acid base imbalances. acid-base regulation body produces significant amounts of carbon dioxide...
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Acid Base Imbalances
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Acid-Base Regulation
Body produces significant amounts of carbon dioxide & nonvolatile acids daily
Regulated by: Renal excretion of acid (H+ combines with
phosphate or ammonia, which are excreted) Respiratory excretion of CO2 Buffer systems (hemoglobin, phosphate,
bicarbonate, proteins)
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Measurement
Arterial: Normal pH 7.36-7.44; normal HCO3 25;
normal pCO2 40 Peripheral venous:
pH is 0.02-0.04 lower than arterial HCO3 is 1-2 mEq/L higher than arterial pCO2 is 3-8 mmHg higher, depending on
peripheral extraction and use of O2
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Respiratory Acidosis
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Definition
Decreased pH due to pulmonary CO2 retention (hypoventilation causes hypercapnea)
CO2 retention causes increased H2CO3 production – causes acidemia
Serum HCO3 is normal acutely, and increases as compensation occurs
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Causes
Increase in PaCO2 Anything which causes a decrease in
minute ventilation has the potential to cause respiratory acidosis Airway CNS depression Pulmonary disease Hypoventilation of neuromuscular conditions
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Symptoms
CO2 narcosis: Headache, blurred vision Asterixis, tremors, weakness Confusion, somnolence
If prolonged: Signs of increased ICP Papilledema
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Compensation
Acutely: intracellular proteins buffer HCO3 is formed by the intracellular buffers Compensation is insignificant
Chronically Renal retention of HCO3 is the primary
buffering system Onset: 6-12 hrs, takes days to complete
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Compensation
Acute: HCO3 increases 1 mEq/L for every 10 mmHg
rise in PCO2 Insignificant effect on pH
Chronic: HCO3 increases 3.5-5 mEq/L for every
10mmHg rise in PCO2 Can almost normalize pH Usually results in hypochloremia
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Management
Must increase minute ventilation Must also improve ventilation
Bronchodilators, postural drainage, antibiotics (i.e. treat underlying cause)
Role of hypoxic drive???
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Respiratory Alkalosis
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Causes
Increased minute ventilation Leads to low pCO2, high pH If acute, HCO3 is normal If chronic, HCO3 will drop due to renal comp.
Causes: CNS diseases, hypoxemia, anxiety,
hypermetabolic states, toxic states, hepatic insufficiency, assisted ventilation
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Symptoms
Mimic hypocalcemia Depend on degree, acuity & cause Due to irritability of CNS & PNS, and
increased cerebral vascular resistance Paresthesias of lips, extremities;
lightheadedness, dizziness, muscle cramps, carpopedal spasms
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Management
Treat underlying cause i.e. remove stimulus
Treat symptoms E.g. benzos, pain medication, rebreathing
mask (allows CO2 retention)
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Metabolic Alkalosis
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Definition
Low pH due to increased HCO3 or decreased H+
Requires loss of H+ or retention of HCO3 Must know PCO2… elevation of HCO3
could be due to renal compensation for chronic respiratory acidosis
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Causes
Increased HCO3 reabsorption due to volume, K+ or Cl- loss
Loss of H+ and Cl- from vomiting and NG suctioning can lead to HCO3 retention
Renal impairment of HCO3 excretion
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Causes
Hypovolemic Vomiting/suction, diuretics, adenomas
Euvolemic/Hypervolemic Exogenous mineralocorticoids, ectopic ACTH,
Cushing’s, severe hypoK, adenoCA Unclassified
Milk-alkali syndrome, IV PCN rx, metabolism of organic acid anions, massive transfusion, nonparathyroid hypercalcemia
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Treatment
Treat underlying causes Replace losses May be saline-responsive or saline
resistant
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Metabolic Acidosis
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Mechanism
Increased production of acids Decreased renal excretion of acids Loss of alkali
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Alcoholic Ketoacidosis
Normal glucose High ketones Drinking binge; starvation
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Lactic Acidosis
2 different forms; l- and d- Increased production vs. decreased
elimination Systemic
Sepsis, hypovolemia, hypoxia Localized
E.g. bowel ischemia, metformin, HIV meds
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Treatment
Correct underlying cause Reduce O2 demand Ensure adequate O2 delivery to tissues
HCO3 Given to improve hemodynamic
consequences of acidosis
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Summary
Look at pH Look at pCO2 and HCO3 Look at patient!!
Treat the patient, not the numbers
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