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IM - ACID BASE DISORDERS

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tonystep1's version from 2017-08-02 06:42

CAUSES OF ACID BASE DISORDERS

Question Answer
Increased Anion Gap acidosisKetoacidosis // Lactic acidosis // Renal Failure // Intoxication (Salicylate (aspirin) • Methanol • Ethylene glycol)
Normal AG acidosis (hyperchloremic metabolic acidosis)Renal loss of bicarbonate // GI loss of HC03 -
Saline-sensitive metabolic alkalosis (urine chloride < 10 mEq!L)Vomiting or nasogastric suction // Diuretics // Villous adenoma of colon, diarrhea with high chloride content
Saline-resistant metabolic alkalosis (urine chloride > 20 mEq!L)Most are secondary to adrenal disorders (primary hyperaldosteronism) . // Cushing's syndrome, severe K+ deficiency, Barrter's syndrome, and diuretic abuse.
Respiratory AcidosisCauses-alveolar hypoventilation l. Primary pulmonary diseases-e.g., COPD, airway obstruction 2. Neuromuscular diseases-e.g., myasthenia gravis 3. CNS malfunction-injury to brainstem 4. Drug-induced hypoventilation (e.g., from morphine, anesthetics, or sedatives)Narcotic overdose in postoperative patients is a possibility (look for pinpoint pupils) . 5. Respiratory muscle fatigue
Respiratory AlkalosisB. Causes-alveolar hyperventilation l. Anxiety 2. Pulmonary embolism, pneumonia, asthma 3. Sepsis 4. Hypoxia-leads to increased respiratory rate 5. Mechanical ventilation 6. Pregnancy-Increased serum progesterone levels cause hyperventilation. 7. Liver disease (cirrhosis) 8. Medication (salicylate toxicity) 9. Hyperventilation syndrome
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CLINICAL FEATURES OF ACID BASE DISORDERS

Question Answer
Metabolic AcidosisHyperventilation (deep rhythmic breathing) , also known as Kussmaul's respiration // Decreased cardiac output and decreased tissue perfusion
Metabolic AlkalosisThere are no characteristic signs or symptoms. 2. The patient's medical history is most helpful (look for vomiting, gastric drainage, diuretic therapy, and so on) .
Respiratory Acidosisl. Somnolence, confusion, and myoclonus with asterixis // Headaches, confusion, and papilledema are signs of acute C02 retention
Respiratory Alkalosisl. Symptoms are mostly related to decreased cerebral blood flow (vasoconstriction) lightheadedness, dizziness, anxiety, paresthesias, and perioral numbness. 2. Tetany (indistinguishable from hypocalcemia) 3. Arrhythmias (in severe cases)
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DIAGNOSIS OF ACID BASE DISORDERS

Question Answer
Suspected Metabolic AcidosisHistory is important. 2. Calculate the AG. 3. Winter's formula: expected Paco2 = 1.5 (measured HC03 -) + 8 ± 2.
Simple Metabolic AcidosisWinter's formula: expected Paco2 = 1.5 (measured HC03 -) + 8 ± 2.///If the Paco2 falls within the predicted range, then the patient has a simple metabolic acidosis with an appropriate secondary hypocapnia.
Metabolic acidosis with Respiratory acidosisWinter's formula: expected Paco2 = 1.5 (measured HC03 -) + 8 ± 2. /// If the actual Paco2 is higher than the calculated Paco2, then the patient has metabolic acidosis with respiratory acidosis. This is a serious finding because this failure of compensation can be a sign of impending respiratory failure.
Metabolic acidosis with Respiratory alkalosisWinter's formula: expected Paco2 = 1.5 (measured HC03 -) + 8 ± 2. /// If the actual Paco2 is lower than the calculated Paco2, then the patient has metabolic acidosis with respiratory alkalosis.
Metabolic Alkalosisl . Elevated HC03 - level, elevated blood pH 2. Hypokalemia is common (due to renal loss of K+ ) . 3 . Paco2 i s elevated a s a compensatory mechanism (due to hypoventilation) . It is rare for a compensatory increase in Paco2 to exceed 50 to 55 mm Hg (the respiratory rate to achieve this is so low that Pao2 would b e decreased) . A higher value implies a superimposed respiratory acidosis.
Acute respiratory acidosisDefined as a reduced blood pH and Paco2 >40 mm Hg /// There is an increase of l mmol/L of HC03- for every 10 mm H g increase in Paco2
Chronic respiratory acidosisDefined as a reduced blood pH and Paco2 >40 mm Hg /// HC03- increases by 4 mmol/L for every l0 mm Hg increase in Pacor
Acute Respiratory AlkalosisCharacterized by an increased blood pH and decreased Paco2 /// for each l0 mm Hg decrease in Paco2, plasma HC03 - decreases by 2 mEq/L and blood pH increases by 0.08 mEq/L.
Chronic Respiratory Alkalosisfor each l0 mm Hg decrease in Paco2, plasma HC03- decreases by 5 to 6 mEq/L and blood pH decreases by 0.02 mEq/L.
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TREATMENT OF ACID BASE DISORDERS

Question Answer
Metabolic Non AG Acidosisl. Treatment varies depending on the cause. 2. Sodium bicarbonate is sometimes needed (especially for normal AG acidosis) . In correcting metabolic acidosis (correct severe acidosis to a pH of 7.20)
Metabolic Acidosis i f the patient is fatigued from prolonged hyperventilation, especially in DKA.Mechanical ventilation may be required
Saline-sensitive metabolic alkalosis (urine chloride < 10 mEq!LNormal saline plus potassium will restore the ECF volume if the patient is volume contracted.
Saline-resistant metabolic alkalosis (urine chloride > 20 mEq!L)Address the underlying cause (or prescribe spironolactone) if the patient is volume expanded.
Respiratory AcidosisTreatment l. Verify patency of the airway. 2. If Pao2 is low ( <60 mm Hg) , initiate supplemental oxygen 3 . Correct reversible causes. 4. Any measure to improve alveolar ventilation 5. Intubation and mechanical ventilation may be necessary to relieve the acidemia and hypoxia that result from hypoventilation.
Respiratory AlkalosisTreatment l. Correct the underlying cause. 2. Sometimes this does not need to be treated (e.g. , in the case of pregnancy) . 3. An inhaled mixture containing C02 or breathing into a paper bag may be useful.
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