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Journal of Indian Association of Pediatric Surgeons
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Year : 2023  |  Volume : 28  |  Issue : 5  |  Page : 445-446

Change in Qmax in the presence of catheter during invasive urodynamics

1 Department of Pediatric Surgery, AMRI Hospitals (Mukundapur), Kolkata, India
2 Pediatric Nephrology Division, Department of Pediatrics, Institute of Child Health, Kolkata, India

Date of Submission05-May-2023
Date of Decision02-Jun-2023
Date of Acceptance04-Jun-2023
Date of Web Publication05-Sep-2023

Correspondence Address:
Poonam Guha Vaze
CG - 223, Sector - 2, Salt Lake, Kolkata - 700 091, West Bengal
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiaps.jiaps_99_23

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How to cite this article:
Vaze PG, Saha S, Sinha R. Change in Qmax in the presence of catheter during invasive urodynamics. J Indian Assoc Pediatr Surg 2023;28:445-6

How to cite this URL:
Vaze PG, Saha S, Sinha R. Change in Qmax in the presence of catheter during invasive urodynamics. J Indian Assoc Pediatr Surg [serial online] 2023 [cited 2023 Oct 2];28:445-6. Available from: https://www.jiaps.com/text.asp?2023/28/5/445/385153


There is a very scanty literature on voiding parameters during invasive urodynamics in children, especially that of flow rates. No published studies till date have documented flow rates observed in children in the presence of perurethral catheters. The existing definitions of outflow obstruction or underactivity use terms such as “poor flow rates,” but there are no set standards for flow rates during invasive urodynamic studies (UDS).

We studied the pressure flow data in 86 children who underwent invasive urodynamics for varied indications. The children were a heterogeneous group with age range from 6 months to 16 years. Almost 70% of the children had a history of posterior urethral valves (had undergone fulguration) and 30% had features of lower urinary tract symptoms or repeated urinary tract infections.

The children were made to perform free-flow uroflowmetry before catheter insertion for invasive UDS. Six Fr double lumen catheter was used for all children irrespective of age and filling/voiding cystometry was performed in upright (sitting/standing) position.

Both UFQmax and UDSQmax were seen to increase with age significantly (P < 0.005). This is explained by the dependence of UFQmax on voided volume and increase in bladder volume with age [Figure 1].
Figure 1: Variation of UFQmax and UDSQmax with age – value of UDSQmax was approximately 27% lower than UFQmax

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For similar voided volumes, UDSQmax and UFQmax correlated significantly (P < 0.0001), but the UDS Qmax (9.4 ± 5.1) was significantly lower than UF Qmax (13.7 ± 4.9) (P < 0.0001) [Figure 2]. The value of UDSQmax was around 27% lower than the value of UF Qmax. The reduction of Qmax during UDS compared to UFQmax was not dependent on age or diagnosis but increased with increasing UFQmax.
Figure 2: Correlation between Uroflow Qmax (UF Qmax) and UDS Qmax

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In 12 patients, UDSQmax was seen to be higher than UFQmax – in all these children, the voided volume during invasive urodynamics was significantly higher than that voided during free-flow uroflowmetry.

Earlier studies have documented that the presence of perurethral catheters or size of catheters does not affect the voiding pressures in children. Ichino et al.[1] performed voiding studies with two different-sized catheters in nine boys aged 2–17 months and documented that Pdetmax does not vary with the size of urethral catheters (10 2 ± 22.5 vs. 94.7 ± 25.6 cm H2O with 18G and 7.5 Fr sized catheters, respectively). Wen and Tong[2] also documented that the presence of perurethral catheter raised the voiding pressures by 16% compared to the presence of suprapubic catheter, but the difference was statistically insignificant. We found that the Qmax observed during invasive UDS is much less than the flow rate observed during free-flow uroflowmetry, i.e., the presence of the smallest sized UDS catheter (6 Fr) also influences voiding parameters significantly. Several adult studies have also documented that even a 5 Fr catheter causes elevation in voiding pressures in adult males.[3] Thus, the finding of no effect of the presence or size of catheters on voiding parameters in children is difficult to comprehend.

These findings are important because:

  1. It shows some quantitative estimation of the impact of the presence of smallest size catheter on pressure flow dynamics in children, which has not been elucidated before
  2. The relatively poor flow rate observed during invasive UDS should not be used to assess the flow pattern of a patient. Rather, if only UDSQmax is available for any particular patient, it can be assumed that the UFQmax will be around 36% higher than UDSQmax (for similar voided volumes) and the calculation of adequacy of flow rate can be based thereon
  3. The flow rates observed during invasive urodynamics should be assessed in the light of the corresponding voiding pressures to give an impression about detrusor contractility or outflow resistance during voiding.

Thanking you,

Yours Truly,

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Ichino M, Igawa Y, Seki S, Iijima K, Ishizuka O, Nishizawa O. The nature of high-pressure voiding in small boys and its relation with the influence of a transurethral catheter. Neurourol Urodyn 2008;27:319-23.  Back to cited text no. 1
Wen JG, Tong EC. Cystometry in infants and children with no apparent voiding symptoms. Br J Urol 1998;81:468-73.  Back to cited text no. 2
Klingler HC, Madersbacher S, Schmidbauer CP. Impact of different sized catheters on pressure-flow studies in patients with benign prostatic hyperplasia. Neurourol Urodyn 1996;15:473-81.  Back to cited text no. 3


  [Figure 1], [Figure 2]


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