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  • Image not available.The strong ion difference, Pco2, and total weak acid concentration (ATOT) best explain acid–base balance in physiological systems.
  • Image not available.The bicarbonate buffer is effective against metabolic but not respiratory acid–base disturbances.
  • Image not available.In contrast to the bicarbonate buffer, hemoglobin is capable of buffering both carbonic (CO2) and noncarbonic (nonvolatile) acids.
  • Image not available.As a general rule, Paco2 can be expected to increase 0.25–1 mm Hg for each 1 mEq/L increase in [HCO3].
  • Image not available.The renal response to acidemia is 3-fold: (1) increased reabsorption of the filtered HCO3, (2) increased excretion of titratable acids, and (3) increased production of ammonia.
  • Image not available.During chronic respiratory acidosis, plasma [HCO3] increases approximately 4 mEq/L for each 10 mm Hg increase in Paco2 above 40 mm Hg.
  • Image not available.Diarrhea is the most common cause of hyperchloremic metabolic acidosis.
  • Image not available.The distinction between acute and chronic respiratory alkalosis is not always made, because the compensatory response to chronic respiratory alkalosis is quite variable: plasma [HCO3] decreases 2–5 mEq/L for each 10 mm Hg decrease in Paco2 below 40 mm Hg.
  • Image not available.Vomiting or continuous loss of gastric fluid by gastric drainage (nasogastric suctioning) can result in marked metabolic alkalosis, extracellular volume depletion, and hypokalemia.
  • Image not available.The combination of alkalemia and hypokalemia can precipitate severe atrial and ventricular arrhythmias.
  • Image not available.Changes in temperature affect measurements of Pco2 and Po2 directly and measurements of pH indirectly. Both Pco2 and Po2 therefore decrease during hypothermia, but pH increases because temperature does not appreciably alter [HCO3]: Paco2 decreases, but [HCO3] is unchanged.

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Nearly all biochemical reactions in the body are dependent on maintenance of a physiological hydrogen ion concentration. The latter is closely regulated because changes in hydrogen ion concentration produce widespread organ dysfunction.

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This regulation—often referred to as acid–base balance—is of prime importance to anesthesiologists. Changes in ventilation and perfusion and the infusion of electrolyte-containing solutions are common during anesthesia and can rapidly alter acid–base balance. A thorough understanding of acid–base disturbances, their physiological effects, and treatment is thus essential for proper anesthetic management.

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Image not available.Our understanding of acid–base balance is evolving. In the past, we focused on the concentration of hydrogen ions [H+], CO2 balance, and the base excess/deficit. We now understand that the strong ion difference (SID), Pco2, and total weak acid concentration (ATOT) best explain acid–base balance in physiological systems.

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This chapter examines acid–base physiology, common disturbances, and their anesthetic implications. Clinical measurements of blood gases and their interpretation are also discussed.

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Acid–Base Chemistry

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Hydrogen Ion Concentration & pH

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In any aqueous solution, water molecules reversibly dissociate into hydrogen and hydroxide ions:

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Image not available.

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This process is described by ...

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