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Calculate bladder volume and post-void residual (PVR)
Or, if this is a post-void scan, the calculated volume is your PVR
Volume = 0.52 × W × H × D
Prolate ellipsoid approximation (cm to mL)
Note: Elderly patients may have higher normal values (up to 100 mL)
Ultrasound estimates are typically within 15-20% of true volume. Accuracy decreases at very low or very high volumes. Dedicated bladder scanners have built-in correction factors.
Normal functional capacity is 400-600 mL. First sensation to void typically occurs at 150-250 mL. Maximum capacity under anesthesia can reach 1000+ mL.
PVR is measured AFTER voiding. The patient empties their bladder, then the residual volume is measured either by catheterization or ultrasound scan.
Anxiety, rushed voiding, dehydration, medications, time since last void, and bladder overdistension can all affect PVR. Consider repeat measurement if results seem inconsistent.
Catheterization is more accurate but invasive with infection risk. Ultrasound is non-invasive and preferred for routine use. Catheter measurement may be needed for precise values.
Depends on clinical situation. For BPH monitoring, every 6-12 months. For neurogenic bladder, may need weekly or monthly checks. After surgical intervention, closely until stable.
A single elevated PVR should be confirmed with repeat measurement. Volume can vary significantly based on hydration, anxiety, and timing. Consistently elevated PVR warrants further evaluation.