Na reabsorption bicarbonate reabsorption in proximal

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↑ Na+ reabsorption ↑ bicarbonate reabsorption in proximal tubule ↑ H+ secretion in distal tubule Caused by excessive H+ loss, diuretic use, or administration of bicarbonate-rich fluids Urinary chloride < 10mEq/L
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Maintenance of Metabolic Alkalosis Volume-independent (NaCl-resistant) H+ excretion stimulated by Excess mineralocorticoids Hypokalemia Urinary chloride > 20mEq/L
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Metabolic Alkalosis Signs and Symptoms Hypoventilation Difficult weaning from mechanical ventilation Cardiac arrhythmias Neuromuscular Tetany Hyperactive reflexes Muscle cramping Paresthesias Confusion
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Metabolic Alkalosis Respiratory Compensation Mechanism: Hypoventilation  Decreased CO2 excretion Occurs immediately
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CW has the following ABG: pH 7.5, PaCO2 = 29, HCO3- = 21 What is her acid-base disturbance? 1. Metabolic alkalosis, compensated 2. Metabolic alkalosis, not compensated 3. Respiratory alkalosis, compensated 4. Respiratory alkalosis, not compensated
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Compensation of Respiratory Alkalosis Degree of compensation depends on acuity of disorder Acute respiratory alkalosis HCO3- should decrease by 0.2 times the decrease in PaCO2 in mmHg (but usually not to < 18 mEq/L) Chronic respiratory alkalosis HCO3- should decrease by 0.35 times the decrease in PaCO2 in mmHg (but usually not to < 14 mEq/L)
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Compensation of Respiratory Alkalosis Acute respiratory alkalosis HCO3- should decrease by 0.2 times the decrease in PaCO2 in mmHg PaCO2 = 40 mmHg – 29 mmHg = 11 mmHg 11 mmHg x 0.2 = 2.2 HCO3- = 24 mEq/L – 2.2 = 21.8 mEq/L Actual HCO3- = 21 Appropriate compensation
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Respiratory Alkalosis Is pH high or low? Is the primary disturbance with HCO3- or PaCO2? Is the most common acid-base disturbance
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Causes of Respiratory Alkalosis Central stimulation of respiration Anxiety, pain Fever Head trauma, brain tumor Pregnancy Certain medications Mechanical ventilation Hypoxemia High altitude Shock Pneumonia Anemia Hyperventilation  increased CO2 excretion
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Respiratory Alkalosis Chronic respiratory alkalosis Tends to be mild Asymptomatic Patients with acute or severe respiratory alkalosis can experience: Light-headedness, confusion Muscle cramps, tetany Syncope (fainting), seizures Cardiac arrhythmias
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Respiratory Alkalosis Metabolic Compensation Mechanism: Initially, chemical buffering occurs H+ are released from buffers Occurs over minutes If the respiratory alkalosis lasts for > 12 hours, metabolic compensation begins Renal bicarbonate reabsorption is inhibited Occurs over 1-2 days
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Respiratory Alkalosis Chronic respiratory alkalosis Metabolic compensation has occurred Acute respiratory alkalosis Metabolic compensation has NOT occurred
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CB has the following ABG: pH 7.25, PaCO2 = 60, HCO3- = 26 What is his acid-base disturbance?
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