Evaluating abdominal oedema during experimental sepsis using an isotope technique

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.

Inter-electrode tissue resistance is not affected by tissue oedema when electrically stimulating the lower limb of sepsis patients

ICU patients typically are given large amounts of fluid and often develop oedema. The purpose of this study was to evaluate whether the oedema would change inter-electrode resistance and, thus, require a different approach to using non-invasive electrical stimulation of nerves to assess muscle force. Inter-electrode tissue resistance in the lower leg was measured by applying a 300 µs constant current pulse and measuring the current through and voltage across the stimulating electrodes. The protocol was administered to nine ICU patients with oedema, eight surgical patients without oedema and eight healthy controls. No significant difference in inter-electrode resistance was found between the three groups. For all groups, resistance decreased as stimulation current increased. In conclusion, inter-electrode resistance in ICU patients with severe oedema is the same as the resistance in regular surgical patients and healthy controls. This means that non-invasive nerve stimulation devices do not need to be designed to accommodate different resistances when used with oedema patients; however, surface stimulation does require higher current levels with oedema patients because of the increased distance between the skin surface and the targeted nerve or muscle.

Mechanical ventilation worsens abdominal edema and inflammation in porcine endotoxemia

INTRODUCTION

We hypothesized that mechanical ventilation per se increases abdominal edema and inflammation in sepsis and tested this in experimental endotoxemia.

METHODS

Thirty anesthetized piglets were allocated to one of five groups: healthy control pigs breathing spontaneously with continuous positive pressure of 5 cm H2O or mechanically ventilated with positive end-expiratory pressure of 5 cm H2O, and endotoxemic piglets during mechanical ventilation for 2.5 hours and then continued on mechanical ventilation with positive end-expiratory pressure of either 5 or 15 cm H2O or switched to spontaneous breathing with continuous positive pressure of 5 cm H2O for another 2.5 hours. Abdominal edema formation was estimated by isotope technique, and inflammatory markers were measured in liver, intestine, lung, and plasma.

RESULTS

Healthy controls: 5 hours of spontaneous breathing did not increase abdominal fluid, whereas mechanical ventilation did (Normalized Index increased from 1.0 to 1.6; 1 to 3.3 (median and range, P<0.05)). Endotoxemic animals: Normalized Index increased almost sixfold after 5 hours of mechanical ventilation (5.9; 4.9 to 6.9; P<0.05) with twofold increase from 2.5 to 5 hours whether positive end-expiratory pressure was 5 or 15, but only by 40% with spontaneous breathing (P<0.05 versus positive end-expiratory pressure of 5 or 15 cm H2O). Tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 in intestine and liver were 2 to 3 times higher with mechanical ventilation than during spontaneous breathing (P<0.05) but similar in plasma and lung. Abdominal edema formation and TNF-α in intestine correlated inversely with abdominal perfusion pressure.

CONCLUSIONS

Mechanical ventilation with positive end-expiratory pressure increases abdominal edema and inflammation in intestine and liver in experimental endotoxemia by increasing systemic capillary leakage and impeding abdominal lymph drainage.