Mechanical ventilation worsens abdominal edema and inflammation in porcine endotoxemia

Duodenum edema due to reduced lymphatic drainage leads to increased inflammation in a porcine endotoxemic model

Background

Interventions, such as mechanical ventilation with high positive end-expiratory pressure (PEEP), increase inflammation in abdominal organs. This effect could be due to reduced venous return and impaired splanchnic perfusion, or intestinal edema by reduced lymphatic drainage. However, it is not clear whether abdominal edema per se leads to increased intestinal inflammation when perfusion is normal. The aim of the presented study was to investigate if an impaired thoracic duct function can induce edema of the abdominal organs and if it is associated to increase inflammation when perfusion is maintained normal. In a porcine model, endotoxin was used to induce systemic inflammation. In the Edema group (n = 6) the abdominal portion of the thoracic duct was ligated, while in the Control group (7 animals) it was maintained intact. Half of the animals underwent a diffusion weighted-magnetic resonance imaging (DW-MRI) at the end of the 6-h observation period to determine the abdominal organ perfusion. Edema in abdominal organs was assessed using wet–dry weight and with MRI. Inflammation was assessed by measuring cytokine concentrations in abdominal organs and blood as well as histopathological analysis of the abdominal organs.

Results

Organ perfusion was similar in both groups, but the Edema group had more intestinal (duodenum) edema, ascites, higher intra-abdominal pressure (IAP) at the end of observation time, and higher cytokine concentration in the small intestine. Systemic cytokines (from blood samples) correlated with IAP.

Conclusions

In this experimental endotoxemic porcine model, the thoracic duct’s ligation enhanced edema formation in the duodenum, and it was associated with increased inflammation.

Necrotizing enterocolitis and the gut-lung axis

The recently recognized connection between the gut microbiota and pulmonary disease has been termed the gut-lung axis. However, broader connections link the gut and the lungs and these organ systems are tightly interrelated in both homeostasis and disease. This concept is often ignored in the compartmentalized treatment of pulmonary or gastrointestinal disease. In newborns, the most severe gastrointestinal complication of prematurity, necrotizing enterocolitis, and the most severe pulmonary complication, bronchopulmonary dysplasia, both produce significant systemic morbidity. In this review, we highlight the often neglected pathophysiology of the gut-lung axis contributes to increased risk of bronchopulmonary dysplasia in premature infants with necrotizing enterocolitis.

Effect of mechanical ventilation versus spontaneous breathing on abdominal edema and inflammation in ARDS: an experimental porcine model

Background

Mechanical ventilation (MV), compared to spontaneous breathing (SB), has been found to increase abdominal edema and inflammation in experimental sepsis. Our hypothesis was that in primary acute respiratory distress syndrome (ARDS) MV would enhance inflammation and edema in the abdomen.

Methods

Thirteen piglets were randomized into two groups (SB and MV) after the induction of ARDS by lung lavage and 1 h of injurious ventilation.

1. SB: continuous positive airway pressure 15 cmH₂O, fraction of inspired oxygen (FIO₂) 0.5 and respiratory rate (RR) maintained at about 40 cycles min^− 1 by titrating remifentanil infusion.

2. MV: volume control, tidal volume 6 ml kg^− 1, positive end-expiratory pressure 15 cmH₂O, RR 40 cycles min^− 1, FIO₂ 0.5.

Main outcomes: abdominal edema, assessed by tissues histopathology and wet-dry weight; abdominal inflammation, assessed by cytokine concentration in tissues, blood and ascites, and tissue histopathology.

Results

The groups did not show significant differences in hemodynamic or respiratory parameters. Moreover, edema and inflammation in the abdominal organs were similar. However, blood IL6 increased in the MV group in all vascular beds (p < 0.001). In addition, TNFα ratio in blood increased through the lungs in MV group (+ 26% ± 3) but decreased in the SB group (− 17% ± 3).

Conclusions

There were no differences between the MV and SB group for abdominal edema or inflammation. However, the systemic increase in IL6 and the TNFα increase through the lungs suggest that MV, in this model, was harmful to the lungs.

Mechanical ventilation as a surrogate for diagnosing the onset of abdominal compartment syndrome (ACS) in severely burned patients (TIRIFIC-study Part II)

Intra-abdominal compartment syndrome (ACS) is a devastating complication in burn patients with a high mortality. Apart from high-volume resuscitation as known risk factor, also mechanical ventilation seems to influence the development of ACS. The TIRIFIC trial is a retrospective, matched-pair analysis. Thirty-eight burn patients with ACS were matched for burned total body surface area (TBSA), age and mechanical ventilation (MV). In contrast to the already published part I addressing fluid resuscitation as a risk factor, the parameters analyzed in part II were maximum and average PEEP and peak pressure levels as well as serum lactate levels and prokinetic therapy. For subgroup-analysis the ACS-group was split up into an early-onset and late-onset ACS-group according to the median time between burn trauma and ACS. The groups were analyzed with a two-sided Mann-Whitney-U-test with significance set at p < 0.05. In the ACS-group all ventilation pressures (maximum and average PEEP and peak pressure levels) were significantly increased compared to control. The subgroup-analysis showed significantly increased maximum PEEP and peak pressure levels in early- and late-onset ACS-groups versus control. However, the average ventilation pressure levels were only increased in the early-onset ACS-group (average PEEP p = 0.0069; average peak pressure p = 0.05). The TIRIFIC trial showed significantly increased ventilation pressures in the ACS group in general as a surrogate parameter to support early diagnostics. Especially, maximum PEEP levels and peak pressures are significantly increased in both, early- and late-onset ACS. As an addition to the actual WSACS guidelines we suggest IAP measurement in mechanically ventilated burn patients if ventilating pressures are rising continuously without a clear pulmonary or otherwise identifiable reason.

Rethinking our definition of operative success: predicting early mortality after emergency general surgery colon resection

Background

The postoperative outcomes of emergency general surgery patients can be fraught with uncertainty. Although surgical risk calculators exist to predict 30-day mortality, they are often of limited utility in preparing patients and families for immediate perioperative complications. Examination of trends in mortality after emergent colectomy may help inform complex perioperative decision-making. We hypothesized that risk factors could be identified to predict early mortality (before postoperative day 5) to inform operative decisions.

Methods

This analysis was a retrospective cohort study using the American College of Surgeons National Surgical Quality Improvement Program database (2012-2014). Patients were stratified into three groups: early death (postoperative day 0-4), late death (postoperative day 5-30), and those who survived. Multivariable logistic regression was used to explore characteristics associated with early death. Kaplan-Meier models and Cox regression were used to further characterize their impact.

Results

A total of 18 803 patients were analyzed. Overall 30-day mortality was 12.5% (3316); of these, 37.1% (899) were early deaths. The preoperative factors most predictive of early death were septic shock (OR 3.62, p<0.001), ventilator dependence (OR 2.81, p<0.001), and ascites (OR 1.63, p<0.001). Postoperative complications associated with early death included pulmonary embolism (OR 5.78, p<0.001), presence of new-onset or ongoing postoperative septic shock (OR 4.45, p<0.001) and new-onset renal failure (OR 1.89, p<0.001). Patients with both preoperative and postoperative shock had an overall mortality rate of 47% with over half of all deaths occurring in the early period.

Conclusions

Nearly 40% of patients who die after emergent colon resection do so before postoperative day 5. Early mortality is heavily influenced by the presence of both preoperative and new or persistent postoperative septic shock. These results demonstrate important temporal trends of mortality, which may inform perioperative patient and family discussions and complex management decisions.

Level of evidence

Level III. Study type: Prognostic.

Abdominal organ perfusion and inflammation in experimental sepsis: a magnetic resonance imaging study

Diffusion-weighted magnetic resonance imaging (DW-MRI) uses water as contrast and enables the study of perfusion in many organs simultaneously in situ. We used DW-MRI in a hypodynamic sepsis model, comparing abdominal organ perfusion with global hemodynamic measurements and inflammation. Sixteen anesthetized piglets were randomized into 3 groups: 2 intervention (sepsis) groups: HighMAP (mean arterial pressure, MAP > 65 mmHg) and LowMAP (MAP between 50 and 60 mmHg), and a Healthy Control group (HC). Sepsis was obtained with endotoxin and the desired MAP maintained with norepinephrine. After 6 h, DW-MRI was performed. Acute inflammation was assessed with IL-6 and TNFα in abdominal organs, ascites, and blood and by histology of intestine (duodenum). Perfusion of abdominal organs was reduced in the LowMAP group compared with the HighMAP group and HC. Liver perfusion was still reduced by 25% in the HighMAP group compared with HC. Intestinal perfusion did not differ significantly between the intervention groups. Cytokine concentrations were generally higher in the LowMAP group but did not correlate with global hemodynamics. However, cytokines correlated with regional perfusion and, for liver and intestine, also with intra-abdominal pressure. Histopathology of intestine worsened with decreasing perfusion. In conclusion, although a low MAP (≤60 mmHg) indicated impeded abdominal perfusion in experimental sepsis, it did not predict inflammation, nor did other global measures of circulation. Decreased abdominal perfusion partially predicted inflammation but intestine, occupying most of the abdomen, and liver were also affected by intra-abdominal pressure. NEW & NOTEWORTHY The study increases the knowledge of abdominal perfusion during sepsis. We used diffusion weighted imaging to assess perfusion simultaneously and noninvasively in different abdominal organs. The technique has not been used in a sepsis model before. Cytokine concentrations were measured in different abdominal organs and vascular beds and related to regional perfusion. Decreased abdominal perfusion, but not global measures of circulation, predicted inflammation. Intestine, occupying most of the abdomen, and liver were also affected by intra-abdominal pressure.