Acid-Base Physiology Flashcards
Golden Rules of Simple Acid-base disorders
- PCO2 and HCO3 always change in the same direction
- The secondary physiologic compensatory mech must be present
- The compensatory mechs never fully correct pH
Acid-base disorder that reduces plasma bicarbonate
Metabolic Acidosis
Causes of Metabolic Acidosis
- Increased acid generation:
- Lactic acidosis, Ketoacidosis, ingestion (aspirin, ethylene glycol, methanol), dietary protein intake (animal source) - Loss of Bicarbonate:
- Gastrointestinal (diarrhea, intestinal fistulas)
- Renal: type 2 proximal renal tubular acidosis - Decreased Acid excretion:
- impaired NH4+ excretion
- Renal failure (reduced GFR) decreased ammonium excretion
- Type I (distal) renal tubular acidosis
- Type 4 renal tubular acidosis (hypoaldosteronism)
Acid-base disorder characterized by excessive plasma CO2
Respiratory Acidosis
- induced by hypercapnia (inadequate alveolar ventilation)
- can be acute or chronic
Common causes of acute respiratory acidosis?
- General anesthesia
- Sedative overdose
- Cardiac arrest
- Pneumothorax
- Pulmonary edema
- severe pneumona
Common causes of chronic respiratory acidosis?
- COPD
- Primary alveolar hypoventilation
- Brain tumor
- Respiratory nerve damage
- myopathy involving respiratory muscles
- restrictive disease of the thorax (scleroderma)
Acid-base disorder characterized by reduced CO2 (due to increased alveolar ventilation)
Respiratory Alkalosis
Acid-base disorder characterized by increased plasma bicarbonate
Metabolic Alkalosis
T or F: Acute respiratory acid base disorders always have a greater change in pH than chronic resp. disorders
True
How does plasma Cl change in relation to plasma HCO3 in respiratory disorder
Equally and inversely
How does the plasma anion gap change in respiratory disorders?
It does NOT change
T or F: Plasma sodium is directly altered in acid base disorders
False
- Plasma sodium in INDIRECTLY altered
Causes of Metabolic alkalosis?
- Loss of hydrogen ions from GI tract:
- Vomiting - Loss of hydrogen ions from the urine
- diuretics - excessive urinary acid excretion
- hyperaldosteronism - Movement into the cells
- hypokalemia
Normal Arterial pH?
7.4
Metabolic alkalosis with:
- Urine Cl- conc > 30 mmol/l
Chloride-resistant (metabolic alkalosis)
Metabolic alkalosis with:
- Urine Cl- conc
Chloride-resistant (metabolic alkalosis)
Metabolic alkalosis with:
- Urine Cl- conc
Chloride-responsive (metabolic alkalosis)
Normal plasma bicarbonate levels
24 meq/L
Normal plasma CO2 concentration
40 mmHg
Metabolic Acidosis with:
- increased [Cl-]
- low plasma [bicarbonate]
Metabolic acidosis w/ Normal Anion Gap
Metabolic Acidosis with:
- normal [Cl-]
- low plasma [bicarbonate]
- increased unmeasured anions
Metabolic acidosis w/ Increased Anion Gap
Clinical signs:
Tachypnea (hyperventilation) think…
Respiratory Alkalosis
high bicarb => high CO2
Clinical signs:
obstruction of airway or inability to breath think…
Respiratory Acidosis
Clinical signs:
Nausea and vomiting, think….
Metabolic Alkalosis
- (Chloride depletion)
Clinical signs:
Diarrhea, think…
normal anion gap metabolic
acidosis
- due to direct bicarbonate loss from gut
Clinical signs:
Type I diabetic off his insulin
think…
suggests ketoacidosis, which is a cause of increased anion gap metabolic
acidosis.
Normal Plasma [Na+]
140 meq/l
Norma plasma [Cl-]
104 meq/l
Equation for calculating URINE anion gap
UAG = (Na + K) - (Cl)
AG - normal
Urine Anion Gap = Positive
What is the cause of the non-anion gap Metabolic acidosis?
Renal = cause (RPGN)
UAG = (Na + K) - (Cl)
- positive because Cl- is not being excreted which means H+/NH4+ is not being excreted (it’s building up)
- Type I RTA (distal tubular)
AG - normal
Urine Anion Gap = Negative
What is the cause of the non-anion gap Metabolic acidosis?
GI = Cause (RPGN)
- due to diarrhea
When do you use the Urine Anion gap?
When there is a non-gap metabolic acidosis
Equation for calculating the pCO2 from bicarbonate?
When is this used?
PCO2 = 1.5 (HCO3-) + 8
- only for Metabolic acidosis
In ACUTE respiratory alkalosis,
how much does the bicarbonate increase for every 10mmHg pCO2 increase?
2 meq/L for every 10mmHg increase of pCO2
In CHRONIC respiratory alkalosis,
how much does the bicarbonate increase for every 10mmHg pCO2 increase?
4 meq/L for every 10mmHg increase of pCO2
In CHRONIC respiratory acidosis,
how much does the bicarbonate increase for every 10mmHg pCO2 increase?
3.5 meq/L for every 10mmHg increase of pCO2
In ACUTE respiratory acidosis,
how much does the bicarbonate increase for every 10mmHg pCO2 increase?
1 meq/L for every 10mmHg increase of pCO2
Compensation mechanism for metabolic Acidosis?
Hyperventilation (decreases pCO2)
Compensation mechanism for metabolic Aklalosis?
Hypoventilation (Retains/increases pCO2)
Compensation mechanism for respiratory acidosis?
Increase bicarbonate
- increase bicarbonate reabsorption
- increase H+ secretion
Compensation mechanism for respiratory alkalosis
Decrease bicarbonate
- decrease bicarbonate reabsorption
- decrease bicarbonate secretion
