Oliguria

As always... back to the basics:

What is oliguria?
Low urine output (UOP)

What is "normal" adult UOP?
About 30cc/hr

How might you write a post op floor order for this?
"call house officer if 2 hour UOP is < 60cc"

What are the possible causes?
Think pre renal/renal/post renal causes

What is the most common cause?
Pre renal!

Causes of Renal Failure

Causes of Renal Failure broken down by pre-renal, renal, and post-renal.

Source: Clinical Survival Guide for PA Students by G.Broughton, MD, PhD

Diabetes Insipidus, Part 2

Diagnosing DI

Polyuria = urine vol > 3L in 24 hrs - there are many causes of polyuria and it is important to figure out if the cause is DI or something else prior to establishing treatment

Urine osmolality (osm) of > 300 mOsmol/kg + high serum glucose --> think diabetes mellitus
Urine osmolality (osm) of > 300 mOsmol/kg + high serum urea --> think renal dz
Urine osmolality (osm) of < 200 mOsmol/kg + polyuria --> think DI

So you have a patient that has urine ohm < 200 + polyuria and you are thinking DI... how do you differentiate between central DI and nephrogenic DI?

Answer: water deprivation test

Findings:
Central DI
urine osm < plasma osm after dehydration
after ADH injections urine osm increases by >50%

Psychogenic DI

urine osm > plasma osm after dehydration

after ADH injections urine osm increases minimally

Nephrogenic DI

urine osm < plasma osm after dehydration

after ADH injections urine osm increases by <50%

Source: 
Makaryus/Mcfarlane. DI: diagnosis and treatement of a complex disease Cleveland Clinic Journal of Medicine Jan 2006 Vol 73:1
pic source: medicaltextboks.blogspot.com

Approach to Volume Disorders, Part 3

Fluid Replacement Therapy

 I have also attached a chart that should be helpful in understanding when to give which type of fluid.

Approach to Volume Disorders, Part 2

Assessing Volume Status

http://cutcaster.com/photo/100023974-IV-Drip/

• Track ins and outs (Is & Os) - this is not an exact science because you can't exactly measure insensible losses, but it will give you an idea of the volume status
• Normal urine output of an adult = 1mL/kg per hr 
• Skin turgor and mucous membranes are difficult to assess and are not always reliable
• Daily wts are a good way to assess volume trends
• Don't lose sight of the BIG PICTURE. What is the overall health of your patient?
• Pts with: fever, burns, open wounds have a higher insensible loss
• For each degree over 37 degree C, estimate an increase in loss of 100mL/ day
• Pts with CHF may have pulmonary edema so pay close attention to their volume status
• Pts with end stage renal dz are prone to hypervolemia
• Pts with hypOalbuminemia tend to "3rd space" fluids out of vasculature and are therefore total body hypervolemic, but intra-vascularly depleted

Source: Step up to Medicine (Agabegi and Agabegi)

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)