Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content +++ INTRODUCTION ++ Acid–base disorders are caused by disturbances in hydrogen ion (H+) homeostasis, which is ordinarily maintained by extracellular buffering, renal regulation of hydrogen ion and bicarbonate excretion, and ventilatory regulation of carbon dioxide (CO2) elimination. +++ GENERAL PRINCIPLES ++ Buffering refers to the ability of a solution to resist change in pH after the addition of a strong acid or base. The body’s principal extracellular buffer system is the carbonic acid/bicarbonate (H2CO3/HCO3−) system. Most of the body’s acid production is in the form of CO2 and is produced from catabolism of carbohydrates, proteins, and lipids. There are four primary types of acid–base disturbances, which can occur independently or together as a compensatory response. Metabolic acid–base disorders are caused by changes in plasma bicarbonate concentration (HCO3−). Metabolic acidosis is characterized by decreased HCO3−, and metabolic alkalosis is characterized by increased HCO3−. Respiratory acid–base disorders are caused by altered alveolar ventilation, producing changes in arterial carbon dioxide tension (Paco2). Respiratory acidosis is characterized by increased Paco2, whereas respiratory alkalosis is characterized by decreased Paco2. +++ DIAGNOSIS ++ Blood gases (Table 72–1), serum electrolytes, medical history, and clinical condition are the primary tools for determining the cause of acid–base disorders and for designing therapy. Arterial blood gases (ABGs) are measured to determine oxygenation and acid–base status (Fig. 72–1). Low pH values (<7.35) indicate acidemia, whereas high values (>7.45) indicate alkalemia. The Paco2 value helps determine whether there is a primary respiratory abnormality, whereas the HCO3− concentration helps determine whether there is a primary metabolic abnormality. Steps in acid–base diagnosis and interpretation are described in Tables 72–2 and 72–3. ++Table Graphic Jump LocationTABLE 72–1Normal Blood Gas ValuesView Table||Download (.pdf) TABLE 72–1 Normal Blood Gas Values Arterial Blood Mixed Venous Blood pH 7.40 (7.35–7.45) 7.38 (7.33–7.43) Po2 80–100 mm Hg (10.6–13.3 kPa) 35–40 mm Hg (4.7–5.3 kPa) Sao2 95% (0.95) 70–75% (0.70–0.75) Pco2 35–45 mm Hg (4.7–6.0 kPa) 45–51 mm Hg (6.0–6.8 kPa) HCO3– 22–26 mEq/L (22–26 mmol/L) 24–28 mEq/L (24–28 mmol/L) (HCO3–, bicarbonate; Pco2, partial pressure of carbon dioxide; Po2, partial pressure of oxygen; Sao2, saturation of arterial oxygen.) ++ FIGURE 72–1. Analysis of arterial blood gases (ABGs). (HCO3−, bicarbonate; Pco2, partial pressure of carbon dioxide.) Graphic Jump LocationView Full Size||Download Slide (.ppt) ++Table Graphic Jump LocationTABLE 72–2Steps in Acid–Base DiagnosisView Table||Download (.pdf) TABLE 72–2 Steps in Acid–Base Diagnosis Obtain ABGs and electrolytes simultaneously Compare [HCO3–... Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth