HY USMLE RENAL - #266 — Transcript

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1. 0:00this is a very challenging question for
2. 0:02me to discuss
3. 0:03not because this is overwhelmingly
4. 0:05difficult but because
5. 0:07there's so much to talk about and it can
6. 0:09be confusing to learn this stuff
7. 0:11so to try to make a consolidated clip
8. 0:14okay not make this
9. 0:1527 minutes i know you don't want to see
10. 0:17a clip that's long like that
11. 0:18so i'm going to try to be as concise as
12. 0:20i can all right
13. 0:21this has been destroying students on the
14. 0:23usmle on the step 1 and vietnamese
15. 0:26these types of questions regarding
16. 0:28pre-renal intra-renal post renal
17. 0:30etiologies okay so just cutting to the
18. 0:33chase here
19. 0:34we've got congestive heart failure
20. 0:35that's a high-yield pre-renal
21. 0:38uh azotemia etiology for the step
22. 0:41if your heart's not pumping as well as
23. 0:42it should be isn't it safe to say you're
24. 0:45not going to be perfusing your kidneys
25. 0:46as well as you should be
26. 0:48so irrespective of your actual plasma
27. 0:50volume
28. 0:51the kidneys not receiving as much blood
29. 0:54flow
30. 0:54as it should be so it says [ __ ]
31. 0:57we need to reabsorb more fluid to
32. 0:59compensate that's what the kidney thinks
33. 1:02okay so it's going to reabsorb it's
34. 1:05going to jack up
35. 1:06its proximal convoluted tubular
36. 1:08reabsorption
37. 1:09of urea and sodium to compensate so
38. 1:12what's the result
39. 1:13we get a high bu endocrine ratio 20
40. 1:16or greater in pre-renal we get low
41. 1:18urinary sodium
42. 1:20fractional excretion of sodium under one
43. 1:22percent because the pct
44. 1:24is pulling all that urea and sodium out
45. 1:26of the urine right
46. 1:27and then because it's pulling urea and
47. 1:30sodium out of the urine
48. 1:31and water follows sodium we're going to
49. 1:34be making the urine more concentrated
50. 1:36that can sound confusing to students
51. 1:38when you say but i don't
52. 1:40get it if we're pulling sodium out of
53. 1:42the urine
54. 1:43isn't it like how are we making the
55. 1:45urine more concentrated
56. 1:46it's because sodium in and of itself is
57. 1:48not dictating urinary osmolality
58. 1:50it's we're drawing so much extra water
59. 1:53out of the urine
60. 1:54early in the pct that the net result of
61. 1:57the urine
62. 1:58leaving the nephron is going to be more
63. 2:00concentrated
64. 2:01okay so in pre-renal ideologies diuretic
65. 2:06use
66. 2:06really high yield nsaid use and
67. 2:09congestive heart failure these are the
68. 2:10three most important causes for us
69. 2:12smelly
70. 2:13we're going to have a b under crowning
71. 2:14ratio 20 or greater we're going to have
72. 2:16fractional excretion of sodium under one
73. 2:17percent
74. 2:18and we're going to have a high urinary
75. 2:20osmolality
76. 2:21and specific gravity if it's high that's
77. 2:24concentrated urine
78. 2:26if specific grav so we so we have a high
79. 2:28specific gravity
80. 2:29if we have a low specific gravity that's
81. 2:31dilute urine
82. 2:33now i should just make a point about
83. 2:35these numbers for specific gravity
84. 2:37around one is as dilute as you get so
85. 2:40one point
86. 2:41in terms of what i've observed on nbme
87. 2:42questions 1.001 to 1.005
88. 2:47that's diabetes insipidus psychogenic
89. 2:50polydipsia range
90. 2:51when we talk about 1.025 to 1.030
91. 2:55that's siadh severe dehydration range
92. 2:58okay so when we see these values of
93. 3:011.025 we can say yeah those are more
94. 3:03concentrated
95. 3:04and that's what we expect in this case
96. 3:06and choice c is the only answer
97. 3:08where we have a bunny crowning ratio
98. 3:11greater than 20
99. 3:12we have low urinary sodium and we have a
100. 3:14high urinary specific gravity so we have
101. 3:15concentrated urine
102. 3:17important causes of intrarenal for
103. 3:20the step acute tubular necrosis okay so
104. 3:24gentamicin cisplatin classically
105. 3:26nephrotoxic drugs that cause atn
106. 3:28i should make a point that nsaids
107. 3:31do not cause acute tubular necrosis at
108. 3:34least on usmla okay nsaids can cause
109. 3:36pre-renal they can cause chronic
110. 3:38analgesic nephropathy interstitial
111. 3:40nephropathy with eosinophils in the
112. 3:42urine
113. 3:43but nsaids aren't going to cause acute
114. 3:44tumor necrosis so when we have nsaids
115. 3:47beta lactams
116. 3:48cephalosporins that's tubular
117. 3:50interstitial nephropathy
118. 3:52interstitial nephritis same thing
119. 3:54whereas drugs like
120. 3:55gentamicin aminoglycosides and cisplatin
121. 3:59cause acute tubular necrosis ischemia
122. 4:02also super high yield
123. 4:04due to decreased blood flow this is
124. 4:05going to be real [ __ ] confusing
125. 4:07if you exsanguinate eg patient loses
126. 4:10blood during surgery
127. 4:11temporarily drops to a blood pressure of
128. 4:1380 on 40 for a minute before being
129. 4:15resuscitated
130. 4:15or a patient has ventricular
131. 4:17fibrillation with 30 seconds
132. 4:19of loss of perfusion to the kidney
133. 4:21before being resuscitated
134. 4:23that's an acute ischemia and the pct
135. 4:26has lots of atpase pumps that have high
136. 4:29oxygen demand
137. 4:30we get slothing of the renal tubules we
138. 4:33have acute tubular necrosis
139. 4:35versus and that's intra-renal versus
140. 4:39nsaid use over four to six weeks is more
141. 4:42sub-acute
142. 4:42that causes pre-renal congestive heart
143. 4:45failure it's more of a sub-acute to
144. 4:46chronic process
145. 4:48that's pre-renal diuretic use
146. 4:51it's not going to cause renal ideologies
147. 4:53right away it might take a few weeks of
148. 4:54patients being on diuretics being
149. 4:56dehydrated
150. 4:57before they get pre-renal see the
151. 4:59difference it's really high yields so if
152. 5:01the yosemite gives you a one-liner
153. 5:03patient loses blood during surgery
154. 5:05patient is v-fib
155. 5:06for 30 seconds what's the diagnosis
156. 5:09you're going to choose intrarenal which
157. 5:12is going to be a b
158. 5:13b when a chronium ratio under 20
159. 5:15fractional excretion of sodium greater
160. 5:17than one percent
161. 5:18and a more dilute urine okay
162. 5:21this can get really confusing i know but
163. 5:23i just want to make a point that
164. 5:25i have observed nvme questions where the
165. 5:27bu endocrine ratio does not
166. 5:29match up to what we expect maybe about
167. 5:3120 of the time
168. 5:33it's the fractional excretion of sodium
169. 5:35that matters so
170. 5:36you might get a question where they say
171. 5:38patient is on diuretics for the past two
172. 5:40months
173. 5:41and has they'll tell you the fractional
174. 5:43excretion of sodium is under one percent
175. 5:45you're like cool
176. 5:46this is pre-renal and then you'll see
177. 5:47the blue endocrine ratio is 19 and
178. 5:49you're like what the [ __ ] you're like
179. 5:50how is that possible i thought it was
180. 5:51supposed to be 20 or greater
181. 5:52as i said this will happen about 20 of
182. 5:55the time is my guess
183. 5:56uh so it's the fractional excretion of
184. 5:59sodium that's more accurate
185. 6:00bu endocrine ratio can occasionally be
186. 6:02off okay
187. 6:04um i should also point out that
188. 6:07first aid will make a distinction
189. 6:08between uh insurinal and post renal
190. 6:11post renal classically being like bph
191. 6:15okay or even a cancer like cervical
192. 6:17cancer impinging on the ureters
193. 6:19or some sort of strictures of the
194. 6:21urethra okay
195. 6:23but first aid will make a distinction
196. 6:25between intrarenal and post renal for
197. 6:27its bu and accreting ratio they'll have
198. 6:29at least at this point in time they've
199. 6:31had for many years uh intrarenal
200. 6:33under 15 for bu and a creatinine ratio
201. 6:36post renal 15-20
202. 6:37it's [ __ ] wrong because on nvme
203. 6:40questions
204. 6:40you'll see a q-tubular necrosis where
205. 6:43they'll eg
206. 6:43give you b on a criminal ratio 17 18
207. 6:46okay
208. 6:47the same way they might give you
209. 6:48pre-renal occasionally that's 19.
210. 6:50so just the point i teach now is just
211. 6:54most of the time pre-renal 20 or greater
212. 6:57most of the time
213. 6:58not pre-renal just under 20. okay
214. 7:01uh so acutely necrosis we said ischemia
215. 7:04classically
216. 7:05uh drugs such as aminoglycoside cis plan
217. 7:07also myoglobinuria and the setting of
218. 7:09rhabdomyoglobin's nephrotoxic
219. 7:11and also classically iv contrast
220. 7:15so once again this can be an extended
221. 7:17clip
222. 7:18don't worry i'm going to make more
223. 7:19content on this stuff it can be really
224. 7:21annoying when you're learning this
225. 7:23material initially
226. 7:24but your short recapitulation is
227. 7:25congestive heart failure high yield
228. 7:27cause of pre-renal azotemia for the step
229. 7:30kidney senses decrease blood flow it's
230. 7:32going to jack up reabsorption of urea
231. 7:34and sodium to compensate
232. 7:36so you have a high bu and acrylic ratio
233. 7:38you have low
234. 7:39urinary sodium and your urine becomes
235. 7:41more concentrated
236. 7:42you're gonna have a high urinary
237. 7:44specific gravity okay
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240. 7:49and i appreciate your time that's it