Which of the following mechanisms explains the impaired renal function seen in patients receiv-ing ventilatory support with positive pressure?

1. Decreased secretion of aldosterone
2. Decreased intravascular volume
3. Increased secretion of vasopressin
a. 1 only
b. 2 only
c. 1 and 3 only
d. 1, 2, and 3

ANS: B
Results of more recent analysis tend to refute this explanation, instead showing that impaired re-nal function during positive-pressure ventilation is better associated with a decrease in intravas-cular volume.