Effective Strong Ion Difference Research Articles

Acid-base variables in patients with acute kidney injury requiring peritoneal dialysis in the pediatric cardiac care unit

We aimed to clarify the acid-base abnormalities of patients with acute kidney injury (AKI) requiring peritoneal dialysis (PD) in pediatric cardiac care units. A retrospective observational study was conducted in a pediatric cardiac care unit in a tertiary care university hospital. The subjects were 40 patients with AKI requiring PD between 2003 and 2005, and controls matched by type of surgery and body weight. Acid-base variables, including blood gas data and electrolytes, were assessed. The Stewart-Figge variables, including strong ion difference apparent (SIDa), strong ion difference effective (SIDe), and strong ion gap (SIG), were calculated. Blood gas analyses showed that the PD group was more acidemic, with a lower mean bicarbonate and a lower mean base excess, typical features of metabolic acidosis. The strong ion analyses revealed that the PD group had lower mean sodium and albumin concentrations. Based on the Stewart-Figge methodology, SIDa was smaller in the PD group than in the control group, but SIG was similar in the two groups. Receiver-operating characteristic curve analyses showed that serum albumin was the only prognostic factor associated with PCCU mortality, even after adjustment for PD treatment. Patients with AKI requiring PD in a pediatric cardiac care unit had significant metabolic acidosis compared to controls matched by the type of surgery and body weight. Hyponatremia and hypoalbuminemia were characteristics of these patients. The calculated SIDa was smaller in the PD than in the control group. Only the serum albumin had a significant prognostic value.

Acid–base disorders evaluation in critically ill patients: we can improve our diagnostic ability

To determine whether Stewart's approach can improve our ability to diagnose acid-base disorders compared to the traditional model. This prospective cohort study took place in a university-affiliated hospital during the period of February-May 2007. We recorded clinical data and acid-base variables from one hundred seventy-five patients at intensive care unit admission. Of the 68 patients with normal standard base excess (SBE) (SBE between -4.9 and +4.9), most (n = 59; 86.8%) had a lower effective strong ion difference (SIDe), and of these, 15 (25.4%) had SIDe < 30 mEq/L. Thus, the evaluation according to Stewart's method would allow an additional diagnosis of metabolic disorder in 33.7% patients. The Stewart approach, compared to the traditional evaluation, results in identification of more patients with major acid-base disturbances.

Switching from Three Times a Week to Short Daily Online Hemodiafiltration: Effects on Acid-Base Balance

This study examines the effect of a change from the standard 4-5 hours 3 times a week of online hemodiafiltration (OL-HDF) to 2-2.5 hours daily (6 times a week) OL-HDF, on acid-base balance, and attempts assess the modifications of acid-base parameters, ionic concentration, and electrical charges of albumin and phosphate available for diffusion and convection mechanisms across the membrane and subsequent infusion. In 18 patients on online HDF, blood gas, electrolytes (Na, K, Cl), lactate, phosphate, albumin, apparent strong ion difference (SIDa), effective strong ion difference (SIDe), strong ion gap (SIG), anion gap (AG), and bicarbonate and pH time-averaged concentration (TAC) and time-averaged deviation (TAD) variables were evaluated at baseline, and 1, 3, 6, 9, and 12 months after patients were switched to daily OL-HDF. Additionally, in 12 patients, the same parameters measured simultaneously at dialyzer inlet, outlet, and after reinfusion were studied. Throughout the study, weekly single-pool Kt/V, equilibrated Kt/V, and TAC urea remained constant. However, standard Kt/V increased and TAD urea decreased on daily OL-HDF. There were no statistical differences during the time span of 12 months in pH, cations (Na, K), anions (Cl, HCO3(-) AG, and lactate), or SIDa, SIDe, and SIG pre-HDF; while pH and HCO3(-) TAD decreased from 0.02 and 1.02 +/- 0.74 mEq/L, to 0.01 and 0.64 +/- 0.52 mEq/L, respectively (p<0.01). Net albumin charge and AG increased significantly at dialyzer outlet and decreased after reinfusion. We did not observe changes in the acid-base balance in patients who switched from 3 times a week to short daily OL-HDF. The main benefit observed was a lower pH and bicarbonate TAD. This shows a better physiology for daily OL-HDF.

Clinical Significance of Strong Ion Gap: between ICU and Hemodialysis Patients with Metabolic Acidosis

Metabolic acidosis is the most frequent acid-base disorder in critically ill patients and dialysis patients. This study is to compare the conventional approach with the physicochemical approach between the intensive care unit (ICU) and hemodialysis (HD) patients. Fifty-seven ICU patients and 33 HD patients were enrolled. All data sets included simultaneous measurements of arterial blood gas with base deficit (BD), serum electrolytes, albumin, lactate, and calculated anion gap observed (AGobs). Physiochemical analysis was used to calculate the albumin and lactate-corrected anion gap (AGcorr), the base deficit corrected for unmeasured anions (BDua), the strong ion difference apparent (SIDa), the strong ion difference effective (SIDe), and the strong ion gap (SIG). The SIDa (37.5±5.3 vs 33.9±9.0, p=0.045) and SIG (12.3±5.3 vs 8.6±8.8, p=0.043) was significantly higher in the HD group than the ICU group. SIG in the ICU group showed the highest correlation coefficient with AGobs, whereas SIG in the HD group with AGcorr. Concerning the contributions of the three main causes of metabolic acidosis, increased SIG was comparable between the ICU and HD group (n=48, 90.6% vs n=30, 93.8%), whereas hyperlactatemia (n=9, 17.0% vs n=0, 0%) and hyperchloremia (n=20, 35.1% vs n=2, 6.1%) was significantly increased in the ICU group compared with the HD group. Multiple underlying mechanisms are present in most of the ICU patients with metabolic acidosis compared with the HD patients. In conclusion, the physicochemical approach can elucidate the detailed mechanisms of metabolic acidosis in ICU and HD patients compared with conventional measures.

Diagnosis of Acid-Base Derangements and Mortality Prediction in the Trauma Intensive Care Unit: The Physiochemical Approach

Conventional measures such as anion gap and base deficit can be inadequate for defining and managing complex acid-base derangements. Physiochemical analysis is an alternative approach based on the principles of electroneutrality and conservation of mass, and may be more accurate for defining the presence and type of acidosis and unmeasured anions. We retrospectively analyzed 2,152 sets of laboratory data from 427 trauma patients admitted to the intensive care unit. All data sets included simultaneous measurements of an arterial blood gas with base deficit (BD), serum electrolytes, albumin, lactate, and a calculated anion gap (AG). Physiochemical analysis was used to calculate the corrected anion gap (AGcorr), the apparent strong ion difference, the effective strong ion difference, the strong ion gap (SIG), and the base deficit corrected for unmeasured anions (BDua). Statistical analysis comparing AG and BD to the physiochemical measures was performed on all data and the subset of admission laboratory data only (n = 427). Unmeasured anions as defined by an elevated SIG were present in 92% of patients (mean SIG, 5.9 +/- 3.3), whereas hyperlactatemia and hyperchloremia were present in only 18% and 21%, respectively. The physiochemical approach yielded a different clinical interpretation of the acid-base status than the conventional approach in 597 (28%) of the data sets. Lactate level was more strongly correlated with the physiochemical measures of SIG (r = 0.48) and AGcorr (r = 0.47) than with the conventional measures of AG (r = 0.24) and BD (r = 0.36, p < 0.01 for all). Both admission BD and BDua were significantly elevated in nonsurvivors, and logistic regression analysis for prediction of mortality revealed an area under the curve of 0.70 for BDua (p < 0.01) versus 0.65 for BD (p < 0.01). AGcorr and SIG did not differentiate survivors from nonsurvivors in the group as a whole. However, analysis of patients with a normal admission lactate level (n = 322) demonstrated a significant difference between survivors and nonsurvivors in SIG (7 vs. 5, p = 0.009), BDua (-4.2 vs. -2.0, p = 0.004), and AGcorr (21 vs. 19, p = 0.04), whereas the conventional measures of BD and AG showed no significant discriminatory ability. Unmeasured anions are the most common component of metabolic acidosis in trauma intensive care unit patients. The physiochemical approach can significantly alter the acid-base diagnosis compared with conventional measures. The SIG, AGcorr, and BDua may be particularly helpful in predicting acid-base derangements and mortality in patients with normal serum lactate levels.

Strong ion difference and strong anion gap: The Stewart approach to acid base disturbances

More than 20 years ago Stewart proposed a method for acid–base analysis moving from a new definition of neutrality, acidity and alkalinity. 10 years later Figge defined more precisely the quantitative role of plasmatic nonbicarbonate buffers. Scientific literature studying this physicochemical approach to acid–base balance found controversial results. The aim of this article is to review the basic principles of the approach to acid–base developed by Stewart and Figge. The definitions of apparent and effective strong ion difference (SID) and of strong ion gap (SIG) will be also reviewed considering the findings of the scientific literature regarding these two main parameters related to this approach. Several clinical conditions of acid–base imbalances will be reviewed using the physicochemical approach described by Stewart. He identified the independent variables determining pH; they include SID, carbon dioxide partial pressure and the serum concentration of weak acids. SIG reflects the contribution of unidentified anions to SID. The physicochemical approach to acid–base developed by Stewart and Figge provides more details about complex acid–base abnormalities than does the classic approaches developed by Henderson–Hasselbach and Siggaard–Andersen. However the prognostic role of SID and SIG is still not well established. Moreover, the Stewart and Figge approach requires complicated calculations at the bedside and a simpler adjustment of the anion gap for albumin concentration may result in the same clinical conclusions as the physicochemical approach. Even if the pure Stewart approach to acid–base is difficult to apply in daily clinical practice and its simplifications seem more practical, it is noteworthy that Stewart improved significantly the approach to acid–base abnormalities by providing a better understanding of many acid–base imbalances.

Adding lactate to the prime solution during hypothermic cardiopulmonary bypass: a quantitative acid–base analysis

The effect of adding lactate to the cardiopulmonary bypass (CPB) prime was investigated using Stewart's quantitative acid-base approach. According to this quantitative model, serum pH and bicarbonate are determined by three independent factors: the partial pressure of carbon dioxide (PCO(2)), the total concentration of weak acids (e.g. albumin), and the strong ion difference. The apparent strong ion difference is calculated as the sum of sodium, potassium, magnesium and calcium minus chloride concentrations. The pH decreases with a smaller strong ion difference and vice versa. Twenty patients scheduled for coronary surgery were studied prospectively. All patients were treated identically, except for the prime, which either contained lactate or was lactate free. Just before bypass and before coming off bypass, haemoglobin, glucose, plasma osmolality and colloid osmotic pressure were determined; albumin, lactate, sodium, potassium, ionized calcium, magnesium, phosphate, arterial pH, PCO(2), bicarbonate, and base excess were measured for use in Stewart's analysis. Metabolic acidosis had resolved by the end of bypass with the lactated prime. Although the strong ion gap (apparent minus effective strong ion difference) increased significantly in both groups, its composition differed significantly between the groups. The Stewart technique detected polyanionic gelatin as a weak acid component contributing to the unidentified anion fraction. Colloid osmotic pressure was maintained in both groups. Exogenous lactate attenuates acidosis related to CPB. The oncotic and weak acid deficits produced by hypoalbuminaemia may be compensated for temporarily during CPB by polyanionic synthetic colloids such as succinylated gelatin.

Splanchnic buffering of metabolic acid during early endotoxemia

Purpose: We sought to determine the sites of metabolic acid production and clearance during acute endotoxemia. Materials and Methods: In 10 pentobarbital-anesthetized dogs, flow was measured (ultrasonic probes) for the portal vein, hepatic artery, and renal artery. Catheters were inserted into the hepatic vein, pulmonary artery, renal vein, and portal vein. Measurements of blood gases and strong ions were obtained from each site during control conditions and after 30 minutes of intravenous infusion of 1 mg/kg of Escherichia coli endotoxin. The total metabolic acid flux across each organ was calculated using the standard base excess formula and the effective strong ion difference method. Pa CO 2 was maintained by controlled ventilation. Results: Mean arterial pH decreased from 7.34 to 7.22 with acute endotoxemia. Although transvisceral pH gradients revealed net acid release, the source of this was purely respiratory (carbon dioxide). During early endotoxemia, the gut significantly increased metabolic acid uptake (36.60 ± 6.60 mmol/h, P < .05). Conclusions: We conclude that during early endotoxemia in the dog, the gut is a major site of metabolic acid removal.

Disproportional changes in hematocrit, plasma volume, and proteins during exercise and bed rest.

The interrelationships between the changes in plasma volume, hematocrit, and plasma proteins during muscular exercise and bed rest were investigated. Proportionally, the changes in hematocrit are always smaller than the changes in plasma volume. For this reason changes in the concentration of blood constituents can only be quantitated on the basis of plasma volume changes. During short periods of intensive exercise, there was a small loss of plasma proteins. With prolonged submaximal exercise there was a net gain in plasma protein, which contributes to stabilization of the vascular volume. Prolonged bed rest induced hypoproteinemia; this loss of plasma protein probably plays an important role in recumbency hypovolemia.