Acid-Base Balance Flashcards
Normal pH range is?
7.4 (7.35-7.45)
What blood pH is considered acidosis? How about alkalosis?
Acidosis = pH < 7.4
Alkalosis = pH > 7.4
What are the 2 organs that are primarily responsible for maintaining acid-base homeostasis?
- Lungs regulate pH via carbon dioxide (CO2), which is acidic
- Kidneys regulate pH via bicarb (HCO3-), which is basic
What is respiratory acidosis and alkalosis?
- When increased CO2 is the primary abnormality -> respiratory acidosis
- When decreased CO2 is the primary abnormality -> respiratory alkalosis
What is metabolic acidosis and alkalosis?
- When decreased HCO3 is the primary abnormality -> metabolic acidosis
- When increased HCO3 is the primary abnormality -> metabolic alkalosis
For any respiratory abnormality, the kidneys compensate by adjusting ___________ ______________
bicarbonate concentrations
For any metabolic abnormality, the lungs compensate by adjusting ___ ______________
CO2 concentrations
What are the roles of the lungs in acid-base balance? (3)
- Sense alterations in blood pH
- Adjust breathing rate to increase or decrease PaCO2 (acidic)
- Acidosis (pH < 7.4) -> lungs increase respiratory rate -> ↓ PaCO2 -> ↑ pH toward normal
- Alkalosis (pH > 7.4) -> lungs decrease respiratory rate -> ↑ PaCO2 -> ↓ pH toward normal - The lungs are able to make adjustments to respiratory rate (and PaCO2) relatively quickly (within minutes-hours)
What are the roles of the kidneys in acid-base balance? (3)
- Sense alterations in blood pH
- Adjust rate of bicarbonate excretion to increase or decrease bicarb (HCO3-) (basic)
- Acidosis (pH < 7.4) -> kidneys decrease bicarbonate excretion -> ↑ serum bicarbonate -> ↑ pH toward normal
- Alkalosis (pH > 7.4) -> kidneys increase bicarbonate excretion -> ↓ serum bicarbonate -> ↓ pH toward normal - The kidneys’ response to acid-base changes is slower (2-3 days)
What pCO2 levels are indicative of respiratory alkalosis and acidosis?
<40 mmHg = respiratory alkalosis
>40 mmHg = respiratory acidosis
What mEq/L bicarb levels are indicative of metabolic alkalosis and acidosis
<22 mEq/L = metabolic acidosis
>28 mEq/L = metabolic alkalosis
What are the 3 steps in assessing acid-base balance?
Step 1: Evaluate the “emia” (is it an acidic or basic disturbance)?
Step 2: Evaluate the “osis” (is the problem metabolic or respiratory)?
Step 3: Evaluate whether appropriate compensation has occurred to correct the disturbance
How to interpret the following parameters for respiratory acidosis?
1. pH
2. Primary disturbance
3. Compensation
- Decrease
- Increase PaCO2
- Increase HCO3-
How to interpret the following parameters for metabolic acidosis?
1. pH
2. Primary disturbance
3. Compensation
- Decrease
- Decrease HCO3-
- Decrease PaCO2
How to interpret the following parameters for respiratory alkalosis?
1. pH
2. Primary disturbance
3. Compensation
- Increase
- Decrease PaCO2
- Decrease HCO3-
How to interpret the following parameters for metabolic alkalosis?
1. pH
2. Primary disturbance
3. Compensation
- Increase
- Increase HCO3-
- Increase PaCO2
How to treat metabolic acidosis?
- Identify and correct cause
- Bicarb administration
Metabolic acidosis may be due to: (2)
- Accumulation of acidic anions (increased anion gap metabolic acidosis)
1a. Lactic acidosis
- Shock, severe hypoxemia
- Liver disease
- Drugs – metformin (0.03/1000), propofol (in children)
1b. Ketoacidosis
1c. Intoxications e.g. methanol, ethylene glycol, salicylates - Disturbance of endogenous H+/HCO3- (hyperchloremic – normal anion gap)
2a. Renal tubule acidosis
2b. Diarrhea (leads to bicarbonate loss)
2c. Drugs
- Lithium
- Carbonic anhydrase inhibitors (e.g. acetazolamide)
- Amphotericin B
- Topirimate
What are the most common causes of metabolic alkalosis? (3)
- Loss of gastric acid due to persistent vomiting
- Loss of intravascular volume and chloride due to diuretics
- Iatrogenic: Improper anion balance in parenteral nutrition or overzealous correction of metabolic acidosis with bicarbonate
What is the treatment of metabolic alkalosis? (3)
- Correct underlying factors (e.g. anti-emetics, stop or reduce diuretics)
- Volume repletion with normal saline
- Carbonic anhydrase inhibitors (e.g. acetazolamide) -> ↑serum carbonic acid levels
What is treatment for respiratory alkalosis?
Identify and correct underlying cause
- Manage pain, decrease anxiety, correct hypoxemia, oxygen if necessary
What to know about respiratory alkalosis in terms of acute/chronic? (3)
- Metabolic compensation occurs slowly
- If the disturbance is acute (< 24h), serum bicarbonate will still be normal
- If the disturbance is chronic (> 24h) serum bicarbonate will be decreased to compensate
What to know about respiratory acidosis in terms of acute/chronic? (3)
- Metabolic compensation occurs slowly
- If the disturbance is acute (< 24h), serum bicarbonate will still be normal
- If the disturbance is chronic (>24h) serum bicarbonate will be increased to compensate
How is chronic respiratory acidosis treated?
Chronic, compensated respiratory acidosis (e.g. COPD) may not require treatment
* Exacerbations may occur (e.g. AECOPD, initiation of drugs that suppress respiration such as narcotics, benzodiazepines) -> supplemental O2, supportive care
How is acute respiratory acidosis treated?
- Severe hypoxia present and is the immediate threat – increase tissue oxygenation (ventilation)
- Treat the underlying cause and the acidosis will correct rapidly
