High urine output

Most important differentiation: diuresis vs natriuresis

• Diuresis: losing free water thus ↓UOsm
  1. Cause: inadequate DDAVP effect e.g.
     • ?inadequate dose
     • DDAVP administration not early enough
     • Nephrogenic DI (unlikely in the setting of hypoNa)
     • DDAVP effect offset by other factors e.g. Lasix
  2. This usually occurs earlier in the course of regular DDAVP
  3. Treatment: proper DDAVP administration ± ↑dose
     • (dose up to 4mcg Q4H has been used)
     • if diuresis with UO > 250ml/h, consider temporarily ↑frequency of blood/urine sampling (e.g. to Q3H) to make sure [Na] does not bump up suddenly
       • if ↑↑UO may need to compensate with D5 bolus meanwhile before DDAVP effect kicking in

• Natriuresis: losing salt with water thus ↑UOsm and ↑Urine [Na+K]
  1. Cause: renal salt losing e.g.
     • Thiazide diuretics
       • → review medication Hx
     • Desalination (usually occurs later in the course of DDAVP)
       • Can be part of renal homeostasis from ↑Na load
       • Usually occurs ~Day 3 after DDAVP-HTS combo
  2. Treatment:
     • Thiazide: usually natriuresis isn’t severe thus SNa should still be able to rise with HTS but in a slower rate
       • → wait till its effect wearing off
     • Desalination
       • Read this dedicated guide: In the case of desalination from renal salt loss