Metabolic alkalosis

Question 1

Metabolic alkalosis

Answer 1

pH > 7.45, increased HCO3-, and a compensatory hypoventilation resulting in increased PaCO2

Question 2

Pathophysiology

Answer 2

Primary rise in HCO3- can occur through:

1. Loss of acid from GI tract or urine
2. Administration of HCO3- or a bicarbonate precursor
3. Contraction alkalosis

Sometimes, there is an impairment in renal function that results in the maintenance of metabolic acidosis

Volume and chloride depletion

Question 3

Saline Responsive

Answer 3

Urinary chloride < 10-20 mEq/L

Question 4

Diuretic therapy

Answer 4

most common cause of saline responsive alkalosis

Enhances excretion of NaCl and water, resulting in extracellular volume contraction

Volume contraction stimulates aldosterone release

Aldosterone increases distal tubular Na+ reabsorption and induces H+ and K+ secretion

H+ secretion is associated with HCO3- reabsorption in the proximal tubule and HCO3- generation in distal tubule

Na and H exchange in distal tubule

In response to hypokalemia, there is stimulation of movement of hydrogen ions intracellularly

K+ moves extracellularly to fight off hypokalemia, in exchange for K+, Na+ gets reabsorbed

Hypochloremic state: normally Cl- is anion absorbed with Na+, without Cl-, Na is reabsorbed with HCO3-

Question 5

Vomiting and NG suction

Answer 5

2nd most common cause of alkalosis

1L/day may be lost with vomiting

1L of fluid contains: 200 mEq Cl-, 25-100 mEq H+

Question 6

Exogenous HCO3- administration or blood transfusions

Answer 6

Blood transfusions: HCO3- in fluids, LR, TPN’s

Citrate (preservative in blood products) breaks down to HCO3-

Question 7

Saline resistant alkalosis

Answer 7

urinary chloride > 20 mEq/L

Enhanced renal H+ excretion and HCO3- reabsorption

Key difference: no chloride depletion or this is an inability to reabsorb chloride

Question 8

Increased mineralcorticoid activity

Answer 8

Causes of saline resistance

Directly stimulates collecting duct H+ secretion and indirectly increase ammoniagenesis by causing hypokalemia

Question 9

Hypokalemia

Answer 9

Cause of saline resistance

Increased H+ secretion with HCO3- reabsorption and ammoniagenesis

Question 10

Renal tubular chloride wasting (Bartter’s syndrome)

Answer 10

Impaired NaCl reabsorption

Volume depletion activates RAA system–>increase aldosterone

Question 11

Symptoms of alkalosis

Answer 11

Muscle cramps, weakness, paresthesias

Postural dizziness

Cellular hypoxia, mental confusion, coma, seizures

Direct myocardial suppression; CV collapse; arrhythmias

Question 12

Treatment of alkalosis

Answer 12

Treat underlying cause

Rapid correction not necessary but treatment still needed

Question 13

Treatment for saline responsive

Answer 13

SALINE

Fluid/electrolyte replacement with NaCl or KCl

Allows more Na+ to be reabsorbed with Cl- vs. getting exchanged with H+ or reabsorbed with HCO3-

Increases the plasma K+ concentration which reduces renal H+ secretion

Use caution in patients with HF or hepatic/renal failure

Potassium supplementation

May also use lactated ringers for certain patients

Question 14

Monitoring

Answer 14

I/O, BP, HR, lung sounds, electrolytes, edema

Question 15

Carbonic anhydrase inhibitors for treatment of saline responsive

Answer 15

Used in patients who cannot tolerate excess fluids or sodium

Decreases HCO3- reabsorption in proximal tubule

Adverse consequence is K+ wasting: caution in already hypokalemic patients

Not helpful in volume depletion, renal dysfunction, or severe alkalosis (pH > 7.55)

Question 16

Other alternatives for persistant alkalosis

Answer 16

HCl: for failure of previous therapies, or confirmed severe metabolic alkalosis pH >7.55 or HCO3- > 50

Ammonium chloride

Question 17

Adjunct therapies

Answer 17

For patients with vomiting or NG suction as their cause: H2 antagonist or PPIs

Question 18

Treatment of saline resistant

Answer 18

Correct hypokalemia with potassium-sparing diuretic or KCl supplementation

Decrease dose of mineralcorticoid or change steroids to one with less activity

Spironolactone

Correct hyperaldosteronism-fluids