A 65-year-old man was first admitted for treatment of chronic obstructive lung disease, renal insufficiency, and significant cardiomegaly. Pertinent laboratory data on admission (5/31) are shown in Case Study Table 12.1.1.

CASE STUDY TABLE 12.1.1 Laboratory Results?First Admission

Because of severe respiratory distress, the patient was transferred to the intensive care unit, placed on a respirator, and given diuretics and intravenous (IV) fluids to promote diuresis. This treatment brought about a significant improvement in both cardiac output and renal function, as shown by laboratory results several days later (6/3). After 2 additional days on a respirator with IV therapy, the patient?s renal function had returned to normal and, at discharge, his laboratory results were within normal limits (6/7).

The patient was readmitted 6 months later because of the increasing inability of his family to arouse him. On admission, he was shown to have a tremendously enlarged heart with severe pulmonary disease, heart failure, and probable renal failure. Laboratory studies on admission were as shown in Case Study Table 12.1.2. Numerous attempts were made to improve the patient?s cardiac and pulmonary function, all to no avail, and the patient died 4 days later.

CASE STUDY TABLE 12.1.2 Laboratory Results?Second Admission

Question

1. ? ?What is the most likely cause of the patient?s elevated urea nitrogen? Which data support your conclusion?