Does intravesical pressure as an estimation of intra-abdominal pressure predict effects on portal circulation?

Introduction

In the clinical setting, the measurement of intravesical pressure (IVP) has evolved to the gold standard for estimating intra-abdominal pressure (IAP) in critically ill patients. However, in order to study the interplay between flow and pressure in selected regions of the splanchnic circulation (e.g. in the portal vein), direct pressure measurements might be indispensable once IVP proves not accurate enough as an indirect estimate. The intention of our present study was therefore to compare IVP, a surrogate measure of IAP, and portal vein pressure (PVP) simultaneously with portal vein flow (Qpv) measurements in a pig model of fecal peritonitis.

Methods

In six anesthetized, mechanically ventilated, and instrumented pigs, fecal peritonitis was induced by inoculating autologue feces pellets suspended in saline. The IVP, PVP, and Qpv were measured before as well as 12 and 24 hours after peritonitis induction. The IAP was measured by sequentially filling with 25 and 200 ml urine and subsequently re-empting the bladder to 25 ml. The Qpv was measured by ultrasound Doppler flowmetry. IVP values at each filling step were compared with the simultaneously recorded PVP values using a Bland-Altman plot.

Results

During peritonitis, IVP overestimates PVP, especially when the bladder is filled with large fluid volumes (200 ml). Furthermore, under these conditions even the precision of IVP as an estimate of PVP vanishes, as shown in the plots by the larger SD. Regardless of the increases in IVP and PVP, Qpv also increased with peritonitis.

Conclusion

We conclude that IVP should be interpreted cautiously as an estimate of IAP in the presence of fecal peritonitis in pigs. Under these experimental conditions, the use of a rather small filling volume is recommended to increase the accuracy of the measurements. IVP (and PVP) alone do not predict effects on portal vein flow, at least up to moderately increased levels.

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