Inhibition of nitric oxide synthesis improves arterial oxygenation in ethchlorvynol-induced acute lung injury in dogs

In both humans and in experimental animals, acute lung injury (ALI) is characterized by the development of pulmonary edema and arterial hypoxemia. It has been reported that the hypoxemia of ALI is related to the failure of those mechanisms that result in the diversion of blood flow away from hypoxic (edematous) lung units to those that are well oxygenated. One such mechanism is hypoxic pulmonary vasoconstriction (HPV). In the pulmonary circulation, endogenous nitric oxide (NO) has been shown to oppose HPV and, thereby, to support blood flow to hypoxic alveoli. In the present work we investigated the hypothesis that, in ALI, endogenous NO, by virtue of its ability to oppose HPV, supports blood flow to hypoxic lung units resulting in increases in venous admixture (Qva/Qt) and decreases in arterial oxygen tension (PaO2). In anesthetized and mechanically ventilated dogs, the intravenous administration of ethchlorvynol (ECV, 15 mg/kg) resulted in an increase in extravascular lung water (EVLW) of 10 +/- 1 ml/kg body wt (p < 0.001) as well as a 120 +/- 45% increase in Qva/Qt (p < 0.01) and a 23 +/- 5% decrease in PaO2 (p < 0.01) (n = 3). L-NAME (1 mg/kg iv, followed by 5 mg/kg/h, iv), administrated 60 min after ethchlorvynol (ECV), prevented entirely the ECV-induced increase in Qva/Qt and fall in PaO2 with minimal effect on EVLW (n = 3). We conclude that, in this model of ALI, endogenous NO is present in the lung and acts to support blood flow to poorly oxygenated lung units resulting, thereby, in reductions in PaO2.

Effect of hydroxyethyl starch on alveolar flooding in acute lung injury in dogs

The efficacy of hydroxyethyl starch (HES) in limiting alveolar flooding after acute lung injury was investigated using ethchlorvynol (ECV)-induced low pressure pulmonary edema in dogs. Harvested autologous plasma (PL) (control, n = 8) or 6% HES (n = 8) was infused (25 ml/kg) along with packed cells to result in an isovolemic, normochromic preparation before the administration of ECV. Extravascular thermal volume significantly increased after ECV administration in both groups of animals (6.6 to 13.4 ml/kg in PL, 6.5 to 15.0 ml/kg in HES). Systemic arterial PO2 decreased from 216 +/- 4 to 113 +/- 20 mm Hg, and venous admixture increased from 2.8 to 12.8% in the PL group but was not significantly changed in the HES group (219 +/- 5 to 203 +/- 8 mm Hg, and 2.9 to 4.4%, respectively). Epithelial lining fluid volumes after ECV administration increased in both groups but were elevated in the PL group to a greater extent than in the HES group (13.5 ml in HES versus 24.8 ml in PL). In the HES group there appeared to be no difference in the ability of plasma proteins to move across the alveolar epithelium. These results suggest that HES attenuates the flooding of the alveolar space and the resulting alterations in gas exchange during the development of low pressure pulmonary edema. The replacement of the plasma proteins with HES and the apparent inability of HES to cross the epithelial barrier into the alveoli may account for the protective effect of HES in these experiments.

Bronchoalveolar lavage in an animal model of acute lung injury. Relationship between enhanced membrane permeability and transvascular neutrophil flux

Results of studies utilizing bronchoalveolar lavage (BAL) have led workers to propose that the neutrophil serves as the pivotal cellular element responsible for promoting enhanced alveolar capillary membrane (ACM) permeability in certain forms of acute lung injury. The authors performed BAL on anesthetized, intubated, instrumented sheep before and after the administration of 15 mg/kg ethchlorvynol, a known pulmonary edemagenic agent. Bronchoalveolar lavage fluid (BALF) protein content increased from 0.62 +/- 0.05 to 1.5 +/- 0.15 mg/ml, and the percentage of neutrophils recovered from 2% +/- 1% at baseline to 35% +/- 7% (P less than 0.01) 60 minutes after infusion of ethchlorvynol. After ethchlorvynol infusion into neutropenic sheep (less than 500 cells/microliter), BALF protein content increased from 0.35 +/- 0.08 to 1.5 +/- 0.69 mg/ml (P less than 0.01) with no increase in BALF neutrophil count. In 3 non-neutropenic sheep BAL was performed at 15 and 30 minutes after ethchlorvynol infusion. BALF protein content increased significantly within 15 minutes, whereas the percentage of neutrophils did not change. These findings suggest coexistent ACM injury as reflected by increases in BALF protein content and increased number of neutrophils in BALF does not necessarily imply a cause-and-effect relationship in certain forms of acute lung injury.

Ethchlorvynol-induced pulmonary edema: a chronically instrumented, awake sheep model mimicking human disease

Ethchlorvynol injection in humans leads to a clinical picture consistent with increased permeability pulmonary edema, ie, the adult respiratory distress syndrome. There has been only one such case reported in which the pulmonary wedge pressure was measured. In an attempt to mimic the human disease, the authors established the awake, unanesthetized chronic sheep lung lymph fistula model and injected 15 mg/kg of ethchlorvynol intravenously after a baseline period. There were transient increases in pulmonary artery and systemic blood pressure with decreases in cardiac output. Lymph flow increased five-fold and remained elevated for 24 hr, returning to normal by 48 hr. All animals survived. Pulmonary morphologic changes consisted of alveolar and interstitial edema and some disruption of endothelial and epithelial cells. These findings resolved by 48 hr postinjection. The authors conclude that this model mimics the findings in humans who have injected ethchlorvynol intravenously.

Increased leukotriene C4 in ethchlorvynol-induced acute lung injury in dogs

We investigated whether ethchlorvynol (ECV)-induced acute lung injury (ALI) is associated with an increase in leukotriene C4 (LTC4) production. In six pentobarbital sodium-anesthetized dogs, ECV (15 mg/kg iv) introduced into the pulmonary circulation resulted in a 164 +/- 31% increase in extravascular lung water 120 min after ECV administration. Concomitantly, the mean (+/- SE) concentration of LTC4 in arterial plasma measured by radioimmunoassay following 80% EtOH precipitation, XAD-7 extraction and high-pressure liquid chromatography purification was 5.0 +/- 1.3 pg/ml, unchanged from control (pre-ECV) values. In contrast, in pulmonary edema fluid 120 min post-ECV, the LTC4 concentration was 35.2 +/- 10.8 pg/ml, sevenfold greater than those values found in the arterial plasma (P less than 0.01). In six additional dogs, 120 min after unilateral ALI had been induced with ECV (9 mg/kg iv), LTC4 in the bronchoalveolar lavage (BAL) of the uninjured lung was 12.1 +/- 1.5 pg/ml, unchanged from pre-ECV values, whereas, LTC4 in the BAL of the injured lung increased from a control value of 10.2 +/- 1.6 to 24.2 +/- 3.5 pg/ml (P less than 0.01) 120 min after ECV administration. These results demonstrate that, in ECV-induced acute lung injury, LTC4 concentrations in pulmonary edema fluid are considerably greater than those found in arterial plasma in the case of bilateral acute lung injury and significantly greater in the BAL of the injured lung compared with the uninjured lung in the case of unilateral acute lung injury. The results are a necessary first step in support of the hypothesis that leukotrienes participate in the altered permeability of ECV-induced acute lung injury.

Indomethacin and ketanserin block ethchlorvynol-induced hypoxemia in dogs

Intravenous injection of ethchlorvynol (ECV) leads to hypoxemia and a permeability pulmonary edema. Whether the hypoxemia is directly attributable to the pulmonary edema or caused by release of mediators has not been explored. Three groups of dogs were studied: (1) ECV, (2) indomethacin--ECV, and (3) ketanserin--ECV. In group 1, 25 to 30 mg/kg of ECV caused a significant fall in PaO2 at 4 min (92 +/- 12.6 to 77 +/- 21 mm Hg, p less than 0.05), which persisted throughout the experiment. The P(A-a)O2 gradient widened significantly at 3 min (22 +/- 11 to 31 +/- 16.8 mm Hg, p less than 0.05) and remained abnormal for the remainder of the experiment. There was no significant fall in PaO2 in groups 2 and 3. Lung tissue water to dry weight ratio increased significantly in all groups at 60 min. Lung tissue water to dry weight ratios were normal at 10 min after ECV injection in additional groups. It was concluded that ECV causes hypoxemia, which is mediated by cyclooxygenase products and 5 hydroxytryptamine. This hypoxemia can be prevented by the administration of drugs that block these products.

Pulmonary edema induced by intravenous ethchlorvynol

The intravenous injection of ethchlorvynol is an uncommon cause of noncardiac pulmonary edema. Two cases of intravenous ethchlorvynol-induced pulmonary edema are presented. The patients fell asleep after injecting the liquid contents of Placydil capsules (ethchlorvynol) and awoke several hours later with severe dyspnea. Arterial blood gases demonstrated marked hypoxia. Chest radiographs revealed bilateral diffuse alveolar densities. The patients' symptoms and radiographic findings resolved after several days of supportive care. Changes in the lung caused by ethchlorvynol may be the result of direct effect of the drug on the lung.

Effect of cyclooxygenase inhibition on ethchlorvynol-induced acute lung injury in dogs

In anesthetized dogs ethchlorvynol (ECV, 9 mg/kg) was selectively administered into the right pulmonary circulation to produce unilateral acute lung injury (ALI) characterized by nonhydrostatic pulmonary edema and systemic hypoxemia. To investigate the hypothesis that products of cyclooxygenase activity are mediators of the arterial hypoxemia, but not the edema formation in this injury, animals were pretreated with one of two chemically dissimilar cyclooxygenase inhibitors, indomethacin (5 mg/kg), or ibuprofen (12.5 mg/kg), or vehicle (0.1 M sodium carbonate) prior to the administration of ECV. Pretreatment with either inhibitor prevented the ECV-induced systemic hypoxemia observed in animals pretreated with vehicle (P less than 0.01). Despite this protection of systemic oxygenation, there was no redistribution of blood flow to the uninjured lung following unilateral ECV administration. Cyclooxygenase inhibition prior to ALI did not attenuate the accumulation of lung water. In the ibuprofen group, left atrial pressure increased significantly following ECV administration. We conclude that a product(s) of cyclooxygenase-mediated arachidonic acid metabolism is responsible for the altered vascular reactivity and consequent systemic hypoxemia in this model, but that the edema formation following ECV is not related to cyclooxygenase activity. In addition, ibuprofen, administered prior to the induction of ALI, exhibits properties not shared by indomethacin but is not different in its capacity to attenuate hypoxemia or in its failure to limit edema formation.

Contemporary drugs of abuse

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Early tissue damage in ethchlorvynol-induced alveolar edema in rabbit lung

The purpose of this study was to examine the morphologic changes that occur in the early stages of intraalveolar edema. Anesthetized rabbits were intravenously administered a bolus of 40 mg/kg of ethchlorvynol, a mild hypnotic known to induce respiratory distress syndrome in humans and laboratory animals when given intravenously. After 15 min their lungs were fixed for transmission electron microscopy. Examination revealed variable amounts of irregularly distributed intraalveolar edema with erythrocytes and fibrin strands that coexisted with modest or nonexisting interstitial edema suggesting that primary hemorrhagic alveolar flooding had taken place. Most alveolar epithelial and endothelial cells appeared normal except in localized areas. In lungs fixed by vascular perfusion, in which normal capillaries were flushed, obstructions were noticed in alveolar corner capillaries. These areas were identified by light microscopy and selectively sectioned for electron microscopy. They contained intravascular cell-fibrin aggregates consisting of plugs of degranulated platelets, fibrin, erythrocytes, and leukocytes. Endothelial and epithelial cells in the vicinity of the plugs showed variable degrees of injury. In places the damage was so severe that vascular and alveolar spaces were separated only by the basal lamina. Our work shows the previously unnoticed existence of capillary microemboli or microthrombi in a well-known experimental model of respiratory distress syndrome and suggests extravasation of blood elements through discrete sites of cell injury associated with the fibrin-platelet aggregates rather than diffuse increase of permeability as cause of early alveolar flooding.

Indomethacin blunts ethchlorvynol-induced pulmonary hypertension but not pulmonary edema

Ethchlorvynol (10 mg/kg) causes transient pulmonary hypertension and an increased permeability pulmonary edema in sheep. To determine the role of cyclooxygenase and its metabolites, histamine, and catecholamines in both phenomena, we studied five groups of sheep: group I, placebo; group II, ethchlorvynol; group III, indomethacin with ethchlorvynol; group IV, diphenhydramine with ethchlorvynol; group V, phentolamine with ethchlorvynol. Indomethacin, but not diphenhydramine or phentolamine, blunted the pulmonary hypertensive response seen immediately following the ethchlorvynol injection. However, none of the drugs had any effect on the increased permeability pulmonary edema. We conclude that cyclooxygenase or its metabolites partially mediates the hypertensive response but not the increased permeability pulmonary edema seen in sheep following ethchlorvynol injection.

The role of leukocytes in ethchlorvynol-induced pulmonary edema

Intravenous administration of ethchlorvynol (Placidyl) is known to produce noncardiogenic pulmonary edema in animals and humans. Since intrapulmonary sequestration of leukocytes has been observed to occur following injection of ethchlorvynol, we evaluated the role of these elements of the blood in producing pulmonary edema. In vivo studies in dogs showed intrapulmonary trapping of leukocytes, as evidenced by increasing leukocyte differences between blood from the pulmonary artery and arterial blood. In both animals with normal leukocyte counts and those depleted of leukocytes (less than 500 cells per millimeter), pulmonary edema occurred, as evidenced by increased pulmonary water after injection of ethchlorvynol. Preparations of isolated lung perfused with either whole blood or leukocyte-poor plasma had similar gains in weight following injection of ethchlorvynol, in spite of marked differences in leukocyte counts. We conclude that intrapulmonary sequestered leukocytes do not play a role in ethchlorvynol-induced pulmonary edema.

A CLINICAL EVALUATION OF FOUR HYPNOTIC AGENTS, USING A LATIN-SQUARE DESIGN

A double-blind study with a Latin-square design was undertaken on 25 elderly patients, using a placebo and four hypnotic drugs: ethchlorvynol 500 mg., glutethimide 500 mg., chloral hydrate 500 mg., and secobarbital sodium 100 mg. The trial lasted for five weeks. The drugs were all effective compared with the placebo, differences in sleeping time being statistically significant. Differences between these four drugs were not statistically significant. Sleep was induced soonest by secobarbital and ethchlorvynol. Ethchlorvynol and glutethimide had a relatively somewhat longer period of activity than the others. Glutethimide produced most side effects, especially morning drowsiness. Ethchlorvynol and chloral hydrate produced relatively few cases of drowsiness.