Physiology II
Cardiovascular Case
Respiratory Case B

The Patient: a 63-year-old woman

Principal Complaint: dyspnea and severe chest pain over the left side

History: The patient had been hospitalized for a myocardial infarction eight months before the current admission. Her medications included agents to improve myocardial contractility and to reduce cardiac work (and therefore myocardial oxygen demand) through peripheral vasodilatation. After initial stabilization and subsequent maintenance on this treatment regimen, her condition had begun to deteriorate, and she was re-admitted for evaluation.

Clinical Examination: The patient’s arterial pressure was 105/62 mm Hg, and the heart rate was 155 beats/min. Rales were heard over both lower lung fields and radiographic examination revealed consolidation in the right lower lobe, an elevated right hemidiaphragm, and an enlarged heart. An electrocardiogram indicated a massive, healed myocardial infarction. With the patient breathing a mixture of room air and oxygen (F_IO₂ = 30%), PaO₂ was measured to be 64 mm Hg, the PaCO₂ was 26 mm Hg, and the bicarbonate concentration was 22.3 mEq/l. Pulmonary artery pressure was 42/28 mm Hg, and the pulmonary wedge pressure was 26 mm Hg (normal, 3-11 mm Hg). Her cardiac output was 3.45 l/min (66% of predicted). She could not get her breath unless she was propped up to an almost sitting position with four pillows. Her D_LCO was 25% of normal.

FIO2	PAO2	PaO2	PaCO2	A-a O2 difference	FIO2 helpful?
30%	181.4	64	26	118	No

STUDY QUESTIONS:

1. Explain the nature of the impairment of gas exchange in this patient using data from the blood gas values obtained while she was breathing an oxygen-enriched gas mixture.  Her A-a difference is greatly elevated.  Even with O₂ supplementation her P_aO₂ isn't brought up to a normal level.  This is a shunt.

2. What is the most likely cause of the elevated pressures within the pulmonary vascular bed of this patient?  This lady has a pretty bad case of CHF.  The left side of her heart is not pumping very well (notice the elevated PCWP) and fluid is backing up into the lungs causing the increased pressures.

3. Why does propping up a patient to a near-sitting position improve pulmonary gas exchange?  The patient gets a better gas exchange in this position.

4. Explain the rapid deterioration that commonly occurs in such patients leading to cardiac and respiratory failure and death.  The decrease in cardiac performance causes some fluid backup into the lungs.  This creates a condition where there is less O₂ diffusing.  The lowered P_aO₂ creates an even worse environment for the heart to live in so its performance is decreased again thus causing more CHF.  The spiral begins.

5. What is this patient’s calculated alveolar PO₂ while breathing 30% oxygen?  181.4

Last Updated 09/06/01 08:53:27 PM
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