Acid-Base Balance Flashcards
What three mechanisms are used to defend against changes in body fluid pH?
Extra- and intracellular buffering
Adjustments in PCO2 by alterations in ventilatory rate
Adjustments in renal acid excretion
What is the most important extracellular buffer?
Bicarbonate buffering system, response is virtually instantaneous
*Other extracellular buffers are protein and Phosphate
What is intracellular buffering?
Involves H into and out of the cells
Inside the cells it is titrated by Phosphate and proteins
How is the respiratory mechanisms mediated?
Chemoreceptors sensing PCO2
What three things happen in the renal defense of acidosis?
Increase H secretion
Entire filtered load of bicarb is reabsorbed
Increased production and excretion of ammonia
What happens in the renal defense of alkalosis?
Decreased secretion of H
Decreased bicarb reabsorption
What is the primary alteration in metabolic acidosis/alkalosis?
Change in ECF bicarb concentration
Describe metabolic acidosis
Low plasma bicarb and low pH
Can develop by: addition of nonvolatile acid, Loss of nonvolatile alkali, failure of kidneys to excrete sufficient net acid
What is the anion gap?
Represents anions in the plasma that are not measured
Used to help in the differential diagnosis of metabolic acidosis
Normal is 16 (or 12 if K is not used in calculation)
What does metabolic acidosis with high anion gap indicate?
Decreased bicarbonate is replaced by unmeasured anions
DKA, salicylate poisoning, Lactic acidosis
What does metabolic acidosis with a normal anion gap indicate?
Decreased bicarb is replaced by Cl
Diarrhea, drainage of pancreatic juice
Describe metabolic alkalosis
Increased plasma bicarb and pH
Can develop by addition of noonvolatile alkali (antacid ingestion), loss of nonvolatile acid
What are the compensation mechanisms for metabolic alkalosis?
Hypoventilation, increased renal excretion of bicarbonate
Describe respiratory acidosis
Elevated PCO2 and reduced plasma pH
Can develop by, inadequate ventilation, impaired gas diffusion
Buffering occurs in the intracellular compartment only
What is the renal compensation for resp. acidosis?
Increase bicarb reabsorption and ammonium excretion
Takes several days, acute and chronic phases
Describe respiratory alkalosis
Reduced PCO2 and elevated plasma pH
Can develop by stimulation of the respiratory centers
Buffering is intracellular
What is the renal compensation for resp. alkalosis?
Inhibition of bicarb reabsorption and reduced ammonium excretion
What is a combined complex acid-base disorder?
Normal compensation for a primary acid/base disorder
What is a combined simple disorder?
Describes a second acid/base disturbance compounding the first acid-base disturbance
E.g. respiratory failure followed by renal failure both resulting in acidosis (IRDS)
or a hyperventilating patient begins severe vomiting
What is renal tubular acidosis?
Group of diverse conditions that cause non anion gap metabolic acidosis in the presence of normal GFR
Classified as type 1, 2, and 4
What is type 1 RTA?
Distal RTA
Characteristics: impaired H secretion by the distal segments, urine pH>5.3
Renal defect: Decreased H-K ATPase, Increased tubule permeability, allowing H backflow
Etiology: Sjogren syndrome, Rheumatoid arthritis drugs
What is type 2 RTA?
Proximal RTA
Characteristics: Impaired proximal Bicarb reabsorption, low plasma bicarb
Renal defect: Nonspecific tubule dysfunction or mutation in genes involved in bicarb reabsorption
Etiology: Fanconi syndrome, CA inhibitors
What is type 4 RTA?
Hypoaldosteronism
Characteristics: impaired aldosterone release or response, urine pH < 5.3, hyperkalemia
Renal defect: Impaired Na reabsorption via epithelial Na channel
Etiology: Congenital hypoaldosteronism (addison disease), aldosterone resistance, diabetic nephropathy
