An alternative approach to acid-base abnormalities in critically ill patients (original) (raw)
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Critical care (London, England), 2005
Acid-base abnormalities are common in critically ill patients. Our ability to describe acid-base disorders must be precise. Small differences in corrections for anion gap, different types of analytical processes, and the basic approach used to diagnose acid-base aberrations can lead to markedly different interpretations and treatment strategies for the same disorder. By applying a quantitive acid-base approach, clinicians are able to account for small changes in ion distribution that may have gone unrecognized with traditional techniques of acid-base analysis. Outcome prediction based on the quantitative approach remains controversial. This is in part due to use of various technologies to measure acid-base variables, administration of fluid or medication that can alter acid-base results, and lack of standardized nomenclature. Without controlling for these factors it is difficult to appreciate the full effect that acid-base disorders have on patient outcomes, ultimately making result...
ENCYCLOPEDIA OF RESPIRATORY MEDICINE. Acid-base balance (feb 2005) Acid-Base Balance
The acid-base balance or neutrality regulation maintains a pH around 7.4 in the extracellular fluid by excreting carbon dioxide in the lungs and non-carbonic acid or base in the kidneys. The result is a normal acid-base status in blood and extracellular fluid, i.e. a normal pH, a normal carbon dioxide tension (pCO 2), and a normal concentration of titratable hydrogen ion (ctH +). A pH, log pCO 2 chart illustrates the acid-base status of the arterial blood. The chart shows normal values as well as values to be expected in typical acid-base disturbances, i.e. acute and chronic respiratory acidosis and alkalosis, and acute and chronic non-respiratory (metabolic) acidosis and alkalosis. The chart allows estimation of the concentration of titratable H + of the extended extracellular fluid (including erythrocytes), ctH + Ecf. This quantity is also called standard base deficit but the term base does not directly indicate that the quantity refers to the excess or deficit of hydrogen ions. ctH + Ecf is the preferred indicator of a non-respiratory acid-base disturbance being independent of acute changes in pCO 2 in vivo. While pH and pCO 2 are directly measured, ctH + Ecf is calculated from pH and pCO 2 using the Henderson-Hasselbalch equation and the Van Slyke equation. Description The acid-base balance or neutrality regulation maintains a pH around 7.4 in the extracellular fluid by excreting carbon dioxide in the lungs and non-carbonic acid or base in the kidneys. The result is a normal acid-base status in blood and extracellular fluid, i.e. a normal pH, a normal carbon dioxide tension (pCO 2), and a normal concentration of titratable hydrogen ion (ctH +). A graphical illustration is an aid in the description of the acid-base status of the blood (Fig. 1). pH and the Hydrogen Ion Concentration (cH +) pH and cH + of the plasma are both indicated on the abscissa of the chart (Fig. 1). cH + is calculated as 10 9-pH nmol/L. pH and pOH are closely related: pH + pOH = pK w = 13.622 at 37 °C, where K w is the ionization constant of water. If H + is considered a key component of an aqueous solution, then OH¯ is a derived component. Accounting for H + and H 2 O, indirectly accounts for OH¯ as well. It is the authors conviction that the relevant component is the hydrogen ion, not hydrogen ion binding groups (base) nor hydroxyl ions. Carbon Dioxide Tension of the Blood (pCO 2) pCO 2 , i.e. the partial pressure of carbon dioxide in a gas phase in equilibrium with the blood, is shown on the ordinate on a logarithmic scale. When pCO 2 increases, the concentration of dissolved carbon dioxide and carbonic acid increases, and hence the hydrogen ion concentration increases: CO 2 + H 2 O → H 2 CO 3 → H + + HCO 3 ⎯ .. Concentration of Titratable Hydrogen Ion (ctH +) ctH + is indicated on the scale in the upper left corner of the chart. The amount of hydrogen ion added or removed in relation to a reference pH of 7.40 may be determined by titration to pH = 7.40 at pCO 2 = 5.33 kPa (= 40 mmHg) at 37 °C using strong acid or base, depending upon the initial pH. Titratable hydrogen ion or hydrogen ion excess, is also called base deficit, or with opposite sign base excess. Unfortunately, the term base is ambiguous (has been associated with cations) and does not directly indicate that the relevant chemical component is the hydrogen ion. If a nick name is needed it may be hydrogen ion excess; acronym: HX. Note: by definition ctH + of blood refers to the actual hemoglobin oxygen saturation, not the fully oxygenated blood. Acid and base are defined by the equilibrium: Acid z H + + Base z-1 , where Acid z and Base z-1 is a conjugate acid-base pair. The charge number z may be positive, zero, or negative. A strong acid, e.g. HCl, dissociates completely: HCl → H + + Cl⎯. A strong base, e.g. OH⎯, associates completely with hydrogen ion: OH⎯ + H + → H 2 O. A weak acid (buffer acid) is in
Physiology of Acid Base Balance
Journal of Evidence Based Medicine and Healthcare, 2014
Acid-base, electrolyte, and metabolic disturbances are common in the intensive care unit. Almost all critically ill patients often suffer from compound acid-base and electrolyte disorders. Successful evaluation and management of such patients requires recognition of common patterns (e.g., metabolic acidosis) and the ability to dissect one disorder from another. The intensivists needs to identify and correct these condition with the easiest available tools as they are the associated with multiorgan failure. Understanding the elements of normal physiology in these areas is very important so as to diagnose the pathological condition and take adequate measures as early as possible. Arterial blood gas analysis is one such tool for early detection of acid base disorder. Physiology of acid base is complex and here is the attempt to simplify it in our day to day application for the benefit of critically ill patients.
2013
Copyright © 2013 Atef Redwan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objective: The traditional approach for acid base interpretation is based on Handerson-Hasselbalch formula and in-cludes Base Excess (BE), bicarbonate (HCO3), albumin corrected anion gap. The Physicochemical approach is centered on the Carbon Dioxide tension (PCO2), the strong ion difference (SID), strong ion gap (SIG) = SID apparent-SID effec-tive and totally weak acids (Atot). The study aims to compare between the traditional approach and the physicochemical approach in acid base disorder interpretation. Design: Prospective observational study in an adult Intensive Care Unit (ICU) recruiting six hundred and sixty one patients. Methods: Arterial blood samples were analyzed to measure pH, PaCO2 sodium, potassium, chloride and lactate. V...
Open Journal of Respiratory Diseases, 2013
The traditional approach for acid base interpretation is based on Handerson-Hasselbalch formula and includes Base Excess (BE), bicarbonate (HCO 3 ), albumin corrected anion gap. The Physicochemical approach is centered on the Carbon Dioxide tension (PCO 2 ), the strong ion difference (SID), strong ion gap (SIG) = SID apparent-SID effective and totally weak acids (Atot). The study aims to compare between the traditional approach and the physicochemical approach in acid base disorder interpretation. Design: Prospective observational study in an adult Intensive Care Unit (ICU) recruiting six hundred and sixty one patients. Methods: Arterial blood samples were analyzed to measure pH, PaCO 2 sodium, potassium, chloride and lactate. Venous blood samples were analyzed to measure ionized calcium, magnesium, phosphorous and albumin. These samples were interpreted by both techniques. Results: Normal HCO 3 and BE were detected by traditional approach in 49 cases of which SIG acidosis was detected in 22 cases (46%) and Hyperchloremic acidosis was detected in 29 cases (60%) by physicochemical method. SIG was elevated in 72 cases (58%) of 124 cases with high anion gap acidosis. SIDeff and BE were strongly correlated, r = 0.8, p < 0.0001, while SIG and Albumin corrected Anion Gap (ALAG) were moderately correlated r = 0.56, p < 0.0001. Conclusion: Both approaches are important for interpretation of the acid base status. Traditional approach identifies the diagnostic description without many calculations and detects body compensatory response to acid base disorders. Physicochemical approach is essential to identify the exact causation and the severity of the acid base disorders.
Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas / Sociedade Brasileira de Biofisica ... [et al.]
The aims of this study were to determine whether standard base excess (SBE) is a useful diagnostic tool for metabolic acidosis, whether metabolic acidosis is clinically relevant in daily evaluation of critically ill patients, and to identify the most robust acid-base determinants of SBE. Thirty-one critically ill patients were enrolled. Arterial blood samples were drawn at admission and 24 h later. SBE, as calculated by Van Slyke's (SBE VS) or Wooten's (SBE W) equations, accurately diagnosed metabolic acidosis (AUC = 0.867, 95%CI = 0.690-1.043 and AUC = 0.817, 95%CI = 0.634-0.999, respectively). SBE VS was weakly correlated with total SOFA (r = -0.454, P < 0.001) and was similar to SBE W (r = -0.482, P < 0.001). All acid-base variables were categorized as SBE VS <-2 mEq/L or SBE VS <-5 mEq/L. SBE VS <-2 mEq/L was better able to identify strong ion gap acidosis than SBE VS <-5 mEq/L; there were no significant differences regarding other variables. To demonst...
Clinical review: Acid-base abnormalities in the intensive care unit -- part II
Critical care (London, England), 2005
Acid-base abnormalities are common in the critically ill. The traditional classification of acid-base abnormalities and a modern physico-chemical method of categorizing them will be explored. Specific disorders relating to mortality prediction in the intensive care unit are examined in detail. Lactic acidosis, base excess, and a strong ion gap are highlighted as markers for increased risk of death.