Stones Flashcards by mike g

2 basic ways ESWL breaks stones

cavitation and 2. direct stress (comprssive and shear)

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at what point does cavitation have its effect

negative portion of pressure wave

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at what point does direct stress have its effect

positive portion of pressure wave

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cavitation in eswl and tissue injury

formation of microbubbles in renal tissue parenchyma/blood vessels proposed as mediator of ESWL induced tissue injury

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absolute contraindications to ESWL - 5

pregnancy, coagulopathy, distal obstruction, calcified renal artery aneurism, untreated UTI

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if cant correct coagulopathy/ stop antiplatelet - stone tx of choice

URS

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what is max skin to stone distance and where is this applicable

< 10 cm on axial CT as MEAN distance at 0,45,90 deg in obese people

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BMI and ESWL

BMI is independent predictor of ESWL failure

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SFR for 2 cm stone with ESWL

20%

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stone hounsefield and ESWL success

> 1000 = inferior SFR rate

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stone types that dont work in ESWL

CaOx monohydrate, cystine, brushite

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infundibulopelvic angle and ESWL

> 70 is good

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infundibular width and ESWL

< 5 mm is good

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infundibular length and ESWL

> 3 cm is good

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ESWL machine with higher perinephric hematoma rate

SLX-F2 (3%)

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RF’s for bleeding - 4

DM, HTN, obesity, coagulopathy

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mechanical percussion and inversion

helps in SFR after ESWL

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alpha blockers after ESWL

helps in SFR after ESWL, and pain

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when to place stent prior to ESWL - 2

large stone burden with steinstrasse risk, high grade obstruction

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ideal shock wave rate

60/min= higher stone clearance/reduce retreatment

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stricture rate for URS

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ureteral perforation rate for urs

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why get renal access to calyx end-on vs side-on

end on have lower risk of hitting interlobular arteries which cross infundibula

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4 indications for PCNL other than stone > 2 cm

lower pole stone > 1 cm, cystine stone, pts who must be stone free (pilots), anatomic abnormalities

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location of ideal calyx for PCNL access

upper pole calyx eventhough there is risk of pulm complications

absolute indications for tube after pcnl besides stones - 5

significant collecting system inj, excessive hemorrhage, multiple tracts, pyonephrosis

hydrothorax rate for PCNL

prone considerations in anesthesia for obese pts - 2

reduced total lung capacity and FRC w abd compression, IVC compression with reduced preload and impaired oxygenation

ways to overcome anesthesia considerations for obese patients - 3

1. lateral decubitus and supine positioning, 2. awake endotracheal intubation and self positioning, 3. PCNL under local anesthesia and sedation.

indications for PCNL - 7

> 2 cm stone, staghorn, lower pole > 1 cm, cystine stone, pts who must be stone free (pilots), failure of other treatments, assd anatomical abnormalites

3 differences in pcnl outcome in obese patients

1. longer operative time, 2. decreased SFR, 3. significantly higher retreatment rate

problem with stent/nephrostomy during pregnancy

increased # procedures due to encrustation and pain

ureteroscopy in obese patients

equal outcome to non-obese

imaging for stones in pregant females

can do ultra low does ct - not associated with fetal or maternal harm

stone passage and location at dx

20% @ prox ureter, 70% @ diatal ureter

who gets expectant mgmt of stone

< 10 mm and well controlled sx + periodic evaluation + medical therapy

2 medical adjuncts

CCB (65% passage) and alpha blockers (55% passage)

why alpha blocker

less side effects vs ccb

how meds work in stones

stops ureteral spasm

"indication" to ESWL

uncomplicated < 2 cm

contraindications - 6

1. bleeding problm, 2. preg, 3. aneurism (aortic > 5 cm, renal > 2 cm), 4. untx UTI, 5. obstruction distal to stone, 6. inability to visualize stone

4 effects of ESWL on stone

1. spall, 2. cavitation, 3. squeezing aka sheer stress, 4. superfocusing

what is squeezing/ sheer stress?

shock wave passes through stone faster than water resulting in acoustic mismatch and squeezing effect on surface

what is superfocusing

as shock wave moves through stone (moves faster) wake of pressure forms behind shock wave and focus in mid stone.

what is spall

Some energy is internally reflected into stone

what is cavitation

negative pressure of shock wave creates cavitation bubble

4 factors affecting ESWL outcome

1. body habitus, 2. stone size, 3. stone location, 4. stone composition

ideal skin to stone distance

< 10 cm ideal, >12 cm is bad

how to determine skin to stone distance

PICTURE p.406

stone free rate for 1, 1.5, 2 cm stone

80%, 72%, 60%

J urol 2001, albala and woods - ESWL vs PCNL for lower pole stones

SWL 35%, PCNL 95% stone free

stone density and ESWL success

hounsfield units suggest stone fragility - HU < 500 = 100% success, > 1000 = 50% success

SWL attributes affecting stone fragmentation

acoustic output and focal volume

focal zone vs focal point

focal point - acoustic energy focused to a point in space. Focal zone - zone of high pressure (50% focal point) around focal point. The latter varies by lithotriptors

2 biggest effects on stone breakage

acoustic mismatch causing sheer stress and cavitation - both happen on SURFACE of stone

effect of focal zone size on stone breakage

focal zone should include stone surface to expose stone to cavitation/sheer stress

stone motion and focal zone

larger focal zone keeps stone exposed to shock wave during motion (breathing)

4 physician controlled variables in SWL

1. coupling, 2. rate, 3. anesthesia, 4. power

what is coupling

joining pt to lithotriptor via medium (water bath, or jel)

potential effect of coupling

air pockets can form at junction btw pt and coupler - more bubbles = poorer effect. 8% coverage by air pockets = 60% decrease breakage

anesthesia effect on stone free rate

GETA 90% stone free, sedation 55%

power effect on stone

shocks cause hematoma on kidney. pre-treatment with low energy shock waves can have protective effect on kidney - vasoconstrictive effect on kidney

complications of SWL

hematoma, ureteral obstruction, delayed issues (DM/HTN)

effect of SWL on HTN

dose dependent, and older ppl more suceptible

indications for URS

unfavorable for SWL (HU >1000, lower pole), bleeding diathesis

holmium stone breakage MOA

photothermal

Stones Flashcards

(66 cards)