What is the recommended approach to fluid management in adult patients undergoing anesthesia, considering their preoperative condition, type of surgery, and potential fluid shifts?

Fluid Management in Anaesthesia

Perioperative fluid management should target a mildly positive balance of 1-2 liters by the end of surgery using buffered crystalloid solutions, avoiding both hypovolemia and fluid overload, as both extremes significantly increase morbidity and mortality. 1

Preoperative Phase

Allow clear fluids until 2 hours before surgery to prevent dehydration and reduce insulin resistance. 2, 3 Prolonged fasting should be avoided, particularly in elderly patients where preoperative intravenous fluid substitution of 2-3 liters crystalloid is recommended if dehydration is present. 1

Intraoperative Fluid Strategy

Choice of Fluid Type

Use buffered crystalloid solutions (Ringer's Lactate or Plasmalyte) as the primary intraoperative fluid with 98% expert consensus supporting this approach. 1, 2, 4 These solutions prevent hyperchloremic metabolic acidosis, renal vasoconstriction, and acute kidney injury that occur with 0.9% saline. 2, 5, 4

Avoid routine use of synthetic colloids or albumin for volume replacement (90% expert agreement), as they offer no mortality benefit and carry potential risks including acute kidney injury and death in critically ill patients. 2, 5, 4

Volume Administration

Administer crystalloids at 2-6 mL/kg/hour during surgery, targeting a positive balance of 1-2 liters by procedure completion. 2, 4 A large multicenter RCT of 3000 patients demonstrated that stringently restrictive "zero-balance" regimens resulted in significantly higher acute kidney injury rates compared to modestly liberal regimens. 2, 4

Critical threshold: never exceed 6 mL/kg/hour, as rates of 8 mL/kg/hour are associated with a relative risk of 6.4 for pulmonary complications. 4

Goal-Directed Fluid Therapy (GDFT)

Consider GDFT with minimally invasive cardiac output monitoring for high-risk patients (mortality risk >20%, major abdominal/cardiac/vascular surgery, significant cardiovascular comorbidities) or those with anticipated significant blood loss. 2, 5

GDFT uses stroke volume optimization to maintain patients on their individual Frank-Starling curve, with meta-analyses demonstrating significant reductions in postoperative morbidity and hospital stay. 5, 4 Key hemodynamic targets include:

• Cardiac index >3.0 L/min/m² in high-risk patients 5
• Stroke volume variation <10% 4
• Optimize stroke volume response to fluid challenges rather than using fixed protocols 5

Use minimally invasive devices such as esophageal Doppler, transpulmonary dilution techniques, or advanced arterial waveform analysis for cardiac output measurement. 5

Surgery-Specific Considerations

Major Abdominal Surgery

Target 1-2 liter positive balance using buffered crystalloids at 2-6 mL/kg/hour, with GDFT for high-risk patients. 2, 4 In patients with anastomoses, avoid overly restrictive regimens (<1.5 liters total), as this may increase anastomotic leak risk. 2

Thoracic Surgery

Strict restriction to 2-6 mL/kg/hour maximum is essential, avoiding positive balance in the first 24 postoperative hours. 4, 6 Intraoperative fluid volume is an independent risk factor for pulmonary complications (OR 1.3 per increment). 4

Neurosurgery

Avoid both albumin and hypotonic solutions (88% and 100% expert agreement, respectively). 4 In traumatic brain injury specifically, 0.9% saline is preferred over buffered solutions. 4

Kidney Transplantation

Buffered crystalloid solutions are strongly recommended over 0.9% saline (99% expert agreement). 4

Minor Noncardiac Surgery

A mildly positive fluid balance reduces postoperative nausea and vomiting (93% expert agreement). 4

Special Population Adjustments

Elderly Patients

Fluid therapy should be administered with great care in divided boluses to allow assessment of response, as pathophysiological changes reduce homeostatic compensation for both fluid loss and administered boluses. 1 Consider intra-arterial blood pressure monitoring earlier in elderly unwell patients. 1

Patients with Comorbidities

Use the lower limit of the fluid range (2-4 mL/kg/hour) in patients with heart failure, chronic kidney disease, or lung disease, as they have decreased fluid tolerance and higher risk of fluid accumulation. 4 Consider hemodynamic monitoring with stroke volume variation to guide therapy. 4

Vasopressor and Inotrope Management

Optimize intravascular volume first before initiating vasopressors. 5 Once optimal volume is achieved:

• Use norepinephrine to maintain adequate perfusion pressure in normovolemic patients 5, 4
• Consider dobutamine when low cardiac output persists despite adequate volume and blood pressure 5

Critical Pitfalls to Avoid

Fluid overload (>2.5 kg perioperative weight gain) significantly increases complications including anastomotic leak, pulmonary complications, ventilator dependence, intestinal edema, and poor wound healing. 2, 5, 4

Large volumes of 0.9% saline cause hyperchloremic acidosis and renal dysfunction through renal vasoconstriction and increased acute kidney injury risk. 2, 5, 4

Do not use GDFT as justification for liberal fluid administration - the goal is optimization, not maximization of volume. 5

Do not rely solely on central venous pressure (CVP) - use dynamic variables of fluid response such as stroke volume variation. 5

Avoid prolonged intraoperative hypotension while optimizing volume, which may require early vasopressor use. 5

Postoperative Management

Continue buffered crystalloids postoperatively, avoiding both hypovolemia and fluid overload. 4 Early initiation of oral intake and cessation of intravenous therapy are recommended. 3