Anesthesia aggravates lung damage and precipitates hypotension in endotoxemic sheep

Oxygen saturation in intraosseous sternal blood measured by CO-oximetry and evaluated non-invasively during hypovolaemia and hypoxia - a porcine experimental study

PURPOSE

This study intended to determine, and non-invasively evaluate, sternal intraosseous oxygen saturation (SsO₂) and study its variation during provoked hypoxia or hypovolaemia. Furthermore, the relation between SsO₂ and arterial (SaO₂) or mixed venous oxygen saturation (SvO₂) was investigated.

METHODS

Sixteen anaesthetised male pigs underwent exsanguination to a mean arterial pressure of 50 mmHg. After resuscitation and stabilisation, hypoxia was induced with hypoxic gas mixtures (air/N₂). Repeated blood samples from sternal intraosseous cannulation were compared to arterial and pulmonary artery blood samples. Reflection spectrophotometry measurements by a non-invasive sternal probe were performed continuously.

RESULTS

At baseline SaO₂ was 97.0% (IQR 0.2), SsO₂ 73.2% (IQR 19.6) and SvO₂ 52.3% (IQR 12.4). During hypovolaemia, SsO₂ and SvO₂ decreased to 58.9% (IQR 16.9) and 38.1% (IQR 12.5), respectively, p < 0.05 for both, whereas SaO₂ remained unaltered (p = 0.44). During hypoxia all saturations decreased; SaO₂ 71.5% (IQR 5.2), SsO₂ 39.0% (IQR 6.9) and SvO₂ 22.6% (IQR 11.4) (p < 0.01), respectively. For hypovolaemia, the sternal probe red/infrared absorption ratio (SQV) increased significantly from baseline (indicating a reduction in oxygen saturation) + 5.1% (IQR 7.4), p < 0.001 and for hypoxia + 19.9% (IQR 14.8), p = 0.001, respectively.

CONCLUSION

Sternal blood has an oxygen saturation suggesting a mixture of venous and arterial blood. Changes in SsO₂ relate well with changes in SvO₂ during hypovolaemia or hypoxia. Further studies on the feasibility of using non-invasive measurement of changes in SsO₂ to estimate changes in SvO₂ are warranted.

Sub-anesthesia Dose of Isoflurane in 60% Oxygen Reduces Inflammatory Responses in Experimental Sepsis Models

BACKGROUND

Sepsis is a major cause of mortality in Intensive Care Units. Anesthetic dose isoflurane and 100% oxygen were proved to be beneficial in sepsis; however, their application in septic patients is limited because long-term hyperoxia may induce oxygen toxicity and anesthetic dose isoflurane has potential adverse consequences. This study was scheduled to find the optimal combination of isoflurane and oxygen in protecting experimental sepsis and its mechanisms.

METHODS

The effects of combined therapy with isoflurane and oxygen on lung injury and sepsis were determined in animal models of sepsis induced by cecal ligation and puncture (CLP) or intraperitoneal injection of lipopolysaccharide (LPS) or zymosan. Mouse RAW264.7 cells or human peripheral blood mononuclear cells (PBMCs) were treated by LPS to probe mechanisms. The nuclear factor kappa B (NF-κB) signaling molecules were examined by Western blot and cellular immunohistochemistry.

RESULTS

The 0.5 minimum alveolar concentration (MAC) isoflurane in 60% oxygen was the best combination of oxygen and isoflurane for reducing mortality in experimental sepsis induced by CLP, intraperitoneal injection of LPS, or zymosan. The 0.5 MAC isoflurane in 60% oxygen inhibited proinflammatory cytokines in peritoneal lavage fluids (tumor necrosis factor-alpha [TNF-β]: 149.3 vs. 229.7 pg/ml, interleukin [IL]-1β: 12.5 vs. 20.6 pg/ml, IL-6: 86.1 vs. 116.1 pg/ml, and high-mobility group protein 1 [HMGB1]: 323.7 vs. 449.3 ng/ml; all P< 0.05) and serum (TNF-β: 302.7 vs. 450.7 pg/ml, IL-1β: 51.7 vs. 96.7 pg/ml, IL-6: 390.4 vs. 722.5 pg/ml, and HMGB1: 592.2 vs. 985.4 ng/ml; all P< 0.05) in septic animals. In vitro experiments showed that the 0.5 MAC isoflurane in 60% oxygen reduced inflammatory responses in mouse RAW264.7 cells, after LPS stimulation (all P< 0.05). Suppressed activation of NF-κB pathway was also observed in mouse RAW264.7 macrophages and human PBMCs after LPS stimulation or plasma from septic patients. The 0.5 MAC isoflurane in 60% oxygen also prevented the increases of phospho-IKKβ/β, phospho-IκBβ, and phospho-p65 expressions in RAW264.7 macrophages after LPS stimulation (all P< 0.05).

CONCLUSION

Combined administration of a sedative dose of isoflurane with 60% oxygen improves survival of septic animals through reducing inflammatory responses.

Plasma volume expansion by 0.9% NaCl during sepsis/systemic inflammatory response syndrome, after hemorrhage, and during a normal state

OBJECTIVE

The objective of this study was to determine the degree of plasma volume expansion by 0.9% NaCl in relation to the infused volume, in sepsis/systemic inflammatory response syndrome (SIRS), after a standardized hemorrhage, and in a normal condition.

DESIGN

Prospective, randomized animal study.

SETTING

The study was performed at a university hospital laboratory.

SUBJECTS

Thirty anesthetized adult male rats were included in the study.

INTERVENTIONS

The study was performed in three groups: a sepsis/SIRS group (the S group), in which sepsis/SIRS was induced by cecal ligation and incision; a hemorrhage group (the H group), in which the rats were left without intervention for 4 h and bled 8 mL/kg thereafter; and a group that was left without intervention (the N group). Then, 4 h after baseline, all three groups were given an infusion of 0.9% NaCl (32 mL/kg) for 15 min. Baseline was defined as the time point when the surgical preparation was finished.

MEASUREMENTS AND MAIN RESULTS

Plasma volumes were measured using I-albumin dilution technique at baseline, after 4 h, and 20 min after the end of infusion. The plasma volume-expanding effect 20 min after end of infusion was 0.6% ± 2.9% in the S group, 20% ± 6.4% in the H group, and 12% ± 11% in the N group, compared with just before start of infusion.

CONCLUSIONS

The present study in rats showed that the plasma volume-expanding effect after an infusion of 0.9% NaCl was smaller in a septic/SIRS state than after hemorrhage and in a normal state. This indicates that the plasma volume-expanding effect of a crystalloid is dependent on pathophysiologic changes in sepsis/SIRS.

Renal bioenergetics during early gram-negative mammalian sepsis and angiotensin II infusion

PURPOSE

To measure renal adenosine triphosphate (ATP) (bioenergetics) during hypotensive sepsis with or without angiotensin II (Ang II) infusion.

METHODS

In anaesthetised sheep implanted with a renal artery flow probe and a magnetic resonance coil around one kidney, we induced hypotensive sepsis with intravenous Escherichia coli injection. We measured mean arterial pressure (MAP), heart rate, renal blood flow RBF and renal ATP levels using magnetic resonance spectroscopy. After 2 h of sepsis, we randomly assigned sheep to receive an infusion of Ang II or vehicle intravenously and studied the effect of treatment on the same variables.

RESULTS

After E. coli administration, the experimental animals developed hypotensive sepsis (MAP from 92 ± 9 at baseline to 58 ± 4 mmHg at 4 h). Initially, RBF increased, then, after 4 h, it decreased below control levels (from 175 ± 28 at baseline to 138 ± 27 mL/min). Despite decreased RBF and hypotension, renal ATP was unchanged (total ATP to inorganic phosphate ratio from 0.69 ± 0.02 to 0.70 ± 0.02). Ang II infusion restored MAP but caused significant renal vasoconstriction. However, it induced no changes in renal ATP (total ATP to inorganic phosphate ratio from 0.79 ± 0.03 to 0.80 ± 0.02).

CONCLUSIONS

During early hypotensive experimental gram-negative sepsis, there was no evidence of renal bioenergetic failure despite decreased RBF. In this setting, the addition of a powerful renal vasoconstrictor does not lead to deterioration in renal bioenergetics.

In-vitro validation of cytokine neutralizing antibodies by testing with ovine mononuclear splenocytes

Cytokines have gained increasing attention as therapeutic targets in inflammation-related disorders and inflammatory conditions have been investigated in sheep. Monoclonal antibodies (mAbs) specific for the ovine pro-inflammatory cytokines interleukin (IL)-1β and IL-6 could be used to study the effects of blocking pro-inflammatory cytokines in sheep. Ovine-specific IL-1β and IL-6 proteins and mAbs specific for these molecules were produced and the ability of the mAbs to neutralize the proteins was tested in cultures of ovine splenic mononuclear cells. Expression of nuclear factor (NF)-κβ and signal transducer and activator of transcription (STAT)-3 was evaluated by western blotting and densitometric quantification. Treatment with purified IL-1β and IL-6 proteins increased NF-κβ (P < 0.001) and STAT-3 (P < 0.01) expression, respectively, in cell culture. Treatment with these proteins that were pre-incubated with IL-1β and IL-6 mAbs attenuated (P < 0.01) these effects. These results confirm the bioactivity of ovine IL-1β and IL-6 proteins and the neutralizing capacity of anti-ovine-IL-1β and -IL-6 mAbs in vitro. These mAbs could be used to investigate anti-inflammatory strategies for attenuation of the effects of these pro-inflammatory cytokines in sheep.

The effects of isoflurane anesthesia and mechanical ventilation on renal function during endotoxemia

BACKGROUND

Isoflurane is a common anesthetic agent used in human surgery and in animal models of sepsis. It has been suggested to have beneficial anti-inflammatory properties and to protect kidney function. Here, we investigated the effect of isoflurane on the development of kidney injury and dysfunction during 48-h endotoxemia in sheep.

METHODS

Before the experiments, the sheep (n=16) were surgically equipped with transit-time flowprobes around the renal, femoral and superior mesenteric artery. The animals were randomized to either be anesthetized with isoflurane and mechanically ventilated or to remain conscious while they received intravenous Escherichia coli lipopolysaccharide (LPS) for 48 h (25 ng/kg/min). In two animals in each group, the LPS was excluded to investigate any effect of isoflurane per se over time.

RESULTS

Endotoxemia caused cardiovascular changes typical for hyperdynamic sepsis and, although renal hyperemia occurred, impaired renal function in both groups. Compared with conscious animals, isoflurane significantly (P<0.05) reduced urine output, renal creatinine clearance, fractional sodium excretion and renal blood flow during endotoxemia. Furthermore, the plasma concentrations of urea and creatinine increased more in the anesthetized animals. Isoflurane anesthesia also enhanced neutrophil activity and accumulation in the kidney during endotoxemia. N-acetyl-β-D-glucosaminidase was significantly increased, with no inter-group difference as an indication of tubular injury.

CONCLUSIONS

The results of the current study suggest that isoflurane anesthesia (minimum alveolar concentration 1.0) with mechanical ventilation aggravates renal dysfunction during 48 h of endotoxemia and does not significantly reduce the inflammatory response or signs of tubular damage.