Fluid Management in Patients 

Introduction 

Fluid management is a core clinical skill. Correct use of intravenous fluids affects circulation, electrolyte balance, acid–base status, and organ perfusion. 

Body Fluid Compartments 
• Total body water ≈ 60% of body weight 
Of which: 
• Intracellular fluid: 40% 
• Extracellular fluid: 20% (Interstitial 15%, Intravascular 5%) 

Types of IV Fluids 

Crystalloids: 

Water (small molecules) with solutes that freely cross capillary membranes, commonly: 
• 0.9% Normal Saline – used in hypovolemia, shock 
• Hartman’s (Ringer’s Lactate) – used in trauma, sepsis 
• 5% Dextrose – used in maintenance and hypoglycemia 

How they work: 
~25% stays intravascular 
~75% moves to interstitial space 

Watch out for: 
Oedema 
Dilutional anaemia 
Normal Saline can cause hyperchloremic metabolic acidosis 

Colloids and blood products: 

Fluids with large molecules which remain intravascular for longer than crystalloids 
• Albumin (limited indications) 
Gelofusin 
Voluplex 
Fresh Frozen Plasma 
Packed red cells 

How they work: 
Increase oncotic pressure 
Pull fluid into vessels 

Common uses: 
Hypoalbuminemia (Albumin) 
Cirrhosis and paracentesis  
Burns 
Blood loss 

Watch for: 
Anaphylaxis risk 
Fluid overload 
Blood transfusion reactions (and Transfusion related lung injury (TRALI) in larger volumes) 
 
Indications for Fluid Therapy:

1. Resuscitation – shock, hypotension 
2. Maintenance – poor oral intake 
3. Replacement – ongoing losses (vomiting, diarrhoea, drains) 

Assessment of Fluid Status:
 
History: fluid losses, intake 
Examination: BP, pulse, JVP, oedema, mucous membranes, skin turgor 
Monitoring: urine output, U&E, daily weight 

Special Situations:

• AKI – avoid overload, monitor potassium 
• Heart failure – cautious fluids 
• Sepsis – early aggressive fluids (evidence suggests 30 mL/kg) 

Key Principles 

• Fluid is a drug: prescribe carefully 
• Reassess after every fluid decision 
• Monitor urine output (≥ 0.5 mL/kg/hr)