Stones Flashcards
2 basic ways ESWL breaks stones
- cavitation and 2. direct stress (comprssive and shear)
at what point does cavitation have its effect
negative portion of pressure wave
at what point does direct stress have its effect
positive portion of pressure wave
cavitation in eswl and tissue injury
formation of microbubbles in renal tissue parenchyma/blood vessels proposed as mediator of ESWL induced tissue injury
absolute contraindications to ESWL - 5
pregnancy, coagulopathy, distal obstruction, calcified renal artery aneurism, untreated UTI
if cant correct coagulopathy/ stop antiplatelet - stone tx of choice
URS
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
BMI and ESWL
BMI is independent predictor of ESWL failure
SFR for 2 cm stone with ESWL
20%
stone hounsefield and ESWL success
> 1000 = inferior SFR rate
stone types that dont work in ESWL
CaOx monohydrate, cystine, brushite
infundibulopelvic angle and ESWL
> 70 is good
infundibular width and ESWL
< 5 mm is good
infundibular length and ESWL
> 3 cm is good
ESWL machine with higher perinephric hematoma rate
SLX-F2 (3%)
RF’s for bleeding - 4
DM, HTN, obesity, coagulopathy
mechanical percussion and inversion
helps in SFR after ESWL
alpha blockers after ESWL
helps in SFR after ESWL, and pain
when to place stent prior to ESWL - 2
large stone burden with steinstrasse risk, high grade obstruction
ideal shock wave rate
60/min= higher stone clearance/reduce retreatment
stricture rate for URS
2%
ureteral perforation rate for urs
5%
why get renal access to calyx end-on vs side-on
end on have lower risk of hitting interlobular arteries which cross infundibula
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
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
2%
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
- 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
- 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
- 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
- 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
- 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
- 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
1 year recurrence rate after 1st stone
10-15%
5 year recurrence rate after 1st stone
50-60%