What IV fluids should be started for an adult patient who is nil per os awaiting surgery, with no fluid restriction, normal electrolytes, and no cardiac or renal failure?

IV Fluid Selection for NPO Patients Awaiting Surgery

For adult patients who are NPO awaiting surgery with normal electrolytes and no cardiac or renal failure, start with balanced crystalloid solutions such as lactated Ringer's or Plasma-Lyte rather than 0.9% normal saline. 1, 2

Primary Fluid Choice: Balanced Crystalloids

Balanced crystalloid solutions (lactated Ringer's, Plasma-Lyte) should be the first-line choice for routine perioperative fluid management in most surgical patients. 1, 2

• Balanced crystalloids have sodium, potassium, and chloride content closer to extracellular fluid composition, preventing hyperchloremic metabolic acidosis that occurs with normal saline. 1, 2
• Plasma-Lyte contains sodium 140 mEq/L, potassium 5 mEq/L, and chloride 98 mEq/L with osmolarity of 295 mOsm/L, closely matching plasma composition. 1, 3
• Lactated Ringer's contains sodium 130 mEq/L, potassium 4 mEq/L, and chloride 108 mEq/L with osmolarity of 277 mOsm/L. 1
• Randomized trials demonstrate that balanced crystalloids reduce the need for vasopressors and prevent metabolic acidosis compared to normal saline in the operating room. 2

When to Use Normal Saline Instead

Switch to 0.9% normal saline specifically for neurosurgical patients or those with traumatic brain injury. 1

• Normal saline (sodium 154 mEq/L, osmolarity 308 mOsm/L) is recommended as first-line therapy in traumatic brain injury to maintain plasma osmolarity and prevent cerebral edema. 1
• Hypotonic solutions like lactated Ringer's should be avoided in neurosurgical patients due to lower osmolarity (277 mOsm/L) which can worsen cerebral edema. 1
• Buffered isotonic solutions like Plasma-Lyte may be acceptable alternatives to normal saline in neurosurgery as they avoid hyperchloremic acidosis while maintaining appropriate osmolarity. 1

Important Caveats and Pitfalls

Do not worry about the potassium content in balanced crystalloids (4-5 mEq/L) even in patients with mild hyperkalemia. 1

• Large randomized studies involving 30,000 patients found comparable plasma potassium concentrations between normal saline and balanced fluid groups. 1
• Physiologically, it is not possible to create potassium excess using a fluid with potassium concentration lower than the patient's serum level. 1

Avoid albumin and synthetic colloids (hydroxyethyl starch, gelatin) for routine perioperative fluid management. 1

• Albumin is specifically contraindicated in neurosurgical patients and those with traumatic brain injury due to increased mortality and pulmonary edema risk. 1
• Hydroxyethyl starch increases the risk of acute kidney injury and should be avoided. 1

Administration Guidelines

Administer isotonic crystalloids at maintenance rates (1-1.5 mL/kg/hr) for routine NPO patients, adjusting based on ongoing losses and hemodynamic status. 1, 4

• For patients with signs of dehydration, initial boluses of 20 mL/kg may be required. 4
• Monitor urine output targeting >0.5 mL/kg/hr and maintain adequate central venous pressure. 4
• Plasma-Lyte is compatible with blood products and can be used as a priming solution or administered concurrently with transfusions. 3

Target normovolemia rather than positive fluid balance in most surgical patients. 1

• Avoid fluid overload, particularly in thoracic surgery patients where positive fluid balance in the first 24 hours is associated with worse outcomes. 1
• For minor noncardiac surgery under general anesthesia, a mildly positive fluid balance may reduce postoperative nausea and vomiting. 1