4. Acid-Base Disorders Flashcards
What is the relationship between acid-based disorders and hydrogen ion balance?
What is the daily acid-base balance?
Summarize.
- All based on hydrogen ion balance
—> pH 7.4 = 10-7.4 mol/L [free H+ ion] = 40 nmol/L - Daily acid-base balance:
1. 100 mmol/day net acid production
2. ‘Good’ buffering = carbonic anhydrase
3. ‘Bad’ buffering = bone, Hgb and plasma proteins - Relationship between [H+] and pH is inverse and non-linear
SUMMARY
- pH is less important than the cause of the acid- base disturbance
- If all variables move in same direction the primary disorder is metabolic; discordant is respiratory
- Compensation minimises the change in pH and is always in the same direction as the primary disorder
- Use the anion gap for DDx of metabolic acidosis
- Check osm gap in unexplained metabolic acidosis
What are the problems with pH?
(3)
What is the pH level for Grand Mal Seizure?
- Extremely low concentration: [H+] 100,000-fold lower than K+
- Inverse relationship: [H+] goes up, pH goes down
- Non-linear: Logarithmic scale
- Every change of 0.3 pH units represents change in H+ by a factor of 2
Grand Mal Seizure (ischaemic bowel)
- pH = 6.8
What are the features of acidosis and alkalosis?
2
- Primary disturbance in either HCO3- or pCO2
- Compensation occurs in same direction
- Acidosis or alkalosis:
—> If pH LESS than 7.4 = acidosis
—> If pH GREATER than 7.4 = alkalosis - Respiratory or metabolic:
- If pH, bicarbonate, and pCO2 move in SAME direction (up or down) = metabolic
- If pH, bicarbonate, and pCO2 move in OPPOSITE direction (up or down) = respiratory
What is anion metabolic acidosis?
2
- Anion Gap: Na – (Cl + HCO3)
- Normal AG: 8-12
What is non-anion gap metabolic acidosis?
3
- Chloride intoxication
- Dilutional acidosis
- HCl intoxication
- Chloride gas intoxication
- Early renal failure - GI Loss of HCO3
- Diarrhea
- Surgical drains
- Fistulas
- Uterosigmoidstomy
- Obstructed ureteroileostomy
- Cholestryamine - Renal Loss
- Renal tubular acidosis
- Proximal
- Distal
- Hypoaldosteronism
What are the dx for risen AG metabolic acidosis?
4
- Lactic acidosis
- Renal failure
- Ketoacidosis
- Poisonings
Describe lactic acidosis. What is Type A? What is type B?
4
Type A: tissue hypoxia (shock - septic, hemorrhagic, neurogenic, carcinogenic - respiratory failure, anemia, CO poisoning)
Type B: mitochondrial failure (cyanide, malignancy, medications (anti-HIV, Metformin, Aspirin), Thiamine deficiency
- Studies show N or increase organ O2 levels during sepsis with hyperlactataemia
- Metabolic fuel for the heart and brain under stress conditions
- Lactate production driven by endogenous adrenaline stimulating aerobic glycolysis via beta-2 receptors
Describe renal failure.
- Failure to fully excrete daily acid intake of 1 mmol/kg
- New set-point serum HCO3 ~ 18 mmol/l
- Vulnerable to acute acidosis in setting of acid load
- Raised AG due to retention of multiple anions
Describe ketoacidosis.
- Decreased carb in diet = ketogenic
- Alcohol also stimulates lipolysis
- Alcohol depletes the NAD+ supply needed for gluconeogenesis
- No gluconeogenesis causes hypoglycaemia which prevents insulin secretion
- Tx: glucose, B vitamins (NOT INSULIN)
Describe poisonings.
- Clinical suspicion: coma, seizures, shock mean generated toxic acids
- Don’t treat if patient is drunk or a small OG or AG on their own
- Treatment:
- Isotonic NaHCO3 to keep pH > 7.35 (1C)
- Fomepizole if osmolar gap
- Dialysis if elevated toxic alcohol, severe acid base disorder or target organ damage
- B vitamins
What does GOLDMARK stand for and what is it used for?
- Causes of high anion gap metabolic acidosis
G: glycolysis - ethylene, propylene O: oxoprolinuria L: L-lactic acidosis D: D-lactic acidosis M: methanol A: aspirin R: renal failure K: ketoacidosis: diabetic, alcoholic
