Question

A 33-year-old woman was admitted with headache, lethargy, and intractable muscle spasms. Upon review of her medical history she was found to have been recently diagnosed with stage II hypertension and has begun taking a thiazide diuretic. Arterial blood was drawn, revealing the following:

pH	7.50
pCO2	50 mm Hg
pO2	90 mm Hg
Hemoglobin - O2 saturation	97%
[HCO3-]	32 meq / liter

Questions:

1. How would you classify this woman's acid-base status? (Be sure to address whether it is “with” or “without” compensation.)

2. Be able to describe the physiologic mechanism of the compensation that could occur for this acid-base disturbance.

3. Which of the following side effects of thiazide diuretics could result in this type of metabolic imbalance?

Dehydration

Dyspepsia

Potassium excretion

Impaired respiration

4. Which of the following could also cause of this type of acid-base disturbance?

Intractable hyperemesis

Renal failure

Encephalophathy

Stroke

5. Reducing which dietary micronutrient might help improve her pre-existing diagnosis (hypertension)?

Answer 1

1. pH > 7.45 (alkalemia) → primary disorder is an alkalosis

2. (Reference range: 33–45 mm Hg) pCO₂ and pH change in the same direction → metabolic disorder

↑ pH & ↑ pCO₂ → metabolic alkalosis

3. Evaluate HCO₃^- (Reference range: 22–28 mEq/L)

High → metabolic alkalosis or compensated respiratory acidosis

1. Thus the woman is suffering from compensated respiratory acidosis or metabolic alkalosis.

2. In metabolic disorders: rapid compensation within minutes by changes in minute ventilation

Arterial and CSF pH → ↓ stimulation of the medullary chemoreceptors → ↓ in respiratory rate and/or tidal volume → ↑ CO₂ retention

3. Metabolic alkalosis can be generated by a shift of hydrogen ions into the cells. This most often occurs in patients with potassium deficits and hypokalemia. The increased hydrogen ion loss can lead to metabolic alkalosis. Part of the loss of potassium and hydrogen ion by loop and thiazide diuretics results from activation of the renin-angiotensin-aldosterone system that occurs because of reduced blood volume and arterial pressure.

4.  In severe (hyperemesis gravidarum) and intractable vomiting can cause fluid loss and electrolyte disturbances. The acid-base result is typically ametabolic alkalosis but ketosis may also occur if oral intake is poor.

5. Reducing NaCl concentration in diet can reduce hypertension. Eating salt raises the amount of sodium in your bloodstream and wrecks the delicate balance, reducing the ability of the kidneys to remove the water. The result is a higher blood pressure due to the extra fluid and extra strain on the delicate blood vessels leading to the kidneys.