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

Intra-abdominal pressure (IAP) is an important parameter and prognostic indicator of the patient's underlying physiologic status. Correct IAP measurement, therefore, is crucial. Most of the direct and indirect techniques are not free from risks and require some time and skills. This study looks at the possibility of using the abdominal perimeter (AP) as a quick estimation for IAP.

In total, 237 paired measurements were performed in 26 intensive care unit patients. The IAP was measured according to the recommendations of the World Society on Abdominal Compartment Syndrome via an indwelling bladder catheter using a pressure transducer. The AP was defined as the abdominal circumference at its largest point using body marks as reference for consecutive measurements.

The male:female ratio was 1:1, age 69.8 +/- 15.2 yrs, Acute Physiology and Chronic Health Evaluation II score 26.5 +/- 9.2, and Simplified Acute Physiology Score II score 58 +/- 15.5. The number of measurements in each patient was 9.4 +/- 4.6. The IAP was 10.8 +/- 4.9 mm Hg, and the AP was 101 +/- 19.2 cm. There was a poor but statistically significant correlation between IAP and AP: AP = 1.8 x IAP + 81.6 (R2 = 0.21, p = 0.04), but the bias was considerable. The correlation was somewhat better between DeltaIAP (the difference between two consecutive IAP measurements) and DeltaAP (the difference between two consecutive AP measurements) in 210 paired measurements: DeltaAP = 0.4 x DeltaIAP + 0.1 (R2 = 0.24, p < 0.0001). The analysis according to Bland and Altman showed that DeltaIAP was almost identical to DeltaAP with a mean difference or bias of 0 +/- 3 (95% confidence interval: -0.4 to 0.4); however, the limits of agreement were large and thus reflect poor agreement.

In view of the poor correlation between IAP and AP, the latter cannot be used as a clinical estimate for IAP. The correlation between DeltaIAP and DeltaAP was somewhat better, meaning that DeltaAP can be used as an estimate of the evolution of IAP over time; however, for making a definite diagnosis of intra-abdominal hypertension or abdominal compartment syndrome, the exact value of IAP needs to be measured.