What is the first intervention to increase urine output in a patient with oliguria and signs of hypovolemia, such as tachycardia, hypotension, and delayed capillary refill?

Immediate Fluid Resuscitation with Normal Saline

The first intervention should be a fluid challenge of 500 ml normal saline over 10 minutes (Option B). This patient presents with clear signs of hypovolemic shock—tachycardia (125 bpm), hypotension (95/68 mmHg), delayed capillary refill, oliguria (30 ml in 3 hours), and pale conjunctiva suggesting anemia—following major orthopedic surgery with cemented hemiarthroplasty, which carries significant risk of perioperative blood loss 1.

Clinical Reasoning for Fluid Challenge

This patient demonstrates classic pre-renal oliguria from hypovolemia, not intrinsic renal pathology. The concentrated urine indicates intact renal concentrating ability, and the clinical picture points to inadequate intravascular volume 1. The 12-hourly maintenance fluid rate is grossly insufficient for a post-operative patient with ongoing losses and likely significant intraoperative blood loss 2.

Why Normal Saline Over Other Options

• Crystalloids are the fluid of choice for initial resuscitation in hypovolemic patients, with normal saline being appropriate for rapid volume expansion 2
• 5% dextrose (Option A) is inappropriate because it distributes throughout total body water and provides minimal intravascular volume expansion—it would be ineffective for treating hypovolemic shock 2
• The catheter does not need flushing (Option C) as it is draining concentrated urine, indicating patency and appropriate renal response to hypovolemia 1
• Antibiotics for sepsis (Option D) are not indicated given the absence of fever (37.3°C is normal), no source of infection, and the clinical picture is entirely consistent with hypovolemia from blood loss 2
• Stopping the PCA (Option E) addresses potential opioid-induced hypotension but does not address the primary problem of hypovolemia; fluid resuscitation must come first 1

Expected Response to Fluid Challenge

A positive response includes ≥10% increase in blood pressure, ≥10% reduction in heart rate, and/or improvement in urine output 2, 1. The Surviving Sepsis Campaign guidelines, while focused on septic shock, provide applicable principles for any hypovolemic state: continue fluid administration as long as hemodynamic factors improve 2.

Monitoring During Resuscitation

• Assess response after each 500 ml bolus by checking blood pressure, heart rate, capillary refill, and mental status 1, 3
• Continue fluid challenges if hemodynamic improvement occurs with each bolus 2, 3
• Stop if signs of fluid overload develop (pulmonary crackles, worsening oxygenation) or if no hemodynamic improvement occurs 2
• Monitor for improvement in urine output as a secondary endpoint, though this may lag behind hemodynamic improvement 4

Subsequent Management Considerations

After initial fluid resuscitation, investigate and address the source of hypovolemia. The pale conjunctiva strongly suggests anemia from perioperative blood loss 1. Check hemoglobin urgently and consider blood transfusion if significant anemia is confirmed, as this patient may have lost substantial blood during surgery 2.

Common Pitfalls to Avoid

• Never assume oliguria requires diuretics—this patient needs volume, not diuresis 1, 5
• Never use 5% dextrose for volume resuscitation—it lacks the osmotic properties needed for intravascular expansion 2
• Never delay fluid resuscitation to obtain invasive monitoring in obvious hypovolemia—clinical assessment is sufficient to initiate treatment 2
• Never attribute all post-operative hypotension to anesthesia or opioids without first ensuring adequate volume status 1
• Never give maintenance fluids alone when a patient shows signs of shock—bolus therapy is required 2

Algorithm for Ongoing Fluid Management

1. Administer 500 ml normal saline over 10 minutes 2
2. Reassess hemodynamics immediately after bolus 3
3. If improved but still hypotensive/tachycardic: repeat 500 ml bolus 2, 3
4. If no improvement after 1-2 liters: consider blood transfusion and vasopressor support 2
5. Once stabilized: investigate source of blood loss and optimize hemoglobin 1
6. Transition to maintenance fluids only after hemodynamic stability achieved 6