An examination of the modifiable technical factors of ESWL on effective and efficient urinary stone fragmentation
Thesis DisciplineHealth Sciences
Degree GrantorUniversity of Canterbury
Degree NameMaster of Health Sciences
There are pressures from the medical community to reduce total shock numbers during extracorporeal shockwave lithotripsy (ESWL) to reduce renal damage. This in vitro study looked at the modifiable factors of the technique to increase the effectiveness and efficiency. This is important as faster, more efficient, stone elimination would reduce symptom duration and limit the adverse effects of an acute episode of renal colic. Furthermore this would reduce the likelihood of incomplete fragmentation of the stones leading to readmission. An in vitro model for the kidney was designed. This enabled the systematic scientific study of fragmentation and its relationship with the parameters studied: shock rate, shock power1, power ramping2, and coupling gel consistency to discover which technical factor settings allow the most effective and efficient urolith fragmentation. Mathematical models, theories and hypotheses pertaining to these phenomena were employed. Each effect was tested individually by setting up the model kidney and using the ESWL machine to fragment a mock kidney stone. The results of 534 completed tests showed that shock rate had less impact on stone fragmentation than power in this model. The rate experiments showed no statistical difference between the rates tested; however our observational evidence showed that stone fragments after ESWL to be smaller and more dust-like at the lower rates (60 and 70 shockwaves per minute (SW/min)) than the larger more sand-like particles when the testing was completed at faster rates (90 and 100 SW/min). This may be of clinical significance. While examining power, the most effective and efficient power was 80%, however again the clinical significance of using higher powers may outweigh the time savings. The requirement of a gas free coupling cannot be stressed enough as the tests conducted without gas in the coupling medium required both fewer shocks and lower powers (p<0.001). In conclusion, the results showed that diligent care during the ESWL procedure to choose the most effective and efficient shock rate and power, and the conscientious removal of gas from the coupling medium before treatment, improved the results of stone fragmentation.