Disease - Fluids

From CambridgeNotes

  • 2/3 of average persons weight is water
  • 2/3 of water intracellular fluid (ICF), 1/3 extracellular fluid (ECF)
  • 1/5 of extracellular fluid is plasma, 4/5 is not

Requirements

  • Adult: 30-40ml/kg/day; urine output 0.5ml/kg/hr
  • Child: 100 ml/kg/day for first 10kg, 50ml/kg/day for second 10kg, and 20ml/kg/day thereafter; urine output 1ml/kg/h
  • Na+: 1-2mmol/kg/day
  • K+: 0.5-1mmol/kg/day
  • Ongoing losses e.g. pyrexia, gastrointestinal losses, third space losses

Disturbances

  • Intravascular depletion: % blood lost (ATLS)
Level of consciousness Pulse rate Blood pressure Respiratory rate Urine output
0-15% Anxious <100 -BP 14-20 >30
15-30% Agitated >100 -BP 20-30 20-30
30-40% Confused >120 ↓BP 30-40 5-15
>40% Depressed >140 ↓BP >35 Negligible
  • Dehydration: % weight loss in infants/children
Level of consciousness Refill Mucous membranes Tears
5%/3% Alert 2s OK OK
10%/6% Lethargic 2-4s Dry Less
15%/9% Obtunded >4s Cracked Absent
  • Dehydration in adults: postural tachycardia (>30) and dizziness are best signs (JAMA 1999)

Treatment

  • Crystalloids are small molecules dissolved in water
    • Normal saline (NS 0.9%) → ECF; side effects include ↑Cl ↓pH
    • Dextrose 5% (D5W) → ECF and ICF; 1L = 200kCal
    • Dextrose saline (Dextrose 4%, NaCl 0.18%)
    • Hartmann’s (NaCl and lactate, K, Ca)
  • Colloids are large molecules suspended in water
    • Gelofusine, Haemacel → plasma
    • Blood (HCT 0.7)
  • Maintenance (24h): 1L NS and 2L D5W with 20mM K/L → 3L, 150mM Na, 60mM K (avoid Na if liver or heart failure)
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