Acid-base balance Practice Questions

Question 1

A 27-year-old man with a past medical history of type I diabetes mellitus presents to the emergency department with altered mental status. The patient was noted as becoming more lethargic and confused over the past day, prompting his roommates to bring him in. His temperature is 99.0°F (37.2°C), blood pressure is 107/68 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Laboratory values are ordered as seen below.

Serum:
Na+: 144 mEq/L
Cl-: 100 mEq/L
K+: 6.3 mEq/L
HCO3-: 16 mEq/L
BUN: 20 mg/dL
Glucose: 599 mg/dL
Creatinine: 1.4 mg/dL
Ca2+: 10.2 mg/dL

Which of the following is the appropriate endpoint of treatment for this patient?

Accepted Answer

Normal anion gap

Answer

Clinically asymptomatic

Answer

Normal glucose

Answer

Vitals stable

Answer

Normal potassium

Question 2

A 32-year-old man is brought to the emergency department after he was found unresponsive on the street. Upon admission, he is lethargic and cyanotic with small, symmetrical pinpoint pupils. The following vital signs were registered: blood pressure of 100/60 mm Hg, heart rate of 70/min, respiratory rate of 8/min, and a body temperature of 36.0°C (96.8°F). While being assessed and resuscitated, a sample for arterial blood gas (ABG) analysis was taken, in addition to the following biochemistry tests:
Laboratory test
Serum Na+ 138 mEq/L
Serum Cl- 101 mEq/L
Serum K+ 4.0 mEq/L
Serum creatinine (SCr)  0.58 mg/dL
Which of the following values would you most likely expect to see in this patient’s ABG results?

Accepted Answer

pH: decreased, HCO3- : increased, Pco2: increased

Answer

pH: increased, HCO3- : decreased, Pco2: decreased

Answer

pH: decreased, HCO3- : decreased, Pco2: decreased

Answer

pH: increased, HCO3- : increased, Pco2: increased

Answer

pH: normal, HCO3- : increased, Pco2: increased

Question 3

A 24-year-old woman presents to the emergency department after she was found agitated and screaming for help in the middle of the street. She says she also has dizziness and tingling in the lips and hands. Her past medical history is relevant for general anxiety disorder, managed medically with paroxetine. At admission, her pulse is 125/min, respiratory rate is 25/min, and body temperature is 36.5°C (97.7°F). Physical examination is unremarkable. An arterial blood gas sample is taken. Which of the following results would you most likely expect to see in this patient?

Accepted Answer

pH: increased, HCO3-: decreased, Pco2: decreased

Answer

pH: increased, HCO3-: increased, Pco2: increased

Answer

pH: decreased, HCO3-: decreased, Pco2: decreased

Answer

pH: decreased, HCO3-: increased, Pco2: increased

Answer

pH: normal, HCO3-: increased, Pco2: increased

Question 4

A 66-year-old man is brought to the emergency department by his daughter because of 3 days of fever, chills, cough, and shortness of breath. The cough is productive of yellow sputum. His symptoms have not improved with rest and guaifenesin. His past medical history is significant for hypertension, for which he takes hydrochlorothiazide. He has a 30-pack-year history of smoking. His temperature is 38.9 C (102.0 F), blood pressure 88/56 mm Hg, and heart rate 105/min. Following resuscitation with normal saline, his blood pressure improves to 110/70 mm Hg. His arterial blood gas is as follows:

Blood pH 7.52, PaO2 74 mm Hg, PaCO2 28 mm Hg, and HCO3- 21 mEq/L.

Which of the following acid-base disturbances best characterizes this patient's condition?

Accepted Answer

Respiratory alkalosis

Answer

Metabolic acidosis

Answer

Respiratory acidosis

Answer

Normal acid-base status

Answer

Metabolic alkalosis

Question 5

A 50-year-old woman presents to the ED 6 hours after ingesting three bottles of baby aspirin. She complains of nausea, vomiting, dizziness, and tinnitus. Her blood pressure is 135/80 mmHg, pulse is 110/min, respirations are 32/min, temperature is 100.1 deg F (37.8 deg C), and oxygen saturation is 99% on room air. Arterial blood gas at room air shows, PCO2 11 mmHg, and PO2 129 mmHg. Blood salicylate level is 55 mg/dL. Management should involve which of the following acid-base principles?

Accepted Answer

Serum alkalization, urine alkalization

Answer

Serum neutralization, urine alkalization

Answer

Serum neutralization, urine acidification

Answer

Serum acidification, urine acidification

Answer

Serum acidification, urine alkalization

Question 6

A 55-year-old man presents with an unremitting cough and swelling of the lower limbs for the past 2 weeks. He says he has had a chronic cough for years, however, he feels it is getting worse. He reports a 30-pack-year smoking history. Physical examination reveals mild central cyanosis and expiratory wheezes throughout the chest. Oxygen therapy is ordered immediately but, soon after administering it, his respiratory rate starts to slow down and he becomes drowsy. Dysfunction of which of the following receptors most likely led to this patient’s current condition?

Accepted Answer

Peripheral chemoreceptors

Answer

Pleural pain receptors

Answer

Central chemoreceptors

Answer

Airway stretch receptors

Answer

Pulmonary stretch receptors

Question 7

A 72-year-old man being treated for benign prostatic hyperplasia (BPH) is admitted to the emergency department for 1 week of dysuria, nocturia, urge incontinence, and difficulty initiating micturition. His medical history is relevant for hypertension, active tobacco use, chronic obstructive pulmonary disease, and BPH with multiple urinary tract infections. Upon admission, he is found with a heart rate of 130/min, respiratory rate of 19/min, body temperature of 39.0°C (102.2°F), and blood pressure of 80/50 mm Hg. Additional findings during the physical examination include decreased breath sounds, wheezes, crackles at the lung bases, and intense right flank pain. A complete blood count shows leukocytosis and neutrophilia with a left shift. A sample for arterial blood gas analysis (ABG) was taken, which is shown below.
Laboratory test
Serum Na+ 140 mEq/L
Serum Cl- 102 mEq/L
Serum K+ 4.8 mEq/L
Serum creatinine (SCr)  2.3 mg/dL
    Arterial blood gas  
pH 7.12
Po2 82 mm Hg
Pco2 60 mm Hg
SO2% 92%
HCO3- 12.0 mEq/L
Which of the following best explains the patient’s condition?

Accepted Answer

Metabolic acidosis complicated by respiratory acidosis

Answer

Metabolic acidosis complicated by respiratory alkalosis

Answer

Non-anion gap metabolic acidosis

Answer

Respiratory alkalosis complicated by metabolic acidosis

Answer

Respiratory acidosis complicated by metabolic alkalosis

Question 8

A 17-year-old boy is brought to the physician by his father because of a 7-month history of fatigue, recurrent leg cramps, and increased urinary frequency. His pulse is 94/min and blood pressure is 118/85 mm Hg. Physical examination shows dry mucous membranes. Laboratory studies show:
Serum
Na+ 130 mEq/L
K+ 2.8 mEq/L
Cl- 92 mEq/L
Mg2+ 1.1 mEq/L
Ca2+ 10.6 mg/dL
Albumin 5.2 g/dL
Urine
Ca2+ 70 mg/24 h
Cl- 375 mEq/24h (N = 110–250)
Arterial blood gas analysis on room air shows a pH of 7.55 and an HCO3- concentration of 45 mEq/L. Impaired function of which of the following structures is the most likely cause of this patient's condition?

Accepted Answer

Distal convoluted tubule

Answer

Ascending loop of Henle

Answer

Collecting duct

Answer

Descending loop of Henle

Answer

Proximal convoluted tubule

Question 9

A 32-year-old woman is admitted to the emergency department for 36 hours of intense left-sided back pain that extends into her left groin. She reports that the pain started a day after a charitable 5 km (3.1 mi) marathon. The past medical history is relevant for multiple complaints of eye dryness and dry mouth. Physical examination is unremarkable, except for intense left-sided costovertebral pain. The results from laboratory tests are shown.
Laboratory test Result
Serum Na+ 137
Serum Cl- 110
Serum K+ 3.0
Serum creatinine (SCr) 0.82
  Arterial blood gas Result
pH 7.28
pO2 98 mm Hg
pCO2 28.5 mm Hg
SaO2% 98%
HCO3- 15 mm Hg
Which of the following explains this patient’s condition?

Accepted Answer

Decreased renal excretion of hydrogen ions (H+)

Answer

Carbonic acid accumulation

Answer

Decreased bicarbonate renal absorption

Answer

Decreased synthesis of ammonia (NH3)

Answer

Decreased excretion of nonvolatile acids

Question 10

A 24-year-old male is brought in by ambulance to the emergency department after he was found unresponsive at home for an unknown length of time. Upon arrival, he is found to be severely altered and unable to answer questions about his medical history. Based on clinical suspicion, a panel of basic blood tests are obtained including an arterial blood gas, which shows a pH of 7.32, a pCO2 of 70, and a bicarbonate level of 30 mEq/L. Which of the following is most likely the primary disturbance leading to the values found in the ABG?

Accepted Answer

Respiratory acidosis

Answer

Metabolic alkalosis

Answer

Respiratory alkalosis

Answer

Metabolic acidosis

Answer

Mixed alkalosis

Acid-base balance

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Buffer systems (bicarbonate, phosphate, protein)

Henderson-Hasselbalch equation

Renal regulation of acid-base balance

Renal bicarbonate handling

Ammonia production and excretion

Titratable acid excretion

Respiratory regulation of acid-base

Metabolic acidosis mechanisms and compensation

Metabolic alkalosis mechanisms and compensation

Respiratory acidosis mechanisms and compensation

Respiratory alkalosis mechanisms and compensation

Mixed acid-base disorders

Clinical approach to acid-base disorders

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