Metabolic acidosis

Question 1

Metabolic acidosis

Answer 1

pH < 7.35

low serum HCO3- (<24 mEq/L)

decrease in PaCO2 from hyperventilation

Question 2

Anion gap

Answer 2

Na+ - (Cl + HCO3-)

Normal 3-11 mEq/L

Question 3

Pathophysiology of non-anion gap acidosis

Answer 3

Loss of plasma HCO3- replaced by Cl-

Question 4

Gastrointestinal bicarbonate losses

Answer 4

Diarrhea: can lose 5-10 L of fluid; one L has 3050 mEq/L of HCO3-

Pancreatic fistulas/biliary drainage: fluids are rich in HCO3-

Question 5

Renal bicarbonate loss

Answer 5

Type 2 renal tubular acidosis

Causes: can result from various diseases or toxins (heavy metal toxicity, carbonic anhydrase inhibitors, topiramate, fanconi’s syndrome)

Reabsorptive threshold for HCO3- is reduced in the proximal tubule

With enhanced bicarb loss there will be an increase in Na+ and fluid loss, which will then activate angiotensin system leading to hyperaldosteronism

Increased aldosterone augments K+ excretion–>hypokalemia

Urine pH ofter < 5.3

Question 6

Reduced renal H+ excretion

Answer 6

distal tubule RTA’S

Question 7

Type I RTA

Answer 7

hypokalemia RTA

Causes: primary tubule defect, SLE, myeloma, sickle cell, Li+, ampho B, toluene

H+ cannot be pumped into tubule lumen by cells of collecting duct

Urine pH > 5.3

Increase in K+ excretion: H+ cannot be secreted in response to Na+ reabsorption

Question 8

Type IV RTA

Answer 8

hyperaldosteronism or hyperkalemia RTA

Aldosterone stimulates H+ excretion, so with less aldosterone=H+ retention

Hyperkalemia conditions also lead to H+ retention=acidosis

Question 9

Chronic renal failure

Answer 9

decrease H+ excretion

less ammonia production which can’t pick up H+ to make new bicarb

Question 10

Acid and chloride administration

Answer 10

TPN administration

HCl or Ammonium Cl administration

Question 11

Pathophysiology of anion gap acidosis

Answer 11

M: methanol intoxication
U: uremia
L: lactic acidosis
E: ethylene glycol
P: paraldehyde ingestion
A: aspirin
K: ketoacidosis

Question 12

Characteristics of anion gap acidosis

Answer 12

Elevated anion gap

HCO3- losses are replaced with another anion besides Cl-

Question 13

How to calculate delta gap

Answer 13

difference between the patient’s anion gap and the normal anion gap

if the delta gap is added to the measured HCO3- and the answer is an elevated HCO3-, it tells you there is also the presence of a metabolic alkalosis as well as acidosis

Question 14

Causes of anion gap metabolic acidosis

Answer 14

Lactic acidosis

Ketoacidosis

Drug intoxications

Question 15

Lactic acidosis

Answer 15

Lactate formation essential for tissues that need NAD+ to generate energy anaerobically

RBC’s, exercising muscle

1 mEq/L=normal
> 5 mEq/L=diagnostic

Normally enters circulation in small amounts and is promptly removed by the liver

Question 16

Possible causes of lactic acidosis

Answer 16

Shock

Drugs/toxins: ethanol, metformin, NRTIs, linezolid, isoniazid, propofol, topiratmate, propylene glycol

Seizures: self-limiting

Leukemia

Hepatic/renal failure

Diabetes

Malnutrition

Rhabdomyolysis

Question 17

Ketoacidosis

Answer 17

increase acetoacetic acid and B-OH butyric acid

Question 18

Drug intoxications

Answer 18

Salicylate toxicity: respiratory alkalosis from stimulation of respiratory drive, metabolic acidosis from accumulation of acid

Methanol/ethanol glycol ingestion

Question 19

Symptoms of lactic acidosis

Answer 19

Kussmaul respirations

Peripheral vasodilation causing flushing and tachycardia; as acidosis worsens, ventricular arrhythmias may occur

Hyperkalemia

Lethargy/coma

N/V

Bone demineralization in chronic acidotic states

Question 20

Treatment of lactic acidosis

Answer 20

Treat the underlying cause!

Acute bicarbonate therapy
-Consider use if pH < 7.10-7.15

Question 21

Good indications of bicarb

Answer 21

Hyperkalemia, pH < 7.10 with cardiac arrest after defibrillation, ventilation, and medications have been utilized, and overdoses

Question 22

Bicarbonate dose

Answer 22

(mEq)= [0.5 L/kg (IBW)] x (desired HCO3- - actual HCO3-)

desired HCO3- is 12 mEq/L

give 1/3 to 1/2 the calculated dose; monitor ABG

during cardiac arrests, 1 mEq/kg may be given

supplement K+, if needed

Question 23

Hazards of bicarbonate therapy

Answer 23

Overalkanization can reduce cerebral blood flow and can impair oxygen release from Hgb to tissues
-A “shift to the left” on the oxygen-hemoglobin saturation curve
-For any given pO2, Hgb has increase saturation

Hypernatremia, hyperosmolality

CSF acidosis occurs from the CO2 that is generated

Electrolyte shifts

Question 24

Potassium

Answer 24

With acidosis, K+ moves extracellularly and is excreted

When bicarbonate therapy is used to treat the acidosis, K+ moves back into the cells creating even more hypokalemia

Question 25

Calcium

Answer 25

Decreased ionized calcium–>decrease myocardial contractility

Question 26

Chronic bicarbonate therapy

Answer 26

for chronic metabolic acidosis

average dose: 1-3 mEq/kg/day (may go up to 10+ mEq/kg/day