Fig. 1

Illustration of air-capsule-based intra-abdominal pressure measurement system (ACM-IGP). a Schematic illustration of the customized catheter of the air-capsule-based measurement of intra-gastric pressure (ACM-IGP) system, which is equivalent to a special double-lumen 9F nasogastric tube, inserted into the stomach and connected to an ACM-IGP monitor (Illustration courtesy of Spiegelberg Company, Hamburg, Germany). The IAP normally undulates breath-synchronously (here: minimum 9.8 mmHg in expiration, maximum 10.3 mmHg in inspiration and 10.1 mmHg on average). Respiratory variations are considered as a quality criterion for IAP measurement; their absence indicates a malposition of the ACM-IGP or bladder catheter and usually requires their reinsertion. The insertion of an ACM-IGP catheter does not differ from that of a conventional nasogastric tube and is theoretically associated with a similar risk profile (malposition with aspiration, pneumonia, pneumothorax and esophageal or gastric perforation) [23, 24]. In patients beyond infancy, the placement is facilitated by an intraluminal guidewire provided by the manufacturer. In neonates and infants, the ACM-IGP catheter was placed without a guidewire, as the narrow bendig of the rigid guidewire in the pharynx hampers a later removal in this age group. All currently available ACM-IGP catheters do not have a radiopaque contrast. Therefore, the gastric catheter location was additionally verified by abdominal sonography in the present study. b Figure illustrates the ACM-IGP catheter connected to the ACM-IGP monitor. On the right side, the white, thin-skinned air capsule (sized 10 × 3 × 2.3 mm) is displayed at the gastric end of the ACM-IGP catheter, which is used for IAP measurement. The opposite side is connected to the pressure transducer on the left front of the ACM-IGP monitor. In the left lower margin the guide wire for insertion of the ACM-IGP catheter is displayed on the aboral end of the second lumen. Calibration and "zeroing" of the ACM-IGP system are fully automatic and repeated once per hour in the operating mode. During the continuous IAP measurement, the air capsule is filled with a defined air volume of 0.05–0.10 ml. Any pressure applied to the air capsule from outside is registered by the pressure transducer in the monitor and displayed as IAP with a precision of one decimal. c Illustration of a representative ACM-IGP measurement in a critically ill child with intra-abdominal hypertension (IAH) grade III (IAP = 16.9 mmHg). Please note that the displayed pressures with the minimum in exspiration (15.7 mmHg) and maximum in inspiration (17.5 mmHg) represent respiratory variations of IAP