Abstract
The effects of a moderately elevated intra-abdominal pressure (IAP) on lung mechanics in acute respiratory distress syndrome (ARDS) have still not been fully analyzed. Moreover, the optimal positive end-expiratory pressure (PEEP) in elevated IAP and ARDS is unclear. In this paper, 18 pigs under general anesthesia received a double hit lung injury. After saline lung lavage and 2 h of injurious mechanical ventilation to induce an acute lung injury (ALI), an intra-abdominal balloon was filled until an IAP of 10 mmHg was generated. Animals were randomly assigned to one of three groups (group A = PEEP 5, B = PEEP 10 and C = PEEP 15 cmH2O) and ventilated for 6 h. We measured end-expiratory lung volume (EELV) per kg bodyweight, driving pressure (ΔP), transpulmonary pressure (ΔPL), static lung compliance (Cstat), oxygenation (P/F ratio) and cardiac index (CI). In group A, we found increases in ΔP (22 ± 1 vs. 28 ± 2 cmH2O; p = 0.006) and ΔPL (16 ± 1 vs. 22 ± 2 cmH2O; p = 0.007), with no change in EELV/kg (15 ± 1 vs. 14 ± 1 mL/kg) when comparing hours 0 and 6. In group B, there was no change in ΔP (26 ± 2 vs. 25 ± 2 cmH2O), ΔPL (19 ± 2 vs. 18 ± 2 cmH2O), Cstat (21 ± 3 vs. 21 ± 2 cmH2O/mL) or EELV/kg (12 ± 2 vs. 13 ± 3 mL/kg). ΔP and ΔPL were significantly lower after 6 h when comparing between group C and A (21 ± 1 vs. 28 ± 2 cmH2O; p = 0.020) and (14 ± 1 vs. 22 ± 2 cmH2O; p = 0.013)). The EELV/kg increased over time in group C (13 ± 1 vs. 19 ± 2 mL/kg; p = 0.034). The P/F ratio increased in all groups over time. CI decreased in groups B and C. The global lung injury score did not significantly differ between groups (A: 0.25 ± 0.05, B: 0.21 ± 0.02, C: 0.22 ± 0.03). In this model of ALI, elevated IAP, ΔP and ΔPL increased further over time in the group with a PEEP of 5 cmH2O applied over 6 h. This was not the case in the groups with a PEEP of 10 and 15 cmH2O. Although ΔP and ΔPL were significantly lower after 6 hours in group C compared to group A, we could not show significant differences in histological lung injury score.
Highlights
The average intra-abdominal pressure (IAP) on admission of ventilated critical care patients in the intensive care unit is around 10 mmHg [1]
After induction of acute lung injury at hour 0 (H0), there were several significant changes in values compared with baseline data (Table 1): a reduction in end-expiratory lung volume (EELV)(1269 ± 68 vs. 665 ± 54; p < 0.010), Cstat (42 ± 2 vs. 21 ± 1; p < 0.013) and P/F ratio (456 ± 13 vs. 110 ± 13; p < 0.012)
Our study demonstrated that at the end of a 6 h mechanical ventilation, ERS decreased with increasing positive end-expiratory pressure (PEEP) mainly due to the decrease in EL
Summary
The average intra-abdominal pressure (IAP) on admission of ventilated critical care patients in the intensive care unit is around 10 mmHg [1]. The pressure in the abdomen causes a cranial shift of the diaphragm, thereby increasing intra-thoracic pressure and affecting lung volumes and respiratory mechanics [2,3]. The presence of intra-abdominal hypertension (IAH) is associated with a decrease in lung volume [4] and chest wall compliance [5]. The presence of IAH may add to the development of ventilator-induced lung injury (VILI) [10]. In the context of IAH, increased atelectrauma due to increased atelectasis formation and an insufficient positive end-expiratory pressure (PEEP) may further accelerate lung injury [2,3,11]
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