Approach to Volume Disorders, Part 1

Volume disorders are tough. They haven't come easily to me, but I hope once I start practicing the experience will help me along. I will do a 3 part series on the approach to volume disorders.

Fluid Compartments (Normal)

Assessing Volume Status

Fluid Replacement Therapy

Hopefully they will help you in your basic understanding.

Fluid Compartments:

• Men and women are different. Men: TBW* = 60% of body weight, Women: TBW = 50%
• % of TBW decreases with age and increases with obesity (Why? Fat contains little water)
• How is water distributed?
• Intracellular (ICF) = 2/3rd of TBW (the largest proportion of TBW = skeletal muscle mass)
• Extracellular (ECF) = 1/3 of TBW
• Interstitial fluid = 1/3 of ECF
• Plasma = 2/3 of ECF
• Water exchange:
• Intake (normal) = 1500mL PO fluids, 500mL in solids/oxidation PER DAY
• Output (normal) = 800-1500mL in urine daily is normal
• 600-900mL per day is from insensible losses (variable bases on fever, trachs, hyperventilation, etc)
• 250mL lost in stool
• MIN OUTPUT per day = 500-600mL assuming normal kidney function
• Fluid shifts are based on hydrostatic and oncotic pressures (pull out your physiology book for a refresher in this)

TIPS:
For the fluid compartments think 60-40-20!
TBW is 60% of body wt (50% for women)
ICF is 40% of body wt
ECF is 20% of body wt

What are 3 reasons for oliguria?
1. low blood flow to kidneys
2. kideny problem
3. post-renal obstruction (need a Foley cath!)





*TBW = total body water




Source: Step up to Medicine (Agabegi and Agabegi)