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The handbook of the ICU (Fourth edition): Part 2

(BQ) Continued part 1, part 2 of the document The handbook of the ICU (Fourth edition) has contents: Acid-Base disorders, renal and electrolyte disorders, renal and electrolyte disorders, disorders of body temperature, nervous system disorders, critical care drug therapy, toxicologic emergencies, and other contents. Invite you to refer. | Section IX ACID-BASE DISORDERS Life is a struggle not against sin not against money power. but against hydrogen ions. H.L. Mencken Chapter 31 ACID-BASE ANALYSIS Seek simplicity and distrust it. Alfred North Whitehead Managing ICU patients without a working knowledge of acid-base disorders is like trying to clap your hands when you have none i.e. it simply can t be done. This chapter presents a structured approach to the identification of acid-base disorders based on the traditional relationships between the pH PCO2 and bicarbonate HCO3 concentration in plasma. Also included is a section on the evaluation of metabolic acidosis using the anion gap and a measurement known as the gap-gap. Alternative approaches to acid-base analysis such as the Stewart method are not included here because it is unlikely at the present time that these methods will replace the traditional approach to acid-base analysis. BASIC CONCEPTS Hydrogen Ion Concentration and pH The hydrogen ion concentration H in aqueous solutions is traditionally expressed by the pH which apparently means the power of hydrogen and is a logarithmic function of the H i.e. .i.--l ll i 31.1 The physiological range of pH and corresponding H is shown in Table 31.1. The normal pH of plasma is indicated as 7.40 which corresponds to a H of 40 nEq L. Features of the pH The relationships in Table 31.1 illustrate 3 unfortunate features of the pH a it is a dimensionless number which has no relevance in chemical or physiological events b it varies in the opposite direction to changes in H and c changes in pH are not linearly related to changes in H . Note that as the pH decreases the changes in H become gradually larger with each change in pH. This means that changes in pH will have different implications for acid-base balance at different points along the pH spectrum. Although it is unlikely that the pH will be abandoned it is not a representative measure of the acid-base events in the body. Table 31.1 pH and Hydrogen Ion .