Daily balance of sodium and water

Sodium

(g/day)

Intake

• Food = 10.5g

Output

• Sweat = 0.25g
• Feces = 0.25g
• Urine = 10g

Total output = 10.5g

 

Water

(mL/day)

Intake

• Food and drink = 2200mL
• Metabolically produced = 350mL
  * Oxidation of carbohydrate

Total = 2550mL

Output

• Insensible losses (skin and lungs)
  = 900mL
• Sweat = 50mL
• Feces = 100mL
• Urine = 1500mL

Total = 2550mL
* Plus menstrual flow and milk in women

NB:

• Insensible loss through skin is NOT sweat
  * Transepidermal diffusion
  * No associated solute loss (i.e. pure water loss)

[KB2:p21]

• Insensible loss
  * Skin = 400mL/day
  * Respiratory tract = 400mL/day
• Evaporative heat loss associated with insensible loss
  = 464 kcals
  ~ 25% of basal heat production
  * 0.58 kcals per gram of water evaporated

Obligatory water loss

Daily waste products (including urea, sulfate, phosphate)
= 600-700 mOsm/day

Maximum urine concentration
= 1200-1400 mOsm/kg

Thus,

Minimum urine production ~ 0.5L/day

Daily waste product

[KB2:p159]

• Na+ = 100-150 mmol/day
• K+ = 70-100 mmol/day
• Cl- = 150 mmol/day
• Urea = 400 mmol/day

NB:

Creatinine excretion = 12 mmol/day