Adult respiratory distress syndrome (ARDS): the basics

The Management of Sepsis: A Practical Review

The incidence of the sepsis syndrome has increased dramatically in the last few decades. During this time we have gained new insights into the pathophysiologic mechanisms leading to organ dysfunction in sepsis and the importance of the host-bacterial interactions in mediating many of these processes. This knowledge has led to new therapeutic approaches and the investigation of a number of novel agents. An assessment of these approaches is presented to aid clinicians in the management of patients with severe sepsis. Criteria used to select studies included their relevance to the management of sepsis and their pertinence to clinicians. Appropriate antibiotic selection and volume resuscitation remain the cornerstone of treatment of septic patients. Hydroxyethyl starch solutions have theoretical advantages over crystalloids; there is, however, no data that the type of resuscitation fluid alters outcome. Vasoactive agents are required in patients who remain hemodynamically unstable or have evidence of tissue hypoxia after adequate volume resuscitation. Although dopamine is widely used, dobutamine and norepinephrine are our vasoactive agents of choice. Dopamine has no proven role in oliguric patients, with early dialysis recommended in patients with acute renal failure. The preferred method of renal replacement therapy remains to be determined. Blood products should be used cautiously in patients with disseminated intravascular coagulation. Therapeutic strategies that interfere with the immune system have not been proven to improve the outcome in unselected groups of patients. However, immunomodulation may prove to have a role in select subgroups of patients. Antibiotic therapy and intensive physiological support continues to be the main approach to the management of patients with severe sepsis. Despite the development of numerous novel therapeutic agents, these drugs have not been demonstrated to improve patient outcome.

Hypertonic saline reduces skeletal muscle injury and associated remote organ injury following ischemia reperfusion injury

BACKGROUND AND PURPOSE

Pharmacological modulation of skeletal muscle reperfusion injury after traumaassociated ischemia may improve limb salvage rates and prevent the associated systemic sequelae. Resuscitation with hypertonic saline restores the circulating volume and has favorable effects on tissue perfusion and blood pressure. We evaluated the effects of treatment with a bolus of hypertonic saline on skeletal muscle ischemia reperfusion (IR) injury and the associated end-organ injury.

METHODS

Adult male Sprague-Dawley rats (n = 27) were randomized into 3 groups: (1) a control group, (2) an IR group treated with normal saline, and (3) an IR group treated with hypertonic saline. Bilateral hindlimb ischemia was induced by application of a rubber band proximal to the level of the greater trochanters for 2.5 h. The treatment groups received either normal saline (4 mL/kg) or hypertonic saline (4 mL/kg) prior to tourniquet release. Following 12 h of reperfusion, the tibialis anterior muscle was dissected and muscle function was assessed electrophysiologically. The animals were then killed, and skeletal muscle and lung tissue were harvested for evaluation.

RESULTS

Hypertonic saline significantly attenuated skeletal muscle reperfusion injury, as shown by reduced myeloperoxidase content, wet-to-dry ratio, and electrical properties of skeletal muscle. There was a corresponding reduction in lung injury, as demonstrated by reduced myeloperoxidase content and reduced wet-to-dry ratio.

INTERPRETATION

Treatment with hypertonic saline attenuates skeletal muscle ischemia reperfusion injury and its associated systemic sequelae.

Nuclear factor-kappaB decoy oligodeoxynucleotides prevent acute lung injury in mice with cecal ligation and puncture-induced sepsis

The transcription factor nuclear factor-kappaB (NF-kappaB) plays a key role in expression of many inflammatory genes responsible for the pathophysiology of sepsis-induced acute lung injury. We investigated whether the introduction of synthetic double-stranded oligodeoxynucleotides (ODNs) with consensus NF-kappaB sequence as transcription factor decoy can prevent acute lung injury with suppression of pulmonary expression of multiple genes involved in its pathological process in a cecal ligation and puncture septic mouse model. NF-kappaB decoy ODNs were introduced with the aid of the hemagglutinating virus of Japan-envelope vector method. Northern blot analysis indicated that transfection of NF-kappaB decoy ODN, but not of its scrambled form, resulted in a significant inhibition of sepsis-induced gene overexpression of inducible nitric-oxide synthase (iNOS), cyclooxygenase-2, histamine H(1)-receptor, platelet-activating factor receptor, and bradykinin B(1) and B(2) receptors in lung Histological damage in lungs tissues. (wall thickening, inflammatory infiltrate, and hemorrhage), increased pulmonary vascular permeability, and blood gas exchange impairment were clearly documented in mice after cecal ligation and puncture. These changes were strongly eliminated by the introduction of NF-kappaB decoy but not of scrambled ODN. The effects of the iNOS inhibitor FR260330 on these histological and functional derangements compared unfavorably with those of NF-kappaB decoy ODN transfection. Our results suggest that ODN decoy, acting as in vivo competitor for the transcription factor's ability to bind to cognate recognition sequence, may represent an effective strategy in the treatment of septic acute lung injury.

Effects of acute hypoxia and lipopolysaccharide on nitric oxide synthase-2 expression in acute lung injury

The potential role of nitric oxide synthase-2 (NOS2) in acute lung injury (ALI) has gained increasing attention. This study evaluates the effects of hypoxia, an important feature of ALI, on NOS2 expression in a rat model of ALI caused by exposure to hypoxia and LPS. Exposure to hypoxia alone had no effect on the expression of NOS2 in rat lungs. LPS treatment resulted in a significant increase in NOS2 in the lungs, which was further enhanced by concomitant exposure to hypoxia. Immunohistochemical analysis and in situ hybridization showed no changes in the expression of NOS2 in lung resident cells under any conditions. The increase in NOS2 levels is mainly due to the influx of NOS2-expressing inflammatory cells. By morphologic analysis, these inflammatory cells were identified as neutrophils, lymphocytes, and monocytes. In vitro experiments of lung epithelial and endothelial cell lines showed no detectable expression of NOS2 with any of the treatments. In a macrophage cell line, LPS-induced NOS2 expression was not affected by the concomitant exposure to hypoxia. In conclusion, LPS increases NOS2 expression in rat lungs through the recruitment of NOS2-producing leukocytes. Simultaneous exposure to LPS and hypoxia results in a greater influx of inflammatory cells that further enhances NOS2 expression.

A novel therapeutic strategy for attenuating neutrophil-mediated lung injury in vivo

OBJECTIVE

To evaluate the effect of inhalation of aerosolized opsonized dead Escherichia coli on inflammatory pulmonary neutrophil (PMN) apoptosis, lung injury, and survival in a PMN-mediated lung injury model in vivo.

SUMMARY BACKGROUND DATA

Neutrophils that have transmigrated into an inflammatory focus display increased functional capacity and delayed apoptosis, resulting in an increased capacity to injure normal host tissue. The authors have previously shown that E. coli induces PMN apoptosis in vitro.

METHODS

Lung injury mediated by PMNs was established by aortic occlusion and reperfusion. Adult male Sprague-Dawley rats were randomized into four groups: sham ischemia-reperfusion (I/R) treated with intratracheal inhalation of aerosolized normal saline, I/R treated with aerosolized normal saline intratracheally, I/R treated with aerosolized opsonized dead E. coli intratracheally, and I/R treated with aerosolized opsonized dead E. coli and the caspase inhibitor zVAD-FMK intratracheally 5 minutes before reperfusion. Both systemic and bronchoalveolar lavage PMNs were isolated and apoptosis was quantified at 0, 6, 12, 18, and 24 hours. Lung injury parameters including wet/dry lung weight ratio, histology, myeloperoxidase activity, and protein content were also assessed. In addition, a survival study was performed, both in a prophylactic and in a therapeutic setting.

RESULTS

Administration of aerosolized dead E. coli before the reperfusion injury induced pulmonary PMN apoptosis and reversed the delayed apoptosis evident in the I/R plus normal saline group. There was also a significant improvement in lung injury parameters as well as in survival, both prophylactically as well as therapeutically.

CONCLUSIONS

Directly modulating PMN cell death represents a novel mechanism for attenuating PMN-mediated lung injury and may ultimately benefit the outcome in patients with adult respiratory distress syndrome.

Feasibility of a pumpless extracorporeal respiratory assist device

BACKGROUND

Our study evaluated the efficacy and feasibility of a pumpless respiratory assist device and determined its capacity for carbon dioxide removal.

METHODS

In five adult pigs the left femoral vein and artery were cannulated with a 20F cannula and connected to a low-pressure hollow-fiber artificial lung. After we had obtained baseline values of mean arterial pressure, cardiac output, and blood flow across the artificial lung, the mean arterial pressure was reduced 20% and 40% relative to baseline; in a second phase, it was raised 20% and 40. Cardiac output and artificial lung flow were simultaneously recorded. We determined the carbon dioxide removal capacity of the artificial lung by gradually increasing the arterial partial carbon dioxide tension of the animal.

RESULTS

An increase of 10 mm Hg in mean arterial pressure resulted in an increase of flow of 0.14 L/min. The mean pressure drop across the artificial lung was measured at 17 +/- 9 mm Hg. The shunt flow over the artificial lung varied between 14 and 25% of the cardiac output of the animal. Depending on inlet conditions, carbon dioxide removal by the artificial lung was between 62 +/- 22 mL/L/min and 104 +/- 25 mL/L/min.

CONCLUSIONS

A pumpless respiratory assist device can remove a significant proportion of the metabolic carbon dioxide production. However, adequate mean arterial pressure is mandatory to maintain sufficient flow across the device. The technique seems attractive because of its simplicity and can be used in acute lung injury in conjunction of apneic oxygenation for prolonged respiratory support.

Phospholipase A2 mediates nitric oxide production by alveolar macrophages and acute lung injury in pancreatitis

OBJECTIVE

Reportedly, nitric oxide (NO) derived from alveolar macrophages (AMs) and increased serum phospholipase A2 (PLA2) activity are associated with the pathogenesis of lung injury in acute pancreatitis. The authors examined the possibility that PLA2 causes, in part, the induction of NO production by AMs in pancreatitis.

METHODS

Pancreatitis was induced in rats by selective pancreatic duct ligation (SPL). AMs were stimulated with PLA2 or SPL rat serum, with or without administration of the PLA2 inhibitor quinacrine. Then NO production from the AMs was measured by the Griess method, inducible NO synthase mRNA expression of AMs was analyzed by the reverse transcription-polymerase chain reaction, and cytotoxic effects of AMs on human umbilical vein endothelial cells was examined by a 51Cr release assay. In vivo, the effect of quinacrine on lung injury was determined by measuring the arterial blood oxygen pressure (PaO2), lung weight, and lung permeability using Evans blue dye concentration of SPL rat.

RESULTS

In vitro, the serum with high PLA2 activity induced NO production by rat AMs. PLA2 (50 ng/ml) induced significant amounts of NO production, inducible NO synthase mRNA expression, and cytotoxicity toward the human umbilical vein endothelial cells in normal rat AMs, and these activities were significantly inhibited by quinacrine. In vivo, rats with pancreatitis that were given quinacrine showed decreased concentrations of NO2- and NO3- in the bronchoalveolar lavage fluid, and the PaO2, lung edema, and lung permeability were improved significantly.

CONCLUSION

PLA2 induces AMs to release NO, which contributes to lung injury in acute pancreatitis. This lung injury was prevented by the administration of the PLA2 inhibitor quinacrine.

Expression of inducible nitric oxide synthase and inflammatory cytokines in alveolar macrophages of ARDS following sepsis

STUDY OBJECTIVE

The objective of this study was to evaluate the role of inducible nitric oxide synthase (iNOS) and proinflammatory cytokines in alveolar macrophages (AMs) in the pathogenesis of ARDS following sepsis.

SETTING

ICU in a university hospital.

DESIGN

Prospective exploratory, open-labeled study was carried out.

PATIENTS

A total of 24 patients were investigated: 8 patients diagnosed as having ARDS following sepsis (ARDS group); 8 patients under general anesthesia in the operating room whose lung functions were normal (control group); and 8 patients who were intubated and artificially ventilated for 1 week in the ICU whose lung functions were not deteriorated without fulfilling the ARDS criteria and whose general state fulfilled the sepsis criteria (long-term ventilation group, or LTV group).

MEASUREMENTS AND RESULTS

The expression of iNOS, interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and interleukin-8 (IL-8) in AMs obtained from BAL fluid (BALF) was determined by the immunofluorescent technique. We observed the significant expression of iNOS, IL-6, and IL-8 only in the ARDS group. Meanwhile, NOx (the sum of NO2- + NO3-) was elevated in the BALF supernatant, and IL-6 and IL-8 levels in both the BALF supernatant and the serum were also elevated in the ARDS group. No significant expressions were detected in the control and the LTV group.

CONCLUSIONS

The result that iNOS was detected only in ARDS patients following sepsis suggests that iNOS together with proinflammatory cytokines produced by AMs might play a pivotal role in the pathogenesis of acute lung injury and be useful for monitoring disorders in the lung in such conditions.

Pulmonary fluid extraction and osmotic conductance, sigmaK, measured in vivo

The change in aortic blood density in an in vivo rabbit preparation was measured to assess fluid movement at the pulmonary capillaries caused by infusion of hypertonic solution (NaCl, urea, glucose, sucrose, or raffinose in isotonic saline) into the vena cava over 20 s. The hypertonic disturbance increased the plasma osmotic pressure by </=30 mosmol/l. The density change indicates that the fluid extraction from the lung tissue was completed within 10 s. It was followed by a fluid filtration into the lung tissue and then an extraction and filtration from peripheral organs. An exchange model with flow dispersion yields two equations to estimate the osmotic conductance (sigmaK; where sigma is the reflection coefficient of the test solute and K is the filtration coefficient including the total capillary surface area), and the tissue fluid volume from the area and first moment of the measured density change over the extraction phase. The values of sigmaK are 1.40 +/- 0.11, 1.00 +/- 0. 10, 1.71 +/- 0.10, 2.60 +/- 0.23, and 3.73 +/- 0.34 (SE) ml . h-1 . mosmol-1 . l . g-1 for NaCl, urea, glucose, sucrose, and raffinose, respectively. Consistent with the model prediction, the tissue fluid volume (0.28 +/- 0.04 ml/g wet lung tissue) was independent of the solute used. This value suggests that all fluid spaces in the alveolar septa participate in the process of fluid extraction due to an increase in plasma osmotic pressure.

Acute lung failure induced by tricyclic antidepressants

Overdosing of several drugs, such as tricyclic antidepressants, salicylates, and opiates, is known to induce effects like those seen in patients with adult respiratory distress syndrome. By exposing isolated perfused and ventilated rat lungs via the perfusate to six different tricyclic antidepressants (amitriptyline, nortriptyline, imipramine, desipramine, mianserine, and maprotiline), we investigated possible effects on ventilation (conductance and dynamic compliance), lung perfusion flow, and edema formation. The effects of these substances were pronounced and appeared within 15 min after exposure. Amitriptyline was studied in greater detail and caused a dose-related (0.01-1.0 mM) reduction in ventilation and perfusion flow. At the highest drug concentration pronounced lung edema was observed. Morphological studies were conducted with a transmission electron microscope. The microscopic preparations showed dose-related edema (amitriptyline 0.1 and 1.0 mM). The effects noted in our experimental studies are similar to those described in patients who have taken an overdose of tricyclic antidepressants. This emphasizes the possibility of a noncardiogenic edema component in these patients.

Relative quantification of pulmonary edema with noncontrast-enhanced MRI

Pulmonary edema is a debilitating effect of acute respiratory distress syndrome. The ability to measure it noninvasively with high sensitivity and in three dimensions could be useful in not only detection but also in assessment and guidance of treatment. To this end, a three-dimensional MRI pulse sequence to measure the formation of edema was developed and tested. Another sequence was tested to measure blood flow in distal pulmonary arteries. Pulmonary edema was induced in nine dogs via venous injections of oleic acid. Edema was verified by wet-to-dry weight ratio (5.30 +/- .38) and extra-vascular lung water at baseline (2.03 +/- 1.12 ml/g dry lung weight) versus postinjury (3.00 +/- 1.45 ml/g) (P < .005). The signal-to-noise ratio within the lungs increased from 5.47 +/- 1.00 at baseline to 7.51 +/- 1.96 (P < .005), and the time course of edema formation was resolved. Results from MR phase-contrast blood flow measurements were variable. The authors conclude that the three-dimensional scan provides a sensitive relative quantification of pulmonary edema formation without the use of contrast agents or ionizing radiation.

Congestive heart failure and pulmonary edema for the emergency physician

Congestive heart failure (CHF) and pulmonary edema are major health problems in the United States as well as across the rest of the developing world. The prevalence of CHF and pulmonary edema in the general population results in a significant number of these patients presenting to Emergency Departments (EDs). Mortality from these disorders is substantial, with a 5-year mortality rate for patients requiring hospitalization of approximately 50%. Understanding of the clinical syndromes of CHF and pulmonary edema requires review of the basic determinants of cardiovascular performance. Preload, afterload, contractility, and heart rate may all be modified by pharmacological or mechanical techniques. Diuretics, vasodilators, cardiac glycosides, and other inotropes all may play a role in the ED management of CHF. In rare instances, mechanical devices for support of the heart and circulation may be indicated.