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A novel technique of intra-abdominal pressure measurement:validation of two prototypes

Introduction

Intra-abdominal pressure (IAP) is an important parameter and prognostic indicator of the patient's underlying physiologic status [1]. Correct IAP measurement therefore is crucial. The gold standard measurement method via a bladder catheter first described by Kron poses the risk for infection and needle-stick injury and interferes with urinary output estimations [1]. Cheatham and Safcsak reported a revision of Kron's technique limiting these risks but still interfering with urinary output estimation [2]. All these measurements also interfere with nursing time and cannot be done without manipulation of the Foley catheter. A technique for measuring IAP using the patient's own urine as transmitting medium has been described previously [1]. The aim of this study is to validate IAP measurement via two prototypes (Holtech Medical, Kopenhagen, Denmark) using this technique. A 50 ml container fitted with a bio-filter for venting is inserted between the Foley catheter and the drainage bag. The container fills with urine during drainage; when the container is elevated, the 50 ml urine flows back into the patient's bladder, and IAP can be read from the position of the meniscus in the clear manometer tube between the container and the Foley catheter. The first prototype consisted of a 50 ml plastic bag with a bio-filter, inserted between the Foley catheter and the urine collection bag; a major drawback was occasional blocking of the bio-filter, leading to overestimation of IAP in some cases. Another drawback was the occasional presence of air-bubbles in the manometer tube, producing multiple menisci leading to misinterpretation of IAP. In addition, the volume of urine flowing back into the bladder was not well defined. Prototype 2 was adapted to correct for the drawbacks of prototype 1, using a rigid 50 ml reservoir with a large bio-filter surface.

Methods

In total 60 paired measurements were performed in five patients with prototype 1, and 119 paired measurements were performed in seven patients with prototype 2. The IAP was calculated using two different methods: the gold standard via an indwelling bladder catheter using a pressure transducer (IAPves) and via the prototypes using the patient's own urine as transmitting medium (IAPproto1 and IAPproto2). The M/F ratio was 4/1, age 71.4 ± 6.6, MODScore 5.4 ± 3.6, SOFA score 8.4 ± 2.9, APACHE-II score 22.6 ± 4.8, SAPS-II score 51.8 ± 14.4 in the five prototype 1 patients and 4/3, 68.4 ± 18.9, 5.9 ± 3, 7 ± 1.9, 16.6 ± 5.2 and 43.4 ± 11.9 respectively in the seven prototype 2 patients. The number of measurements in each patient was 12 ± 2.7 for prototype 1 and 17 ± 9.8 for prototype 2. Calculation of correlation was done with the Prism GraphPad- software (version 2.00, 31 October 1995), values are mean ± SD.

Results

The values for IAP (mmHg) were 12.6 ± 5.3 (IAPves) versus 11.1 ± 3.7 (IAPproto1) and 10.1 ± 3.6 (IAPves) versus 10.2 ± 3.3 (IAPproto2). There was a good correlation between IAPves and IAPproto1: IAPves = 0.592 × IAPproto1 + 3.666 (R2 = 0.71, P < 0.0001), but the bias was considerable. The analysis according to Bland and Altman showed that IAPproto1 consistently underestimated IAPves with a mean difference or bias of -1.5 ± 2.9 (SD) mmHg (95% confidence interval -2.2 to -0.7); the limits of agreement were -7.3 to 4.4 mmHg (95% CI -8.6 to -6 for the LLA and 3.1 to 5.7 for the ULA), these intervals are large and thus reflect poor agreement. The correlation was better between IAPves and IAPproto2: IAPves = 0.9 × IAPproto2 + 1.17 (R2 = 0.96, P < 0.0001). The analysis according to Bland and Altman showed that IAPproto2 was almost identical to IAPves with a mean difference or bias of 0.17 ± 0.8 (SD) mmHg (95% CI 0.03 to 0.3); with small limits of agreement -1.4 to 1.7 mmHg (95% CI -1.6 to -1.1 for the LLA and 1.5 to 2 for the ULA), these small intervals thus reflect good agreement. A drawback of prototype 2 was the appearance of urine leakage from the rigid 50 ml container's bio-filter in 11 out of 13 devices after 16.7 ± 12.3 hours caused by a technical problem during the assembly of the prototypes.

Conclusions

We found a good correlation between all IAP measurements using the gold standard and both prototypes. Prototype 2 represents a major improvement in the quality and reproducibility of the IAP measurement. With this non-invasive technique using the patient's own urine as transmitting medium nursing time and cost can be significantly reduced. IAP measurement can easily be done at each urine output estimation without interference. The risk of infection and needle-stick injury is reduced. The leakage problem of prototype 2 needs to be corrected.

References

  1. 1.

    Malbrain MLNG: Intra-abdominal pressure in the Intensive Care Unit: Clinical Tool or Toy? In Yearbook of Intensive Care and Emergency Medicine. (Edited by: Vincent JL). Berlin: Springer-Verlag 2001, 547-585.

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    Cheatham ML, Safcsak K: Intraabdominal pressure: a revised method for measurement. J Am Coll Surg 1998, 186: 594-595. 10.1016/S1072-7515(98)00122-7

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Malbrain, M., Léonard, M. & Delmarcelle, D. A novel technique of intra-abdominal pressure measurement:validation of two prototypes. Crit Care 6, P4 (2002). https://doi.org/10.1186/cc1739

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Keywords

  • Foley Catheter
  • Sofa Score
  • Bladder Catheter
  • Paired Measurement
  • Nursing Time