Chapter 8: Blood Gas Data Analysis

An acute increase in PaCO2 of 10 to 15 mm Hg causes a corresponding increase in plasma HCO3- of how many mEq/L? a. 4 b. 3 c. 2 d. 1

d. 1 For acute respiratory acidosis, the plasma HCO3- increases by 1 mEq/L for each 10 to 15 mm Hg that the PaCO2 increases.

What is the normal value for CaO2? a. 4 to 8 mL/dL b. 12 to 16 mL/dL c. 8 to 12 mL/dL d. 16 to 20 mL/dL

d. 16 to 20 mL/dL The normal value is 16 to 20 mL/dL blood.

Which of the following would be best used to assess arterial oxygenation? a. PaO2 b. SaO2 c. P(A-a))2 d. CaO2

d. CaO2 CaO2, because it is the sum of oxygen bound to hemoglobin and that dissolved in plasma. It is thus one of the most important blood gas measurements, because it significantly influences tissue oxygenation.

What could cause tissue hypoxia with normal arterial oxygenation? a. Polycythemia b. Bradypnea c. Leukocytosis d. Inadequate cardiac output

d. Inadequate cardiac output Tissue hypoxia may occur with normal arterial oxygenation when inadequate perfusion exists. Clinical signs of an inadequate cardiac output include hypotension, cool extremities, weak or absent peripheral pulses, reduced urine output, and coma.

A patient has the following ABG results: pH 7.25, PaCO2 32 mm Hg, HCO3- 16 mEq/L, base excess -10 mEq/LBased on these findings, the patient has which of the following? a. Compensated metabolic acidosis b. Compensated respiratory acidosis c. Uncompensated respiratory acidosis d. Uncompensated metabolic acidosis

d. Uncompensated metabolic acidosis Metabolic acidosis is identified when the plasma HCO3- or base excess falls below normal.

Which of the following is a correct representation of the Henderson-Hasselbalch equation? a. pK = pH - log (PaCO2 · 0.03)/HCO3- b. -pH = pK - log HCO3-/(PaCO2 · 0.03) c. pK = pH - log HCO3-/(PaCO2 · 0.03) d. pH = pK + log HCO3-/(PaCO2 · 0.03)

d. pH = pK + log HCO3-/(PaCO2 · 0.03) The Henderson-Hasselbalch equation is written as follows:pH = pK + log HCO3-/(PaCO2 · 0.03).

Which of the following is the best indicator of metabolic acid-base status? a. Standard HCO- b. Base excess c. Plasma HCO- d. T40 HCO-

b. Base excess Base excess provides a more complete analysis of metabolic buffering capabilities.

What is a decrease in tissue oxygenation called? a. Acidosis b. Hypoxia c. Hypoxemia d. Hypercapnia

b. Hypoxia Hypoxia is a term that often is associated with hypoxemia; it indicates a condition in which tissue oxygenation is inadequate.

Which of the following is a true statement regarding the term hypoxemia? a. It is always considered a sever disorder b. It occurs when the patients PaO2 is lower than predicted c. It is independent of the age of the patient d. It indicates a condition in which tissue oxygenation is inadequate

b. It occurs when the patients PaO2 is lower than predicted When the measured PaO2 is below the predicted range for a patient breathing room air, regardless of the actual FIO2, this is called hypoxemia.

You are taking care of a patient receiving invasive mechanical ventilation. You are reading the chart and notice the PaCO2 decreased from 52 to 40 mmHg. What parameter would likely increase? a. COHb b. pH c. Plasma HCO- d. BE

b. pH Carbon dioxide and pH move in opposite directions, so a decrease in carbon dioxide will result in an increase in pH.

What is the normal value for PaO2 in the adult patient breathing room air? a. 60 to 70 mm Hg b. 70 to 80 mm Hg c. 80 to 100 mm Hg d. 50 to 60 mm Hg

c. 80 to 100 mm Hg The normal value is approximately 80 to 100 mm Hg in room air.

A patient is transported to the emergency department after being found unconscious in a vehicle with the engine running and the garage door closed. You apply 15 L/min of oxygen via nonrebreathing mask and obtain the following vital signs: HR: 150, RR: 34, SpO2 100%. Which of the following would you recommend to the attending physician? a. Lowering the flow rate of the nonrebreathing mask to 10 L/min b. ABG analysis c. ABG analysis with CO-oximetry d. Monitor the patient using pulse oximetry

c. ABG analysis with CO-oximetry To detect the presence of abnormal hemoglobin (such as a patient suspected of carbon monoxide poisoning), obtain an arterial blood sample, and analyze it using a CO-oximeter.

Which of the following shifts the oxyhemoglobin dissociation curve to the left? a. Increased body temperature b. Increased PaCO2 c. Fetal hemoglobin d. Decreased pH

c. Fetal hemoglobin Alkalosis, hypocapnia, hypothermia, fetal hemoglobin, and carboxyhemoglobin shift the curve to the left, resulting in higher SaO2 values at the same PaO2.

Which of the following would be the best indicator of tissue oxygenation? a. SaO2 b. CaO2 c. PO2 d. PaO2

c. PO2 One dimension capable of indicating the tissue oxygenation status in most cases is the PO2.

Which of the following could cause metabolic acidosis? a. Hypokalemia b. Vomiting c. Renal disease d. Cardiovascular disease

c. Renal disease Following is an outline of the causes of metabolic acidosis: Loss of HCO3- may be seen with diarrhea or renal disease, and increased metabolic acid production is seen with ketoacidosis, lactic acidosis, ingestion of certain toxins (e.g., methanol), and posthypocapnia disorder.

A 35-year-old, 54 kg woman with congestive heart failure enters the emergency department short of breath. An ABG shows the following results:pH 7.50, PaCO2 30 mm Hg, HCO3- 23 mEq/L, base excess +2 mEq/L The patient's ABG results indicate which of the following? a. Uncompensated metabolic acidosis b. Uncompensated metabolic alkalosis c. Uncompensated respiratory alkalosis d. Compensated respiratory acidosis

c. Uncompensated respiratory alkalosis Respiratory alkalosis, which is identified by a PaCO2 below the expected level, indicates that ventilation is exceeding the normal level. The kidneys compensate for respiratory alkalosis by excreting plasma HCO3-. A normal plasma HCO3- with a low PaCO2 and increased pH is called uncompensated respiratory alkalosis.

What is the most common physiologic cause of hypoxemia in patients with lung disease? a. Hyperventilation b. Diffusion defect c. V/Q mismatch d. Hypoventilation

c. V/Q mismatch V/Q mismatching is the most common physiologic cause of hypoxemia in patients with lung disease.

Before an arterial blood gas (ABG) value is obtained, why should the patient's clotting parameters be evaluated? a. Bleeding time may be prolonged if they are abnormal b. They may affect the accuracy of the sample pH c. They may affect the patient's PaO2 d. If reduced, they may hinder filling of the syringe with blood during the draw.

a. Bleeding time may be prolonged if they are abnormal Before arterial puncture, the clinician may find it helpful to review the patient's chart for clinical laboratory studies that reflect the patient's blood clotting ability (see Chapter 8). Abnormalities such as low platelet count or increased bleeding time may indicate that postpuncture bleeding will pose a problem. In such cases, the puncture site should be pressurized longer than usual to prevent hemorrhage.

Given the following ABG results, interpret the acid-base status: pH 7.44, PaCO2 25 mm Hg, HCO3- 17 mEq/L, base excess -6 mEq/L a. Compensated respiratory alkalosis b. Uncompensated respiratory alkalosis c. Uncompensated respiratory acidosis d. Compensated metabolic acidosis

a. Compensated respiratory alkalosis Compensation for respiratory alkalosis occurs as follows. Partial compensation occurs when the plasma HCO3- falls below normal, but the pH is still above 7.45. Full compensation occurs when the plasma HCO3- decreases enough to return the pH to within normal range.

Which of the following is true regarding respiratory alkalosis? a. The PaCO2 is less than 35 mm Hg b. It is called completely compensated if the pH is 7.52 c. An increase in HCO- compensates for respiratory alkalosis d. It is called partially compensated if the pH is in the normal range

a. The PaCO2 is less than 35 mm Hg Respiratory alkalosis, which is identified by a PaCO2 below the expected level (35 to 45 mm Hg), indicates that ventilation is exceeding the normal level. Hyperventilation usually is the result of an increased stimulus or drive to breathe. This occurs with pain, hypoxemia (PaO2 <60 mm Hg), acidosis, and anxiety.