The question asks you to compare the patient’s measured urine output against a protocol-defined minimum. The calculation itself is straightforward, but the clinical reasoning behind it is what matters for licensure exams.
First, determine the patient’s individualized minimum urine output. The protocol specifies
0.5 mL/kg/h. For a
70 kg patient, the minimum acceptable hourly urine output is
35 mL/h (
0.5 × 70 = 35).
Next, calculate the actual average hourly urine output over the
4-hour window. The recorded hourly outputs are
40, 34, 28, and 22 mL. The total is
124 mL over
4 hours, which averages to
31 mL/h (
124 ÷ 4 = 31).
Comparing the two values,
31 mL/h is below the
35 mL/h minimum. This makes option 1 correct.
The
NG drainage of 600 mL is a separate piece of data and must not be added to urine output. Urine output reflects renal perfusion and glomerular filtration, while NG drainage represents gastrointestinal fluid loss.
NG output is a fluid loss that contributes to hypovolemia, but it is not a measure of kidney function.
The clinical picture is consistent with a small-bowel obstruction. The patient has colicky mid-abdominal pain, bilious vomiting, absent flatus, and radiographic findings of dilated small-bowel loops with air-fluid levels. In bowel obstruction, fluid sequesters into the intestinal lumen, and vomiting or NG suction removes additional fluid from the body.
This third-spacing and external loss reduce circulating blood volume, which in turn decreases renal perfusion and lowers urine output.
Watch out! A common error is adding NG drainage to urine output to “make up” the fluid balance. That is incorrect for assessing renal adequacy. Urine output is evaluated on its own against the weight-based minimum.
Key point! A declining hourly urine trend (
40 → 34 → 28 → 22 mL) is more concerning than a single low value. Even though the average is
31 mL/h, the downward trajectory suggests worsening hypovolemia and warrants prompt reporting.
The pathophysiologic link between bowel obstruction and oliguria is well established. In intestinal obstruction, fluid accumulates in the bowel lumen and wall, and losses from vomiting or NG suction compound the intravascular volume deficit. As circulating volume falls, renal hypoperfusion leads to reduced urine output.
Early recognition of oliguria in a patient with bowel obstruction is a signal of inadequate resuscitation and possible progression toward more severe complications.
| Item | Value | Interpretation |
|---|
| Protocol minimum | 0.5 mL/kg/h × 70 kg = 35 mL/h | Individualized lower limit |
| 4-hour urine total | 40 + 34 + 28 + 22 = 124 mL | Sum of hourly outputs |
| Average hourly urine | 124 ÷ 4 = 31 mL/h | Below the 35 mL/h limit |
| NG drainage | 600 mL over 4 hours | Fluid loss, not a renal measure |
The correct comparison is
31 mL/h, below the
35 mL/h limit. The NG drainage is a separate fluid loss that helps explain why the patient is hypovolemic, but it does not change the urine output calculation. In a patient with bowel obstruction, oliguria combined with large NG losses indicates that intravascular volume depletion is ongoing and requires continued fluid resuscitation and close monitoring.