Flow-dependence of extravascular thermal volume as an index of pulmonary edema

Ethyl pyruvate improves systemic and hepatosplanchnic hemodynamics and prevents lipid peroxidation in a porcine model of resuscitated hyperdynamic endotoxemia

OBJECTIVE

To investigate the systemic, pulmonary, and hepatosplanchnic hemodynamic and metabolic effects of delayed treatment with ethyl pyruvate in a long-term porcine model of hyperdynamic endotoxemia.

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Anesthetized, mechanically ventilated, and instrumented pigs.

INTERVENTIONS

After 12 hrs of continuous infusion of lipopolysaccharide and hydroxyethyl starch to keep mean arterial pressure >60 mm Hg, swine randomly received placebo (Ringer's solution; control group, n = 11) or ethyl pyruvate in lactated Ringer's solution (n = 8; 0.03 g.kg(-1) loading dose over 10 mins, thereafter 0.03 g.kg(-1)hr(-1) for 12 hrs).

MEASUREMENTS AND MAIN RESULTS

Whereas mean arterial pressure significantly decreased in control animals, mean arterial pressure was maintained at the baseline level in pigs treated with ethyl pyruvate. Global oxygen uptake was comparable, so that the trend toward a higher oxygen transport and the significantly higher mixed venous hemoglobin oxygen saturation resulted in a significantly lower oxygen extraction in the ethyl pyruvate group. Ethyl pyruvate reduced intrapulmonary venous admixture and resulted in significantly greater Pa(O2)/F(IO2) ratios. Despite comparable urine production in the two groups during the first 18 hrs of endotoxemia, ethyl pyruvate significantly increased diuresis during the last 6 hrs of the study. Lipopolysaccharide-induced systemic and regional venous metabolic acidosis was significantly ameliorated by ethyl pyruvate. Endotoxemia increased both blood nitrate + nitrite and isoprostane concentrations, and ethyl pyruvate attenuated the response of these markers of nitric oxide production and lipid peroxidation.

CONCLUSIONS

Ethyl pyruvate infusion resulted in improved hemodynamic stability and ameliorated acid-base derangements induced by chronic endotoxemia in pigs. Reduced oxidative stress and an decreased nitric oxide release probably contributed to these effects.

Systemic, pulmonary, and hepatosplanchnic effects of N-acetylcysteine during long-term porcine endotoxemia

OBJECTIVE

Controversial data have been reported on the effects of N-acetylcysteine in patients with septic shock. We therefore investigated the systemic, pulmonary, and hepatosplanchnic hemodynamic, gas exchange, and metabolic effects of N-acetylcysteine during long-term, volume-resuscitated, hyperdynamic porcine endotoxemia, which mimics the features of hyperdynamic human sepsis.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

Investigational animal laboratory.

SUBJECTS

Eighteen pigs were randomized to receive endotoxin alone (controls, n = 9) or endotoxin plus N-acetylcysteine (n = 9).

INTERVENTIONS

Anesthetized, mechanically ventilated, and instrumented animals received continuous intravenous endotoxin and were resuscitated with hydroxyethylstarch to keep mean arterial pressure >60 mm Hg. After 12 hrs of endotoxemia, they were randomized to receive either placebo or N-acetylcysteine (150 mg/kg loading dose over 1 hr followed by 20 mg.kg-1.hr-1 for 11 hrs).

MEASUREMENTS AND MAIN RESULTS

Before as well as 12, 18, and 24 hrs after starting the endotoxin infusion, systemic, pulmonary, and hepatosplanchnic hemodynamics, oxygen exchange, and metabolism as well as nitric oxide, glutathione, and 8-isoprostane concentrations were assessed. N-acetylcysteine failed to improve any of the variables of the systemic, pulmonary, or hepatosplanchnic hemodynamics, gas exchange, and metabolism. Although N-acetylcysteine significantly elevated glutathione concentration, it did not influence the 8-isoprostane concentrations and even further reduced hepatic venous pH.

CONCLUSIONS

Despite the increased glutathione concentration, N-acetylcysteine did not improve systemic, pulmonary, and hepatosplanchnic hemodynamics, oxygen exchange, and metabolism. When compared with previous reports in the literature, a different timing of N-acetylcysteine administration and/or an ongoing or even N-acetylcysteine-induced aggravation of oxidative stress may account for this result.

A new model for the assessment of lung allograft ischemia/reperfusion injury

Lung edema is the main clinical manifestation of reperfusion injury following lung transplantation. The evaluation of strategies to prevent this injury is of high clinical importance. Therefore we developed a large-animal model to study the mechanisms of ischemia/reperfusion injury including dynamics of posttransplant reperfusion edema and their prevention. Left lung allotransplantation was performed in 6 weight-matched pigs (25-31 kg). Donor lungs were flushed with 1.5 L low-potassium dextran (LPD) solution (4 degrees C) and preserved for 20 h at 1 degrees C. One hour after reperfusion the recipient contralateral right lung was excluded from perfusion and ventilation to assess graft function only. Extravascular lung water index (EVLWI), intrathoracic blood volume (ITBV), and cardiac output (CO) were assessed (q = 30 min) with a lung water computer (Cold Z-021, Partig, Munich, Germany) by the thermo-dye technique during a 5-h observation period. Gas exchange (FIO2 = 1.0) was measured hourly, and hemodynamics were monitored continuously. The EVLWI of the recipient contralateral lung together with the donor left lung at the time of reperfusion was 6.5+/-1.1 ml/kg, increasing to 7.1+/-1.0 ml/kg at 60 min after reperfusion. After occlusion of the recipient right lung, EVLWI in the graft further increased within 80 min from 8.1+/-0.5 ml/kg to a peak of 11.4+/-1.3 ml/kg, followed by a decrease to 8.5+/-0.8 ml/kg at 5 h after reperfusion in 5 of 6 animals. In 1 animal a severe alveolar edema developed with subsequent deterioration of gas exchange and death 4.5 h after reperfusion. In this animal, peak EVLWI reached 16.8 ml/kg, PaO2 deteriorated from 60.1 to 7.8 kPa, and CO decreased from 3.1 to 1.4 L/min. In all other animals, ITBV (515+/-51 ml), left atrial pressure (LAP), central venous pressure (CVP), and CO (2.9+/-0.3 L/min) were stable during the 5-h assessment period. We conclude that EVLWI measurement is a reliable and very sensitive method to quantify lung allograft reperfusion edema. It may prove useful in early assessment of lung allograft reperfusion injury in the clinical setting and in experimental models.

Reproducibility of double indicator dilution measurements of intrathoracic blood volume compartments, extravascular lung water, and liver function

STUDY OBJECTIVE

Arterial thermal dye dilution (TDDart) with the COLD system (Munich, Germany) allows measurement of cardiac index (CI), partial blood volumes, lung water, and liver function. The aim of the study was to determine agreement of TDDart measurements with pulmonary artery thermal dilution measurements (TDpa) and to assess the reproducibility of TDDart parameters.

DESIGN

Prospective study.

SETTING

ICU of a university hospital department of cardiac surgery.

PATIENTS

Thirty consecutive patients after coronary artery bypass grafting.

MEASUREMENTS AND RESULTS

Triplicate measurements of TDDart parameters were performed 1, 3, 6, 12, and 24 h postoperatively and coefficients of variation (CVs) were computed. At the 3-h point, additional fivefold TDDart measurements were done and compared with TDpa measurements. The coefficient of correlation for CI from TDDart vs TDpa was 0.96 (p<0.001), and the mean difference was 0.16 L/min/m2 (2.4%). The CVs of the TDDart and TDpa CI measurement were 7.2% and 5.9%; the CVs of other TDDart parameters were 4.6% (cardiac function index), 8.3% (global end-diastolic volume), 7.0% (intrathoracic blood volume), 7.6% (total blood volume), 7.4% (right ventricular end-diastolic volume), 7.4% (right heart end-diastolic volume), 11.3% (left heart end-diastolic volume [LHEDV]), 12.0% (right to left heart volume proportion [R/LHV]), 8.8% (pulmonary blood volume), 10.8% (extravascular lung water), 16.4% (plasma disappearance rate of dye), and 19.8% (dye clearance). The CV did not depend on Glasgow coma scale or on body temperature.

CONCLUSION

The CVs of LHEDV and R/LHV are influenced by asynchronous TDDart and TDpa variation. The CVs of plasma disappearance and dye clearance are increased as the half-life of the dye is longer than the measurement sequence. All other parameters derived from TDDart and TDpa show a clinically sufficient reproducibility.

Usefulness of sodium chloride as a nondiffusible indicator in the measurement of extravascular lung thermal volume in dogs

The authors examined the usefulness of sodium chloride as a nondiffusible indicator during the first passage through dogs' lungs, before and after increased-permeability pulmonary oedema produced by an intravenous injection of alloxan. With an injection of a mixture of ice-cold 3 per cent sodium chloride and indocyanine green dye (a nondiffusible reference indicator), the authors simultaneously recorded three dilution curves from the aortic root: dye dilution, thermal and blood electrical conductivity dilution curves in six dogs. The mean transit time of sodium chloride in the conductivity dilution curve was significantly different from, but fairly equal to, that of indocyanine green dye (6.2 +/- 1.4 s (mean +/- SD) against 6.5 +/- 1.4 s (p < 0.01) in the baseline period, and 7.6 +/- 1.9 s against 8.4 +/- 2.1 s (p < 0.01) in the oedema period, respectively). The calculated extravascular lung thermal volume with the thermal and conductivity dilution method (Y, ml kg-1) correlated well with the gravimetrically determined extravascular lung mass in a total of 12 dogs, including six other dogs without intervention (x, g kg-1) (y = 0.72 x +3.03, r = 0.96). The authors conclude that sodium chloride is useful as a nondiffusible indicator in the first passage through the lungs, and that the thermal and conductivity dilution method is also useful for measuring extravascular lung water mass.

Effects of pleural fluid and positive end-expiratory pressure on the measurement of extravascular lung water by the double-indicator dilution technique

The reliability of the double-indicator dilution technique (dye/cold) for measuring extravascular lung water (EVLW) has been studied in lung-healthy dogs after pleural fluid injection of saline (up to 20 ml/kg) during mechanical ventilation at zero and 10 cmH2O (1.0 kPa) end-expiratory pressure (ZEEP and PEEP, respectively). Pleural fluid injection had no effect on EVLW at either ZEEP or PEEP. PEEP induced changes in cardiac output, and reduced both the intravascular (dye) and the thermal indicator volumes, but with no effect on the calculated EVLW. It is concluded that pleural fluid up to 20 ml/kg and ventilation with PEEP of 10 cmH2O (1.0 kPa) do not affect the reliability of the double-indicator dilution technique for measuring extravascular lung water in the dog.

Extravascular lung water as an indicator of pulmonary dysfunction in acute hemorrhagic pancreatitis

This study quantifies lung water in acute hemorrhagic pancreatitis to determine the degree to which pulmonary dysfunction occurs subclinically, before alterations in the arterial blood gases can be measured. Pancreatitis was induced in ten dogs by injecting 0.5 ml/kg of bile into the pancreatic ducts, which had been surgically cannulated. Pulmonary and systemic blood gases and blood pressures, heart rate, extravascular lung water, and lung blood flows were studied over 5 hours while cardiac output and mean arterial pressure were maintained at control values by Ringer's lactate infusion. The percentage of water in lung tissue was determined at the time of sacrifice using gravimetric measurements. Mean arterial pressure, cardiac output, and pulmonary capillary wedge pressure, reflecting intravascular volume status, did not change through at the experiment. By contrast, major disturbances were measured in the pulmonary bed with pulmonary artery pressures rising from 15.6 +/- 1.8/8.1 +/- 1.3 mmHg to 22.0 +/- 1.2/15.6 +/- 1.7 mmHg over 5 hours (p less than 0.01). Peripheral vascular resistance rose from 3.6 +/- 0.6 units to 6.6 +/- 0.4 units (p less than 0.05), whereas bronchial blood flow to the lung fell significantly. These changes in pulmonary hemodynamics were not reflected by changes in the arterial blood gases. Arterial oxygenation was maintained during 5 hours of pancreatitis. The partial pressure of carbon dioxide and the serum pH did not change significantly. There was, however, a progressive rise in extravascular lung water measured by the double-dilution technique from 10.2 +/- 0.8 ml/kg at control to 18.1 +/- 2.8 ml/kg (p less than 0.01) at 5 hours. This was confirmed by direct gravimetric measurements, which revealed an increase in the water content of the lung from 78.1 +/- 0.3% to 86.4 +/- 2.4% over the course of the experiment. Arterial blood gases, therefore, do not necessarily reflect the pulmonary deterioration in acute pancreatitis. These data supported a mechanism of lung dysfunction independent of the circulatory compromise, which often accompanies the disease in the clinical setting.

Effect of positive-end expiratory pressure on accuracy of thermal-dye measurements of lung water

The thermal-dye indicator dilution technique of measuring extravascular lung water (EVLW-TD) correlates well with gravimetric measurement of lung water (EVLW-GR) when no positive-end expiratory pressure (PEEP) is used in both normal and edematous lungs. PEEP is often used to raise arterial oxygen tension in acute respiratory failure. This study was designed to answer the question: Does PEEP have an effect on the accuracy of the EVLW measurement by thermal dye? Sixteen mongrel dogs were anesthetized and intubated. Arterial and PA catheters were placed. They were divided into three groups and ventilated at PEEP levels of 5, 10, or 15 cm H2O. Fluids were given to minimize decrease in cardiac output with institution of PEEP. They were maintained for 5 hr with measurement of vital signs made hourly and measurement of blood gases and EVLW-TD made at baseline, 1, 3, and 5 hr. After final measurements, gravimetric determination of EVLW was done. Correlation between EVLWTD and EVLWGR remained good when low levels of PEEP were used. At 5 cm H2O PEEP, EVLWTD was 7.5 +/- 0.9 and EVLWGR was 5.4 +/- .3. At 10 cm H2O PEEP, they were 10.0 +/- 0.9 and 6.5 +/- 0.3. The correlations were 0.87 and 0.97, respectively. However, at 15 cm H2O PEEP, EVLWTD was 11.4 +/- 1.3 and EVLWGR was 7.5 +/- 0.6, with a correlation of only 0.59. The correlation between the two techniques seems to break down with higher levels of PEEP in dogs with normal lungs.

Clinical studies of measuring extravascular lung water by the thermal dye technique in critically ill patients

We measured extravascular lung water (EVLW) by the thermal-dye technique in a broad group of critically ill patients who had either acute cardiac or noncardiac illnesses. A portable AP supine chest roentgenogram, reviewed blindly, was used to classify patients as to the presence or absence of pulmonary edema; by clinical history we categorized patients into either a cardiac or noncardiac (ie, ARDS) group. With a normal chest roentgenogram, the mean EVLW was 5.6 +/- 1.8 ml/kg, and the pulmonary capillary wedge pressure (PCWP) was 11.3 +/- 5.3 mm Hg (mean +/- SD). In contrast, patients with pulmonary edema on a cardiac basis had a mean EVLW of 10.2 +/- 3.1 ml/kg (mean PCWP, 20.5 +/- 8.2 mm Hg), while patients with clinically defined noncardiac pulmonary edema and a normal PCWP (11.6 +/- 5.7 mm Hg) had a mean EVLW of 15.8 +/- 4.6 ml/kg, significantly higher than in the cardiac group (p less than 0.001). On a severity system of 014, the EVLW increased in parallel to the severity of the chest radiologic appearance of edema in both the cardiac (r2 = .44; p less than 0.001) and noncardiac (r2 = .59; p less than 0.001) patients. This study defined a normal range of thermal-dye EVLW in critically ill patients without radiologic evidence of pulmonary edema. We further demonstrated the increased pulmonary microvascular permeability of noncardiac pulmonary edema compared with cardiac edema by the greater EVLW at normal microvascular hydrostatic pressures in the former group.