Fluid Management in Surgery
Appropriate fluid management is essential in surgical patients. NICE CG174 recommends individualised, goal-directed fluid therapy using balanced crystalloids as first-line for replacement.
Key Facts
Daily requirements: ~25-30 mL/kg/day water, ~1 mmol/kg/day Na⁺, K⁺, and Cl⁻, ~50-100g/day glucose NICE CG174: Use balanced crystalloids (e.g., Hartmann's) for resuscitation and replacement; 0.9% NaCl causes hyperchloraemic metabolic acidosis Resuscitation fluid: 500mL crystalloid bolus over <15 minutes; reassess — repeat if needed (max 2000mL before senior review) Maintenance: 25-30 mL/kg/day as starting rate; typically 1L 0.18% NaCl / 4% dextrose + 20-40 mmol KCl over 8 hours × 3 Fluid overload: Peripheral oedema, pulmonary oedema, raised JVP — harmful; excess fluid increases complications Hypovolaemia signs: Tachycardia, hypotension, oliguria (<0.5 mL/kg/hr), raised lactate, prolonged CRT Goal-directed fluid therapy (GDFT): Oesophageal Doppler or similar to optimise stroke volume — reduces complications in major surgery Post-operative: Transition to oral fluids as early as possible; stop IV fluids when not needed (ERAS principle)
Overview
Key Facts
Fluid management in surgical patients is a core clinical skill. Both under-resuscitation and over-resuscitation cause harm. Individualised, objective assessment guides therapy.
Epidemiology
Practically all surgical patients require some form of fluid management. Post-operative AKI affects ~5-10% of patients. Fluid overload is associated with increased complications, prolonged ileus, and longer hospital stay.
Aetiology
Causes of fluid imbalance in surgical patients:
- Losses: Blood loss, third-space losses (bowel obstruction, peritonitis, pancreatitis), evaporation from exposed viscera, drains, vomiting, diarrhoea, NG aspirates
- Inadequate intake: NBM status, reduced consciousness
- Excessive administration: Overzealous IV fluids → oedema, anastomotic oedema, pulmonary oedema
Pathophysiology
- Third-spacing: Fluid shifts from intravascular to interstitial space due to inflammation, sepsis, or surgical trauma
- 0.9% NaCl: Contains 154 mmol/L Na⁺ and Cl⁻ (supraphysiological chloride) → hyperchloraemic metabolic acidosis, renal vasoconstriction
- Hartmann's/Ringer's lactate: More physiological (131 Na⁺, 111 Cl⁻, 29 lactate, 5 K⁺, 2 Ca²⁺) — preferred for resuscitation
- Colloids: Remain intravascular longer but no proven mortality benefit over crystalloids (CRISTAL, SAFE trials); gelatin/starch associated with AKI
Clinical Presentation
Assessment of Fluid Status
Hypovolaemia:
- Tachycardia, hypotension, cool peripheries, prolonged CRT (>2 seconds)
- Oliguria (<0.5 mL/kg/hr)
- Dry mucous membranes, reduced skin turgor
- Raised urea (disproportionate to creatinine)
- Raised lactate, metabolic acidosis
Fluid Overload:
- Peripheral oedema, sacral oedema, pulmonary crepitations
- Raised JVP
- Weight gain
- Dyspnoea, hypoxia
Red Flags
- Oliguria with rising creatinine — AKI; assess volume status before giving more fluid
- Post-operative hypotension with tachycardia — exclude haemorrhage before attributing to dehydration
- Pulmonary oedema — stop fluids, sit up, furosemide 40mg IV, O₂
Differential Diagnosis
| Fluid Type | Na⁺ (mmol/L) | K⁺ (mmol/L) | Cl⁻ (mmol/L) | Key Feature |
|---|---|---|---|---|
| 0.9% NaCl | 154 | 0 | 154 | Hyperchloraemic acidosis risk |
| Hartmann's | 131 | 5 | 111 | Physiological; contains lactate, K⁺, Ca²⁺ |
| 5% Dextrose | 0 | 0 | 0 | Free water; distributes across all compartments |
| 0.18% NaCl / 4% dextrose | 31 | 0 | 31 | Maintenance fluid |
| Gelofusine (colloid) | 154 | 0 | 120 | Stays intravascular longer; no mortality benefit |
Diagnosis / Investigation
Bedside
- Observations: HR, BP, RR, SpO₂, temperature
- Urine output: Hourly (catheter); target >0.5 mL/kg/hr
- Fluid balance chart: Strict input/output recording
- Clinical assessment: JVP, oedema, CRT, mucous membranes
Bloods
- U&Es: Na⁺, K⁺, urea, creatinine — guide electrolyte replacement
- ABG/VBG: pH, lactate, base excess — guide resuscitation adequacy
- FBC: Hb (haemodilution or haemorrhage)
- Chloride: If on 0.9% NaCl — monitor for hyperchloraemia
Advanced Monitoring
- Oesophageal Doppler: Stroke volume optimisation (GDFT)
- Pulse pressure variation (PPV): In ventilated patients — >13% suggests fluid responsiveness
- Passive leg raise test: 250-500mL autotransfusion; >10% increase in CO = fluid responsive
Management
Resuscitation (Acute Hypovolaemia/Sepsis)
- 500mL bolus of Hartmann's (or 0.9% NaCl) over <15 minutes
- Reassess clinically after each bolus
- Repeat as needed (senior review if >2000mL given)
- Use blood products if haemorrhage (major haemorrhage protocol if massive blood loss)
Maintenance (NICE CG174)
- 25-30 mL/kg/day water (e.g., ~2-2.5L/day for 70kg patient)
- 1 mmol/kg/day each of Na⁺, K⁺, Cl⁻
- 50-100g/day glucose (to prevent ketosis)
- Typical regimen: 1L 0.18% NaCl / 4% dextrose + 20 mmol KCl over 8 hours × 3 bags/day
- Adjust for ongoing losses, renal function, cardiac status
Replacement of Specific Losses
- Vomiting/NG losses: 0.9% NaCl + KCl (acidic losses → metabolic alkalosis)
- Diarrhoea/small bowel losses: Hartmann's (alkaline losses → metabolic acidosis)
- Blood loss: Crossmatched blood; O-negative in emergency
Post-operative Fluid Management
- ERAS: Early oral intake (within 24 hours); stop IV fluids as soon as tolerating oral
- Avoid routine post-operative IV fluid regimens without assessment
- Daily U&Es and fluid balance review
Referral Criteria
- Persistent oliguria despite adequate resuscitation — nephrology/ICU
- Complex fluid management — ICU for advanced monitoring
Prognosis
- Appropriate fluid management: Reduces AKI, complications, and hospital stay
- Goal-directed fluid therapy: Reduces post-operative complications by ~20-30% in major surgery
- Excess IV fluid: Increases anastomotic leak, pulmonary complications, SSI, and mortality
- Under-resuscitation: AKI, organ failure, increased mortality in sepsis
- Both extremes are harmful — 'too much and too little are both bad'
Other Relevant Information
IV Fluid Composition
| Fluid | Na⁺ | K⁺ | Cl⁻ | Other | Osmolarity |
|---|---|---|---|---|---|
| 0.9% NaCl | 154 | 0 | 154 | — | 308 |
| Hartmann's | 131 | 5 | 111 | Lactate 29, Ca²⁺ 2 | 278 |
| 5% Dextrose | 0 | 0 | 0 | Glucose 50g/L | 278 |
| Plasma | 135-145 | 3.5-5 | 95-105 | — | 275-295 |