Medical topics I still don't understand

[Al Pacino]

I'm an MS4 doing my sub-i in medicine right now. Do you guys ever have topics that you still don't understand, even after attending lectures, reading many books, and talking to attendings and residents?

For example, one topic I still don't quite fully understand is hyponatremia. Hyponatremia, as I understand it, is where there is more water than sodium in the body. Yet, how can hypovolemia lead to hyponatremia? In hypovolemia, there's less water so shouldn't you be hypernatremic?

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[scootad.]

not if the fluid you are losing is hyperosmotic to your bodily fluids.

 

[Blade28]

Remember to assess volume status as well as osmolar state when dealing with hyponatremia.

 

[12R34Y]

Uptodate actually has a pretty decent explanation and flow chart about evaluating it. there is hypervolemic, isovolemic and hypovolemic hyponatremia. They list pretty well the next several steps after volume status. it's pretty readable.

later

 

[powermd]

I'm an MS4 doing my sub-i in medicine right now. Do you guys ever have topics that you still don't understand, even after attending lectures, reading many books, and talking to attendings and residents?

For example, one topic I still don't quite fully understand is hyponatremia. Hyponatremia, as I understand it, is where there is more water than sodium in the body. Yet, how can hypovolemia lead to hyponatremia? In hypovolemia, there's less water so shouldn't you be hypernatremic?

To answer your specific question, the idea is that in hypovolemic hypotonic hyponatremia you are losing water that is in some way hypertonic relative to your circulating blood volume. Losses that can lead to this kind of hyponatremia include sweating, bronchial/tracheal secretions, GI losses (diarrhea/vomiting), and certain kinds of kidney disease causing renal losses.

Not all topics in medicine are perfectly understandable. Sometimes we can describe a phenomenon, but not explain it- that's what reseach is for!

 

[bigfrank]

Do you guys ever have topics that you still don't understand, even after attending lectures, reading many books, and talking to attendings and residents?

Mechanical Ventilation.

 

[Al Pacino]

Thanks for the awesome explanations on my question. How stupid of me to not realize that you could be losing solution that is hyperosmotic to your blood volume? Duh. I guess that's my problem with reading little guidebooks that have great charts, but don't offer depth of understanding.

I think my problem is that most clinical books beyond the MS 2 years describe things, but don't offer refreshers on mechanisms.

 

[Furrball]

Thanks for the awesome explanations on my question. How stupid of me to not realize that you could be losing solution that is hyperosmotic to your blood volume? Duh. I guess that's my problem with reading little guidebooks that have great charts, but don't offer depth of understanding.

I think my problem is that most clinical books beyond the MS 2 years describe things, but don't offer refreshers on mechanisms.

Don't forget that as you lose volume your secretion of ADH will go up causing an increase in the concentration of aquaporin channels in your distal collecting duct causing an increase in reabsorption of free water, furthur decreasing your serum Na concentration. Although ADH secretion by non-osmotic stimulation happens with significant hypovolemia, and ADH release is much more sensitive to hyperosmolarity.

Renal losses could be caused by diuretics, hypoaldosteronism, and salt-wasting nephropathy. Extra-renal losses: GI, third spacing, insensible losses. I think burn patients would also fall into the category of extra renal here.

Also, sweat is normally considered hypotonic relative to serum/plasma unless the pt has other issues such as CF.

 

[Blade28]

Mechanical Ventilation.

I second that. I've had SO many talks on the vent I've lost track, but it still confuses me.

I used to also get confused with hyponatremia...and the Swan-Ganz...and drips.

 

[Halaljello]

Uptodate actually has a pretty decent explanation and flow chart about evaluating it. there is hypervolemic, isovolemic and hypovolemic hyponatremia. They list pretty well the next several steps after volume status. it's pretty readable.

later

uptodate is pretty expensive as well... would you care sharing that flow chart with a few of the negative income med students on this board ?

 

[12R34Y]

I don't have the chart handy and most if not all medical schools and the hospitals they are associated with have an institutional subscription to uptodate for free.

emedicine.com is also a good free site for anyone.

later

 

[DOtobe]

Mechanical Ventilation.

I third this...Hopefully my ICU rotation in about 5 weeks will help

 

[imtiaz]

Mechanical Ventilation.

i hear you on this one. ive been pimped on vents so much its not even funny. how the f--- do i know if SIMV is a weaning mode or not?! is there a good book or something to read that has a comprehensive vent management chapter? better than washington manual of surgery, cause ive already read that and its still confusing to me.

 

[irrka]

I got my mechanical ventilator information off uptodate too... so far it'd been enough for the one week in sicu. not like i remember anything anymore.

 

[supercut]

Vent managment is mostly voo doo.

THere is really no clear data on which modes are best for anything.

What is used as a weaning mode varies from institution to instutution, and often depends on the capability of the particular vents.

At my med school instutution, we used SIMV as wean mode, gradually turning down the rate, and then went to pressure support trials.

At my residency institution, we never use SIMV at all. The wean mode is a pressure support mode that has an automatic rate as a backup. (the vents at my med school didn't have this mode)

Some things that I think are constant, though....use the lowest FIO2 possible. Never use less than 5 of PEEP. Smaller TV are better than large TV. You can always put pt on pressure support and stand there and watch to see what they do to see if they are ready for wean. And the respiratory techs will often do whatever they want despite what you have ordered.

 

[StudKnight]

I've been using Step up medicine and the section on mechanical ventilation is awesome. It's like two and a half pages of great information that is practical. Nowhere have I seen such a nice synopsis of this difficult topic. The section on hyponatremia is great too. I highly recommend this book. Many difficult topics are so nicely outlined in this book.

 

[Teufelhunden]

I've been using Step up medicine and the section on mechanical ventilation is awesome. It's like two and a half pages of great information that is practical. Nowhere have I seen such a nice synopsis of this difficult topic. The section on hyponatremia is great too. I highly recommend this book. Many difficult topics are so nicely outlined in this book.

I can't seem to find this book on Amazon.com. Is the title "Step Up Medicine" ? Who's the author?

 

[StudKnight]

I can't seem to find this book on Amazon.com. Is the title "Step Up Medicine" ? Who's the author?

title is Step Up Medicine
Authors: Steven Agabegi, Elizabeth Derby

 

[Koko]

Barnes and Noble is often cheaper than Amazon and also faster to deliver if you opt for the free delivery service. No, I don't get a kickback.

 

[roja]

For hypo/hypernatremia, etc the Ridiculously made simple book is best.

To make it very simply, remember volume (ie volumia) is a CLINICAL decision. Look at the patient. Do they look dehydrated? (dry mucus membranes, poor skin turgor, decreased UOP or if you med, concentrated urine) If so, they are hypovolemic. If htey look normal, they are normovolemic. If they have signs of volume overload (ie chf type stuff) they are hypervolemic.

Now, check the sodium. If they are low, they are hyponatremic. If they are high, they are hypernatremic.

sodium derangements are WATER problems.

volume are SODIUM problems.

 

[zambezi]

I second that. I've had SO many talks on the vent I've lost track, but it still confuses me.

I used to also get confused with hyponatremia...and the Swan-Ganz...and drips.

check out www.pacep.org for a good site on pa caths