Ringer's solution but not hydroxyethyl starch or modified fluid gelatin enhances platelet microvesicle formation in a porcine model of septic shock †

Stable mixed acidemia in anesthetized pigs--a model for research on biocompatibility of hemofilters under a deteriorated acid-base balance

In recent years, acidosis has been of growing interest in intensive care medicine. Most animal models only provide a short-term investigation of the effects of acidosis. They are not suitable for research on interactions with extracorporeal organ support (here continuous venovenous hemofiltration, CVVH). The rationale for this study was to establish a porcine model of prolonged mixed acidemia, which is suitable for research on the interactions of acidemia and CVVH. After the induction of anesthesia in pigs (40 kg), acidemia was induced and maintained in one group with a bolus of 0.4 mol/L lactic acid followed by continuous infusion and a reduced respiratory frequency (lactic acid-group, n = 4). In another group, mixed acidemia was induced with a 0.4 mol/L acid solution (lactic and hydrochloric acid) and low tidal volume ventilation (mixed acidemia-group, n = 8). To get first proof of the model's suitability to operate over an extracorporeal circuit, CVVH was additionally performed in seven pigs (mixed acidemia/CVVH-group, n = 7). The target for the pH was 7.19-7.24. The targeted pH was constantly missed in the lactic acid group, whereas it was successfully maintained for 3.5 h in four out of eight pigs of the mixed acidemia group, and in five out of seven pigs of the mixed acidemia/CVVH group. The CVVH was performed successfully for 3 h in all pigs of the respective group. The mixed acidemia model was sufficient to maintain a low pH within a narrow range for some hours and enabled research on hemofilters in vivo.

HYDROXYETHYL STARCH NORMALIZES PLATELET AND LEUKOCYTE ADHESION WITHIN PULMONARY MICROCIRCULATION DURING LPS-INDUCED ENDOTOXEMIA

Growing evidence supports substantial pathophysiological impact of platelets and their interactions on the development of septic lung failure. We developed a rat model of endotoxemia for direct in situ visualization of pulmonary microcirculation by in vivo fluorescence videomicroscopy. Male Sprague-Dawley rats were assigned to control, endotoxemia (Escherichia coli LPS, 15 mg/kg, i.v.), and fluid management for treatment of LPS-induced hypovolemia (Ringer lactate, hydroxyethyl starch [HES] 6%) groups (n = 7 each). Leukocytes were labeled in vivo by rhodamine, and 5 x 10(6) Calcein-AM-labeled nonactivated platelets were injected. Microcirculatory parameters (vessel diameter, ventilation-perfusion ratio) and adhesive characteristics of platelets and leukocytes (velocity, rolling, sticking) within the pulmonary microcirculation were quantified after endotoxin application under various regimens of fluid substitution for 60 min. A reduction of cell velocity and enhanced cell adhesion was seen in leukocytes and platelets (P < 0.05) after LPS injection. Fluid treatment with HES 6% resulted in a significant increase of platelet's velocity compared with the LPS group (442.86 +/- 20.60 vs. 343.93 +/- 11.17; P < 0.05), whereas Ringer lactate showed no beneficial effects. Similarly, HES 6% normalized LPS-induced platelet rolling and sticking as well as alterations in ventilation-perfusion ratio. Using direct visualization of the pulmonary microcirculation, we observed that platelet and leukocyte interactions are enhanced in the lung during LPS endotoxemia. Fluid therapy with HES 6% seems to have restorative effects on these cellular functions within the pulmonary microcirculation.

Attenuation of capillary leakage by hydroxyethyl starch (130/0.42) in a porcine model of septic shock

OBJECTIVES

Capillary leakage, a frequent complication in septic shock, is characterized by loss of intravasal fluid resulting in generalized edema and hemodynamic instability despite massive fluid therapy. We have shown that administration of an established colloid 200/0.5 hydroxyethyl starch (HES) stabilized plasma volume in a porcine septic shock model. Recently, a new HES with a low molecular weight (130 kD) and lower molar substitution (0.42) has been developed. In this study, we compared effects of HES 130/0.42 and HES 200/0.5 on capillary leakage in porcine septic shock.

DESIGN

Prospective randomized, controlled animal study.

SETTING

University department of anesthesiology.

SUBJECTS

Fourteen pigs (22.9 +/- 2.8 kg).

INTERVENTIONS

Anesthetized and mechanically ventilated pigs were observed over 6 hrs.

MEASUREMENT AND MAIN RESULTS

Septic shock was induced with fecal peritonitis (0.75 g.kg of body weight autologous feces). Animals were allocated to volume-replacement therapy with either HES 130/0.42 (n = 5) or HES 200/0.5 (n = 5) and compared with nonseptic controls receiving HES 130/0.42 (n = 4). Infusion rate was titrated to maintain a central venous pressure of 12 mm Hg. Albumin escape rate was calculated using iodine 125-labeled albumin. Plasma volume was determined using chromium-51-tagged erythrocytes. Albumin escape rate increased significantly in both groups in comparison to controls (HES 200/0.5, 45% +/- 3; HES 130/0.42, 38% +/- 5), but this increase was significantly smaller with HES 130/0.42. Both HES 200/0.5 (-14%, not significant) and HES 130/0.42 (-1%, not significant) stabilized plasma volume compared with controls. Systemic oxygenation was not significantly altered in either group.

CONCLUSIONS

In this porcine septic shock model, HES 130/0.42 attenuated capillary leakage significantly more effectively than HES 200/0.5.

Reliability of continuous cardiac output determination by pulse-contour analysis in porcine septic shock

BACKGROUND

Pulse-contour analysis represents a technique for cardiac output (CO)-measurement and allows continuously monitoring trends in CO. We evaluated reliability of pulse-contour CO (COpc) in septic shock.

METHODS

Seventeen anaesthetized and mechanically ventilated pigs were investigated. After baseline measurements, 14 animals received 0.75 g/kg body weight faeces into the abdominal cavity to induce sepsis and were observed over 9 h, three animals served as controls. A central venous catheter was inserted into the jugular vein and an arterial catheter for thermodilution was inserted into the femoral artery. Two bedside computers were used for COpc. After induction of sepsis, COpc-computer No. 1 (COpcCAL) was recalibrated hourly. No further calibrations were performed in computer No. 2 (COpcNoCAL). We directly compared COpcCAL hourly before recalibration with COpcNoCAL. One hundred and seventy parallel triplicate determinations of CO were analysed using the method of Bland-Altman.

RESULTS

Three hours after sepsis induction, correlation between recalibrated and non-recalibrated CO was r = 0.74, P < 0.01, at 5 h r = 0.59, P < 0.05 and 9 h r = 0.02, NS. Three hours after sepsis induction, bias +/- SD (limits of agreement) between both groups was 1.6 +/- 15.5 (-29.4-32.6) ml/kg/min, at 5 h -15.0 +/- 24.3 (-63.6-33.7) ml/kg/min and at 9 h -87.0 +/- 90.8 (-268.5-94.6) ml/kg/min.

CONCLUSION

Continuous CO determination using pulse-contour analysis is a reliable method of assessing CO up to 5 h without recalibration in porcine septic shock. Thus, COpc may be a useful tool for assessment of unpredictable haemodynamic changes in sepsis.