Question 1

What is the most common clinical condition associated with respiratory acidosis?

Accepted Answer

Chronic obstructive pulmonary disease (COPD) is the most common cause of respiratory acidosis.

Question 2

When has full acid-base compensation occurred?

Accepted Answer

If the pH has been restored to the normal range (7.35 to 7.45), full compensation has occurred even though pH remains on the acid or alkaline side of the range.

Question 3

Which of the following is the most common cause of iatrogenic respiratory alkalosis?

Accepted Answer

Hyperventilation and respiratory alkalosis may be iatrogenically (via medical treatment) induced. Such hyperventilation is most commonly associated with overly aggressive mechanical ventilation and may also be associated with aggressive deep breathing and lung-expanding respiratory therapy procedures.

Question 4

What is the interpretation of a blood gas that shows a pH of 7.44, a PaCO₂ of 50 mm Hg, a PaCO₂ of 48 mm Hg, and an [HCO₃^-] of 33 mEq/L in a patient with advanced COPD?

Accepted Answer

A patient with advanced but stable COPD and compensated respiratory acidosis may exhibit the following arterial blood gas values: pH = 7.38 PaCO₂ = 58 mm Hg HCO₃^- = 33 mEq/L Note that the HCO₃- level is high due to renal compensatory activity. If the person now experiences an acute exacerbation of his disease and becomes severely hypoxic, this may stimulate the peripheral chemoreceptors enough to increase alveolar ventilation and acutely lower the PaCO? despite the patient's disturbed lung mechanics. In this case, let us assume that the patient was not capable of hyperventilating enough to lower the PaCO₂ all the way down into the normal range. Even though the PaCO₂ is still above normal, the acute lowering of the PaCO₂coupled with the preexisting high compensatory level of HCO₃^- causes the pH to swing from the acidic to the alkalotic side of normal: pH = 7.44 PaCO₂ = 50 mm Hg HCO₃^- = 33 mEq/L If one were to pay attention only to the blood gas data and apply the strict criteria for interpretation, this would lead to the completely incorrect interpretation of compensated metabolic alkalosis. This interpretation would lead the novice to conclude that the patient is hypoventilating to compensate for a preexisting primary metabolic alkalosis; in light of the patient's medical history, this would be an absurd conclusion. This example illustrates the fact that blood gas data alone are not a sufficient basis for rational acid-base assessment. The patient's medical history, the physical examination, and the nature of the current problem are vital in accurately evaluating blood gas abnormalities. The blood gases here are correctly described as acute hyperventilation superimposed on compensated respiratory acidosis.

Question 5

Which of the following are effects of a rapidly rising PaCO₂? I.Increased intracranial pressure II.Myoclonus III.Mental confusion IV.Cerebral vasoconstriction

Accepted Answer

Rapidly rising PaCO₂ causes cerebral vasodilation and increased intracranial pressure, possibly leading to retinal venous distension and retinal hemorrhage. In addition, the patient may develop myoclonus (spasmodic muscle jerks), asterixis (a hand-flapping tremor in which the patient cannot keep the wrists flexed with the arms extended), and mental confusion.

Question 6

Which acute level of PaCO₂ can lead to coma in patients without chronic hypercapnia?

Accepted Answer

Abrupt hypercapnia above a PaCO₂ of 70 mm Hg can lead to coma, although patients with chronic hypercapnia can tolerate much higher levels.

Question 7

Which of the following is the primary disturbance associated with the following blood gas: pH is 7.36, PaCO₃ is 80 mm Hg, and HCO₃^- is 44 mEq/L?

Accepted Answer

The primary disturbance is of respiratory origin, and the increased [HCO₃^-] is a secondary metabolic compensatory response.

Question 8

What is the most common cause of hyperventilation in patients with pulmonary disease?

Accepted Answer

Probably the most common cause of hyperventilation in patients with pulmonary disease is arterial hypoxemia, mediated through the peripheral chemoreceptors.

Question 9

What is the interpretation of the following blood gas reading: pH is 7.15, PaCO₂ is 80 mm Hg, and HCO₃^- is 26 mEq/L?

Accepted Answer

If the pH is 7.15, the PaCO₂ is 80 mm Hg, and the HCO₃^- is 26 mEq/L, no compensation has occurred; that is, the HCO₃^- is still normal, and not high as would be expected if compensatory action were underway.

Question 10

Following a rise in PaCO₂, when is full renal compensation for respiratory acidosis expected to occur?

Accepted Answer

Renal (kidney) compensation for respiratory acidosis begins as soon as PaCO₂ rises. The kidney reclaims HCO₃^- from the renal tubular filtrate, returning it to the blood. This brings the arterial pH into the normal range because the [HCO₃]-dissolved carbon dioxide ratio is restored near its normal 20:1 range. This process cannot keep pace with an acutely rising PaCO₂, however. Full compensation may take several days.

Question 11

Which of the following are causes of hypoxia-induced respiratory alkalosis?
I.High altitude
II.Asthma
III.Pneumonia
IV.Pulmonary edema

Accepted Answer

Hypoxia-induced respiratory alkalosis can be caused by high altitude or pulmonary diseases characterized by intrapulmonary shunting (e.g., pneumonia, pulmonary edema). Other pulmonary diseases associated with hyperventilation and respiratory alkalosis include interstitial fibrosis, pulmonary embolism, and acute asthma.

Question 12

When does renal compensation begin?

Accepted Answer

Renal (kidney) compensation for respiratory acidosis begins as soon as PaCO₃ rises. The kidney reclaims HCO₃^-from the renal tubular filtrate, returning it to the blood. This brings the arterial pH into the normal range because the [HCO₃^-]-dissolved carbon dioxide ratio is restored near its normal 20:1 range. This process cannot keep pace with an acutely rising PaCO₂, however. Full compensation may take several days.

Question 13

When has partial acid-base compensation occurred?

Accepted Answer

Compensation is partial if the pH is still outside the normal range but the noncausative component (either PaCO₂ or HCO₃^-) is also abnormal in a way that brings the pH back toward the normal range.

Question 14

Which of the following are common causes of hypoventilation and respiratory acidosis?
I.Central nervous system depression
II.Extreme obesity
III.Neuromuscular disorders
IV.Pulmonary fibrosis

Accepted Answer

Central nervous system depression (drug-induced), extreme obesity (impaired diaphragmatic movement), and neuromuscular disorders (spinal cord lesions, paralytic neuromuscular diseases) are among the causes of hypoventilation and respiratory acidosis.

Question 15

Which of the following is an early sign of respiratory alkalosis?

Accepted Answer

An early sign of respiratory alkalosis (hypocapnia) is paresthesia, a numbness or tingling sensation in the extremities.

Question 16

Which of the following are associated with hypocapnic cerebral vasoconstriction?
I.Light-headedness
II.Dizziness
III.Tinnitus
IV.Syncope

Accepted Answer

A low PaCO₂ may constrict cerebral vessels enough to impair cerebral circulation, causing light-headedness, dizziness, and syncope (fainting).

Question 17

Which of the following laboratory values is typically ignored in the calculation of the anion gap?

Accepted Answer

Generally, K⁺ is ignored in calculating the anion gap because of its very low concentration: Anion gap (mEq/L) = [Na+] - ([Cl¯] + [HCO₃¯])

Question 18

What is the interpretation of a blood gas that shows a low PaCO₂, a low [HCO₃^-], and an alkaline pH?

Accepted Answer

Partially compensated respiratory alkalosis is characterized by a low PaCO₂, a low [HCO₃^-], and an alkaline pH not quite down in the normal range.

Question 19

What is the interpretation of the following blood gas information: pH is 7.36, PaCO₂ is 80 mm Hg, and HCO₃^- is 44 mEq/L?

Accepted Answer

If the pH is 7.36, the PaCO₂ is 80 mm Hg, and the HCO₃^- is 44 mEq/L, compensation is present because the pH is in the normal range, although it is on the acid side of normal. The primary cause of the original acid-base disturbance (before compensatory activity started) must be the factor that would produce acidemia (i.e., the high PaCO₂ of 80 mm Hg). Thus, this set of blood gases would be classified as signifying compensated (chronic) respiratory acidosis.

Question 20

What is the interpretation of a blood gas that shows a high PaCO₂, a high [HCO₃^-], and an acid pH not quite in the normal range?

Accepted Answer

Partially compensated respiratory acidosis has a high PaCO₂, a high [HCO₃^-], and an acid pH not quite in the normal range.

Quiz 13: Clinical Assessment of Acid-Base and Oxygenation Status

What is the most common clinical condition associated with respiratory acidosis?

When has full acid-base compensation occurred?

Which of the following is the most common cause of iatrogenic respiratory alkalosis?

What is the interpretation of a blood gas that shows a pH of 7.44, a PaCO2 of 50 mm Hg, a PaCO2 of 48 mm Hg, and an [HCO3-] of 33 mEq/L in a patient with advanced COPD?

Which of the following are effects of a rapidly rising PaCO2? I.Increased intracranial pressure II.Myoclonus III.Mental confusion IV.Cerebral vasoconstriction

Which acute level of PaCO2 can lead to coma in patients without chronic hypercapnia?

Which of the following is the primary disturbance associated with the following blood gas: pH is 7.36, PaCO3 is 80 mm Hg, and HCO3- is 44 mEq/L?

What is the most common cause of hyperventilation in patients with pulmonary disease?

What is the interpretation of the following blood gas reading: pH is 7.15, PaCO2 is 80 mm Hg, and HCO3- is 26 mEq/L?

Following a rise in PaCO2, when is full renal compensation for respiratory acidosis expected to occur?

Which of the following are causes of hypoxia-induced respiratory alkalosis? I.High altitude II.Asthma III.Pneumonia IV.Pulmonary edema