Can abdominal perimeter be used as an accurate estimation of intra-abdominal pressure?

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. Most of the direct and indirect techniques are not free of risks and require some time and skills. This study will look at the possibility of using the abdominal perimeter (AP) as a quick estimation for IAP.

Methods

In total, 132 paired measurements were performed in 12 ICU patients. The IAP was calculated using the gold standard via an indwelling bladder catheter using a pressure transducer [1]. The AP was calculated by measuring the abdominal circumference at its largest point using body marks as reference for consecutive measurements. The male/female ratio was 7/5, age 68.5 ± 17.2 years, APACHE II score 27.8 ± 6.5, SAPS II score 58.9 ± 12.5. The number of measurements in each patient was 11 ± 4.2. 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 13.2 ± 12.6 versus 106.7 ± 15.2 for AP. There was a poor but slightly significant correlation between IAP and AP (Fig. 1): AP = 1.0357 × IAP + 94.107 (R² = 0.12, P = 0.042), but the bias was considerable. The correlation was better between Δ IAP (the difference between two consecutive IAP measurements) and Δ AP (the difference between two consecutive AP measurements) in 119 paired measurements (Fig. 2): Δ AP = 0.4598 × Δ IAP + 0.158 (R² = 0.22, P < 0.0001, two-tailed Pearson correlation). The analysis according to Bland and Altman showed that Δ IAP was almost identical to Δ AP with a mean difference or bias of 0.05 ± 3.54 (SD) mmHg (95% CI -0.6 to 0.7); the limits of agreement (LA) were -7.04 to 7.13 mmHg (95% CI -8.16 to -5.92 for the LLA and 6.01 to 8.25 for the ULA), these intervals are large and thus reflect poor agreement.

Figure 1

Figure 2

Conclusions

In view of the poor correlation between IAP and AP, the latter cannot be used as a clinical estimate for IAP. The evolution of AP (Δ AP) can be used as an indicator for the evolution of IAP over time (Δ IAP); however, for making a definite diagnosis of IAH or ACS, the exact value of IAP needs to be measured.