Abstract
BackgroundThe intra-abdominal pressure (IAP) is an important clinical parameter that can significantly change during respiration. Currently, IAP is recorded at end-expiration (IAPee), while continuous IAP changes during respiration (ΔIAP) are ignored. Herein, a novel concept of considering continuous IAP changes during respiration is presented.MethodsBased on the geometric mean of the IAP waveform (MIAP), a mathematical model was developed for calculating respiratory-integrated MIAP (i.e. ), where 'i' is the decimal fraction of the inspiratory time, and where ΔIAP can be calculated as the difference between the IAP at end-inspiration (IAPei) minus IAPee. The effect of various parameters on IAPee and MIAPri was evaluated with a mathematical model and validated afterwards in six mechanically ventilated patients. The MIAP of the patients was also calculated using a CiMON monitor (Pulsion Medical Systems, Munich, Germany). Several other parameters were recorded and used for comparison.ResultsThe human study confirmed the mathematical modelling, showing that MIAPri correlates well with MIAP (R2 = 0.99); MIAPri was significantly higher than IAPee under all conditions that were used to examine the effects of changes in IAPee, the inspiratory/expiratory (I:E) ratio, and ΔIAP (P <0.001). Univariate Pearson regression analysis showed significant correlations between MIAPri and IAPei (R = 0.99), IAPee (R = 0.99), and ΔIAP (R = 0.78) (P <0.001); multivariate regression analysis confirmed that IAPee (mainly affected by the level of positive end-expiratory pressure, PEEP), ΔIAP, and the I:E ratio are independent variables (P <0.001) determining MIAP. According to the results of a regression analysis, MIAP can also be calculated asMIAP=-0.3+IAPee+0.4⋅ΔIAP+0.5⋅IE.ConclusionsWe believe that the novel concept of MIAP is a better representation of IAP (especially in mechanically ventilated patients) because MIAP takes into account the IAP changes during respiration. The MIAP can be estimated by the MIAPri equation. Since MIAPri is almost always greater than the classic IAP, this may have implications on end-organ function during intra-abdominal hypertension. Further clinical studies are necessary to evaluate the physiological effects of MIAP.
Highlights
The intra-abdominal pressure (IAP) is an important clinical parameter with major prognostic impact [1,2]
We believe that the novel concept of mean of the IAP waveform (MIAP) is a better representation of IAP because MIAP takes into account the IAP changes during respiration
Part A: mathematical modelling According to Equation 2, three major independent parameters determine the respiratory-integrated mean intraabdominal pressure (MIAPri): IAP should be measured at end-expiration (IAPee), I:E ratio, and ΔIAP
Summary
The intra-abdominal pressure (IAP) is an important clinical parameter with major prognostic impact [1,2]. The IAP may be affected by conditions influencing intraabdominal volume and abdominal compliance (Cab) [3,8,9]. The complex interaction between intraabdominal volume and Cab during respiration (Figure 1) may significantly [10] and frequently (12 to 40 changes per minute) change the IAP (Figure 2), with more intense effects during positive-pressure mechanical ventilation or the presence of positive end-expiratory pressure (PEEP) [10,11,12]. The intra-abdominal pressure (IAP) is an important clinical parameter that can significantly change during respiration. A novel concept of considering continuous IAP changes during respiration is presented
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