acid base imbalances
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Acid Base Imbalances. 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

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acid base regulation
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)
measurement
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
definition
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
causes
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
symptoms
Symptoms
  • CO2 narcosis:
    • Headache, blurred vision
    • Asterixis, tremors, weakness
    • Confusion, somnolence
  • If prolonged:
    • Signs of increased ICP
    • Papilledema
compensation
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
compensation1
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
management
Management
  • Must increase minute ventilation
  • Must also improve ventilation
    • Bronchodilators, postural drainage, antibiotics (i.e. treat underlying cause)
  • Role of hypoxic drive???
causes1
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
symptoms1
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
management1
Management
  • Treat underlying cause
    • i.e. remove stimulus
  • Treat symptoms
    • E.g. benzos, pain medication, rebreathing mask (allows CO2 retention)
definition1
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
causes2
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
causes3
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, nonparathyroidhypercalcemia
treatment
Treatment
  • Treat underlying causes
  • Replace losses
  • May be saline-responsive or saline resistant
mechanism
Mechanism
  • Increased production of acids
  • Decreased renal excretion of acids
  • Loss of alkali
alcoholic ketoacidosis
Alcoholic Ketoacidosis
  • Normal glucose
  • High ketones
  • Drinking binge; starvation
lactic acidosis
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
treatment1
Treatment
  • Correct underlying cause
  • Reduce O2 demand
  • Ensure adequate O2 delivery to tissues
  • HCO3
    • Given to improve hemodynamic consequences of acidosis
summary
Summary
  • Look at pH
  • Look at pCO2 and HCO3
  • Look at patient!!
  • Treat the patient, not the numbers
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