Acid base balance3 Dr khuram Shahzad khan Metabolic

Acid base balance(3) Dr. khuram Shahzad khan

Metabolic acidosis is the gain of acid or the loss of bicarbonate. Cause Usual causes are the generation of ketone bodies in uncontrolled diabetes mellitus, diarrhea (loss of bicarbonate), excess protein consumption (breakdown products are amino ACIDS), or excess alcohol consumption: (alcohol formaldehyde acetic acid). Can also be caused by ingestion of an acid (aspirin, ethanol, or antifreeze). Exercise creates a milder, transient metabolic acidosis because of the production of lactic acid. 2

Metabolic acidosis Symptoms Most symptoms are caused by the underlying disease or condition that is causing the metabolic acidosis. Metabolic acidosis itself usually causes rapid breathing. Confusion or lethargy may also occur. Severe metabolic acidosis can lead to shock or death. In some situations, metabolic acidosis can be a mild, chronic (ongoing) condition. 3

Metabolic acidosis Treatment is give i. v. of sodium bicarbonate. The HCO 3 - deficit can be calculated by using the following equation: HCO 3 - deficit = deficit/L (desired serum HCO 3 - - measured HCO 3 -) x 0. 5 x body weight (volume of distribution for HCO 3 -) This provides a crude estimate of the amount of HCO 3 - that must be administered to correct the metabolic acidosis; the serum HCO 3 - level or p. H should be reassessed frequently. 4

Alkalosis is excessive blood alkalinity caused by an overabundance of bicarbonate in the blood or a loss of acid from the blood (metabolic alkalosis), or by a low level of carbon dioxide in the blood that results from rapid or deep breathing (respiratory alkalosis). 5

Alkalosis People may have irritability, muscle twitching, or muscle cramps, or even muscle spasms. Blood is tested to diagnose alkalosis. Metabolic alkalosis is treated by replacing water and electrolytes. Respiratory alkalosis is treated by slowing breathing. 6

Respiratory alkalosis is generally caused by hyperventilation, usually due to anxiety. The primary abnormality is a decreased p. CO 2. Caused from a decrease in CO 2 in the blood because the lungs are hyperventilating (anxiety). Fever or aspirin toxicity may also cause respiratory alkalosis. 7

Respiratory alkalosis Compensation The compensatory response to a respiratory alkalosis is initially a release of hydrogen from extracellular and intracellular buffers. This is followed by reduced hydrogen excretion by the kidneys. This results in decreased plasma bicarbonates. In chronic respiratory alkalosis, compensation can lead to p. H returning to normal. 8

Respiratory alkalosis Symptoms Irritability Muscle twitching Muscle cramps 9

Respiratory alkalosis Treatment for hyperventilation is to breathe into a paper bag for a while, as the person breathes carbon dioxide back in after breathing it out. For severe cases, need to replace the water and electrolytes (sodium and potassium). 10

Metabolic alkalosis is due to the gain of base or the loss of acid. The primary abnormality is an increased HCO 3. Caused from an increase in bicarbonate in the blood because of ingestion of excess bicarbonate in the form of an antacid, eating excess fruits (vegetarian diets and fad diets*), loss of acid from vomiting, or loss of potassium from diuretics. 11

*Fruits are the normal source of alkali in the diet. They contain the potassium salts of weak organic acids. When the anions are metabolized to CO 2 and removed from the body, alkaline potassium bicarbonate and sodium bicarbonate remain. Metabolic alkalosis may be found in vegetarians and fad dieters who are ingesting a low-protein, high fruit diet. 12

Metabolic alkalosis Compensation This is initially buffered by hydrogen buffers (such as plasma proteins and lactate). Chemoreceptors in the respiratory center sense the alkalosis and trigger hypoventilation, resulting in increased p. CO 2. The respiratory system will hypoventilate but this will not be effective because CO 2 will accumulate and the CO 2 receptors will override the p. H receptors. 13

Metabolic alkalosis Compensation Naturally, the extent of respiratory compensation will be limited by the development of hypoxia with continued hypoventilation. The kidney will make more of a difference by not reabsorbing bicarbonate. In addition to respiratory compensation, the kidneys excrete the excess bicarbonate. However, this takes several days to occur. 14

Metabolic alkalosis Symptoms Confusion (can progress to stupor or coma) Hand tremor Light-headedness Muscle twitching Nausea, vomiting Numbness or tingling in the face, hands, or feet Prolonged muscle spasms (tetany) 15

Metabolic alkalosis Treatment is to give an anti-emetic if the problem is from vomiting. If not, give an i. v. of normal saline to increase the blood volume. If potassium is also low, would have to add that to the i. v. 16

Compensation If the kidneys are the problem, the respiratory system can compensate. If the kidneys are secreting too much H+(which makes too much bicarbonate, causing metabolic alkalosis), breathing will become slower so that less CO 2 (an acid) is lost. If the kidneys are reabsorbing too much H+(metabolic acidosis), breathing will become faster. 17

Compensation If the respiratory system is the problem, the kidneys can compensate. If breathing is too rapid (too much CO 2, an acid, is lost, leaving the blood in respiratory alkalosis), Kidneys respond by reabsorbing more H+. If breathing is too shallow (not enough CO 2 is lost, leaving the blood in respiratory acidosis), Kidneys respond by secreting more H+. 18

How the kidneys secrete H+ The intercalated cells secrete H+ if the blood is too acidic. If the blood is too alkaline, the intercalated cells stop secreting H+ 19

How the kidneys make new bicarbonate If there is bicarbonate (HCO 3) in the filtrate, the secreted H+ will combine with it to form carbonic acid (H 2 CO 3). This is taken into the tubular cells. If the blood is too acidic, the carbonic acid will dissociate into bicarbonate, which is sent to the plasma, and the H+ will be excreted. This will raise the blood p. H. If the blood is too alkaline, the H+ will enter the plasma instead, and the bicarbonate will be excreted. 20

How the kidneys reabsorb bicarbonate CO 2 and water in the filtrate enter the tubular cells by diffusion and are transformed into carbonic acid and then into bicarbonate plus H+. Bicarbonate can then be transported into the plasma to raise p. H, or H+ is transported into the plasma to lower p. H. The other product is then excreted. The kidneys also make bicarbonate at the collecting duct. This reaction is also driven by the diffusion of CO 2 into the cell. 21

Definitions Normal p. H is 7. 35 - 7. 45 If this value is normal, but one of the below values is abnormal, the patient has compensated. Normal C 02 is 35 -45 mm. Hg If this value is abnormal, the patient has respiratory acidosis or alkalosis. Normal HC 03 is 22 -26 m. Eq/L If this value is abnormal, the patient has metabolic acidosis or alkalosis Normal O 2 Saturation is 80 -100 ml/dl If this value is normal in a respiratory p. H problem, 22 patient is compensating.