From the Guidelines
The factor most likely to increase the risk of perirenal hematoma after SWL is the higher power density created by some of the second and third generation machines. This is because the higher power density has been reported to increase the potential for postoperative complications, including the incidence of clinically significant perinephric hematoma and need for transfusion 1. Other factors that may contribute to the risk of perirenal hematoma after SWL include:
- The use of newer, second and third generation devices with variable power capabilities and smaller focal regions, which can result in less need for general or regional anesthesia but may also increase the risk of complications 1
- The rate of shock wave administration, with slower rates potentially improving stone-free rates and reducing renal injury 1
- Pretreatment with shock waves at low energy, which can reduce tissue effects during SWL by inducing vasoconstriction and limiting parenchymal injury 1 However, the higher power density created by some of the second and third generation machines is the most significant factor that increases the risk of perirenal hematoma after SWL, as it can cause more significant trauma to the renal blood vessels and increase the likelihood of bleeding 1.
From the Research
Risk Factors for Perirenal Hematoma after SWL
The factor most likely to increase the risk of perirenal hematoma after Shock Wave Lithotripsy (SWL) is:
- Hypertension, as identified in studies 2, 3, 4
- Higher Body Mass Index (BMI), as identified in study 2
- Larger stone size, as identified in study 2
- Use of anticoagulant/antiplatelet medications, as identified in study 4
- Number of shock waves (over 2300), total energy (above 150J), and number of KV (above 17.5), as identified in study 5
- Preoperative microhematuria, perioperative hypertension, cystine lithiasis, hydrocalyx, caliceal localizations, and association of coronary artery disease with hypertension, as identified in study 5
Comparison of Studies
Studies 2, 3, 5, 4 consistently show that hypertension is a significant risk factor for perirenal hematoma after SWL. Study 2 also identifies higher BMI and larger stone size as risk factors, while study 4 identifies the use of anticoagulant/antiplatelet medications as a risk factor. Study 5 identifies several additional risk factors, including number of shock waves, total energy, and number of KV.
Clinical Implications
The identification of these risk factors can help clinicians to better manage patients undergoing SWL and reduce the risk of perirenal hematoma. This may involve closer monitoring of patients with hypertension, higher BMI, or larger stone size, as well as careful consideration of the use of anticoagulant/antiplatelet medications. Additionally, studies 2, 3, 5, 4 suggest that careful follow-up and physical resting may be necessary for patients at high risk of perirenal hematoma after SWL.