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Pilot Study
A Pilot Study of Foley Catheter Balloon Volumes and Pullout Forces in Females Cadavers
James A Greenberg1* and Traci E Ito2
1Harvard Medical School, Brigham & Women’s Hospital, Boston, USA
2Department of Minimally Invasive Gynecology Surgery, University of Louisville Hospital, Louisville, USA

ABSTRACT
Objective
To evaluate the pull-out force needed to dislodge Foley catheters with various volumes of fluid.

Methods and Materials
Data points were measured by randomizing 7 unembalmed female cadavers. Foley catheters were filled with either 5 mL or 10 mL of water. The force needed to pull-out the catheter was measured using a force gauge.

Results
The mean force required to remove a catheter with the balloon filled with 5 mL of water was 1.24 kg where as the mean force required to remove a catheter with 10 mL was 3.82 kg. The secondary phase of the study investigated force required to remove a catheter with the balloon filled with 10 mL after a 5 mL filled balloon had previously been pulled out and this was 2.54 kg (33% reduction).

Conclusion
Foley catheter balloon fill volumes have been standardized without clear data indicating the basis for recommendations. This study provides the first normative data about the pull-out pressures needed to dislodge an indwelling Foley catheter in women.
KEYWORDS
Bladder; Catheter; CAUTI; Foley; Pullout

Introduction
Indwelling Foley catheters are used around the world in every healthcare setting as a means for draining the bladder. Simplified, the Foley catheter is a flexible, hollow tube with an inflatable balloon on the indwelling end that functions to keep the catheter from falling out after it has been placed into the bladder. Despite the ubiquity of this device, the scientifically derived data regarding its use is limited. As one example, manufacturer guidelines for use of a 16 Fr Foley catheter with a 5 mL balloon recommends filling the balloon with 10 mL of sterile water [1]. The 10 mL inflation volume has become an almost universal standard though it is unclear on how this recommendation was derived. A search of the literature revealed only one study investigating balloon fill volumes and pull out forces [2]. This study was performed with three male cadavers. While these data may seem trivial, unnecessarily high catheter balloon volumes may influence catheter-associated patient discomfort, leakage around catheter, catheters related trauma to bladder mucosa or urethra, and possibly Catheter-Associated Urinary Tract Infections (CAUTI’s).

While the most effective method of reducing Foley catheter related complications is by avoiding unnecessary placement, this cannot always be prevented. Infection is a well-known and well-studied complication of indwelling Foley catheters [3]. Leuck et al., reveals that genitourinary trauma may be just as common as CAUTI occurrence. Genitourinary trauma related to catheter use occurred in 1.5% of indwelling urethral catheter days. Reducing the occurrence of trauma would, also, likely reduce hospital stay and chance for infection [4]. Currently, there is no literature investigating the correlation between balloon fill volumes, pull out forces, and genitourinary trauma. It is apparent that further studies must be done to help understand why non-infectious complications arise and how to reduce their occurrence. The pilot study described here was designed to determine the force needed to remove an inflated catheter balloon from female bladders with the goal of providing normative data for potential future research.
Materials and Methods
Seven 16 Fr silicone Foley catheters (CR Bard, Inc., Murray Hill, NJ) were placed into the bladders of seven randomly assigned fresh, unembalmed female cadavers in a standard fashion. Of note, all cadavers were obtained directly by the University of Louisville School of Medicine with the intention of medical training and research. This study is IRB exempt since the subjects are deceased and previously donated their bodies to science. For this same reason, informed consent was not needed. The ex-vivo placed catheters were then randomly assigned to be filled with either 5 mL or 10 mL of water. The approximate measured dimensions of the 5 mL distended balloon were: Height 17 mm, diameter 22 mm. The approximate measured dimensions of the 10 mL distended balloon were: Height 25 mm, diameter 27 mm. The catheters were than forcibly removed and the maximum force was recorded using a force gauge (Force One FDIX, Wagner Instruments, and Greenwich, CT). After the force measurements were obtained from the cadavers with catheters filled with 5 mL, second catheters were placed, filled with 10 mL and forcibly removed to assess the effects of the first pullout on the residual strength of the bladder neck. These secondary measurements were similarly measured with the force gauge. Only two measurements were done on each cadaver to minimize the risk of tissue damage affecting the results. The randomization of the cadavers and the catheters was done using number sequences generated using www.random.org. The pullout force data was compared using an unpaired t test.
Discussion
Clinical presentation of a FMH depends, on the one hand, on the volume of the transfusion and, on the other hand, on the velocity with which it had occurred [5]. The prognosis also depends on the prompt diagnosis and intervention.

FMH can occur as an acute or chronic event. In the chronic presentation, the hemorrhage has been prolonged or repeated during pregnancy, anemia developed slowly, giving the fetus the opportunity to develop hemodynamic compensation. In this case, the diagnosis is often postnatal and these infants may manifest only pallor at birth with no other complications [5].

In opposition, in acute FMH, perinatal hypoxia and intrauterine death or severe anemia and hypoxia at birth can be present [5].

Neonatal anemia was the first manifestation of FMH in 35% of the reported cases. In severe ones, shock and circulatory failure may be present [6].

In our clinical report, it’s more likely to be a chronic transfusion given the rapid ability of the newborn to adapt to extra uterine life despite the hemoglobin value at birth. The absence of fetal movements noted by the mother was not due to the FMH but it was caused by the circular of the umbilical cord around the arms that made it impossible to the fetus to move.

Abdominal trauma and invasive techniques of prenatal diagnosis are related to FMH [1]. Physicians should consider alternative diagnosis to neonatal anemia such as isoimmune hemolytic anemia, congenital infections that result in bone marrow suppression (TORCH), sepsis, congenital erythrocyte defects and congenital hemoglobinopathies [6]. Clinical and laboratory evaluation of infection, Coombs test and viral serology should be performed.

In this case, the diagnosis of FMH was confirmed by the KB test. Pink fetal red blood cells are observed and counted in the mother’s peripheral blood smear because fetal hemoglobin is resistant to acid elution, leaving discolored maternal cells (patients with sickle cell anemia or hereditary persistence of fetal hemoglobin may lead to a false positive result and ABO incompatibility may produce a false negative result) [2].

Although the KB test is inexpensive and requires no special equipment, it lacks standardization and is imprecise [3]. Flow cytometry, based on the use of anti-fetal hemoglobin for detection of fetal cells with fetal hemoglobin, represents an improvement of KB test since is more specific and precise [7].

Although the prognosis of massive FMH is poor, it can be improved if physicians early recognize this condition. When the infant is near-term gestation, immediate cesarean delivery is indicated. If, on the other hand, the fetus is still preterm, in uterus transfusion can be considered and has been shown to be effective and improves the prognosis [6].

Long term outcome for infants affected by massive FMH is unfavorable with death or neurological dysfunction [6]. The prognosis is more directly related to initial hemoglobin value and clinical manifestations post-delivery than with the transfused volume of blood [8].

The case reported emerged from a pregnancy with no risk factors. Mother’s perception of decreased fetal movements, recognition of fetal distress on the CTG, immediate caesarean section and prompt hemodynamic and respiratory support to the newborn with early red blood cells transfusion contributed for this good outcome.
Results
In the initial phase of the study, 4 catheters were filled with 5 mL and 3 catheters were filled with 10 mL and the force required to pull the inflated balloons out of the bladders was recorded. The mean force required to remove a catheter with the balloon filled with 5 cc of water was 1.24 kg whereas the mean force required to remove a catheter with 10 mL was 3.82 kg (p=0.012, range: 1.02 to 4.92 kg, mean difference -2.58, 95% CI -4.24 to -0.92). In the secondary phase of the study, mean force required to remove a catheter with the balloon filled with 10 mL after a 5 mL filled balloon had previously been pulled out was 2.54 kg. This represented a 33% reduction is force (p=0.03, range 1.02 to 2.95 kg, mean difference -1.30, 95% CI -2.45 to -0.15).
Discussion
Establishing the Foley catheter balloon fill volumes required to maintain enough resistance to keep the catheter from falling out of the bladder is an important piece of information to know when designing urinary catheter-related research protocols. Our current study in female cadavers demonstrates a similar mean force required to remove a catheter with the balloon filled with 10 mL as Wu et al., demonstrated in male cadavers (3.84 kg vs. 3.40 kg respectively [2]). In adult men and women, a balloon filled with 10 mL of sterile water has been accepted as sufficient to keep a Foley catheter in place without clear scientific evidence for the basis of this standard. The reduction of force needed to remove a balloon filled with 10 mL after a balloon-filled had previously been pullout out reflects the intuitive conclusion that pulling a balloon-filled catheter through a urethra does cause some damage to its elasticity and integrity though the extent and duration of this effect cannot be determined.

Study limitations include our small sample size, our use of only one catheter type and use of cadavers rather than live subjects. It is possible that in living subjects with normally perfused tissues at normal body temperatures and natural lubricity, our data would be slightly different. However, we stand by the use of fresh, unembalmed cadavers as the closest applicable model for study. We did not design the present study for the male population because we felt Wu et al., had already provided sufficient data in that regard.

Foley catheter balloon fill volumes have been standardized without clear data indicating the basis for recommendations. This study provides the first normative data about the pull-out pressures needed to dislodge an indwelling Foley catheter in women.
Acknowledgement
We are grateful to the University of Louisville Hospital for allowing access to cadavers.
Author’s Contributions
Greenberg JA: Project development, Data collection, Manuscript writing.

Ito TE: Project development, Data collection, Manuscript writing.
Disclosure of Potential Conflicts of Interest
Greenberg JA: Dr. Greenberg is a founder and investor in Emmy Medical, Inc and Nellie Medical, Inc. Both companies manufacture novel urinary drainage catheters.

Ito TE: no conflicts of interest or financial disclosures.
Informed Consent
This study only involved cadavers and was deemed IRB Exempt by the University of Louisville IRB.

Figures


Figure 1: (a) Chemical structures of PAMPS48-PEG227-PAMPS48 (AEA) and PEG47-PMAPTACm (EMm, m = 27,53, and 106).
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.



Figure 2: Time-conversion (?) and the first-order kinetic plots (?) for the polymerization of AMPS in the presence of CPD-PEG-CPD in water at 70oC.
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.



Figure 3: GPC elution curves for a sample of HO-PEG-OH (Mn = 9.40 ? 103; Mw/Mn = 1.06) (----) and triblock copolymer of PAMPS48-PEG227-PAMPS48 (AEA, Mn = 2.32 × 104; Mw/Mn = 1.42) (--).
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.



Figure 4: 1H NMR spectra for (a) EM53, (b) AEA, and (c) AEA/EM53 micelle in D2O containing 0.1 M NaCl at 20°C. Assignments are indicated for the resonance peaks.
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.



Figure 5: (a) Light scattering intensities and (b) Rh for PIC micelles of AEA/EM106 (?), AEA/EM53 (?), and AEA/M27 (?) as a function of fAMPS (= [AMPS]/([AMPS] + [MAPTAC])) in 0.1 M NaCl aqueous solutions. [AMPS] and [MAPTAC] represent the concentrations of the AMPS and MAPTAC units, respectively. The total polymer concentration was kept constant at 1 g/L.
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.



Figure 6: (a) Distributions of Rh for the PIC micelles of AEA/EM106 (?), AEA/EM53 (?), and AEA/EM27 (?) in 0.1 M NaCl aqueous solutions. (b) Relationship between relaxation rate (G) and square of the magnitude of the scattering vector (q2). (c) Plots of Rh as a function of Cp.
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.



Figure 7: A typical example of Zimm plots for AEA/EM106 micelle in 0.1 M NaCl aqueous solution.
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.



Figure 8: TEM images for (a) AEA/EM27, (b) AEA/EM53, and (c) AEA/EM106 micelles.
[M]0 and [M] represent the concentrations of the monomer at polymerization time = 0 and the corresponding time, respectively.

Tables
SamplesMn(theo)a × 10-4Mn(NMR)b ×10-4Mn(GPC)c ×10-4Mw/MncRhd (nm)?-potential (mV)
EM270.780.830.821.034.518.2
EM531.361.411.111.024.324.2
EM1062.522.581.511.026.125.4
AEA3.213.262.321.426.1-14.4
Table 1: Number-average Molecular weight (Mn), Molecular weight distribution (Mw/Mn), hydrodynamic radius (Rh), and ?-potential for the polymers.
aCalculated from Equation (2), bEstimated from 1H NMR, cEstimated from GPC, dEstimated from DLS.

PIC micelles Mwa × 10-5 Rga Rhb Rg/Rh Naggc dPICd

?-potential

(mV)
(nm) (nm)
AEA/EM27 8.48 15.1 15.2 0.99 50 0.096 -0.88
AEA/EM53 189 36.6 41.0 0.89 735 0.109 -0.53
AEA/EM106 111 28.6 32.4 0.88 302 0.129 -0.20
Table 2: Dynamic and static light scattering data for PIC micelles in 0.1 M NaCl.
aEstimated by SLS in 0.1 M NaCl, bEstimated by DLS in 0.1 M NaCl, cAggregation number of PIC micelles calculated from Mw(SLS) of PIC micelles determined by SLS and Mw of the corresponding unimers determined by 1H NR and GPC, dDensity calculated from Equation (3).

Citation: Greenberg JA, Ito TE (2018) A Pilot Study of Foley Catheter Balloon Volumes and Pullout Forces in Females Cadavers. Arch Urol 1: 002