What is the appropriate maintenance fluid regimen for a 108‑lb (≈49 kg) adult female who is nil per os due to ileus or mechanical obstruction?

Maintenance Fluid Regimen for Adult Female with Ileus or Obstruction

For a 108-lb (49 kg) adult female who is NPO due to ileus or mechanical obstruction, administer isotonic crystalloid (0.9% normal saline) at approximately 1,470 mL per day (30 mL/kg/day) intravenously, with careful monitoring for signs of fluid overload and abdominal compartment syndrome. 1, 2

Fluid Calculation and Type

• Daily maintenance volume: 30 mL/kg body weight = 30 × 49 kg = 1,470 mL/day 1
• Use isotonic solutions exclusively (0.9% normal saline or lactated Ringer's), never hypotonic solutions like 5% dextrose or 0.45% saline, as these distribute into intracellular spaces and can worsen intestinal edema 1
• Isotonic solutions distribute more evenly into extracellular spaces (interstitial and intravascular) and are superior for patients with gastrointestinal dysfunction 1

Critical Monitoring Parameters

Monitor closely for complications specific to ileus/obstruction:

• Intra-abdominal pressure: Ileus can cause abdominal fluid sequestration leading to severe systemic hypovolemia, but aggressive fluid resuscitation paradoxically increases risk of abdominal compartment syndrome (IAP >20-25 mmHg) 2, 3
• Urine output: Target minimum 800 mL/day with urinary sodium >20 mmol/L to confirm adequate hydration 2
• Weight monitoring: Daily weights to assess for fluid overload without edema 2
• Electrolytes: Check serum sodium, potassium, chloride, and magnesium at least daily, as intestinal obstruction causes significant losses 2, 4

Electrolyte Replacement Strategy

Add electrolytes to maintenance fluids based on losses:

• Sodium and chloride are lost in significant quantities with intestinal distention and third-spacing 4, 5
• Potassium supplementation (typically 20 mEq/L added to IV fluids) should be initiated once urine output is confirmed 6
• Correct any metabolic abnormalities identified on daily labs 4

Nutritional Considerations During NPO Period

Do not initiate parenteral nutrition immediately:

• During the acute phase of ileus/obstruction, the priority is hemodynamic stability through fluid and electrolyte replacement, not nutritional support 2
• If NPO status extends beyond 5-7 days, consider parenteral nutrition at 20-25 kcal/kg/day (approximately 980-1,225 kcal/day for this patient) to avoid hypercaloric feeding complications 2
• Avoid exceeding actual energy needs, as hypercaloric feeding in patients with ileus is associated with worse outcomes 2

Specific Warnings for Ileus/Obstruction

Critical pitfalls to avoid:

• Fluid overload risk: While these patients often require aggressive fluid resuscitation for hypovolemia from third-spacing, they are simultaneously at high risk for abdominal compartment syndrome from salt and water overload 2, 3
• Avoid hypotonic fluids: Limit water, tea, coffee to <500-1,000 mL/day if any oral intake is permitted, as these worsen sodium losses 2
• Monitor for bacterial translocation: Ileus promotes intestinal bacterial overgrowth and potential systemic infection, requiring vigilance for sepsis 3
• Intestinal ischemia: Intraluminal pressure >30 mmHg impairs microcirculation in obstructed bowel, making adequate perfusion pressure essential 5

Transition Planning

Once obstruction resolves:

• Transition to oral rehydration solutions or maintenance IV fluids with potassium supplementation as bowel function returns 6
• If mechanical obstruction requires surgery, maintain euvolemia perioperatively and continue isotonic crystalloid support 1, 4
• For prolonged ileus, consider prokinetic agents (metoclopramide 10-20 mg PO QID) once mechanical obstruction is excluded 1