Ureteral calculi detection using low dose computerized tomography protocols is compromised in overweight and underweight patients.

PURPOSE: Low dose computerized tomography protocols have demonstrated a reduction in radiation exposure while maintaining excellent sensitivity and specificity in the detection of stones in patients of average size. Low dose computerized tomography protocols have not yet been evaluated in subjects in the extremes of weight. We evaluated the effect of body weight when using low dose protocols to detect ureteral calculi. MATERIALS AND METHODS: Three cadavers of increasing weight (55, 85 and 115 kg) were prepared by inserting 721 calcium oxalate stones (range 3 to 7 mm) in 33 random configurations into urinary tracts. Cadavers were then scanned using a GE LightSpeed® at 7 radiation settings. An independent, blinded review by a radiologist was conducted to generate ROC curves, with areas under the curve compared using a 1-way ANOVA (α = 0.05). RESULTS: Sensitivity and specificity were significantly lower in the low and high weight cadavers compared to the medium weight cadaver at 5 mAs (p <0.001) and 7.5 mAs (p = 0.048). Differences in sensitivity and specificity at radiation settings of 15 mAs or greater were not significant. CONCLUSIONS: The sensitivity and specificity for the detection of ureteral calculi on computerized tomography were decreased for underweight and overweight subjects when using extremely low dose radiation settings (less than 1 mSv). Low dose protocols of 15 mAs (2 mSv) can still be used for these subjects without jeopardizing the ability to identify ureteral stones.

In vitro comparison of changes in effective patient weight between purely laparoscopic and hand-assisted laparoscopic surgery.

BACKGROUND AND PURPOSE: Subclinical rhabdomyolysis (RM) has been reported to occur at a high frequency in patients who are undergoing hand-assisted laparoscopic (HAL) surgery. Compressive forces of the surgeon's hand pushing the patient down onto the operating table may increase the patient's effective weight, a factor that is correlated with risk of RM. The purpose of this study was to evaluate the changes in effective patient weight during pure laparoscopic (PL) and HAL surgery. MATERIALS AND METHODS: Using an in vitro model, 10 subjects performed translocation and knot tying tasks with both PL and HAL techniques. Changes in weight were monitored using a dynamic industrial scale with real-time digital recording. The means of the average changes in effective weight during the different tasks were compared using the Wilcoxon signed rank test with a P value of <0.05 considered significant. RESULTS: The mean of the average weight increases during translocation was 2.99 kg with HAL compared with 0.06 kg with PL (Z=4.3, P<0.05). The mean average weight increase during knot tying was 1.28 kg in HAL compared with 0.02 kg (Z=2.6, P<0.05) in PL. The mean maximum weight increase was 8.70 kg and 8.01 kg in HAL compared with 0.43 kg and 0.59 kg in PL during translocation and knot tying tasks, respectively (P<0.05 for each). CONCLUSIONS: HAL surgery results in a significant increase in effective patient weight compared with PL surgery. This increased effective weight during HAL surgery may increase the risk for subsequent RM.