Podcast
Questions and Answers
What is the primary cause of anatomic shunts in the circulatory system?
What is the primary cause of anatomic shunts in the circulatory system?
- Alveolar fluid accumulation
- Gas exchange in alveoli
- Increased alveolar ventilation
- Blood bypassing alveoli completely (correct)
Which condition is a common cause of capillary shunting?
Which condition is a common cause of capillary shunting?
- Intrapulmonary fistula
- Bronchial venous drainage
- Alveolar fluid accumulation (correct)
- Congenital heart disease
What percentage of cardiac output is considered to be normal for an anatomic shunt in a healthy lung?
What percentage of cardiac output is considered to be normal for an anatomic shunt in a healthy lung?
- 1 percent
- 5 percent
- 10 percent
- 3 percent (correct)
Which of the following conditions can lead to a relative shunt effect?
Which of the following conditions can lead to a relative shunt effect?
Which of the following is NOT a cause of absolute shunting?
Which of the following is NOT a cause of absolute shunting?
Which of the following conditions results from the impairment of alveolar-capillary gas exchange?
Which of the following conditions results from the impairment of alveolar-capillary gas exchange?
What characterizes an absolute shunt?
What characterizes an absolute shunt?
What are common causes for relative shunting?
What are common causes for relative shunting?
What is the normal adult male hemoglobin (Hb) value range?
What is the normal adult male hemoglobin (Hb) value range?
How much oxygen (in mL) can each gram of hemoglobin (g% Hb) carry at full saturation?
How much oxygen (in mL) can each gram of hemoglobin (g% Hb) carry at full saturation?
At a normal partial pressure of oxygen (PaO2) of 100 torr, what is the approximate hemoglobin saturation (SaO2)?
At a normal partial pressure of oxygen (PaO2) of 100 torr, what is the approximate hemoglobin saturation (SaO2)?
Which of the following is NOT one of the normal physiologic shunts affecting Hb saturation?
Which of the following is NOT one of the normal physiologic shunts affecting Hb saturation?
What must be adjusted to account for the arterial oxygen when calculating its amount bound to hemoglobin?
What must be adjusted to account for the arterial oxygen when calculating its amount bound to hemoglobin?
Which of the following units does NOT represent normal hemoglobin range?
Which of the following units does NOT represent normal hemoglobin range?
If a person's hemoglobin level is 15 g percent, what is the expected volume percentage (vol%) of oxygen bound to hemoglobin at full saturation?
If a person's hemoglobin level is 15 g percent, what is the expected volume percentage (vol%) of oxygen bound to hemoglobin at full saturation?
Which of these correctly describes a relationship between grams percent of hemoglobin and milliliters of oxygen carried at full saturation?
Which of these correctly describes a relationship between grams percent of hemoglobin and milliliters of oxygen carried at full saturation?
What is the primary characteristic of hypoxemia?
What is the primary characteristic of hypoxemia?
Which of the following conditions does hypoxemia most frequently lead to?
Which of the following conditions does hypoxemia most frequently lead to?
What factors must be added together to determine total oxygen content in 100 mL of blood?
What factors must be added together to determine total oxygen content in 100 mL of blood?
How can a reduced level of oxygen in arterial blood still maintain tissue oxygenation?
How can a reduced level of oxygen in arterial blood still maintain tissue oxygenation?
Which symptom is NOT typically associated with hypoxia?
Which symptom is NOT typically associated with hypoxia?
What is the formula for calculating oxygen content of arterial blood (CaO2)?
What is the formula for calculating oxygen content of arterial blood (CaO2)?
What type of hypoxia is characterized by low oxygen levels in the environment?
What type of hypoxia is characterized by low oxygen levels in the environment?
In the case study, what was the patient's hemoglobin concentration?
In the case study, what was the patient's hemoglobin concentration?
Which of the following types of hypoxia is caused by inadequate blood flow?
Which of the following types of hypoxia is caused by inadequate blood flow?
How is the volume percentage of oxygen bound to hemoglobin calculated at a saturation of 90% (SaO2)?
How is the volume percentage of oxygen bound to hemoglobin calculated at a saturation of 90% (SaO2)?
Which statement about hypoxia is true?
Which statement about hypoxia is true?
What was the observed respiratory rate of the patient in the case study?
What was the observed respiratory rate of the patient in the case study?
What symptom is associated with both hypoxia and hypoxemia?
What symptom is associated with both hypoxia and hypoxemia?
What were the signs of respiratory distress observed in the patient?
What were the signs of respiratory distress observed in the patient?
What is the normal oxygen binding factor for hemoglobin used in calculations?
What is the normal oxygen binding factor for hemoglobin used in calculations?
What condition was the patient suffering from that impacted her oxygen content?
What condition was the patient suffering from that impacted her oxygen content?
What blood condition is indicated by a hemoglobin level greater than 18.5 g% in men?
What blood condition is indicated by a hemoglobin level greater than 18.5 g% in men?
At what point does cyanosis become apparent in a patient with a normal hemoglobin level of 16 g%?
At what point does cyanosis become apparent in a patient with a normal hemoglobin level of 16 g%?
What is the hallmark feature of polycythemia?
What is the hallmark feature of polycythemia?
What hematocrit percentage indicates polycythemia in women?
What hematocrit percentage indicates polycythemia in women?
What potential problem arises from an increased hematocrit reaching 55 to 60%?
What potential problem arises from an increased hematocrit reaching 55 to 60%?
What is the normal range for hemoglobin levels in women?
What is the normal range for hemoglobin levels in women?
What does blood with a reduced hemoglobin content of at least 5 g% indicate?
What does blood with a reduced hemoglobin content of at least 5 g% indicate?
How does chronic low oxygen levels affect red blood cell counts?
How does chronic low oxygen levels affect red blood cell counts?
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Study Notes
Hemoglobin and Oxygen Transport
- Normal adult male hemoglobin (Hb) value: 14 to 16 grams percent (g%)
- Normal adult female Hb value: 12 to 15 g%
- Normal Hb range: 12 to 16 g/100 ml blood (12 to 16 g percent, 12 to 16 grams per deciliter)
- Each gram percent of Hb can carry 1.34 mL of oxygen at 100% saturation
- If Hb level is 15 g%, and fully saturated, approximately 20.1 vol% of O2 will be bound to Hb
- At a normal PaO2 of 100 torr, Hb saturation (SaO2) is approximately 97% due to physiologic shunts
- Thebesian venous drainage into left atrium
- Bronchial venous drainage into pulmonary veins
- Under-ventilated alveoli (dead space ventilation)
- The amount of arterial oxygen in the oxygen bound to Hb formula must be adjusted to 97%
- Oxygen bound to Hb formula: (1.34 x Hb x SaO2)
- To calculate total oxygen content in 100 mL of blood, add dissolved oxygen and oxygen bound to Hb
- CaO2 (oxygen content of arterial blood) = (bound to Hb) + (dissolved O2)
Case Study: Anemic Patient
- 27-year-old woman with a long history of anemia and signs of respiratory distress
- Decreased hemoglobin concentration
- Respiratory rate of 36 breaths/minute
- Heart rate of 130 beats/minute
- Blood pressure of 155/90 mmHg
- Hemoglobin concentration of 6 g percent
- PaO2 of 80 torr
- SaO2 90 percent
- Oxygen bound to Hb calculation:
- 6 g% Hb x 1.34 (O2 bound to Hb factor) = 8.04 vol% O2 (at SaO2 of 100%)
- 8.04 vol% O2 x 0.90 SaO2 = 7.236 vol% O2
Absolute Shunts
- Blood flows from the right side of the heart to the left side without passing through alveoli for gas exchange
- Divided into anatomic shunts and capillary shunts
- Anatomic shunts:
- Nonoxygenated blood bypassing alveoli and entering the pulmonary vascular system via bronchial venous drainage, or the left atrium via thebesian veins
- Common causes:
- Congenital heart disease
- Intrapulmonary fistula
- Vascular lung tumors
- Capillary shunts:
- Caused by alveolar collapse (atelectasis), fluid accumulation, or consolidation
Relative Shunts
- Pulmonary capillary perfusion exceeds alveolar ventilation
- Common causes:
- Hypoventilation
- Ventilation/perfusion mismatches (chronic emphysema, bronchitis, asthma)
- Alveolar-capillary diffusion defects
Hypoxemia vs. Hypoxia
- Hypoxemia: Abnormally low arterial oxygen tension
- Frequently associated with hypoxia, but does not necessarily mean tissue hypoxia
- Hypoxia: Low or inadequate oxygen for aerobic cellular metabolism
- Characterized by tachycardia, hypertension, peripheral vasoconstriction, dizziness, and mental confusion
- Four main types of hypoxia:
- Hypoxic hypoxia
- Anemic hypoxia
- Circulatory hypoxia
- Histotoxic hypoxia
Cyanosis
- Blue-gray or purplish discoloration on mucous membranes, fingertips, and toes
- Indicative of at least 5 g% of reduced hemoglobin in the blood
Polycythemia
- Abnormally high red blood cell (RBC) count, leading to increased oxygen carrying capacity
- Identified when hematocrit (HCT) is greater than 52% in men and 48% in women
- Hallmark: Elevated hematocrit or hemoglobin
- Problem: Increased blood viscosity
- Can lead to left and right ventricular hypertrophy and cor pulmonale (right heart failure)
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