2. Isohydria, acis-base balance, gasometry Flashcards
What is buffer system and what is its role?
Buffer solution resists pH changes. Typically it’s a mixture of weak acid (or base) and one of its salt.
Most important physics-chemical buffer systems in the body
- carbonic acid - bicarbonate buffer system (CO₂ + H₂O ‹-› H₂CO₃ ‹-› H⁺ + HCO₃⁻)
- primary - secondary phosphate buffer (H₃PO₄ ‹-› H⁺ + H₂PO₃⁻)
- protein - protein ate buffer system (albumin, haemoglobin, cytoplasmic proteins)
Vital buffer systems ?
Kidneys and lungs.
Lungs: can excrete the CO₂ to increase pH (increased H⁺ will move equation to the left -› generating extra CO₂ -› hypercapnia. Response of lungs to change of pH is very fast
Kidneys: can excrete or retain H⁺ and also HCO₃⁻ but it takes some time - hours to days. Example: if CO₂ levels within the body increase, then equation will push to the right and produce excess H⁺ and HCO₃⁻ and then H⁺ and HCO₃⁻ can be eliminated by kidneys
What parameters are measured in routine acid-base analysis ?
- pH - actual pH of the blood (7,35 - 7,45)
- pCO2 - partial CO2 pressure, (35-45 mmHg) respiratory parameter
- HCO3- - bicarbonate conc in the plasma, (21-24 mmol/l) metabolic parameter
- ABE - actual base excess. The amount of acid to base needed to equilibrate blood to pH 7,4, metabolic parameter
- TCO2 - total conc of CO2 in plasma i.e. CO2 content of blood liberated by strong acid. TCO2 may be ignored if HCO3 result is present
What is Kussmaul breathing
Hyperventilation. Very deep breath and longer gas exchange. NOT PAINTING!
Why increase of pCO2 is a shift in acidic direction?
When pCO2 is more than 40 mmHg, more of it bounds to water and forms carbonic acid. Respiratory acidosis.
How does HCO3- change in alkalosis and acidosis?
decreases in acidosis and increases in alkalosis.
How to detect compensatory processes in case of acid-base disturbances?
Compensatory parameter will be shifted in opposite direction compared to the total pH shift
Causes of metabolic acidosis
- HCO3- loss: diarrhoea, kidney tubular disturbances
- increased acid intake (fruits, acidic silage, acidifying drugs, vit C long-term)
- increased acid production (anaerobic glycolysis -› lactic acid; grain overdose in cattle -› volatile acid overproduction
- increased ketogenesis (starvation, DM)
- decreased acid excretion: renal failure
- ion exchange (H+/K+ ion pump)
- ethylene-glycol toxicosis (acidic metabolites)
Signs of metabolic acidosis
- Kussmaul breathing
- Hypercalcemia (increased mobilisation from bones and decreased binding to albumin)
- Hyperkalemia
- increased acidity of urine
What is the treatment of metabolic acidosis?
- adequate ventilation
- if pH ‹ 7,2 then alkaline fluid administration
Anion gap. Hyperchloremic vs normochloremic metabolic acidosis
Decreased pH because of direct loss of HCO3- (diarrhoea) -› less anions, shift in electroneutrality -› increase of Cl- to maintain electroneutrality -› no anion gap, Cl- is increased
Decrease of pH because of accumulation of unmeasured anions (lactate, ketones, …) -› Cl- stays in normal values, anion gap is increased
Causes of metabolic alkalosis
- increased alkaline intake (overdose in carbonates, rotten food)
- increased ruminal alkaline production (high protein, low CH intake)
- increased acid loss (vomiting)
- ion exchange: hypokalemia (Henle-loop diuretics; H+/K+ pump)
Signs of metabolic alkalosis
- low breathing rate, hypoventilation
- muscle weakness (hypokalemia)
- hypocalcemia (increased Ca++ binding to albumin)
- ammonia toxicosis
Causes of respiratory acidosis:
PROBLEMS WITH BREATHING !!!
- upper airway obstruction
- pleural cavity disease (pneumonia, pulmonary oedema, diffuse lung metastasis, pulmonary thromboembolism
- depression of central control of respiration
- neuromuscular depression, muscle weakness
- cardiopulmonary arrest
