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NEPHROLOGY/UROLOGY > 6. Acid Base Disorders and ABG Analysis > Flashcards

6. Acid Base Disorders and ABG Analysis Flashcards

1
Q

Normal pH, PaCO2, HCO3, and PaO2 in the blood

A
  • pH = 7.35-7.45
  • PaCO2 = 35-45 mm Hg (Respiratory Component of ABG / tells us what lungs are doing)
  • HCO3 = 22-26 mEq/L (Metabolic Component of ABG / tells us what kidneys are doing)
  • PaO2 = 80-100 mm Hg (Oxygenation Component of ABG / tells us if patient is oxygenating and not as important in Acid-Base Disorders)
    • FYI 60-80 is moderately oxygenated, <60 is poorly oxygenated
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2
Q

Definition of Acidemia and Alkalemia

A
  • Acidemia - pH of <7.35
  • Alkalemia - pH of >7.45
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3
Q

Definition of Acidosis and Alkalosis

A
  • Acidosis - process that increases H+ and decreases HCO3
  • Alkalosis - process that decreases H+ and increases HCO3
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4
Q

Definition of Base Deficit and Base Excess

A
  • Base Deficit/Excess - a measure of the metabolic component of an acid base disorder (equation normalizes the CO2 / -2.4 - +2.3 mEq)
  • Base Deficit (excess of acid) - may mean Metabolic Acidosis
  • Base Excess - may mean Metabolic Alkalosis
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5
Q

ABG Elements Necessary to Analyze Acid Base Status

A
  • pH
  • PaCO2
  • HCO3
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6
Q

Lungs Role to Maintain pH Balance

A

Lungs - control the PaCO2 in the blood

Compensation: minutes-hours

  1. Arterial chemoreceptors increase or decrease ventilation based on pH, pO2, and pCO2
  2. Hypoventilation increases PaCO2 and increases H+, acidifying the blood
  3. Hyperventilation decreases PaCO2 and decreases H+, alkalinizing the blood
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7
Q

Kidneys Role to Maintain pH Balance

A

Kidneys - control the level of HCO3 in blood

Compensation: 1-2 days

  1. Reabsorption of HCO3 anions
  2. Forming titratable acids (H+ formation)
  3. Retention and excretion of ammonium and hydrogen ions
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8
Q

Physiologic Compensation of Metabolic Acidosis (state of having decreased HCO3)

A
  • Hyperventilation to decrease CO2
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9
Q

Physiologic Compensation of Metabolic Alkalosis (state of having increased HCO3)

A
  • Hypoventilation to increase CO2
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10
Q

Physiologic Compensation of Respiratory Acidosis (state of increased CO2)

A
  • Bicarbonate retention in the kidneys
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11
Q

Physiologic Compensation of Respiratory Alkalosis (state of having decreased CO2)

A
  • Bicarbonate excretion by the kidneys
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12
Q

Differentiate between Full, Partial, and No Compensation

A
  • Full Compensation - pH brought back to normal by buffering from opposite system
  • Partial Compensation - pH is improving but not back to normal due to another process (mixed acid-base disorder)
  • Uncompensated - pH is abnormal because no compensation is occuring
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13
Q

METABOLIC ACIDOSIS

Definition

Etiology

Diagnosis

Mangement

A

DEFINITION:

  • pH = <7.35
  • Gain of acid or loss of HCO3

ETIOLOGY:

  • Gain of Acid
    • Increase of endogenous acids - lactic acid, ketoacid, salicylates
    • Increased toxins - ethylene glycol (Anti-freeze), methanol
    • Decreased renal H+ excretion - Type 1 renal tubular acidosis
  • Loss of HCO3
    • Increased renal HCO3 excretion - Type 2 renal tubular acidosis
    • Diarrhea

DIAGNOSIS:

  • Low CO2 on serum chemistry
  • Low pH on ABG
  • CALCULATE ANION GAP

MANAGEMENT:

  • Correct underlying cause
  • If severe, calculate HCO3 deficit and administer IV NaHCO3 (but use with EXTREME caution)
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14
Q

Normal Sodium, Chloride, Potassium, Carbon Dioxide Values

A
  • Na = 135-145 mEq/L
  • Cl = 98-106 mEq/L
  • K = 3.5-5.5 mEq/L
  • CO2 = 22-28 mEq/L

Serum CO2 is a good surrogate marker for HCO3.

  • CO2 <22 - metabolic acidosis
  • CO3 > 28 - metabolic alkalosis
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15
Q

ANION GAP

Definition

Indication

Calculation

Etiology

A

DEFINITION:

Anion Gap = Na + unmeasured cations = Cl + CO2 + unmeasured anions

INDICATION:

When metabolic acidosis is present to determine if an ABG needs to be ordered

CALCULATION:

Anion Gap = Na - (Cl + CO2)

Normal is 8-16 mEq or 12 +/-2

ETIOLOGY:

“GOLDMARK”

  • Glycols (Ethylene Glycol - antifreeze, Propylene Glycol - solvent in IV lorazepam, phenobarbital, phenytoin, etomidate)
  • Oxoproline (from chronic acetaminophen use
  • L-Lactate (hypoperfusion, shock, sepsis)
  • D-Lactate (short small bowel syndrome - Crohn’s disease, weight loss surgery)
  • Methanol (wood alcohol ingestion)
  • Aspirin
  • Renal Failure
  • Ketoacidosis
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16
Q

Process after Detection of a High Anion Gap

A
  • Delta-Delta Rule - if the increase in anion gap = the decrease in HCO3, the patient is compensating for their metabolic acidosis
    • If not 1:1, patient likely has a mixed disorder
  • Next, obtain Osmolar Gap = Osm(meas.) - Osm(calc.)
    • Calculated Osmolality = [2(Na) + Glu]/18 + BUN/2.8
    • Etiology: “MEDIE”
      • Methanol
      • Ethanol
      • Diuretics (Mannitol)
      • Isopropanol (rubbing alcohol)
      • Ethylene Glycol
  • Management
    • Methanol - Fomepizole + Dialysis
    • Alcohol - correct hypoperfusion, Thiamine + Folate
    • Lactate - correct underlying cause, hypoperfusion, shock, sepsis
    • Ethylene Glycol - Fomepizole + Dialysis
    • Salicylates - Bicarb or Dialysis if severe
17
Q

Special Fact about Isopropyl

A

WIll cause an osmolar gap but not an anion gap

18
Q

NON ANION GAP METABOLIC ACIDOSIS

Workup

A

WORKUP:

  • Obtain a Urine Anion Gap = Na + K - Cl to determine cause
    • +UAG = Renal losses of HCO3 (RTA)
    • -UAG = GI losses of HCO3 (Diarrhea, Pancreatic Fistula)
19
Q

METABOLIC ALKALOSIS

Definition

Workup

Etiology

Management

A

DEFINITION:

  • pH = >7.45
  • Loss of Acid or Gain of HCO3

WORKUP:

  • Obtain a Urine Chloride to determine cause
    • Urine Chloride <10 = Saline Responsive
      • Volume Depletion
      • Diuretics
      • Vomiting
      • Diarrhea (chronic)
      • Cystic Fibrosis
    • Urine Chloride >10 = Saline Resistant
      • Hyperaldosteronism –> hypokalemia causes NaHCO3 reabsorption
      • Cushing’s - ACTH and Cortisol cause hypokalelemia which causes NaHCO3 reabsorption
      • CHF with high diuretic use
      • Cirrhosis with high diuretic use
      • Renal failure (retention of HCO3)

MANAGEMENT:

  • Correct underlying cause (Volume, K Replacement)
  • VERY RARELY, IV Hydrochloric Acid
20
Q

RESPIRATORY ACIDOSIS

Definition

Etiology

Definition of Compensation

A

DEFINITION:

  • pH = < 7.35
  • PaCO2 = >45

ETIOLOGY:

Acute:

  • Hypoventilation
  • Airway Obstruction
  • CNS Depression

Chronic:

  • Sleep Apnea
  • COPD
  • Neuromuscular Disease
  • Restrictive Lung Disease

DEFINITION OF COMPENSATION:

Acute: Every 10 mm increase in PCO2, HCO3 should increase by 1 mm

Chronic: Every 10 mm increase in PCO2, HCO3 should increase by 3.5

21
Q

RESPIRATORY ALKALOSIS

Definition

Etiology

Definition of Compensation

A

DEFINITION:

  • pH = >7.45
  • PaCO2 = <35

ETIOLOGY:

  • Hyperventilation
  • Anxiety
  • Aspirin Ingestion
  • Subarachnoid Hemorrhage
  • Stroke
  • Fever/Sepsis
  • Liver Disease with High Ammonial Level

DEFINITION OF COMPENSATION:

  • Acute: Every 10 mm decrease PCO2, HCO3 decreases by 2 mEq
  • Chronic: Every 10 mm decrease PCO2, HCO3 decreases by 5 mEq

NEPHROLOGY/UROLOGY (3 decks)

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