patients on admission to the adult surgical ICU of the Technical University Munich were reviewed. POCT was performed on a blood gas analyser. The association between acid-base status and mortality was evaluated. Metabolic acidosis was defined by base excess (BE) <-2 mmol/L and, wherever applicable, subdivided into lactic acidosis by lactate >50% of BE, anion gap (AG)-acidosis by AG >16 mmol/L, hyperchloraemic acidosis by chloride >115 mmol/L. Metabolic alkalosis was defined by BE ≥3 mmol/L. Logistic regression analysis identified variables independently associated with mortality.

RESULTS

Overall mortality was 8.8%. Mortality was greater in male patients (p=0.012). Mean age was greater in non-survivors (p<0.0005). Nine hundred and eighty-six patients showed no metabolic acid-base disorder (mortality 7.3%), thereof 26 patients with pCO(2)>55 mm Hg (mortality 23.1%). Three hundred and seventy-seven patients presented with acidosis (mortality 11.4%), thereof 163 patients with lactic acidosis (mortality 19%). Mortality for alkalosis (174 patients) was 12.1%. Mean blood glucose level for non-survivors was higher compared to survivors (p<0.0005). Logistic regression analysis identified lactate, glucose, age, male gender as independent predictors of mortality.

CONCLUSIONS

Lactate and glucose on ICU admission independently predict mortality. BE and AG failed as prognostic markers. Lactic acidosis showed a high mortality rate implying that lactate levels should be obtained on ICU admission. Prevalence of hyperchloraemic acidosis was low. Metabolic alkalosis was associated with an increased mortality. Further studies on this disturbance and its attendant high mortality are warranted.

Evaluation of the efficacy of simplified Fencl-Stewart equation in analyzing the changes in acid base status following resuscitation with two different fluids

Background:

Metabolic acid-base disorders in critically ill patients may not be identified by base excess (BE) approach. Anion gap method can detect approximately 1/3 hidden “gap acidosis”. In such conditions, when adjusted for hypoalbuminemia, Fencl-Stewart's approach can reliably detect the hidden abnormal anions.

Aim:

Evaluate the efficacy of simplified Fencl-Stewart equation in identifying the changes in acid-base status of sepsis patients following resuscitation with two different fluids.

Settings and Design:

Intensive care unit, randomized, prospective, interventional study.

Materials and Methods:

Three hundred adult patients of both sexes presenting with abdominal sepsis, requiring fluid resuscitation were randomly assigned into normal saline (NS) and Ringer's lactate (RL) group, each comprising of 150 patients. 20 ml/kg of NS or RL were administered over a period of 30 min. The changes in the acid-base status were calculated applying the simplified Fencl-Stewart equation and was compared with the measured values obtained through arterial blood gas.

Statistical Methods:

Paired t-test for intra-group while unpaired t-test for inter-group comparison.

Results:

Blood pH and standard BE decreased and the serum Na⁺ and Cl^- level increased significantly in NS group. The serum albumin level significantly decreased in both the groups. Sodium chloride effect on BE significantly increased in NS group. Albumin effect on BE significantly increased in both the groups. Unmeasured ion effect on BE did not significantly change in both the groups. Measured standard BE level was significantly less as compared to unmeasured anion effect on BE, in both the groups.

Conclusion:

Simplified Fencl-Stewart equation is effective in identifying a mixed acid-base disorder, which otherwise would remain undetected.

Evaporation of free water causes concentrational alkalosis in vitro

BACKGROUND

The development of metabolic alkalosis was described recently in patients with hypernatremia. However, the causes for this remain unknown. The current study serves to clarify whether metabolic alkalosis develops in vitro after removal of free water from plasma and whether this can be predicted by a mathematical model.

MATERIALS AND METHODS

Ten serum samples of healthy humans were dehydrated by 29 % by vacuum centrifugation corresponding to an increase of the contained concentrations by 41 %. Constant partial pressure of carbon dioxide at 40 mmHg was simulated by mathematical correction of pH [pH(40)]. Metabolic acid-base state was assessed by Gilfix' base excess subsets. Changes of acid-base state were predicted by the physical-chemical model according to Watson.

RESULTS

Evaporation increased serum sodium from 141 (140-142) to 200 (197-203) mmol/L, i.e., severe hypernatremia developed. Acid-base analyses before and after serum concentration showed metabolic alkalosis with alkalemia: pH(40): 7.43 (7.41 to 7.45) vs 7.53 (7.51 to 7.55), p = 0.0051; base excess: 1.9 (0.7 to 3.6) vs 10.0 (8.2 to 11.8), p = 0.0051; base excess of free water: 0.0 (- 0.2 to 0.3) vs 17.7 (16.8 to 18.6), p = 0.0051. The acidifying effects of evaporation, including hyperalbuminemic acidosis, were beneath the alkalinizing ones. Measured and predicted acid-base changes due to serum evaporation agreed well.

CONCLUSIONS

Evaporation of water from serum causes concentrational alkalosis in vitro, with good agreement between measured and predicted acid-base values. At least part of the metabolic alkalosis accompanying hypernatremia is independent of renal function.

Effects of gas exchange on acid-base balance

This paper describes the interactions between ventilation and acid-base balance under a variety of conditions including rest, exercise, altitude, pregnancy, and various muscle, respiratory, cardiac, and renal pathologies. We introduce the physicochemical approach to assessing acid-base status and demonstrate how this approach can be used to quantify the origins of acid-base disorders using examples from the literature. The relationships between chemoreceptor and metaboreceptor control of ventilation and acid-base balance summarized here for adults, youth, and in various pathological conditions. There is a dynamic interplay between disturbances in acid-base balance, that is, exercise, that affect ventilation as well as imposed or pathological disturbances of ventilation that affect acid-base balance. Interactions between ventilation and acid-base balance are highlighted for moderate- to high-intensity exercise, altitude, induced acidosis and alkalosis, pregnancy, obesity, and some pathological conditions. In many situations, complete acid-base data are lacking, indicating a need for further research aimed at elucidating mechanistic bases for relationships between alterations in acid-base state and the ventilatory responses.

Strong ion difference and gap predict outcomes after adult burn injury

BACKGROUND

The strong ion difference (SID) (apparent [SIDa] and effective [SIDe]) and strong ion gap (SIG) provide a comprehensive method of evaluating acid-base status in critically ill patients. The SID is the difference between strong cations and strong anions in plasma, while the SIG demonstrates the presence of unmeasured ions. This approach accounts for changes in a patient's protein status, which is particularly important in those with burn injuries. We hypothesized that the SIDa, SIDe, and SIG during the first 72 hours after admission would be predictive of mortality in burn patients.

METHODS

This study is a retrospective review of adults with 20% or greater total body surface area burns admitted during a 7-year period to a regional burn center. SIDa, SIDe, and SIG were calculated at admission and for the first 3 days. These results were then compared with Acute Physiology and Chronic Health Evaluation II (APACHE II) and sepsis-related organ failure assessment (SOFA) scores.

RESULTS

A total of 113 patients met the criteria and had full data sets, with mean ± SEM age of 45.4 ± 1.4 years and total body surface area burn of 41.4% ± 1.6%. Mortality was 27.4%. At admission, APACHE II remained most predictive of mortality (p = 0.006). However, admission SIG (SIDa - SIDe) was also predictive of mortality on multivariate analysis (odds ratio, 1.11). Day 1 SIDa (Na+ + K+ + Ca2+ + Mg2+ - Cl-) and SIDe ([1,000 × 2.46 × 10(-11) × PaCO2/10(-pH)] + [[albumin] × (0.123 × pH - 0.631)] + [[PO4] × (0.309) × pH - 0.469)]) were also associated with mortality (odds ratio, 1.16 and 1.13 respectively), and SIDe with length of stay and ventilator days (p < 0.05).

CONCLUSION

The SID and SIG are predictive of mortality, hospital length of stay, and ventilator days in adult burn patients. They also elucidate complex acid-base disorders.

LEVEL OF EVIDENCE

Prognostic study, level II.

Stewart analysis of apparently normal acid-base state in the critically ill

PURPOSE

This study aimed to describe Stewart parameters in critically ill patients with an apparently normal acid-base state and to determine the incidence of mixed metabolic acid-base disorders in these patients.

MATERIALS AND METHODS

We conducted a prospective, observational multicenter study of 312 consecutive Dutch intensive care unit patients with normal pH (7.35 ≤ pH ≤ 7.45) on days 3 to 5. Apparent (SIDa) and effective strong ion difference (SIDe) and strong ion gap (SIG) were calculated from 3 consecutive arterial blood samples. Multivariate linear regression analysis was performed to analyze factors potentially associated with levels of SIDa and SIG.

RESULTS

A total of 137 patients (44%) were identified with an apparently normal acid-base state (normal pH and -2 < base excess < 2 and 35 < PaCO2 < 45 mm Hg). In this group, SIDa values were 36.6 ± 3.6 mEq/L, resulting from hyperchloremia (109 ± 4.6 mEq/L, sodium-chloride difference 30.0 ± 3.6 mEq/L); SIDe values were 33.5 ± 2.3 mEq/L, resulting from hypoalbuminemia (24.0 ± 6.2 g/L); and SIG values were 3.1 ± 3.1 mEq/L. During admission, base excess increased secondary to a decrease in SIG levels and, subsequently, an increase in SIDa levels. Levels of SIDa were associated with positive cation load, chloride load, and admission SIDa (multivariate r(2) = 0.40, P < .001). Levels of SIG were associated with kidney function, sepsis, and SIG levels at intensive care unit admission (multivariate r(2) = 0.28, P < .001).

CONCLUSIONS

Intensive care unit patients with an apparently normal acid-base state have an underlying mixed metabolic acid-base disorder characterized by acidifying effects of a low SIDa (caused by hyperchloremia) and high SIG combined with the alkalinizing effect of hypoalbuminemia.

Strong-ion gap approach in patients with cardiogenic shock following ST-elevation myocardial infarction

OBJECTIVE

Assess if acid-base evaluation by Stewart's approach had a clinical role in cardiogenic shock (CS) following ST-elevation myocardial infarction (STEMI).

SETTING

There are three widely used approaches to investigate metabolic acidosis: base excess (BE), anion gap (AG) and the Stewart's approach or strong ion gap (SIG). Available studies suggest the usefulness of SIG in sepsis and trauma. No data are so far available in CS.

MEASUREMENTS AND RESULTS

We enrolled 63 consecutive patients with CS following STEMI submitted to Percutaneous Coronary Intervention (PCI). On admission, the APACHE II (Acute physiology and chronic health evaluation II) score and HOMA (Homeostasis model assessment) index were assessed together with glomerular filtration rate (eGFR), quantitative BE, AG, lactate values and 12 h lactate clearance. Non-survivors showed a higher incidence of PCI failure, higher APACHE II score, lower LVEF, lower eGFR, lower 12 h lactate clearance; a higher admission lactate and more negative BE. No difference was detectable in AG and SIG. Only 3 patients exhibited pathological values of SIG (≥ 2) and only 1 of these patients died.

CONCLUSIONS

According to our data the SIG approach does not seem to add further information to usual parameters in acid-base evaluation or early risk stratification in CS patients.

The difference between critical care initiation anion gap and prehospital admission anion gap is predictive of mortality in critical illness

OBJECTIVE

We hypothesized that the delta anion gap defined as difference between critical care initiation standard anion gap and prehospital admission standard anion gap is associated with all cause mortality in the critically ill.

DESIGN

Observational cohort study.

SETTING

Two hundred nine medical and surgical intensive care beds in two hospitals in Boston, MA.

PATIENTS

Eighteen thousand nine hundred eighty-five patients, age ≥18 yrs, who received critical care between 1997 and 2007.

MEASUREMENTS

The exposure of interest was delta anion gap and categorized a priori as <0, 0-5, 5-10, and >10 mEq/L. Logistic regression examined death by days 30, 90, and 365 postcritical care initiation and in-hospital mortality. Adjusted odds ratios were estimated by multivariable logistic regression models. The discrimination of delta anion gap for 30-day mortality was evaluated using receiver operator characteristic curves performed for a subset of patients with all laboratory data required to analyze the data via physical chemical principles (n = 664).

INTERVENTIONS

None.

RESULTS

Delta anion gap was a particularly strong predictor of 30-day mortality with a significant risk gradient across delta anion gap quartiles following multivariable adjustment: delta anion gap <0 mEq/L odds ratio 0.75 (95% confidence interval 0.67-0.81; p < 0.0001); delta anion gap 5-10 mEq/L odds ratio 1.56 (95% confidence interval 1.35-1.81; p < 0.0001); delta anion gap >10 mEq/L odds ratio 2.18 (95% confidence interval 1.76-2.71; p < 0.0001); and all relative to patients with delta anion gap 0-5 mEq/L. Similar significant robust associations post multivariable adjustments are seen with death by days 90 and 365 as well as in-hospital mortality. Correcting for albumin or limiting the cohort to patients with standard anion gap at critical care initiation of 10-18 mEq/L did not materially change the delta anion gap-mortality association. Delta anion gap has similarly moderate discriminative ability for 30-day mortality in comparison to standard base excess and strong ion gap.

CONCLUSION

An increase in standard anion gap at critical care initiation relative to prehospital admission standard anion gap is a predictor of the risk of all cause patient mortality in the critically ill.

Trauma and aggressive homeostasis management

Homeostasis refers to the capacity of the human body to maintain a stable constant state by means of continuous dynamic equilibrium adjustments controlled by a medley of interconnected regulatory mechanisms. Patients who sustain tissue injury, such as trauma or surgery, undergo a well-understood reproducible metabolic and neuroendocrine stress response. This review discusses 3 issues that concern homeostasis in the acute care of trauma patients directly related to the stress response: hyperglycemia, lactic acidosis, and hypothermia. There is significant reason to question the "conventional wisdom" relating to current approaches to restoring homeostasis in critically ill and trauma patients.

Use of sodium-chloride difference and corrected anion gap as surrogates of Stewart variables in critically ill patients

Introduction

To investigate whether the difference between sodium and chloride ([Na⁺] – [Cl⁻]) and anion gap corrected for albumin and lactate (AG_corr) could be used as apparent strong ion difference (SID_app) and strong ion gap (SIG) surrogates (respectively) in critically ill patients.

Methods

A total of 341 patients were prospectively observed; 161 were allocated to the modeling group, and 180 to the validation group. Simple regression analysis was used to construct a mathematical model between SID_app and [Na⁺] – [Cl⁻] and between SIG and AG_corr in the modeling group. Area under the receiver operating characteristic (ROC) curve was also measured. The mathematical models were tested in the validation group.

Results

in the modeling group, SID_app and SIG were well predicted by [Na⁺] – [Cl⁻] and AG_corr (R² = 0.973 and 0.96, respectively). Accuracy values of [Na⁺] – [Cl⁻] for the identification of SID_app acidosis (<42.7 mEq/L) and alkalosis (>47.5 mEq/L) were 0.992 (95% confidence interval [CI], 0.963–1) and 0.998 (95%CI, 0.972–1), respectively. The accuracy of AG_corr in revealing SIG acidosis (>8 mEq/L) was 0.974 (95%CI: 0.936–0.993). These results were validated by showing excellent correlations and good agreements between predicted and measured SID_app and between predicted and measured SIG in the validation group (R² = 0.977; bias = 0±1.5 mEq/L and R² = 0.96; bias = −0.2±1.8 mEq/L, respectively).

Conclusions

SID_app and SIG can be substituted by [Na⁺] – [Cl⁻] and by AG_corr respectively in the diagnosis and management of acid-base disorders in critically ill patients.

The significance of albumin corrected anion gap in patients with cardiopulmonary arrest

PURPOSE

The reliable parameter, which can be obtained easily and quickly, is necessary to predict the return of spontaneous circulation (ROSC) of patients with cardiopulmonary arrest (CPA) in the emergency situation. In this study, we evaluated the significance of albumin corrected anion gap (ACAG) for the prediction of ROSC in patients with CPA.

PATIENTS AND METHODS

In 166 patients with CPA between January 2009 and December 2010, 132 patients could be analyzed retrospectively. We compared acute physiology and chronic health evaluation (APACHE) II score, sequential organ failure assessment(SOFA) score, anion gap (AG) and ACAG levels between patients with/without ROSC and evaluated the significance of AG and ACAG to predict ROSC in patients with CPA.

RESULTS

Both AG and ACAG were significantly lower in patients with ROSC than in patients without ROSC. Both AG and ACAG had the relation with APACHE II and SOFA scores, however, coefficients of correlation with APACHE II and SOFA score were higher in ACAG (r = 0.506) than in AG (r = 0.482). The sensitivity, specificity, positive predictive value, and negative predictive value of ACAG for the prediction of ROSC in patients with CPA were better than those of AG.

CONCLUSION

Our study shows that both AG and ACAG have the relation with ROSC and ACAG is better to predict the ROSC following CPR in patients with CPA compared with AG. ACAG can be easily obtained in the emergency situation, and ACAG is a useful parameter to predict ROSC in patients with CPA.

Factors related to post-operative metabolic acidosis following major abdominal surgery

BACKGROUND

Metabolic acidosis is frequently observed in perioperative patients, especially those who undergo major surgery. The aim of this study was to evaluate the factors related to post-operative metabolic acidosis and to attempt to identify the clinical effect of metabolic acidosis following major abdominal surgery.

METHODS

We included 172 patients admitted to a surgical intensive care unit (ICU) following major abdominal surgery. All cases were divided into either the acidosis or the normal group using immediate post-operative standard base excess (SBE). The following clinical data were retrospectively obtained from the chart and ICU database: basic clinical characteristics, operative data, type and volume of fluid infused during the operation, post-operative arterial blood gas analysis, lactate, and central venous oxygen saturation.

RESULTS

The predominant intraoperative fluid was either 0.9% saline or lactated Ringer's solution. The operation length, estimated blood loss, total fluid infused, total saline infused, lactate and corrected chloride were significantly higher in the acidosis group; however, central venous oxygen saturation was lower in the normal group. Among these factors, total infused saline and lactate level were independent factors related to metabolic acidosis. The comparison between the types of fluid revealed that the saline group had a significantly lower SBE, strong ion difference and higher corrected chloride. SBE was significantly correlated with lactate and total infused saline. ICU and hospital length of stay were significantly longer in the acidosis group.

CONCLUSIONS

Post-operative metabolic acidosis following major abdominal surgery was closely related to both hyperchloremic acidosis associated with large saline infusion and lactic acidosis caused by lactataemia.

WITHDRAWN: The association between initial anion gap and outcomes in medical intensive care unit patients

Purpose

Anion gap (AG) metabolic acidosis is common in critically ill patients. The relationship between initial AG at the time of admission to the medical intensive care unit (MICU) and mortality or length of stay (LOS) is unclear. This study was undertaken to evaluate this relationship.

Materials and Method

We prospectively examined the acid-base status of 100 consecutive patients at the time of MICU admission and recorded their mortality and LOS. The etiology of each AG was also recorded. Anion gap was corrected for albumin levels. The patients were divided into 4 stages based on severity of AG. Outcomes based on severity of AG were measured, and comparisons that adjusted for baseline characteristics were performed.

Results

This study showed that increased AG was associated with the higher mortality and that an AG more than 30 had the highest mortality. Mortality was significantly (P = .013) increased, even after accounting for AG etiology. Patients with highest AG also had the longest LOS in the MICU, and patients with normal acid-base status had the shortest MICU LOS (P < .01).

Conclusion

A high AG at the time of admission to the MICU was associated with higher mortality and LOS. Initial risk stratification based on AG and metabolic acidosis may help guide appropriate patient disposition (especially in patients without other definitive criteria for MICU admission) and assist with prognosis. Mixed AG metabolic acidosis with concomitant acid-base disorder was associated with increased MICU LOS.

The incidence and prognostic value of hypochloremia in critically ill patients

Little is known on the clinical effects of chloride on critically ill patients. We conducted this retrospective, observational study in 488 critically ill patients to investigate the incidence of chloride abnormalities, effects of hypochloremia in acid-base disorders, and association between chloride and clinical outcome. The study involved retrieval of arterial blood gas analyses, biochemical and demographical data from electrical records as well as quantitative acid-base analyses. For statistical analysis, the patients were stratified into three groups according to their chloride level (normal range: 98–106 mEq/L). The distribution of chloride levels was hyperchloremia 16.6%, normochloremia 74.6%, and hypochloremia 8.8%. The hypochloremic group was significantly alkalemic (P < 0.0001) and has significantly higher apparent strong ion difference (SIDa) (P < 0.0001) compared to the two other groups. The hypochloremic group had significantly longer stays in the ICU and hospital (P < 0.0001) with higher mortality (P < 0.0001). However, multiple regression analysis showed that chloride was not an independent factor of poorer outcome. In conclusion, the acid-base characteristics of the hypochloremic patients were alkalemia coexisting with higher SIDa. And although it was not an independent prognostic factor, hypochloremia was related to poorer outcome in critically ill settings.

Acid-base disorders in patients with chronic obstructive pulmonary disease: a pathophysiological review

The authors describe the pathophysiological mechanisms leading to development of acidosis in patients with chronic obstructive pulmonary disease and its deleterious effects on outcome and mortality rate. Renal compensatory adjustments consequent to acidosis are also described in detail with emphasis on differences between acute and chronic respiratory acidosis. Mixed acid-base disturbances due to comorbidity and side effects of some drugs in these patients are also examined, and practical considerations for a correct diagnosis are provided.

Quantification of systemic delivery of substrates for intermediate metabolism during citrate anticoagulation of continuous renal replacement therapy

BACKGROUND

There are limited data on systemic delivery of metabolic substrates during citrate anticoagulation. The direct citrate measurements are usually not available.

METHODS

Patients on 2.2% acid-citrate-dextrose (ACD, n = 41) were compared to a control group on unfractionated heparin (n = 17). All were treated on 1.9-m(2) polysulfone filters. Samples were taken from the central venous catheter, ports pre- and post-filter and from effluent.

RESULTS

The gain of citrate in CVVH (n = 18) was not different from CVVHDF (n = 23, p = 0.8). Mean gain of citrate was 25.4 ± 6.4 mmol/h. The systemic loads of lactate (p = 0.12) and glucose (p = 0.23) in CVVH were similar to CVVHDF. Mean inputs of lactate and glucose were 62.9 ± 21.1 and 26.6 ± 10.4 mmol/h, respectively. The mean difference between post- and prefilter unmeasured anions (d-UA) correlated with mean difference of citrate concentrations (p < 0.0001, r(2) = 0.66). The estimated caloric load of the citrate modalities was 5,536 ± 1,385 kJ/ 24 h.

CONCLUSIONS

ACD might represent a significant load of metabolic substrates, particularly if used with lactate buffer. Systemic delivery of citrate can be predicted using d-UA in the extracorporeal circuit.

A comprehensive, computer-model-based approach for diagnosis and treatment of complex acid-base disorders in critically-ill patients

We have developed a computer-model-based approach to quantitatively diagnose the causes of metabolic acid-base disorders in critically-ill patients. We use an interstitial-plasma-erythrocyte (IPE) model that is sufficiently detailed to accurately calculate steady-state changes from normal in fluid volumes and electrolyte concentrations in a given patient due to a number of causes of acid-base disorders. Normal fluid volumes for each patient are determined from their sex, height and weight using regression equations derived from measured data in humans. The model inputs (electrolyte masses and volumes) are altered to simulate the laboratory chemistry of each critically-ill patient. In this process, the model calculates changes in body-fluid volumes, osmolality and yields the individual values of IPE base excess (BE(IPE)) attributed to changes due to: (1) fluid dilution/contraction, (2) gain or loss of Cl(-), (3) hyper- or hypoalbuminemia, (4) presence of unmeasured ions, (5) gain of lactate, (6) gain or loss of phosphate, (7) gain or loss of calcium and magnesium, (8) gain or loss of potassium and (9) gain or loss of sodium. We use critically-ill patient data to show how our new approach is more informative and much simpler to interpret as compared to the approaches of Siggaard-Andersen or Stewart. We demonstrate how the model can be used at the bedside to diagnose acid-base disorders and suggest appropriate treatment. Hence, this new approach gives clinicians a new tool for diagnosing disorders and specifying fluid-therapy options for critically-ill patients.

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.

Fuzzy-based framework for diagnosis of acid-base disorders

The main objective of this research is to develop a fuzzy-based framework for diagnosis of different acid-base disorders. There are several acid-base disorders that cause many clinical complications and their proper diagnosis is the only way for their efficient treatment. The common disorders are metabolic acidosis, metabolic alkalosis, non-anion gap acidosis, anion-gap acidosis, acute respiratory alkalosis and chronic respiratory alkalosis. The proposed fuzzy-based framework was used to diagnose all of these disorders using four parameters directly measured in blood: hydrogen-ion concentration (pH), arterial blood carbon dioxide partial pressure (paCO₂), sodium ions concentration (Na⁺) and chloride ions concentration (Cl⁻) along with 12 features extracted from the directly measured parameters. The validation results showed that the developed framework has an accuracy of 94%, an average sensitivity of 88% and a specificity of 93%. These results imply that the developed fuzzy-based framework is accurate and reliable one and can be used to help clinicians specially the non-expert ones to provide correct and rapid diagnosis of acid-base disorders.

Acid-base disorders in critically ill neonates

Objective:

To study acid–base imbalance in common pediatric diseases (such as sepsis, bronchopneumonia, diarrhea, birth-asphyxia etc.) in neonates.

Design and Setting:

An observational study was conducted in an emergency room of a tertiary teaching care hospital in Haryana, India.

Patients and Methods:

Fifty neonates (from first hour to one month) attending pediatric emergency services with various ailments. Blood gas analysis, electrolytes, plasma lactate, and plasma albumin were estimated in neonates.

Results:

Metabolic acidosis was the most common acid–base disorder. Hyperlactatemia was observed in more than half of such cases. Birth asphyxia was another common disorder with the highest mortality in neonates followed by bronchopneumonia and sepsis. Significant correlation between mortality and critical values of lactate was observed.

Conclusion:

Birth asphyxia with high-lactate levels in neonates constituted major alterations in acid–base disorders seen in an emergency room of a tertiary teaching care hospital. Plasma lactate concentration measurement provides an invaluable tool to assess type of metabolic acidosis in addition to predicting mortality in these neonates.

A mathematical model of blood-interstitial acid-base balance: application to dilution acidosis and acid-base status

We developed mathematical models that predict equilibrium distribution of water and electrolytes (proteins and simple ions), metabolites, and other species between plasma and erythrocyte fluids (blood) and interstitial fluid. The models use physicochemical principles of electroneutrality in a fluid compartment and osmotic equilibrium between compartments and transmembrane Donnan relationships for mobile species. Across the erythrocyte membrane, the significant mobile species Cl−is assumed to reach electrochemical equilibrium, whereas Na+and K+distributions are away from equilibrium because of the Na+/K+pump, but movement from this steady state is restricted because of their effective short-term impermeability. Across the capillary membrane separating plasma and interstitial fluid, Na+, K+, Ca2+, Mg2+, Cl−, and H+are mobile and establish Donnan equilibrium distribution ratios. In each compartment, attainment of equilibrium by carbonates, phosphates, proteins, and metabolites is determined by their reactions with H+. These relationships produce the recognized exchange of Cl−and bicarbonate across the erythrocyte membrane. The blood submodel was validated by its close predictions of in vitro experimental data, blood pH, pH-dependent ratio of H+, Cl−, and HCO3−concentrations in erythrocytes to that in plasma, and blood hematocrit. The blood-interstitial model was validated against available in vivo laboratory data from humans with respiratory acid-base disorders. Model predictions were used to gain understanding of the important acid-base disorder caused by addition of saline solutions. Blood model results were used as a basis for estimating errors in base excess predictions in blood by the traditional approach of Siggaard-Andersen (acid-base status) and more recent approaches by others using measured blood pH and Pco2values. Blood-interstitial model predictions were also used as a basis for assessing prediction errors of extracellular acid-base status values, such as by the standard base excess approach. Hence, these new models can give considerable insight into the physicochemical mechanisms producing acid-base disorders and aid in their diagnoses.

Regional citrate anticoagulation in patients with liver failure supported by a molecular adsorbent recirculating system

OBJECTIVE

Regional citrate anticoagulation has emerged as a promising method in critically ill patients at high risk of bleeding. However, in patients with liver failure, citrate accumulation may lead to acid-base and electrolyte imbalances, notably of calcium. The aim of this study was to evaluate the feasibility and safety of regional citrate anticoagulation during liver support using a molecular adsorbent recirculating system as well as its effects on electrolyte and acid-base balance in patients with liver failure.

DESIGN

Prospective observational study.

SETTING

University hospital.

PATIENTS

Twenty critically ill patients supported by molecular adsorbent recirculating system resulting from liver failure between January 2007 and May 2009.

MEASUREMENTS AND MAIN RESULTS

The median duration of molecular adsorbent recirculating system treatment was 20 hrs (interquartile range, 18-22 hrs). Two of 77 molecular adsorbent recirculating system treatments (2%) were prematurely discontinued as a result of filter clotting and bleeding, respectively. The median citrate infusion rate, necessary to maintain the postfilter ionized calcium between 0.2 and 0.4 mmol/L, was 3.1 mmol/L (interquartile range, 2.3-4 mmol/L) blood flow. The median calcium chloride substitution rate was 0.9 mmol/L (0.3-1.7 mmol/L) dialysate. Total serum calcium remained stable during molecular adsorbent recirculating system treatments. There was a statistically significant increase of the ratio of total calcium to systemic ionized calcium (2.04 ± 0.32 mmol/L to 2.17 ± 0.35; p = .01), which reflected citrate accumulation resulting from liver failure. Under close monitoring, no clinically relevant electrolytes or acid-base disorders were observed.

CONCLUSIONS

Our results suggest that regional citrate anticoagulation is a safe and feasible method to maintain adequate circuit lifespan without increasing the risk of hemorrhagic complications while maintaining a normal acid-base as well as electrolyte balance in patients with liver failure supported by molecular adsorbent recirculating system.

Evaluation of acid-base balance in ST-elevation myocardial infarction in the early phase: a prognostic tool?

OBJECTIVES

Metabolic acidosis has been described after myocardial infarction, but little data are available on the acid-base imbalance in ST-elevation myocardial infarction (STEMI) submitted to mechanical revascularization, and earlier studies on this topic differ with respect to patients' selection criteria, treatment and evaluated parameters.

METHODS

We assessed admission base excess, anion gap, and lactate in 445 consecutive patients with STEMI submitted to primary percutaneous coronary intervention and whether its evaluation could help in identifying patients at a higher risk for in-hospital mortality and complications (acute pulmonary edema and arrhythmias).

RESULTS

At backward stepwise logistic regression analysis, the following variables were independently associated with intra-ICCU mortality: age [odds ratio (OR) 1.05; 95% confidence interval (CI) 1.02-1.10; P = 0.006], estimated glumerular filtration rate (OR 0.98; 95% CI 0.96-0.99; P= 0.010), Tn I (OR 1.006; 95% CI 1.004-1.008; P <0.001), and base excess (OR 0.90; 95% CI 0.82-0.99; P = 0.038); Hosmer-Lemeshow v2: 5.69, P = 0.681. At backward stepwise logistic regression analysis, the following variables were independently associated with intra-ICCU complications: left ventricular ejection fraction (OR 0.95; 95% CI 0.91-0.98; P = 0.005) and lactic acid (OR 1.31; 95% CI 1.10-1.57; P =0.003); Hosmer-Lemeshow v2: 4.11, P = 0.847.

CONCLUSION

According to our findings, the evaluation of base excess and lactate in the early phase of STEMI provides the bedside clinicians with useful tools for early risk stratification. In fact, base excess proved to be an independent predictor for intra-ICCU mortality, whereas lactate represented an independent marker for intra-ICCU complications.

[Acid-base disturbances in intensive-care patients]

BACKGROUND

Acid-base disturbances may cause a variety of symptoms, multi-organ failure and compromised immune defense. The aim of this paper is to provide an overview of acid-base disturbances in intensive-care patients.

MATERIAL AND METHOD

The article is based on a non-systematic search in Pub Med, a textbook on intensive care and the authors' clinical experience.

RESULTS

The Henderson-Hasselbalch equation describes acid-base status by changes in pCO2 and bicarbonate. Changes in pCO2 reflect the respiratory and bicarbonate the metabolic status. Standard base excess describes the metabolic part more exactly. Anion gap is calculated as a supplement. The Stewart method, describes acid-base status through three independent variables (pCO2, weak acids and strong ion difference [SID]) that regulate the dependent variables pH and bicarbonate concentration.

INTERPRETATION

The Henderson-Hasselbalch equation and standard base excess do not consider which acids or bases that are involved, The anion gap may disclose unmeasured anions and distinguish hyperchloremic acidosis from other types of metabolic acidosis, but the calculation is associated with uncertainty. The Stewart method describes the involved ions, but complicated equations makes it unsuitable in clinical practice. A combination of standard base excess and anion gap corrected for albumin levels provide a good description of acid-base status.

Effects of acute dilutional hyponatremia on acid-base changes and electrolyte concentrations in rats with bilateral renal pedicle ligation

OBJECTIVE

To describe the effects of increasing the extracellular fluid (ECF) volume by approximately 20% on acid-base changes and electrolyte concentrations in anesthetized rats.

ANIMALS

18 adult male Sprague-Dawley rats.

PROCEDURES

Rats were assigned to a control group (n = 6 rats) and a treatment group (12). All rats were anesthetized, and instrumentation and bilateral renal pedicle ligation were performed. The treatment group was infused IV with sterile water throughout a 30-minute period. Acid-base variables and concentrations of electrolytes, lactate, albumin, phosphorus, and hemoglobin were measured before (baseline) and 30 and 60 minutes after onset of infusion. Anion gap, strong ion difference, strong ion gap, and contributions of sodium, chloride, albumin, phosphorus, and lactate concentrations to base excess were calculated at each time point.

RESULTS

Infusion of sterile water led to an increase in ECF volume of approximately 18%. This had no effect on acid-base balance, compared with that in control rats. Infusion of sterile water caused a significant decrease in sodium, chloride, ionized calcium, lactate, and albumin concentrations, compared with concentrations in the control group. Anion gap and calculated effects of sodium, chloride, albumin, and lactate concentrations on base excess at 60 minutes differed significantly between infused and control rats.

CONCLUSIONS AND CLINICAL RELEVANCE

Infusion of sterile water did not cause clinically relevant dilutional acidosis. The acidotic impact of water administration was offset by generation of new bicarbonate via carbonic acid equilibration and intracellular buffering in combination with the alkalotic effects of decreases in albumin, phosphorus, and lactate concentrations.

A novel isotonic-balanced electrolyte solution with 1% glucose for perioperative fluid management in children- an animal experimental preauthorization study

BACKGROUND

The recommendations for perioperative maintenance fluid in children have been adapted from hypotonic to isotonic electrolyte solutions with lower glucose concentrations (1-2.5% instead of 5%) to avoid hyponatremia or hyperglycemia.

OBJECTIVE

The objective of this prospective animal study was to determine the margin of safety of a novel isotonic-balanced electrolyte solution with 1% glucose (BS-G1) in comparison with normal saline with 1% glucose (NS-G1) in the case of accidental hyperhydration with a focus on acid-base electrolyte balance, glucose concentration, osmolality and intracranial pressure in piglets.

METHODS

Ten piglets (bodyweight 11.8 +/- 1.8 kg) were randomly assigned to receive either 100 ml.kg(-1) of BS-G1 or NS-G1 within one hour. Before, during and after fluid administration, electrolytes, lactate, hemoglobin, hematocrit, glucose, osmolality and acid-base parameters were measured.

RESULTS

Unlike BS-G1, administration of NS-G1 produced mild hyperchloremic acidosis (base excess BS-G1 vs NS-G1, baseline 1.9 +/- 1.7 vs 2.9 +/- 0.9 mmol.l(-1), study end 0.2 +/- 1.7 vs -2.7 +/- 0.5 mmol.l(-1), P < 0.05, chloride BS-G1 vs NS-G1 baseline 102.4 +/- 3.4 vs 102.0 +/- 0.7 mmol.l(-1), study end 103.4 +/- 1.8 vs 109.0 +/- 1.4 mmol.l(-1)P < 0.05). The addition of 1% glucose led to moderate hyperglycemia (P < 0.05) with a concomitant increase in serum osmolality in both groups (P < 0.05).

CONCLUSION

Both solutions showed a wide margin of safety in the case of accidental hyperhydration with less acid-base electrolyte changes when using BS-G1. This novel solution could therefore enhance patient's safety within the scope of perioperative volume management.

Extreme metabolic alkalosis in intensive care

Metabolic alkalosis is a commonly seen imbalance in the intensive care unit (ICU). Extreme metabolic alkalemia, however, is less common. A pH greater than 7.65 may carry a high risk of mortality (up to 80%). We discuss the entity of life threatening metabolic alkalemia by means of two illustrative cases - both with a pH greater than 7.65 on presentation. The cause, modalities of managing and complications of this condition is discussed from the point of view of both the traditional method of Henderson and Hasselbalch and the mathematical model based on physiochemical model described by Stewart. Special mention to the pitfalls in managing patients of metabolic alkalosis with concomitant renal compromise is made.

A critique of Stewart's approach: the chemical mechanism of dilutional acidosis

OBJECTIVE

While Stewart's acid-base approach is increasingly used in clinical practice, it has also led to new controversies. Acid-base disorders can be seen from different viewpoints: on the diagnostic/clinical, quantitative/mathematical, or the mechanistic level. In recent years, confusion in the interpretation and terminology of Stewart's approach has arisen from mixing these different levels. This will be demonstrated on the basis of a detailed analysis of the mechanism of "dilutional acidosis." In the classical dilution concept, metabolic acidosis after resuscitation with large volumes is attributed to the dilution of serum bicarbonate. However, Stewart's approach rejects this explanation and offers an alternative one that is based on a decrease in a "strong ion difference." This mechanistic explanation is questionable for principal chemical reasons. The objective of this study is to clarify the chemical mechanism of dilutional acidosis.

METHODS

Experimental data and simulations of various dilution experiments, as well as theoretical and chemical considerations were used.

RESULTS

1. The key to understanding the mechanism of dilutional acidosis lies in the open CO2/HCO3 (-)-buffer system where the buffer base (HCO3(-)) is diluted whereas the buffer acid is not diluted (constant pCO2). 2. The categorization in independent and dependent variables depends on the system regarded. 3. Neither the principle of electroneutrality, nor a change in [SID], nor increased H2O dissociation plays a mechanistic role.

CONCLUSION

Stewart's approach is valid at the mathematical level but does not provide any mechanistic insights. However, the quantification and categorization of acid-base disorders, using Stewart approach, may be helpful in clinical practice.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s00134-009-1528-y) contains supplementary material, which is available to authorized users.

[Hypernatremic alkalosis. Possible counterpart of hyperchloremic acidosis in intensive care patients?]

BACKGROUND

With broad acceptance of Stewart's acid-base model "hyperchloremic acidosis" is regarded as an independent form of metabolic disorder. It is unknown whether hypernatremia plays a corresponding role with respect to the development of alkalosis.

METHODS

A total of 201 artificially ventilated, critically ill patients were monitored for hypernatremic episodes. Inclusion criterion was a serum sodium concentration above 145 mmol/l.

RESULTS

In 20 patients a total of 78 periods of elevated plasma sodium levels lasting at least 24 h were observed. In 86% of these cases sodium and chloride concentrations were simultaneously increased. The development of alkalosis correlated with the strong ion difference (r=0.80, p<0.01) but not with the serum sodium concentration (r=-0.031, p=0.78). In cases without accompanying hyperchloremia (13%) metabolic alkalosis regularly occurred and a correlation between serum sodium concentration and base excess could be verified (r=0.66, p=0.03). Alkalosis occurred in 84.8% of cases where the strong on difference exceeded 39 mmol/l.

CONCLUSION

From the available data hypernatremic alkalosis could not be defined as an independent metabolic disorder. In would seem more appropriate to use the term "strong ion alkalosis" in this context.

An assessment of the population variance of the strong ion gap using Monte Carlo simulation

The strong ion gap is a derived parameter used to quantify clinically significant but unmeasured charged species in human plasma. In the general population the strong ion gap has a mean value of approximately 0.0 mEq/l, but at present no reference range exists. This severely limits its clinical application. In order to establish a reference range, a 95% confidence interval around the population mean must be calculated. As each of the variables that make up the strong ion gap have their own unique and different means and standard deviations, simple methods of pooled variance can not be used to calculate this interval. In place of a direct solution, Monte Carlo methodology was employed using known reference standard deviations to construct a large sample of a simulated population. In addition, the partial correlation between the plasma concentrations of sodium and chloride was included in the calculations. Sample sets of 20,000 were simulated, each giving a normally distributed strong ion gap. A 95% confidence interval of 3.9+/-6.4 mEq/l was derived. Depending on the degree of strong ion correlation, minima and maxima for this reference range were calculated as 3.9+/-5.1 mEq/l and 3.9+/-7.6 mEq/l respectively. Reasons for the positive bias in the mean strong ion gap result are examined briefly.

Effect of pump prime on acidosis, strong-ion-difference and unmeasured ions during cardiopulmonary bypass

We tested the hypothesis that a cardiopulmonary bypass prime with lactate would be associated with less acidosis than a prime with only chloride anions because of differences in the measured strong-ion-difference. We randomised 20 patients to a 1500 ml bypass prime with either a chloride-only solution (Ringer's Injection; anions: chloride 152 mmol/l) or a lactated solution (Hartmann's solution; anions: chloride 109 mmol/l, lactate 29 mmol/l). Arterial blood was sampled before bypass and then two, five, 15 and 30 minutes after initiating bypass. We used repeated measures analysis of variance to compare groups. In both groups, the base-excess and measured strong-ion-difference decreased markedly from baseline after two minutes of bypass. The chloride-only group had greater acidosis with lower base-excess and pH (P < 0.05), greatest after five minutes of bypass (C5). Contrary to our hypothesis, however, the difference between the groups was not due to a difference in the measured strong-ion-difference, P = 0.88. At C5 when the difference in standard base-excess between the groups was greatest, 1.9 mmol/l (95% confidence interval: 0.1 to 3.6 mmol/l, P < 0.05), the difference in the measured strong-ion-difference was only 0.2 mmol/l (95% confidence interval: -2.4 to 2.7 mmol/l, P > 0.05). There was, however a difference in the net-unmeasured-ions (strong-ion-gap). We conclude that acid-base changes with cardiopulmonary bypass may differ with the prime but that the early differences between chloride-only and lactated primes appear not to be due to differences in the measured strong-ion-difference. We suggest future studies examine other possible mechanisms including unmeasured ions.