A total of 936 surgical patients with complete data on maximum bladder volume entered the study. The average preoperative determined MBC was 611mL (SD ±209mL, range 150 to 1400mL). The incidence of urinary catheterization was 9.1% (85/936) (Table 2).
Table 2. Demographic and clinical characteristics of the study patients
MBC group
|
N = 936
|
Patient data
|
|
Women, No. (%)
|
493 (53)
|
Age, mean (SD), y
|
47.9 (15)
|
Height, mean (SD), cm
|
176 (10)
|
Weight, mean (SD), kg
|
81.4 (17)
|
BMI, mean (SD), kg/m2
|
26.3 (5)
|
Type of Surgery, No. (%)
|
|
Head/Neck
|
209 (22)
|
Thoracic/Breast
|
77 (8)
|
Spine
|
33 (4)
|
Abdominal
|
273 (29)
|
Extremities
|
344 (37)
|
Study Data
|
|
MBC, mean (SD), ml
|
611 (209)
|
Residual volume, mean (SD), ml
|
33 (53)
|
Voided before surgery, No. (%)
|
877 (94)
|
Time before surgery, mean (SD), min
|
59 (48)
|
Volume at Holding, mean (SD), ml
|
52 (81)
|
General Anesthesia, No. (%)
|
639 (68)
|
Spinal Anesthesia, No. (%)
Articaine, No. (%)
Bupivacaine, No. (%)
|
297 (32)
235 (79)
62 (21)
|
Total volume infused, mean (SD), ml
|
1,492 (647)
|
Procedure time, mean (SD), minutes
|
61 (40)
|
BMI – Body Mass Index, MBC – Maximum Bladder Capacity, SD – Standard Deviation
UNIVARIATE RISK FACTORS FOR URINARY CATHETERIZATION
Modifiable risk factors
Figure A shows all identified (un)modifiable risk factors potentially associated with urinary catheterization (p <0.10). Spinal anesthesia was the strongest modifiable risk factor for urinary catheterization. Coupled to spinal anesthesia, and therefore not displayed in Figure A-C, was the regression of the sensory block. If the sensory block was higher than dermatome T12, voiding was difficult and 69% of these patients had to be catheterized (RR 12.8, 95%CI 8.4 to 18.3; p<0.0001). When the sensory block had regressed below dermatome S3, the incidence was 5.7% (RR 0.8, 95%CI 0.4 to 1.6; p=0.49). A preoperative bladder volume of 150mL or more represented another modifiable risk factor (RR≥150mL 2.4, 95%CI 1.6 to 3.5; p<0.02). The total infused volume exceeding 1 liter was not a significant risk factor for urinary catheterization (RR 0.7, 95%CI 0.4 to 1.1, p=0.09). Other non-significant risk factors included drugs used perioperatively, e.g. the opioid piritramide (i.v. or s.c.) (RR 1.0, 95%CI 0.7 to 1.6; p=0.91), ephedrine (RR 1.3, 95%CI 0.8 to 2.0, P=0.33) and atropine (RR 1.2, 95%CI 0.7-1.9, p=0.5). For phenylephrine the numbers were too small to analyze.
Unmodifiable risk factors
A smaller MBC was associated with an increased incidence of urinary catheterization. Of the 300 patients with an MBC <500mL, 14% was catheterized as compared to 9% of 398 patients with an MBC between 500 and 800mL and 2% of 199 patients with an MBC ≥800mL (MBC <500mL RR 7.0, 95%CI 2.5 to 19.1; p<0.001). In addition, age ≥60 years increased the risk of catheterization (RR 3.3, 95%CI 2.2 to 4.9; p<0.0001), and, when considering the univariate analysis, a higher IPSS was a risk factor as well. In patients with ‘severe’ symptoms (IPSS 20-35 points) the incidence of urinary catheterization was 22% (RR 2.7, 95%CI 1.5 to 5.2, p=0.002).
The strongest unmodifiable risk factor ‘related to surgery’ was the duration of surgery (RR30-60 4.5, 95%CI 1.8 to 11.3, RR>60 5.1, 95%CI 2.1 to 12.8; p<0.001). For the location of surgery, comparing surgeries on head/neck/thoracic (general anesthesia) with those on the abdomen or extremities (general or spinal anesthesia), the incidence increased from 4.9 to 11.8 and 10.2%, respectively (RRabdomen 2.4, 95%CI 1.3 to 4.4; p<0.004 and RR lower extremity 2.1, 95%CI 1.1 to 3.7; p=0.012). Another unmodifiable risk factor was bladder volume ≥250mL on the first postoperative scan at the PACU (incidence 18.6% compared to 6.3% <250mL)(RR 3.0, 95%CI 1.9 to 4.4; p<0.001).
Interestingly, ‘having no urge to void’ when the MBC was reached turned out to be an unmodifiable risk factor as well. Of the 84 patients who were catheterized, 60 patients had no urge to void (71%) (RR 4.8, 95%CI 3.1 to 5.9; p<0.001). The influences of gender (RR 0.8, 95%CI 0.5 to 1.2, p=0.31) and existing preoperative hypertension (RR 1.6, 95%CI 1.0 to 2.5, p=0.07) did not reach statistical significance in any of the analyses. Anti-depressant drugs were used by 58 patients (6%) of which 18% was catheterized (RR 2.8; p< 0.001), and 61 patients used diazepam (6.5%) of which 23% was catheterized (RR 1.8; p=0.02). For diabetes, the numbers were too small to analyze (26 patients =3.1%).
FULL MULTIVARIABLE ANALYSIS
Figure B shows the full multivariable analysis for urinary catheterization in the MBC group and includes all potential risk factors with a level of p<0.10 (as determined by the univariate analysis). Using the backward elimination strategy, location of surgery and ‘severe’ IPSS were not identified as independent risk factors in the multivariable analysis.
FINAL MULTIVARIABLE ANALYSIS
The final multivariable model is displayed in Figure C. Spinal anesthesia was the main modifiable risk factor with RR values of 8.1 and 3.1 for hyperbaric bupivacaine and articaine, respectively. The unmodifiable risk factors MBC (RR 6.7), duration of surgery (RR 5.5), first scan at PACU ≥250mL (RR 2.1) and age ≥60 (RR 2.0) were identified as independent risk factors for catheterization.
TIME OF VOIDING or CATHETERIZATION and RATE of BLADDER FILLING
Table 3 displays the elapsed time from the start of anesthesia to when patients voided or were catheterized. The rate of bladder filling over this period was estimated by subtracting the preoperative scanned bladder volume from the final scanned bladder volume before spontaneous voiding or catheterization. Both for general and spinal anesthesia, spontaneous voiding occurred after 280min (4.5hrs). The scanned bladder volume amounted to approximately 450mL with a filling rate of 100mL/u. Catheterization after general anesthesia was performed significantly later than after spinal anesthesia (352 ±157min versus 205 ±74min, p<0.001). Spinal anesthesia patients who were catheterized (203 ±94 mL/hour, p=0.005) produced almost twice the amount of urine as those who voided spontaneously (107 ±63mL/hour).
Table 3. Time to catheterization/voiding after general or spinal anesthesia, scanned bladder volumes, and bladder filling rates.
|
N
|
MEAN
|
STANDARD DEVIATION
|
MINIMUM
|
MAXIMUM
|
GENERAL ANESTHESIA
|
|
|
|
|
|
Spontaneous
|
|
|
|
|
|
Time (minutes)
|
580
|
282#
|
±117
|
70
|
808
|
Scan volume (mL)
|
595
|
412
|
±206
|
0
|
1000
|
Rate (mL/hour)
|
569
|
100
|
±66
|
0
|
388
|
Catheter
|
|
|
|
|
|
Time (minutes)
|
26
|
352#*
|
±157
|
178
|
710
|
Scan volume (mL)
|
31
|
602
|
±216
|
298
|
1000
|
Rate (mL/hour)
|
25
|
137
|
±84
|
32
|
317
|
SPINAL ANESTHESIA
|
|
|
|
|
|
Spontaneous
|
|
|
|
|
|
Time (minutes)
|
238
|
273^
|
±82
|
99
|
712
|
Scan volume (mL)
|
238
|
452
|
±224
|
49
|
999
|
Rate (mL/hour)
|
234
|
107&
|
±63
|
11
|
379
|
Catheter
|
|
|
|
|
|
Time (minutes)
|
44
|
205^*
|
±74
|
99
|
397
|
Scan volume (mL)
|
52
|
626
|
±179
|
330
|
999
|
Rate (mL/hour)
|
43
|
203&
|
±94
|
94
|
469
|
N, with missing data
Time = time to catheterization or voiding
Scan volume = scanned bladder volume before voiding or catheterization
Rate = bladder filling rate from start of anesthesia till voiding or catheterization
# General anesthesia spontaneous (282min) versus catheterization (352min), p=0.032
^ Spinal anesthesia spontaneous (273min) versus catheterization (205min), p< 0.001
* Spinal anesthesia (205min) versus general anesthesia (352min) with catheterization, p<0.001
& Spinal anesthesia bladder filling rate, catheterization (203mL/hour) versus spontaneous (107mL/hour), p=0.005