the foley catheter has been a staple of medical care since its inception in 1935 by american urologist frederic foley ( 1 ) . though there have been modifications in the 80 years since its creation , the foley catheter has withstood the test of time and is considered an acceptable means for bladder drainage in the appropriate setting . one of the main complications of its use is catheter - associated urinary tract infection ( cauti ) . the prevalence of cauti is high , as up to 40% of catheterized patients in the acute hospital care setting develop cauti ( 2 ) . this , in conjunction with the fact that up to 25% of patients admitted to hospitals have a urinary catheter placed at some point during their stay highlights the healthcare burden generated by cauti ( 3 ) . although the cost of each cauti is estimated to be less than $ 600 , the additive cost to hospitals for lack of medicare and medicaid reimbursement of a  preventable complication  is considerable ( 4 , 5 ) . for each day that a catheter is in place , 3 - 7% of patients may develop a cauti ( 6 ) . by the 30th day of catheterization , the incidence of cauti or catheter - associated asymptomatic bacteriuria ( caasb ) is almost 100% ( 7 ) . failure to keep the urinary collection bag in a gravity dependent position is the most commonly violated catheter care - related recommendation , and can double the relative risk of developing cauti or caasb ( 8) . one potentially modifiable factor to impact the incidence of cauti is inadequate drainage of the bladder . stoller et al . suggested that foley catheters do not consistently and constantly drain urine from the bladder , with 43% of patients found to have a residual urine volume > 50 ml ( 8) . a previous study found that clinically asymp tomatic men with a post - void residual volume ( pvr ) of > 180 ml are at high risk for developing bacteriuria ( 9 ) . further , pvr > 150 ml in a non  catheterized patient is associated with an increased risk of developing a urinary tract infection ( 10 ) . taking these findings together , it would seem logical that we can reduce the incidence of cauti by addressing the problem of inadequate bladder drainage by foley catheters . as such , the purpose of our study was to evaluate the efficacy of the foley catheter in bladder drainage . after obtaining approval from our institutional review board ( approved protocol # 3309371 ) , we retrospectively identifed 167 consecutively catheterized patients via contrast enhanced and non - enhanced abdominal and pelvic ct studies from 7/1/2011 - 6/30/2012 . we assessed residual urine volume ( ruv ) by utilizing the 5 mm axial section demonstrating the greatest bladder cross sectional area . using coronal multiplanar reformatted images to determine maximum bladder height , ruv was calculated by means of the formula for the volume ( v ) of a sphere in a cube with a given length ( l ) , width ( w ) , and height ( h ) : v=(/6)*(w*l*h ) . patients were stratified into three groups : ruv = 0 ( n=68 , 40.7% ) , ruv > 0 and < 50 ml ( n=95 , 56.9% , mean=6.7 ml , standard deviation ( st dev ) = 7.9 ml ) , and ruv 50 ml ( n=4 , 2.4% , mean=394.7 ml , two of the four patients with ruv 50 ml were found to have improperly placed catheters by ct . the overall mean ruv was 13.2 ml with a st dev of 75.9 ml and margin of error of 11.6 ml for a 95% confidence interval . thirty nine women ( 41% ) had ruv = 0 ml , 54 ( 57% ) had a ruv > 0 ml and < 50 ml ( mean=8.0 ml , st dev=8.3 ml ) , and 2 ( 2% ) had ruv 50 ml , ( mean=301.4 ml , st dev=172.6 ml ) . the overall mean ruv for women was 10.9 ml with a st dev of 50.0 ml . twenty nine men ( 40.3% ) had ruv=0 ml , 41 ( 57% ) had a residual urine volume of > 0 ml and < 50 ml , ( mean=4.9 ml , st dev = 7.0 ml ) , and 2 ( 2.8% ) had ruv > 50 ml ( mean=488.1 ml , st dev=362.8 ml ) . the overall mean ruv for men was 16.2 ml , with a st dev of 100.2 ml . contrary to the study performed by stoller et al . , we found that the vast majority of our patients ( 97.6% ) had a ruv of < 50 ml . further , 40.7% of our patients were found to have no residual volume at all . this contrast may be attributed to differences in study design . in stoller 's study , bladder sonography was performed at the bedside whereas in the present cohort , the patient was transported to the ct department . it is possible that during transport , manipulation and movement of the foley , as well as changes in abdominal pressure during transfer resulted in drainage in urine from the bladder . since patients either move or are turned / moved frequently while in hospital beds , we feel that ct - derived measurement of bladder volume still represents a  real world  situation amongst catheterized inpatients . further , sonographic measurement of the bladder is less precise when the bladder is collapsed ( 11 , 12 ) . in the present study , while only 2% of patients had a ruv of > 50 ml , 59% of patients a ruv of > 0 ml , indicating that for most patients the foley catheter does not completely drain the bladder . though some of the smaller volumes may be considered negligible , 16% of our patients ( n=26 ) had a ruv of > 10 ml . we found that half ( 2/4 ) of the patients with a ruv > 50 ml had an improperly placed catheter , emphasizing the importance of catheter placement technique and urine output monitoring . hence , the vast majority of properly placed catheters appear to drain the bladder at least moderately well with an arbitrary  cut point  of 50 ml . the importance of finite ruv < 50 ml in catheterized patients has yet to be determined . in summary , our retrospective study provides three principal findings : for the vast majority of patients the foley catheter adequately drained the bladder ; there were no gender differences in the efficacy of the foley catheter in bladder drainage ; improper placement of a foley catheter can lead to significant urinary retention .
abstractintroduction : the foley catheter has been widely assumed to be an effective means of draining the bladder . 
 however , recent studies have brought into question its efficacy . 
 the objective of our study is to further assess the adequacy of foley catheter for complete drainage of the bladder.materials and methods : consecutive catheterized patients were identified from a retrospective review of contrast enhanced and non - contrast enhanced computed tomo - graphic ( ct ) abdomen and pelvis studies completed from 7/1/2011 - 6/30/2012 . 
 residual urine volume ( ruv ) was measured using 5 mm axial ct sections as follows : the length ( l ) and width ( w ) of the bladder in the section with the greatest cross sectional area was combined with bladder height ( h ) as determined by multiplanar reformatted images in order to calculate ruv by applying the formula for the volume ( v ) of a sphere in a cube : v=(/6)*(l*w*h).results : ruvs of 167 ( mean age 67 ) consecutively catheterized men ( n=72 ) and women ( n=95 ) identified by ct abdomen and pelvis studies were calculated . 
 the mean ruv was 13.2 ml ( range : 0.0 ml-859.1 ml , standard deviation : 75.9 ml , margin of error at 95% confidence:11.6 ml ) . 
 four ( 2.4% ) catheterized patients had ruvs of > 50 ml , two of whom had an improperly placed catheter tip noted on their ct-reports.conclusions:previous studies have shown that up to 43% of catheterized patients had a ruv greater than 50 ml , suggesting inadequacy of bladder drainage via the foley catheter . 
 our study indicated that the vast majority of patients with foley catheters ( 97.6% ) , had adequately drained bladders with volumes of < 50 ml .