Differentiating causes of hypoxemia, Biology

Study and complete the following Mini Clini: Differentiating Causes of Hypoxemia. Explain the pathophysiological mechanism of how the following disorders cause hypoxia:

  • Pleural effusion
  • Parkinson's Disease
  • Guillian Barre

Write a 400-500 word summary and use at least one scientific/medical resource for support.

Use standard essay format in APA style, including an introduction, conclusion, and title page. Cite in-text and in the References section.

Mini Clini: Differentiating Causes of Hypoxemia


Two patients present with the following ABGs at sea level:

Patient A

pH                   7.45

PaCO2 33mmHg

PaO2                40mmHg

HCO3              22mEq/L

SaO2                70%

FIO2                0.21

Patient B

pH                   7.21

PaCO2             72mmHg

PaO2                53mmHg

HCO3              28mEq/L

SaO2                81%

FIO2                0.21

1. Define the respiratory condition indicated by each ABG analysis.

2. What is the P(A-a)O2 for each blood gas?

3. Identify the type of respiratory failure in each of those cases.

4. In which case would administration of 100% FIO2 help determine therapy?


1. Patient A exhibits uncompensated respiratory alkalosis with hypoxemia. Patient B exhibits partially compensated respiratory acidosis with hypoxemia.

2. Patient A:



P(A-a)O2=108-40=68mmHg on room air

Patient B:



P(A-a)O2=60-53=7mmHg on room air

The normal values for P(A-a)O2 range from 10mmHg in young people to approximately 25mmHg in the elderly while breathing room air.

3. Patient A is a case of hypoxemic respiratory failure (type I) as characterized by the below normal PaO2 (40mmHg). The PaCo2 is also below normal (33mmHg) indicating hyperventilation is taking place in an effort to improve the oxygenation. Patient B is a case of hypercapnic respiratory failure (type II) as characterized by the above normal PaCO2 (72mmHg) indicating hypoventilation (ventilatory failure) is occurring. This is also known as acute ventilatory failure superimposed on chronic ventilatory failure. This patient is also hypoxemic (53 mmHg). There is a slight elevation of the HCO3 (28mEq/L) indication an element of chronic respiratory failure may be present, which has now become acute.

4.Patient A has hypoxemic respiratory failure with a P(A-a)O2 of 68mmHg, which is well above normal, indicating an oxygenation defect. The administration of 100% O2 in this case would help to determine the cause of the defect. Significant response to the 100% FIO2 would point to V/Q mismatch as the cause, while shunt would be implicated if the PaO2 did not respond to the increase in delivered O2. In the latter, some form of PEEP would be necessary to improve gas exchange by improving FRC.

Patient B has hypercapnic respiratory failure (ventilatory failure) with hypoxemia, but with a P(A-a)O2 of 7mmHg which is within the normal range. This indicates a pure ventilatory defect as the cause of the hypoxemia, and administration of 100% FIO2 would not help to determine therapy. Depending on the full patient scenario, this patient may require intubation and mechanical ventilation to restore normal acid-base status.

Posted Date: 2/25/2013 4:19:40 AM | Location : United States

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