Perioperative Care: Fluids and Electrolytes

by Kevin Pei, MD

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    00:01 Welcome back.

    00:02 Thanks for joining me on this discussion of fluids and electrolytes in the section of perioperative care.

    00:09 Fluids and electrolytes are incredibly important to maintain daily physiologic function, but also it’s incredibly high yield for standardized examinations.

    00:19 So, I hope you're paying close attention.

    00:22 Let's start the discussion by an estimation of total body water.

    00:27 Total body water when expressed in liters is approximately two thirds or 0.6 times your total body weight in kilograms.

    00:36 For example, a standard 70 kilo patient would have approximately 42 liters of fluid.

    00:42 That's a lot of fluid.

    00:44 Now, the distribution of the fluid is equally important.

    00:48 The vast majority of that 42 liters of fluid is actually intracellular to the tune of two-thirds.

    00:56 One-third of your total body water is actually extracellular and only a very small percentage one-third of one-third is contained in your intravascular or circulating volume.

    01:08 When you do all the math, you figure that 7% of your total body weight is actually intravascular.

    01:14 That's how we get the value of approximately 5 liters of fluid in your total circulating volume.

    01:23 Our body does an amazing job of maintaining intake and output homeostasis.

    01:29 On a daily basis, we approximately ingest 500 in – or potentially excess depending on how much water you drink.

    01:37 In our food, we probably take in about 800 cc of fluid.

    01:41 And normal cellular processes contribute about 300 cc.

    01:46 In our output, we make about 500 cc of urine a day.

    01:50 Our skin and insensible losses account for approximately 500 cc.

    01:55 Breathing alone, because of the humidity, loses about 400 cc.

    01:59 And our stool, although mostly without fluid, still contains about 200 cc.

    02:05 And that's an important point, because patients with diarrhea can lose fair amount of fluid through their stools.

    02:14 Electrolytes are incredibly important and will be the focus of the majority of this lecture module.

    02:20 Remember, potassium is mostly intracellular.

    02:24 If you forget that, all you have to do is look at standard chemistry laboratory values.

    02:29 The potassium is rarely ever greater than 4.

    02:33 Aldosterone is a very important – has a very important mechanism in the distal collecting system to maintain not only fluid homeostasis, but affect the potassium channels.

    02:45 Aldosterone increases sodium reabsorption at the expense of excreting potassium.

    02:53 This allows it to maintain electrical neutrality because otherwise we would have entropy.

    02:59 Potassium-sparing diuretics, however, antagonize the action of aldosterone on potassium.

    About the Lecture

    The lecture Perioperative Care: Fluids and Electrolytes by Kevin Pei, MD is from the course Special Surgery.

    Included Quiz Questions

    1. One
    2. Two
    3. Four
    4. Zero
    5. Three
    1. Antagonize the effect of aldosterone on potassium.
    2. Antagonize the effect of angiotensin II on potassium.
    3. Antagonize the effect of ADH on potassium.
    4. Agonize the effect of aldosterone on potassium.
    5. Agonize the effect of renin on potassium.

    Author of lecture Perioperative Care: Fluids and Electrolytes

     Kevin Pei, MD

    Kevin Pei, MD

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