[Retracted] The High Risk Factors and Preventive Measures of Percutaneous Nephrolithotomy under the Guidance of B-Ultrasound in the Treatment of Postoperative Renal Calculi

Table 3

Univariate analysis of the data related to surgical operations in the two groups.

High risk factors		Bleeding group (n = 36)	Nonbleeding group (n = 184)	χ^2	p
Staged surgery	Stone extraction at the first phase	26 (72.22)	86 (46.74)	3.912	0.029
	Stone extraction at the second phase	10 (27.78)	98 (53.26)
Operation time	<60 min	2 (5.56)	60 (32.61)	11.240	0.012
	60∼90 min	6 (16.67)	58 (31.52)
	>90 min	28 (77.78)	66 (35.87)
Puncture path	Upper calyx	14 (38.89)	62 (33.70)	0.353	0.198
	Middle calyx	12 (33.33)	58 (31.52)
	Lower calyx	10 (27.78)	64 (34.78)