What are the essential fluid and electrolyte questions and their answers as presented in Schwartz's Principles of Surgery?

Perioperative Fluid and Electrolyte Management: Evidence-Based Recommendations

Preoperative Management

Keep preoperative fasting time short—allow clear fluids up to 2 hours before surgery to prevent dehydration and reduce thirst. 1 This includes water, pulp-free juice, and tea or coffee without milk.

Intraoperative Fluid Strategy

Volume Goals

Administer an adequate volume of fluid intraoperatively, generally targeting 1-2 L positive balance by the end of major surgery. 1 This recommendation balances the risks of both hypovolemia and fluid overload:

• Both insufficient and excessive fluid administration increase hospital stay and morbidity
• "Zero-balance" strategies showed benefits in some colorectal and abdominal aortic aneurysm surgeries
• However, a large trial (3000 patients) demonstrated that modestly liberal regimens were safer than stringently restrictive approaches

The key principle: individualize based on patient comorbidities and fluid tolerance. Patients with heart failure, chronic kidney disease, and lung disease have lower fluid tolerance and higher risk of accumulation. 1

Crystalloid Selection

Use buffered crystalloid solutions (e.g., Plasmalyte®, Ringer's lactate) as first-line therapy in the absence of hypochloraemia. 1, 2

The evidence strongly supports this:

• Large volumes of 0.9% saline cause hyperchloraemic acidosis and renal vasoconstriction
• Registry studies (>30,000 patients) showed fewer complications with buffered crystalloids
• The SALT trial demonstrated higher rates of major adverse kidney events with 0.9% saline
• Hyperchloraemia (present in ~20% of surgical patients) associates with increased 30-day mortality

Important exception: Use 0.9% saline as first-line in traumatic brain injury patients. 1 The salt load or tonicity appears protective in brain-injured patients, though the exact mechanism remains unclear.

Colloid Use

Avoid routine use of albumin or synthetic colloids (HES, gelatins) for intraoperative fluid administration. 1

The rationale:

• Synthetic colloids in critically ill patients increase risk of complications
• The crystalloid-to-colloid equivalence ratio is approximately 1:1, negating volume-sparing arguments
• No mortality benefit demonstrated in surgical patients
• Cost considerations without proven benefit

Surgery-Specific Recommendations

Kidney Transplantation

Use buffered crystalloid solutions over 0.9% saline. 1 This reduces the risk of hyperchloraemic acidosis in the transplanted kidney.

Cardiopulmonary Bypass

• Avoid routine albumin or synthetic colloids for circuit priming 1
• Avoid excessive ultrafiltration (>30 ml/kg) 1

Lung Resection Surgery

Avoid positive fluid balance in the first 24 hours postoperatively. 1 Restrictive protocols result in perioperative oliguria but don't increase AKI risk, while positive balance worsens pulmonary outcomes.

Neurosurgery

The primary goals are maintaining normal blood volume, optimizing cerebral blood flow, and avoiding reduced plasma osmolarity. 1

Four critical recommendations:

1. Avoid albumin in neurosurgical patients 1—the ALIAS trials showed no benefit and six-fold higher pulmonary edema rates

2. Avoid hypotonic solutions (Hartmann's, Ringer's lactate) 1—these reduce plasma osmolarity and worsen cerebral edema

3. Use 0.9% saline as first-line in traumatic brain injury 1—maintains osmolarity and cerebral perfusion

4. Avoid hypervolemia in subarachnoid hemorrhage 1—worsens outcomes through increased extracerebral organ dysfunction, particularly pulmonary complications

Minor Noncardiac Surgery

Maintain mildly positive fluid balance to reduce postoperative nausea and vomiting. 1 PONV occurs in 30% of general surgery patients and up to 80% in high-risk procedures.

Critical Care Considerations

In critically ill patients, use strategies that minimize fluid accumulation and promote intravascular normovolemia. 1

Key principles:

• Use buffered crystalloids unless hypochloraemia present 1
• Avoid synthetic colloids 1—large trials show increased hazard
• Avoid routine albumin 1—mixed data, no clear benefit justifying cost
• Fluid overload and accumulation clearly associate with adverse outcomes

Common Pitfalls to Avoid

1. Don't use large volumes of 0.9% saline except in TBI—causes hyperchloraemic acidosis and renal dysfunction

2. Don't assume "more is better"—both hypovolemia AND hypervolemia cause organ dysfunction

3. Don't ignore patient-specific factors—heart failure, kidney disease, and lung disease patients tolerate fluids poorly

4. Don't use hypotonic solutions in neurosurgical patients—worsens cerebral edema

5. Don't pursue hypervolemia in SAH patients—increases mortality through pulmonary complications

Acid-Base and Electrolyte Considerations

The strong-ion approach helps predict how administered fluids interact with plasma charge and influence pH. 3 Buffered solutions maintain better acid-base balance than 0.9% saline, particularly with large volumes (>2-3 L). 1

Monitor for hyperchloraemia—present in ~20% of surgical patients and independently associated with increased mortality. 1