By Joel Topf, MD - 10th Aug 2015 - Course previews

The philosophy of diuretics

Every clinician should understand how to handle diuretics and most do–but do you know what to do when diuresis is not sufficient? Or how to choose the ideal diuretic in each patient? In this video from our Fluids and Electrolytes Masterclass, you'll go through important principles about diuretic therapy and managing diuresis.

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Video Transcript

[00:00:00] If the patient isn't volume depleted, they will be volume overloaded. It is the law of the hospital. So every doctor is endlessly prescribing diuretics. These drugs are the cornerstone of hypertension, heart failure, and nephrology. In these lessons, we'll go over the four classes of diuretics and the optimal use of each one. We'll discuss some of the variables that distinguish the different loop and thiazide diuretics from each other. One of the most important things we will go over, however, is how to adapt when a diuretic isn't working. Knowing how to turn around 

[00:00:30] a failed diuresis is an awesome skill to have in your back pocket. Humans normally live in sodium equilibrium. The kidney excretes exactly as much sodium as the body absorbs. You can think of the kidneys as perfectly accurate atomic balancing machines. Sodium in equal sodium out and if not, you get pathologic conditions. For example, 

[00:01:00] if sodium intake exceeds sodium excretion, the patient will develop edema. This is what happens regardless if the edema is due to cirrhosis or heart failure or nephrotic syndrome. In all those situations, sodium intake is exceeding sodium excretion. If sodium excretion exceeds sodium intake, the patient becomes volume depleted. This is what happens in diarrhea, 

[00:01:30] vomiting, and with diuretics. In fact, that's the whole point of diuretics. Diuretics poison normal kidney function such that renal sodium excretion exceeds sodium intake. Diuretics lower total body sodium but they don't do that forever. Eventually, patients reach a new steady state where, once again, sodium intake equals sodium excretion. 

[00:02:00] It just exists at a lower level of total body sodium than they did without the diuretics. Once they stopped the diuretics, their sodium balance returns to normal. Let's take a little closer look at renal sodium handling. Normal GFR is 100 mL / min, normal sodium concentration is 140 and you've got 1440 minutes in a day. Multiply those together and you get 20,160 mmol of sodium that are filtered every 

[00:02:30] day. How much sodium is excreted? Well, it's equivalent to the dietary intake. Call it at roughly 100 mmol per day though often quite a bit more. Take that 20 160, subtract that 100 and that leaves you 20 060 mmol of sodium that needs to be reabsorbed, 99.5% of the sodium filtered is reabsorbed by the nephron. That is the job of the nephros, it needs to reabsorb all that sodium so you can remain in sodium 

[00:03:00] balance. Every segment of the nephron is involved in sodium reabsorption—the proximal tubule, the thick ascending limb of the loop of Henle, the distal convoluted tubule, and the cortical collecting duct. And each one of these is targeted by a unique class of diuretics. See one of these types in the next chapters bearing diuretics. We're going to go over each one of these types in the next chapters.