Acid-Base Disorders Flashcards
Acidosis
Clinical Consequences
pH<7.35
- REDUCED EXCITABILITY; esp. in heart and CNS
– decreased sensitivity to catecholmine (dopamine,..)
- Headache, Lethargy, anorexia (an eating disorder that by restricting food intake), nasusea, vomiting, diarrhea, warm skin, increased intracranial pressure
- EXTRACELLULAR shift of potassium and phosphate
- Respiratory response: deep and rapid KUSSMAUL breaths
Alkalosis
Clinical Consequences
pH>7.45
- INCREASED excitability: including muscle cramps, hyperactive reflexes, tetany, convulsion, atrial tachycardia, cerrbral vasoconstriction
- Decreased cardiac muscle excitability
- INTRACELLULAR shift of potassium
- Respiratory response: slow and shallow breath
Acid-Base Disturbances
Metabolic Acidosis:(pH<7.35):(pCO2:40mmHg- normal):(HCO3:<24mEq/L)
Metabolic Alkalosis:(pH>7.45):(pCO2:40mmHg- normal):(HCO3:>24mEq/L)
Respiratory Acidosis:(pH<7.35):(pCO2:>50mmHg):(HCO3:24mEq/L- normal)
Respiratory Alkalosis:(pH>7.45): (pCO2:<35mmHg):(HCO3:24mEq/L- normal)
Partial pressure of carbon dioxide = pCO2
HCO3 = bicarbonate
Respiratory Acidosis
Main problem is the retained CO2 (high CO2)
- Caused by decreased respiration
– Lead to decreased pH
This causes: pCO2 to increase (20:2 instead of 20:1)
- Body compensate by increasing HCO3- (30:2)
– Kidney conserve HCO3- and eliminate H+ in acidic urine
- Restore the balance is need so therapy (ex. lactate solution: converted into bicarbonate ions in liver) =>40:2
Causes of Respiratory Acidosis
Hypercapnia: Excess CO2 in blood
- Increased CO2 in air
Decreased Ventilation
- CNS depression; Sedative/Hypnotic drugs
- Obstructive lung disease: COPD, Edema, Bronchitis
- Chest wall disorders: Flail Chest (ex. broken ribs)/ Penumothorax (collection of air or gas btw wall of lungs and chest wall)
- Head injury
- Myopathy of respiratory muscles: Muscular dystrophy, myasthenia gravis
Treatment include improving ventilation to decrease pCO2
Respiratory Alkalosis
Main problem is loss of CO2 (low)
- Caused by Increased respiration
– Lead to an increased pH
This causes low pCO2 (20:0.5 instead of 20:1)
- Body compensate by decreasing HCO3- (15:0.5)
– kidney conserve H+ ion and eliminate HCO3- in alkaline urine
- Therapy (ex. Cl containg solution) required to restore balance to (10:0.5)
Causes of Respiratory Alkalosis
Hypocapnia: decreased CO2 in blood
- Hyperventilation
- Anxiety/fear
- Fever
- Encephalitis (inflammation of brain)
- Salicylate poisoning
Treatment include treating the underlying cause of hyperventilation
Metabolic Alkalosis
Cause:
- Increased HCO3- (pH increase) (can be caused by loss of Cl-) or decreased Fixed acids (40:1)
- Body compensate by DECREASING respiration which increase pCO2 (30:1.25)
– kidney conserve H+ ion and eliminate HCO3- in alkaline urine
- Therapy (ex. Cl- containg solution) needed to restore body balance (20:1)
Causes of Metabolic Alkalosis
Gain in Bicarbonate
- Ingestion (NaHCO3, alkaline salts)
- Contraction Alkalosis: fluid loss
- Milk-alkali Syndrome (Burnett syndrome): XS Calcium Carbonate
- Diuretics: Volume and Cl- loss
– Used to treat CHF and hypertension as it remove fluid from the body
Loss of Metabolic Acids (esp. vomiting and GI suctioning)
- Loss of HCl from kidney or stomach
Treatment include correcting underlying problem (ie. Cl-) or ISOTONIC IV solution
Metabolic Acidosis
Cause:
- Decreased HCO30- (pH decrease) or increased fixed acid (10:1)
- Body compensate by INCREASING respiration which will decrease pCO2 (10:0.75)
- Therapy (ex. lactate containg solution) is required to restore body balance (10:0.5)
Causes of Metabolic Acidosis
Increased Metabolic Acids:
- Ketoacidosis (diabetes, starvation, ethanol)
- Lactic acidosis (increased metabolic demand, reduced tissue O2 delivery/utilization, drugs)
- Chemical Ingestion: methanol, salicylate, ethylene glycol (anitfreeze)
- Decreased H+ excretion (Mainly treated by IV sodium bicarbonate)
Loss of HCO3- or gain of chloride
- Diarrhea
- Early renal failure/renel tubule acidosis
- Carbonic anhydrase inhibitors (acetazolamide)
Anion Gap/Metabolic Acidosis
Anion Gap: UNMEASURED ANION in plasma
- Based on the idea that cation and anion balance eachother out
Cation:
- Na+ (mostly), other include K+, Ca+, Mg2+
Anion:
- HCO3-
- Cl-
- Unmeasured anions
– Albumin. phosphate, sulfate
– Lactate, acetoactate
Anion Gap/Metabolic Acidosis
Calculation
[NA+]-([HCO3-]+[Cl-]) = Anion Gap
140-(24+105)=11
- Normal = 12 (10-14) nEq/L
- Use venous blood result to calculate
Clinically:
- Used to identify the cause of some cases of Metabolic acidosis
- HCO3- decreases as it buffers fixed/non-volatile acids
– this leads to increased anion gap (higher than 14)
MUDPILES
Causes of Anion Gap Elevation
- Methanol
- Uremia (sever kidney disease)
- Diabetic ketoacidosis (not taking care of their hypoglycemia)
- Prophylene Glycol, Paraldehyde
- Isoniazid, Iron
- Lactic acidosis
- Ethylene Glycol
- Salicylates, solvent
All these cause metabolic acidosis with elevated anion gap but there are other cases of metabolic acidosis WITHOUT anion gap like diarrhea (lose of bicarbonate)
What happens if you take 35 asprin (325mg)
Two type of toxicity with salicylates
- Respiratory Alkalosis: Stimulation of respiratory center in brain (initial)
- Metabolic Acidosis: Acetylasalicylic acid lead to greater acid burden
Therapy:
- Rehydrate with normal saline
- Urinary alkalization with IV bicarbonate to achieve urine pH=7.5-8.0
Salicylic Acid (weak acid-toxic) => Salicylic anion (Eliminated in urine)
