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.

Prognosis of critically ill patients with extreme acidosis: A retrospective study.

OBJECTIVE: This study aims to assess the impact of different subtypes of extreme acidosis on the mortality of critically ill patients. METHODS: This retrospective cohort study included critically ill patients who were admitted to the intensive care unit (ICU) with a pH level <7. Clinical data and blood gas analyses were collected from electronic medical records. The primary outcome was in-hospital mortality. The use of vasopressors, mechanical ventilation (MV), and renal replacement therapy (RRT), the duration of MV and RRT, and the length of ICU and hospital stay were secondary outcomes. The simplified Stewart approach to acid-base disorders was used to analyze the causes of acidosis. RESULTS: A total of 231 patients with 371 arterial blood gas analyses with pH < 7 were admitted from January 2012 to December 2021 and 222 were included in the study. Out of the 222 patients analyzed, respiratory acidosis was the primary disorder in 11.3% of patients (n = 25), metabolic acidosis in 33.8% (n = 75), and mixed acidosis in 55% (n = 122). Overall mortality was 42.8% (n = 95). No significant difference was observed in mortality among patients with respiratory, metabolic, or mixed acidosis (28%, 42.7%, and 45.9%, respectively; p = 0.26). The primary disorder affected the use of vasopressors and MV, the duration of MV, and the length of ICU and hospital stay. Patients with extreme acidosis due to unmeasured anions with lactate levels of 4 mmol/L or higher had higher mortality compared with patients with lactate levels <4 mmol/L (55.6% and 27.7%, respectively; p = 0.007). CONCLUSION: Among critically ill patients with extreme acidosis, the primary disorder is not associated with mortality, but it is associated with the use of vasopressors and MV, the duration of MV, and the length of ICU and hospital stay. Additionally, hyperlactatemia is a predictor of poor prognosis in patients with extreme acidosis.

Clinical Approach to Assessing Acid-Base Status: Physiological vs Stewart.

Evaluation of acid-base status depends on accurate measurement of acid-base variables and their appropriate assessment. Currently, 3 approaches are utilized for assessing acid-base variables. The physiological or traditional approach, pioneered by Henderson and Van Slyke in the early 1900s, considers acids as H+ donors and bases as H+ acceptors. The acid-base status is conceived as resulting from the interaction of net H+ balance with body buffers and relies on the H2CO3/HCO3- buffer pair for its assessment. A second approach, developed by Astrup and Siggaard-Andersen in the late 1950s, is known as the base excess approach. Base excess was introduced as a measure of the metabolic component replacing plasma [HCO3-]. In the late 1970s, Stewart proposed a third approach that bears his name and is also referred to as the physicochemical approach. It postulates that the [H+] of body fluids reflects changes in the dissociation of water induced by the interplay of 3 independent variables-strong ion difference, total concentration of weak acids, and PCO2. Here we focus on the physiological approach and Stewart's approach examining their conceptual framework, practical application, as well as attributes and drawbacks. We conclude with our view about the optimal approach to assessing acid-base status.

Hyperchloremic metabolic acidosis due to saline absorption during laser enucleation of the prostate: a case report.

BACKGROUND: Recent technological advancements have enabled the use of electrolyte solutions such as saline or buffered electrolyte solution during transurethral resection or laser enucleation of the prostate. However, saline absorption may cause hyperchloremic metabolic acidosis. CASE PRESENTATION: A male in his late seventies underwent holmium laser enucleation of the prostate under a combination of subarachnoid block and general anesthesia. Intraoperatively, abdominal distension prompted the attending anesthesiologist to consider the possibility of SGA malposition, and the trachea was intubated. Oropharyngeal and neck edema was observed, and laboratory examination revealed considerable acidosis with hyperchloremia. Further evaluation confirmed the absorption of a large amount of saline into the circulation via the perforated bladder. Application of the simplified Stewart approach clearly suggested that hyperchloremia was the principal cause of metabolic acidosis. The dilution of albumin attenuated acidosis. CONCLUSIONS: Absorption of normal saline during laser enucleation of prostate caused hyperchloremic metabolic acidosis and airway edema.

Revisiting Stewart's Approach toward Assessment of Unidentified or Complex Acid-Base Disorders.

How to cite this article: Gopaldas JA. Revisiting Stewart's Approach toward Assessment of Unidentified or Complex Acid-Base Disorders. Indian J Crit Care Med 2022;26(1):5-6.

Utility of Stewart's Approach to Diagnose Missed Complex Acid-Base Disorders as Compared to Bicarbonate-anion Gap-based Methodology in Critically Ill Patients: An Observational Study.

BACKGROUND: Traditional arterial blood gas (ABG) analysis may miss out on some metabolic acid-base disorders. We prospectively compared Stewart's approach in critically ill patients to traditional bicarbonate-anion gap-based methods (with and without correction for albumin) to diagnose acid-base disorders. PATIENTS AND METHODS: Five hundred ABG samples from medical or surgical patients in the ICU were analyzed with traditional bicarbonate-anion gap-based methodology with and without correction for albumin and Stewart's biochemical approach. The primary outcome identification of additional metabolic disorders diagnosed with Stewart's approach in comparison to bicarbonate system-based approaches. We also looked at the correlation between the strong ion gap (SIG) and the albumin-corrected anion gap (acAnion Gap). RESULTS: Stewart's approach detected missed metabolic disorders in 58 (11.6%) blood gas results reported as "within normal limits" with the bicarbonate-uncorrected anion gap approach. In 50 (10%) of these ABGs, the acAnion Gap approach was able to diagnose the missed metabolic disorders. Thus, the albumin-corrected anion gap method had a similar diagnostic performance to Stewart's approach, as it missed additional disorders in only eight (1.6%) blood gases. CONCLUSION: In this study, we found that the acAnion Gap approach was similar in diagnostic performance to Stewart's approach. We feel that the corrected anion gap approach can be safely used if a ready calculator for Stewart's approach is not available. HOW TO CITE THIS ARTICLE: Paliwal R, Pakavakis A, Divatia JV, Kulkarni AP. Utility of Stewart's Approach to Diagnose Missed Complex Acid-Base Disorders as Compared to Bicarbonate-anion Gap-based Methodology in Critically Ill Patients: An Observational Study. Indian J Crit Care Med 2022;26(1):23-32.

Describing acid-base balance using three different methods of analysis in a feline acute haemorrhage-resuscitation model.

OBJECTIVE: To describe acid-base status using the Henderson-Hasselbalch, Stewart and semi-quantitative methods of analysis in a feline haemorrhage-resuscitation model. STUDY DESIGN: Randomized crossover study. ANIMALS: A total of six domestic cats (mean age, 21 months; weight, 4.9 kg). METHODS: Venous blood samples were taken before haemorrhage, after haemorrhage at 30 minute intervals during fluid resuscitation and at 24 hours. The cats were anaesthetized and underwent following treatments: no purposeful haemorrhage and resuscitation (NoPHR), purposeful haemorrhage followed by either lactated Ringer's solution (LRS) or 6% tetrastarch 130/0.4 (Voluven) for resuscitation. LRS and Voluven were administered at 60 and 20 mL kg-1 hour-1, respectively, for 120 minutes. Variables used for the analysis methods were measured or calculated from the blood samples and then compared among treatments over time using a general linear mixed model (p < 0.05; data reported as mean and standard deviation). RESULTS: The total blood loss at 120 minutes was 10.2 ± 2.3, 29.3 ± 9.0 and 29.1 ± 6.3 mL kg-1 for NoPHR, LRS and Voluven, respectively. Total volumes of LRS and Voluven administered were 120 and 40 mL kg-1, respectively. All cats became acidaemic during anaesthesia regardless of treatment. The Henderson-Hasselbalch method indicated that anaesthetized cats undergoing severe haemorrhage and resuscitation manifest a mixed acidosis. The Stewart method indicated two counter metabolic processes that contributed to the overall pH-decrease in apparent strong ion difference (acidosis) and decrease in total weak acids (alkalosis). The semi-quantitative method identified the free water and chloride effects as variables causing acidosis and the albumin effect causing alkalosis. CONCLUSIONS AND CLINICAL RELEVANCE: In an experimental haemorrhage and resuscitation model in cats, blood pH was similar among treatments over time regardless of severe haemorrhage and resuscitation with LRS or Voluven or mild haemorrhage and no resuscitation.

Total Carbon Dioxide in Adult Standardbred and Thoroughbred Horses.

The TCO2 (total carbon dioxide) test is performed on the blood of racehorses as a means of combatting the practice of administering alkalizing agents for the purpose of enhancing performance. The purposes of this review are to present an overview of the factors contributing to TCO2 and to review the literature regarding TCO2 in adult Standardbred and Thoroughbred horses to demonstrate the range of variability of TCO2 in horses. Most of the research published on the topic of TCO2 or bicarbonate measurement in racehorses was accessed and reviewed. PubMed and Google Scholar were the primary search engines used to source the relevant literature. The main physicochemical factors that contribute to changes in TCO2 in horses at rest are changes in strong ions concentration, followed by changes in weak acid (i.e. plasma albumin) concentrations. There is a wide normal distribution of TCO2 in horses ranging from 23 mmol/L to 38 mmol/L. Independent of administration of alkalizing agents, blood TCO2 is affected mainly by feeding, time of day (diurnal variation), season and exercise. There are few studies that have reported hour-by-hour changes in TCO2. Racehorse population studies suffer from lack of validation regarding whether or not a horse was administered an alkalizing agent. It is concluded that the normal range of TCO2 in non-alkalized Standardbred and Thoroughbred horses is significantly wider than has been appreciated, that periods of elevated TCO2 appear to be normal for many horses at rest, and that a TCO2 test alone is not definitive for the purposes of determining of an alkalizing agent has been administered to a horse.

Stewart analysis unmasks acidifying and alkalizing effects of ionic shifts during acute severe respiratory alkalosis.

PURPOSE: Although both the Henderson-Hasselbalch method and the Stewart approach can be used to analyze acid-base disturbances and metabolic and respiratory compensation mechanisms, the latter may be superior in detecting subtle metabolic changes. MATERIALS AND METHODS: We analyzed acid-base disturbances using both approaches in six healthy male volunteers practicing extreme voluntary hyperventilation. Arterial blood gas parameters were obtained during a breathing exercise consisting of approximately 30 cycles of powerful hyperventilation followed by breath retention for approximately 2 min. RESULTS: Hyperventilation increased pH from 7.39 ± 0.01 at baseline to 7.74 ± 0.06, PaCO2 decreased from 34.1 ± 1.1 to 12.6 ± 0.7 mmHg, PaO2 increased from 116 ± 4.6 to 156 ± 4.3 mmHg. Baseline apparent strong ion difference was 42.3 ± 0.5 mEq/L, which decreased to 37.1 ± 0.7 mEq/L following hyperventilation. The strong ion gap significantly decreased following hyperventilation, with baseline levels of 10.0 ± 0.9 dropping to 6.4 ± 1.1 mEq/L. CONCLUSIONS: Henderson-Hasselbalch analysis indicated a profound and purely respiratory alkalosis with no metabolic compensation following extreme hyperventilation. The Stewart approach revealed metabolic compensation occurring within minutes. These results challenge the long-held axiom that metabolic compensation of acute respiratory acid-base changes is a slow process.

Effect of sodium-chloride ion difference on pH regulation.

BACKGROUND: In the Stewart approach, the difference between the cation and anion concentrations, especially between sodium, accounting for the majority of cations, and chloride, comprising the majority of anions, is an important factor in pH regulation. This study investigated the effect of sodium-chloride ion difference (SCD) on pH regulation comparing with those of PaCO2 and lactate. METHODS: Arterial blood gas samples measured at our pediatric intensive care unit of a tertiary children's hospital between January and June 2020 were included. Samples that met the following criteria were excluded: samples collected from patients taking potassium bromide and samples with lactate concentration of >25 mmol/L. From the eligible data, pH was chosen as the dependent variable and SCD, lactate, and PaCO2 as independent variables, and then, a multiple regression analysis was performed. RESULTS: In total, 5360 samples were included. Of these, five samples were excluded according to the exclusion criteria. Finally, 5355 samples were analyzed. As the variance inflation factors were <2.0 for all three variables, there was no multicollinearity. The following model was derived: pH = 7.384 + [0.97 × SCD (mEq/L) - 0.66 × PaCO2 (mmHg) - 1.33 × Lac (mmol/L)] × 10-2 (adjusted R-squared = 0.73; P value < 0.001). Based on the standardized partial regression coefficients (ß), pH was affected in the order of PaCO2 (ßPaCO2 = -0.95), SCD (ßSCD = 0.72), and lactate (ßlactate = -0.33). CONCLUSIONS: The prevention of SCD reduction, together with respiratory and metabolic management, is important for pH regulation.

The Impact of Intravenous Fluid Therapy on Acid-Base Status of Critically Ill Adults: A Stewart Approach-Based Perspective.

One of the most important tasks of physicians working in intensive care units (ICUs) is to arrange intravenous fluid therapy. The primary indications of the need for intravenous fluid therapy in ICUs are in cases of resuscitation, maintenance, or replacement, but we also load intravenous fluid for purposes such as fluid creep (including drug dilution and keeping venous lines patent) as well as nutrition. However, in doing so, some facts are ignored or overlooked, resulting in an acid-base disturbance. Regardless of the type and content of the fluid entering the body through an intravenous route, it may impair the acid-base balance depending on the rate, volume, and duration of the administration. The mechanism involved in acid-base disturbances induced by intravenous fluid therapy is easier to understand with the help of the physical-chemical approach proposed by Canadian physiologist, Peter Stewart. It is possible to establish a quantitative link between fluid therapy and acid-base disturbance using the Stewart principles. However, it is not possible to accomplish this with the traditional approach; moreover, it may not be noticed sometimes due to the normalization of pH or standard base excess induced by compensatory mechanisms. The clinical significance of fluid-induced acid-base disturbances has not been completely clarified yet. Nevertheless, as fluid therapy may be the cause of unexplained acid-base disorders that may lead to confusion and elicit unnecessary investigation, more attention must be paid to understand this issue. Therefore, the aim of this paper is to address the effects of different types of fluid therapies on acid-base balance using the simplified perspective of Stewart principles. Overall, the paper intends to help recognize fluid-induced acid-base disturbance through bedside evaluation and choose an appropriate fluid by considering the acid-base status of a patient.

Relationship Between Partial Carbon Dioxide Pressure and Strong Ions in Humans: A Retrospective Study.

Little is known about the role of a strong ions in humans with respiratory abnormalities. In this study, we investigated the associations between partial carbon dioxide pressure (pCO2) and each of sodium ion (Na+) concentrations, chloride ion (Cl-) concentrations and their difference (SIDNa-Cl). Blood gas data were obtained from patients in a teaching hospital intensive care unit between August 2013 and January 2017. The association between pCO2 and SIDNa-Cl was defined as the primary outcome. The associations between pCO2 and [Cl-], [Na+] and other strong ions were secondary outcomes. pCO2 was stratified into 10 mmHg-wide bands and treated as a categorical variable for comparison. As a result, we reviewed 115,936 blood gas data points from 3,840 different ICU stays. There were significant differences in SIDNa-Cl, [Cl-], and [Na+] among all categorized pCO2 bands. The respective pCO2 SIDNa-Cl, [Cl-], and [Na+] correlation coefficients were 0.48, -0.31, and 0.08. SIDNa-Cl increased and [Cl-] decreased with pCO2, with little relationship between pCO2 and [Na+] across subsets. In conclusion, we found relatively strong correlations between pCO2 and SIDNa-Cl in the multiple blood gas datasets examined. Correlations between pCO2 and chloride concentrations, but not sodium concentrations, were further found to be moderate in these ICU data.

Midazolam Alters Acid-Base Status Less than Azaperone during the Capture and Transport of Southern White Rhinoceroses (Ceratotherium simum simum).

Acidemia represents a major life-threatening factor during rhinoceros capture. The acid-base status during rhinoceros transport is unknown. The purpose of this study was to describe changes in acid-base status during rhinoceros capture and transport and compare these changes between rhinoceroses sedated with azaperone or midazolam. Twenty-three wild white rhinoceros bulls were road-transported 280 km for reasons unrelated to this study. Rhinoceroses were captured with etorphine-azaperone (Group A) or etorphine-midazolam (Group M). During transport, azaperone (Group A) or midazolam (Group M) was re-administered every 2 h and venous blood collected. Changes in blood pH and associated variables were compared over time and between groups using a general linear mixed model. Rhinoceroses of both groups experienced a respiratory and metabolic acidosis during capture (pH 7.109 ± 0.099 and 7.196 ± 0.111 for Group A and Group M, respectively) that was quickly compensated for by the start of transport (pH 7.441 ± 0.035 and 7.430 ± 0.057) and remained stable throughout the journey. Rhinoceroses from Group M showed a smaller decrease in pH and associated variables at capture than rhinoceroses from Group A (p = 0.012). The use of midazolam instead of azaperone could therefore improve the success of rhinoceros capture and thus, contribute to the outcome of important conservation translocations.

Blood acid-base status in impala (Aepyceros melampus) immobilised and maintained under total intravenous anaesthesia using two different drug protocols.

BACKGROUND: In mammals, homeostasis and survival are dependent on effective trans-membrane movement of ions and enzyme function, which are labile to extreme acid-base changes, but operate efficiently within a narrow regulated pH range. Research in patients demonstrating a pH shifts outside the narrow regulated range decreased the cardiac output and systemic vascular resistance and altered the oxygen binding to haemoglobin. These cardiopulmonary observations may be applicable to the risks associated with anaesthesia and performance of wildlife ungulates on game farms. The aim of this study was to compare blood pH changes over time in impala immobilised and anaesthetised with two different drug protocols (P-TMP - immobilisation: thiafentanil-medetomidine; maintenance: propofol-ketamine-medetomidine; P-EME - immobilisation: etorphine-medetomidine; maintenance: etorphine-ketamine-medetomidine). Additionally, we discuss the resultant blood pH using both the Henderson-Hasselbalch and the Stewart approaches. Two data collection time points were defined, Time1 before maintenance of general anaesthesia and Time 2 at end of maintenance of general anaesthesia. We hypothesise that blood pH would not be different between drug protocols and would not change over time. RESULTS: Significant differences were detected over time but not between the two drug protocols. Overall, the blood pH decreased over time from 7.37 ± 0.04 to 7.31 ± 0.05 (p = 0.001). Overall, over time arterial partial pressure of carbon dioxide changed from 51.3 ± 7.5 mmHg to 72.6 ± 12.4 mmHg (p < 0.001); strong ion difference from 44.6 ± 2.4 mEq/L to 46.9 ± 3.1 mEq/L (p < 0.001); anion gap from 15.0 ± 3.1 mEq/L to 10.9 ± 2.2 mEq/L (p < 0.001); and total weak acids from 16.1 ± 1.2 mmol/L to 14.0 ± 1.1 mmol/L (p < 0.001). The bicarbonate changed from 29.6 ± 2.7 mEq/L to 36.0 ± 4.1 mEq/L (p < 0.001); and lactate changed from 2.9 ± 1.5 mEq/L to 0.3 ± 0.03 mEq/L (p < 0.001) over time. CONCLUSIONS: The profound increase in the partial pressure of carbon dioxide that worsened during the total intravenous anaesthesia in both protocols initiated a substantial metabolic compensatory response to prevent severe acidaemia. This compensation resulted in a clinically acceptable mild acidaemic state, which worsened over time but not between the protocols, in healthy impala. However, these important compensatory mechanisms require normal physiological function and therefore when immobilising ill or anorexic wild ungulates their acid-base status should be carefully assessed.

Brecha de iones fuertes y su cinética de aclaramiento como marcador de mortalidad en pacientes con choque séptico / Strong ion gap and its clearance kinetics as a mortality marker in septic shock patients / Hiato de íons fortes e sua cinética de aclaramento como marcador da mortalidade em pacientes com choque séptico

Resumen: Introducción: Existe evidencia clínica de que la brecha de iones fuertes obtenida por el método de Stewart de equilibrio ácido-base es mejor predictora de mortalidad que los parámetros tradicionales en algunos pacientes críticamente enfermos. Objetivo: Evaluar la cinética de depuración de la brecha de iones fuertes en individuos con choque séptico durante las primeras 48 horas de estancia en la unidad de cuidados intensivos. Material y métodos: Se trata de un estudio retrospectivo observacional, con datos obtenidos del expediente clínico, realizado en una unidad de cuidados intensivos adultos en un hospital privado de la ciudad de Monterrey, Nuevo León. Se evaluaron variables demográficas, así como datos obtenidos de gasometrías y química sanguínea al ingreso, a las 24 y 48 horas posteriores, para calcular parámetros tradicionales del equilibrio ácido-base y los obtenidos por el método de Stewart. Se calculó también la cinética de eliminación de dichos parámetros para evaluar sus cambios a través del tiempo y su relación con la mortalidad. Resultados: Se estudiaron 91 personas con choque séptico entre junio de 2014 y junio de 2016, con una mortalidad de 28.6%. La depuración de lactato, brecha aniónica corregida y brecha de iones fuertes a 48 horas no fueron capaces de predecir mortalidad, aunque sí los niveles individuales de dichos parámetros a las 48 horas. El mejor predictor de mortalidad fue AGCOR a 48, con un área bajo la curva ROC de 0.71805, contrario a la brecha de iones fuertes (SIG por sus siglas en inglés) a 48 horas, con un área bajo la curva ROC de 0.67367. Conclusiones: Los cambios a través de las primeras 48 horas de la brecha de iones fuertes son asociados a mortalidad, pero no aportan mayor beneficio que los parámetros tradicionales en sujetos con choque séptico.

Abstract: Introduction: There is clinical evidence that the strong ion gap obtained by Stewart's acid-base approach is a better predictor of mortality than those obtained by the traditional approach in some critically ill patients. Objective: To evaluate the strong ion gap clearance kinetics in patients with septic shock during the first 48 hours in the intensive care unit. Material and methods: A retrospective, observational study obtained from a patient database in a private intensive care unit in Monterrey, Nuevo León. Patient's demographics were analyzed, along with data collected from their laboratory work at admission and at 24 and 48 hours to calculate traditional acid-base parameters and parameters obtained by the Stewart's method. Clearance at 48 hours was also calculated to track their changes over time and to evaluate their relation to patient mortality. Results: Data from 91 patients with septic shock admitted between June 2014 and June 2016 were studied, with a 28.6% mortality rate. Lactate clearance, corrected anion gap clearance and strong ion gap clearance at 48 hours were not related to patient mortality, although their individual values at 48 hours were able to predict mortality. The best predictor of mortality was AGCOR at 48, with an area under the ROC curve of 0.71805, compared with an area under the ROC curve of 0.67367 for SIG at 48 hours. Conclusions: Strong ion gap changes over the first 48 hours were associated with mortality; however, they do not offer any advantage over traditional acid-base parameters in patients with septic shock.

Resumo: Introdução: Existe evidência clínica que o hiato de íons fortes, obtido pelo método de Stewart de ácido-base, é melhor preditor de mortalidade que os parâmetros tradicionais em alguns pacientes graves. Objetivo: Avaliar a cinética de depuração do hiato de íons fortes em pacientes com choque séptico durante as primeiras 48 horas de estadia na unidade de terapia intensiva. Material e métodos: Um estudo retrospectivo, observacional com dados obtidos a partir do prontuário médico. Realizado na UTI de um hospital particular na cidade de Monterrey, em Nuevo León. Foram avaliadas as variáveis ​​demográficas e os dados obtidos a partir da gasometria e química sanguínea na admissão, 24 horas e 48 horas posteriores para calcular os parâmetros tradicionais do equilíbrio ácido-base e os obtidos pelo método de Stewart. Calculou-se também as cinéticas de eliminação destes parâmetros e assim avaliar as alterações ao longo do tempo e a sua relação com a mortalidade. Resultados: Foram estudados 91 pacientes com choque séptico entre junho de 2014 e junho de 2016, com uma taxa de mortalidade de 28.6%. A depuração de lactato, hiato aniônico corrigido e hiato de íons fortes às 48 horas não foram capazes de prever a mortalidade, se bem que previram os níveis individuais de estes parâmetros às 48 horas. O melhor preditor de mortalidade foi AGCOR às 48 com uma área sob a curva ROC de 0.71805, contrário ao SIG às 48 horas com uma área sob a curva ROC de 0.67367. Conclusões: As alterações através das primeiras 48 horas do hiato de íons fortes está associada com a mortalidade, mas não fornecem maior benefício que os parâmetros tradicionais em pacientes com choque séptico.

Hyperchloremic acidosis is associated with acute kidney injury after abdominal surgery.

AIM: Hyperchloremic acidosis may have an important role as a precursor of acute kidney injury (AKI) in the hyperchloremic environment induced by chloride-rich fluids, but this remains unclear. We tested the hypothesis that hyperchloremic acidosis assessed by the Stewart approach is associated with postoperative AKI. METHODS: A historical cohort study was conducted in adult patients who had normal renal function preoperatively and required admission to the intensive care unit after elective abdominal surgery. The Risk, Injury, Failure, Loss of kidney function, End stage kidney disease (RIFLE) classification was used for definition of AKI. RESULTS: Of 206 patients (144 male, 69.9%) included in the study, 42 (20.4%) had postoperative AKI (AKI group) and 164 (79.6%) did not (non-AKI group). Base excess-chloride (BE-Cl) and strong ion difference (SID, approximated as Na-Cl) decreased, and the chloride level on postoperative day 1 increased compared with preoperative values in both groups (P < 0.05). In the AKI group, BE-Cl and SID were lower, and chloride was higher than in the non-AKI group (P < 0.05). The intraoperative load of chloride ions in fluids increased the risk of postoperative AKI (P < 0.01). In multivariate logistic regression analysis, postoperative BE-Cl < -7 mEq/L (i.e. SID <31 mEq/L) was an independent risk factor for AKI (odds ratio; 2.8, 95% CI; 1.2-6.4, P = 0.01). In the AKI group, stays in the intensive care unit and in hospital were longer than those in the non-AKI group (P < 0.05). CONCLUSION: Hyperchloremic acidosis is associated with postoperative AKI, and this may be attenuated by reducing the intraoperative chloride load.

Assessing Acid-Base Status: Physiologic Versus Physicochemical Approach.

The physiologic approach has long been used in assessing acid-base status. This approach considers acids as hydrogen ion donors and bases as hydrogen ion acceptors and the acid-base status of the organism as reflecting the interaction of net hydrogen ion balance with body buffers. In the physiologic approach, the carbonic acid/bicarbonate buffer pair is used for assessing acid-base status and blood pH is determined by carbonic acid (ie, Paco2) and serum bicarbonate levels. More recently, the physicochemical approach was introduced, which has gained popularity, particularly among intensivists and anesthesiologists. This approach posits that the acid-base status of body fluids is determined by changes in the dissociation of water that are driven by the interplay of 3 independent variables: the sum of strong (fully dissociated) cation concentrations minus the sum of strong anion concentrations (strong ion difference); the total concentration of weak acids; and Paco2. These 3 independent variables mechanistically determine both hydrogen ion concentration and bicarbonate concentration of body fluids, which are considered as dependent variables. Our experience indicates that the average practitioner is familiar with only one of these approaches and knows very little, if any, about the other approach. In the present Acid-Base and Electrolyte Teaching Case, we attempt to bridge this knowledge gap by contrasting the physiologic and physicochemical approaches to assessing acid-base status. We first outline the essential features, advantages, and limitations of each of the 2 approaches and then apply each approach to the same patient presentation. We conclude with our view about the optimal approach.

An acid-base disorders analysis with the use of the Stewart approach in patients with sepsis treated in an intensive care unit.

BACKGROUND: Patients with sepsis admitted to the intensive care unit often present with acid-base disorders. As the traditional interpretation might be clinically misleading, an alternative approach described by Stewart may allow one to quantify the individual components of acid-base abnormalities and provide an insight into their pathogenesis. The aim of our study was to compare the traditional and Stewart approaches in the analysis of acid-base disturbance. METHODS: We analyzed arterial blood gases (ABG) taken from 43 ICU septic patients from admission to discharge categorising them according to SBE values. The traditional concept analysis was compared with the physicochemical approach using the Stewart equations. RESULTS: 990 ABGs were analysed. In the SBE < -2 mEq L⁻¹ group, hyperlactatemia was observed in 34.7% ABG, hypoalbuminemia in 100% and SIG acidosis in 42% ABG. Moreover, a Cl/Na ratio > 0.75 was present in 96.9% ABG. In the normal range SBE group, elevated lactates were present in 21.3% ABG, SIG acidosis in 14.9%, elevated Cl/Na ratio in 98.4% and hypoalbuminemia in all 324 ABG. In the metabolic alkalosis group (SBE > +2 mEq L⁻¹), hyperlactatemia was observed in 18.4% ABG, SIG acidosis in 5% ABG, Cl/Na ratio> 0.75 in 88.8%, while 99.1% samples revealed hypoalbuminemia. CONCLUSION: The use of the Stewart model may improve our understanding of the underlying pathophysiological mechanism and the true etiology of the derangements of acid-base disorders. Indeed, it proves that patients may suffer from mixed arterial blood gas disorders hidden under normal values of SBE and pH.

Assessment of acid-base balance. Stewart's approach.

The study of acid-base equilibrium, its regulation and its interpretation have been a source of debate since the beginning of 20th century. Most accepted and commonly used analyses are based on pH, a notion first introduced by Sorensen in 1909, and on the Henderson-Hasselbalch equation (1916). Since then new concepts have been development in order to complete and make easier the understanding of acid-base disorders. In the early 1980's Peter Stewart brought the traditional interpretation of acid-base disturbances into question and proposed a new method. This innovative approach seems more suitable for studying acid-base abnormalities in critically ill patients. The aim of this paper is to update acid-base concepts, methods, limitations and applications.

Over ten thousand cases and counting: acidbase.org is serving the critical care community.

Acidbase.org has been serving the critical care community for over a decade. The backbone of this online resource consists of Peter Stewart's original text "How to understand Acid-Base" which is freely available to everyone. In addition, Stewart's Textbook of Acid Base, which puts the theory in today's clinical context is available for purchase from the website. However, many intensivists use acidbase.org on a daily basis for its educational content and in particular for its analysis module. This review provides an overview of the history of the website, a tutorial and descriptive statistics of over 10,000 queries submitted to the analysis module.