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Filtration gradient and abdominal perfusion pressure do not correlate with urinary output in patients at risk for intra-abdominal hypertension and normal serum creatinine

Introduction

In patients with intra-abdominal hypertension (IAH), decreased urinary output is an early sign of renal impairment. The exact mechanisms remain unknown, but decreased perfusion pressure, increased pressure on the venous outflow tract, and increased tubular pressure are possible explanations. Because the abdominal perfusion pressure (APP = MAP - IAP) does not take the increased tubular pressure into account, the filtration gradient (FG = glomerular filtration pressure - proximal tubular pressure = MAP - 2 × IAP) has been proposed as a better reflection of renal pressure gradients.

Objective

The aim of this analysis was to study the correlation between urinary output (UO) and APP or FG at the individual patient level in patients with normal serum creatinine, and to compare the correlations between FG and UO with APP and UO.

Methods

We studied 27 surgical ICU patients at risk for IAH. Causes of intra-abdominal hypertension included primary and secondary IAH. Median age was 60 years (IQR 36–74 years), median APACHE II score on admission 13 (IQR 10–19).

IAP was measured transvesically after instillation of 20 ml saline. IAH was defined as a sustained IAP >12 mmHg, according to the World Society of Abdominal Compartment Syndrome guidelines. The APP, FG and UO (expressed as ml/kg/hour) were calculated for each IAP measurement. For each individual patient, the correlation coefficient between urinary output and APP or FG was calculated. When serum creatinine levels were above 1.2 mg/dl or when patients were anuric at the moment of IAP measurements, observations were not taken into consideration for analysis of the correlation between the parameters studied.

Results

Four hundred and thirty-one paired datasets were available for analysis. Mean IAP in all observations was 13 ± 5.2 mmHg, mean APP 73 ± 16.0 mmHg and mean FG 60 ± 18.7 mmHg. IAH was present in 40% of the observations.

There was no significant correlation between APP and UO in 24/27 patients, and no significant correlation between FG and UO in 23/27 patients. When the correlation was significant for both parameters, FG correlated better with UO than APP in all patients.

Conclusion

In this sample of critically ill patients with normal serum creatinine and at risk for IAH, there was no correlation at the individual patient level in the majority of the patients. The correlation between FG and UO was better than between APP and UO when there was a significant correlation.

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De Waele, J., Hoste, E., Blot, S. et al. Filtration gradient and abdominal perfusion pressure do not correlate with urinary output in patients at risk for intra-abdominal hypertension and normal serum creatinine. Crit Care 9, P359 (2005). https://doi.org/10.1186/cc3422

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Keywords

  • Urinary Output
  • Compartment Syndrome
  • Abdominal Compartment Syndrome
  • Individual Patient Level
  • Normal Serum Creatinine