tailieunhanh - Chapter 048. Acidosis and Alkalosis (Part 3)

Figure 48-1 Acid-base nomogram. Shown are the 90% confidence limits (range of values) of the normal respiratory and metabolic compensations for primary acidbase disturbances. (From DuBose, used with permission.) Mixed Acid-Base Disorders Mixed acid-base disorders—defined as independently coexisting disorders, not merely compensatory responses—are often seen in patients in critical care units and can lead to dangerous extremes of pH (Table 48-2). A patient with diabetic ketoacidosis (metabolic acidosis) may develop an independent respiratory problem leading to respiratory acidosis or alkalosis. Patients with underlying pulmonary disease may not respond to metabolic acidosis with an appropriate ventilatory response because of insufficient respiratory reserve | Chapter 048. Acidosis and Alkalosis Part 3 Figure 48-1 Arterial triood H- nmoLlj Acid-base nomogram. Shown are the 90 confidence limits range of values of the normal respiratory and metabolic compensations for primary acid base disturbances. From DuBose used with permission. Mixed Acid-Base Disorders Mixed acid-base disorders defined as independently coexisting disorders not merely compensatory responses are often seen in patients in critical care units and can lead to dangerous extremes of pH Table 48-2 . A patient with diabetic ketoacidosis metabolic acidosis may develop an independent respiratory problem leading to respiratory acidosis or alkalosis. Patients with underlying pulmonary disease may not respond to metabolic acidosis with an appropriate ventilatory response because of insufficient respiratory reserve. Such imposition of respiratory acidosis on metabolic acidosis can lead to severe acidemia and a poor outcome. When metabolic acidosis and metabolic alkalosis coexist in the same patient the pH may be normal or near normal. When the pH is normal an elevated anion gap AG see below denotes the presence of a metabolic acidosis. A discrepancy in the AAG prevailing minus normal AG and the AHCO3 normal minus prevailing HCO3- indicates the presence of a mixed high-gap acidosis metabolic alkalosis see example below . A diabetic patient with ketoacidosis may have renal dysfunction resulting in simultaneous metabolic acidosis. Patients who have ingested an overdose of drug combinations such as sedatives and salicylates may have mixed disturbances as a result of the acid-base response to the individual drugs metabolic acidosis mixed with respiratory acidosis or respiratory alkalosis respectively . Even more complex are triple acid-base disturbances. For example patients with metabolic acidosis due to alcoholic ketoacidosis may develop metabolic alkalosis due to vomiting and superimposed respiratory alkalosis due to the hyperventilation of hepatic dysfunction or .