ACID BASE DISTURBANCES

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• ACID BASE DISTURBANCES

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Normal Values

• pH 7.35 to 7.45
• paCO2 36 to 44 mm Hg
• HCO3 22 to 26 meq/L

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Acid-base balance

• Biochemical reactions influenced by pH of
  surrounding fluids (pH -logH)
• pH of tissues regulated by
• chemical buffers (very rapid)
• Bicarbonate
• Phosphate
• Protein
• respiratory compensation
• Elimination of volatile acid (carbonic acid) by
  exhalation of CO2
• renal compensation
• Excretion of non-volatile acids (cannot be
  eliminated by exhaling CO2)

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• pH 6.1 log HCO3-/0.03 x PCO2
• Plasma pH may be affected by a change in either
  the bicarbonate or the PCO2
• When the primary change is in the PCO2, the
  disturbance is called respiratory when it is the
  bicarbonate, it is called metabolic
• ? PCO2 will decrease pH
• ? PCO2 will increase pH
• ? HCO3- will decrease pH
• ? HCO3- will increase pH

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Acid-base changes in acidosis and alkalosis
pH, PCO2 in opposite directions HCO3- will
follow PCO2
pH, HCO3- in same direction PCO2 will
follow HCO3-
Thicker arrows indicate primary disorder
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Compensation

• The purpose of the compensation is to return the
  blood pH to normal
• The change in the PCO2 in the metabolic disorders
  represents the lungs role in compensation
• The change in the bicarbonate level represents
  the kidneys attempt to compensate for the
  respiratory acidosis or alkalosis

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Metabolic and Respiratory Acid-Base Changes in
Blood
?decreased ?increased Nnormal
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Acute Respiratory Acidosis

• Acceptable ventilatory and metabolic acid-base
  status
• Respiratory acidosis (alveolar hypoventilation) -
  acute, chronic
• Respiratory alkalosis (alveolar hyperventilation)
  - acute, chronic
• Metabolic acidosis uncompensated, compensated
• Metabolic alkalosis uncompensated, partially
  compensated

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Chronic Respiratory Acidosis

• paCO2 is elevated with a pH in the acceptable
  range
• Renal mechanisms increase the excretion of H
  within 24 hours and may correct the resulting
  acidosis caused by chronic retention of CO2 to a
  certain extent

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Chronic Respiratory Acidosis

• Causes
• Chronic lung disease (BPD )
• Neuromuscular disease
• Extreme obesity
• Chest wall deformity

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Acute Respiratory Alkalosis

• paCO2 is low and the pH is alkalotic
• The increase in pH is accounted for entirely by
  the decrease in paCO2
• Bicarbonate and base excess will be in the normal
  range because the kidneys have not had sufficient
  time to establish effective compensatory
  mechanisms

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Respiratory Alkalosis

• Causes
• Pain
• Anxiety
• Hypoxemia
• Restrictive lung disease
• Severe congestive heart failure
• Pulmonary emboli

• Drugs
• Sepsis
• Fever
• Thyrotoxicosis
• Pregnancy
• Overaggressive mechanical ventilation
• Hepatic failure

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Uncompensated Metabolic Acidosis

• Normal paCO2, low HCO3, and a pH less than 7.30
• Occurs as a result of increased production of
  acids and/or failure to eliminate these acids
• Respiratory system is not compensating by
  increasing alveolar ventilation (hyperventilation)

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Compensated Metabolic Acidosis

• paCO2 less than 30, low HCO3, with a pH of
  7.3-7.4
• chronic metabolic acidosis are unable to
  hyperventilate sufficiently to lower paCO2 for
  complete compensation to 7.4

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Metabolic Acidosis Elevated Anion Gap

• Methanol
• Uremia
• Diabetic ketoacidosis
• Paraldehyde
• INH
• Lactic acidosis
• Ethylene Glycol
• Salicylate

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Non Gap Acidosis

• H hyperalimentation
• A acetazolamide
• R RTA
• D diarrhea
• U rectosigmoidostomy
• P pancreatic fistula

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ABG analysis

• Arterial Blood Gas (ABG) interpretation
• Always evaluate PH first
• Alkalosis PH gt 7.45
• Acidosis PH lt 7.35
• Determine anion gap (AG) AG NA (HCO3 CL)
• AG metabolic acidosis
• Non AG acidosis determined by delta gap
• Winters formula
• Calculates expected PaCO2 for metabolic acidosis
• PaCO2 1.5 x HCO3 8

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• Delta gap
• Delta HCO3 HCO3 (electrolytes) change in AG
• Delta gap lt 24 non AG acidosis
• Delta gap gt 24 metabolic alkalosis

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THANK YOU