The dynamic renal system – the “poor man’s Swan”


In a nutshell : urine is formed in proportion to the cardiac output exerted on the nephron.

If the clinician is improving cardiac output, the urine output should improve.

Ex :

give Epinephrine  >> cardiac output increases >> urine output increases !

give 500cc NSS in a dehydrated patient >> cardiac output increases >> urine output increases !

apply Alveolar Recruitment Techniques (ART)  >> cardiac output increases >> urine output increases !

decrease PEEP (in a stellar pulmonary status patient)  >>  cardiac output increases >> urine output increases !


The “long winded story” :

The renal system in all of its dynamic glory is a beautiful passive organ system.

The dynamic renal system is referred to as the “poor man’s Swan”.

It’s state of flux demonstrates the strength of the cardiodynamic system.

When cardiac output is strong, urine is formed quickly and flows to the urimeter quickly.

When cardiac output is weak, urine is formed slowly and flows to the urimeter slowly.

For doctors / hospitals / states / countries that cannot afford the luxury of a Swan-Ganz catheter, the urine collection system is thus referred to as the “poor mans Swan”.

As long as there is integrity in the system from the nephron (beginning)  to the end (the urimeter), it is a great way to tell of the cardiodynamic status.

This attached movie clip (p1090771 – activate the “replay” feature on your PC’s movie player app) will allow you to envision the urine formation.

The process :   cardiodynamics will bring blood from  :    LV  >> LVOT >> Ao  >> descend Ao >> renal artery >> nephron  >> renal collecting tubules >> bladder >> urimeter.

In this movie clip, the patient had excellent cardiodyanmics and was given Lasix (forced diuresis) so the patient was literally “pouring out” urine.

Traumatic brain injury (TBI) / nueuro-injury may result in sequelae to include SIADH (syndrome of inappropriate anti-diuretic hormone) which allows urine to “pour out” as well.

The beauty of this movie clip is to envision for “x” amount of heart beats, a drop of urine is formed.  When you see urine forming at the rate you see in this movie clip, one has to stand in awe of a passive physiologic process.


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