Correct Answer: A

Rationale: The correct answer is A because renin activates the renin-angiotensin-aldosterone cascade. Renin is released by the kidneys in response to low blood pressure or low sodium levels. It acts on angiotensinogen to form angiotensin I, which is then converted to angiotensin II by angiotensin-converting enzyme. Angiotensin II causes vasoconstriction, leading to increased blood pressure, and stimulates aldosterone release, promoting sodium and water retention. Choice B is incorrect because renin does not suppress angiotensin production; it actually initiates the process. Choice C is incorrect because renin's action leads to increased sodium reabsorption by stimulating aldosterone release. Choice D is incorrect because renin does not inhibit aldosterone release; it promotes it as part of the renin-angiotensin-aldosterone cascade.

Correct Answer: B

Rationale: The correct answer is B: Hypovolemic shock. After pituitary surgery, patients are at risk for hypovolemic shock due to potential intraoperative blood loss and fluid shifts. Monitoring for signs of shock, such as hypotension and tachycardia, is crucial for early intervention. A: Congestive heart failure is less likely immediately post-surgery. C: Infection is a concern but not the highest priority in the immediate postoperative period. D: Volume overload is not a common immediate complication of pituitary surgery.

Correct Answer: D

Rationale: The correct answer is D because if a reliable 24-hour urine collection is not possible, a standardized formula can be used to estimate the GFR. This is typically done using the patient's serum creatinine level, age, sex, and race. It is a validated method when direct measurement is not feasible. A: Incorrect. It is still possible to estimate GFR using formulas when 24-hour urine collection is not possible. B: Incorrect. BUN alone is not sufficient to accurately determine renal function. C: Incorrect. BUN/Creatinine ratio is not a direct measure of GFR and may be influenced by other factors.

Correct Answer: B

Rationale: The correct answer is B: deficiency of corticosteroids. Acute adrenal crisis is caused by a sudden and severe deficiency of cortisol and aldosterone, which are essential corticosteroids produced by the adrenal glands. Without these hormones, the body cannot regulate blood pressure, electrolyte balance, and respond to stress adequately. Acute renal failure (choice A) does not directly lead to adrenal crisis. High doses of corticosteroids (choice C) can suppress the adrenal glands but do not cause acute adrenal crisis. Overdose of testosterone (choice D) does not impact the production of cortisol and aldosterone, thus not causing acute adrenal crisis.

Correct Answer: D

Rationale: The correct answer is D because continuous venovenous hemodiafiltration (CVVHDF) combines ultrafiltration, convection, and dialysis to maximize fluid and solute removal. Ultrafiltration removes plasma water, convection removes fluids and solutes, and dialysis facilitates solute removal through diffusion. Choice A is incorrect because convection alone does not remove solutes, but CVVHDF combines convection with other methods. Choice B is incorrect because CVVHDF is not specifically used for volume overload, although it does remove fluids. Choice C is incorrect because CVVHDF does not involve adding dialysate to remove solutes; instead, it relies on diffusion for solute removal. In summary, the correct answer D is the best choice as it encompasses all the components needed for comprehensive fluid and solute removal in CVVHDF.