Following surgery, a patient develops oliguria. You believe the patient is hypovolemic, but you seek corroborative data before increasing intravenous fluids. The best data is ?
|A||Urine sodium of 28 meq/L|
|B||Urine chloride of 15 meq/L|
|C||Fractional excretion of sodium less than 1|
|D||Urine/ Serum creatinine ratio of 20|
a. The most common form of ARF is prerenal ARF, which occurs in the setting of renal hypoperfusion.
b. Prerenal ARF is generally reversible when renal perfusion pressure is restored.
c. By definition, renal parenchymal tissue is not damaged.
d. More severe or prolonged hypoperfusion may lead to ischemic injury, often termed acute tubular necrosis, or ATN.
e. Thus, prerenal ARF and ischemic ATN fall along a spectrum of manifestations of renal hypoperfusion.
f. Hypovolemia leads to a fall in mean systemic arterial pressure, which is detected as reduced stretch by arterial (e.g., carotid sinus) and cardiac baroreceptors.
g. In turn, this triggers a coordinated series of neurohormonal responses that aim to restore blood volume and arterial pressure.
h. These include activation of the sympathetic nervous system and renin-angiotensin-aldosterone system, as well as release of arginine vasopressin.
i. Relatively "nonessential" vascular beds (such as the musculocutaneous and splanchnic circulations) undergo vasoconstriction in an attempt to preserve cardiac and cerebral perfusion pressure.
j. In addition, salt loss through sweat glands is inhibited, and thirst and salt appetite are stimulated. Renal salt and water retention also occur.
k. Severe hypovolemia due to hemorrhage should be corrected with packed red cells, whereas isotonic saline is usually appropriate replacement for mild to moderate hemorrhage or plasma loss (e.g., burns, pancreatitis).
l. Subsequent therapy should be based on measurements of the volume and ionic content of excreted or drained fluids.
m. Serum potassium and acid-base status should be monitored carefully, and potassium and bicarbonate supplemented as appropriate.
n. Invasive hemodynamic monitoring may be required in selected cases to guide therapy for complications in patients in whom clinical assessment of cardiovascular function and intravascular volume is difficult.