Advances in fluid resuscitation of hemorrhagic shock.

The optimal fluid for resuscitation in hemorrhagic shock would combine the volume expansion and oxygen-carrying capacity of blood without the need for cross-matching or the risk of disease transmission. Although the ideal fluid has yet to be discovered, current options are discussed in this review, including crystalloids, colloids, blood and blood substitutes. The future role of blood substitutes is not yet defined, but the potential advantages in trauma or elective surgery may prove to be enormous.

Skin only or silo closure in the critically ill patient with an open abdomen.

BACKGROUND: The morbidity and mortality of various open abdominal techniques remains unclear. METHODS: A retrospective review was made of all trauma or general surgery patients who underwent an open abdominal closure from January 1997 to December 2000, at a large urban acute care hospital. Data are mean +/- SD. RESULTS: From 1997 to 2000, 181 patients (aged 39.8 +/- 16.5 years) had an open abdomen for abdominal infection, planned reexploration, abdominal compartment syndrome, inability to reapproximate fascia, or as part of a "damage control" procedure. Twenty-three patients went on to develop an abdominal compartment syndrome. Gastrointestinal fistulas occurred in 26 patients, and 9 patients had a dehiscence. The overall mortality was 44.7%. Of the survivors, 52% went on to fascial closure, requiring 1 to 7 additional abdominal operations. CONCLUSIONS: The morbidity of the open abdomen varies with the particular indication. Gastrointestinal fistulas are the most common acute complication and an abdominal wall hernia, the most common chronic complication.

Pulmonary surfactant is altered during mechanical ventilation of isolated rat lung.

OBJECTIVE: To test the hypothesis that the lung injury induced by certain mechanical ventilation strategies is associated with changes in the pulmonary surfactant system. DESIGN: Analysis of the pulmonary surfactant system from isolated rat lungs after one of four different ventilatory strategies. SETTING: A research laboratory at a university. SUBJECTS: A total of 45 Sprague-Dawley rats. INTERVENTIONS: Isolated lungs were randomized to either no ventilation (0-TIME) or to ventilation at 40 breaths/min in a humidified 37 degrees C chamber for either 30 mins or 120 mins with one of the following four strategies: a) control (CON, 7 mL/kg, 3 cm H2O positive end-expiratory pressure); b) medium volume, zero end-expiratory pressure (MVZP, 15 mL/kg, 0 cm H2O end-expiratory pressure); c) medium volume, high positive end-expiratory pressure (MVHP, 15 mL/kg, 9 cm H2O positive end-expiratory pressure); and d) high volume, zero end-expiratory pressure (HVZP, 40 mL/kg, 0 cm H2O end-expiratory pressure). MEASUREMENTS: Pressure-volume curves were determined before and after the ventilation period, after which the lungs were lavaged for surfactant analysis. MAIN RESULTS: Compared with 0-TIME, 30 mins of ventilation with the HVZP strategy or 120 mins of ventilation with CON and MVZP strategies caused a significant decrease in compliance. Groups showing a decreased compliance had significant increases in the amount of surfactant, surfactant large aggregates, and total lavage protein compared with 0-TIME. CONCLUSIONS: A short period of injurious mechanical ventilation can cause a decrease in lung compliance that is associated with a large influx of proteins into the alveolar space and with alterations of the pulmonary surfactant system. The changes of surfactant in these experiments are different from those seen in acute lung injury, indicating that they may represent an initial response to mechanical ventilation.

A new ventilator for monitoring lung mechanics in small animals.

Researchers investigating the genetic component of various disease states rely increasingly on murine models. We have developed a ventilator to simplify respiratory research in small animals down to murine size. The new ventilator provides constant-flow inflation and tidal volume delivery independent of respiratory parameter changes. The inclusion of end-inspiratory and end-expiratory pauses simplifies the measurement of airway resistance and compliance and allows the detection of dynamic hyperinflation (auto-positive end-expiratory pressure). After bench testing, we performed intravenous methacholine challenge on two strains of mice (A/J and C57bl/bj) known to differ in their responses by using the new ventilator. Dynamic hyperinflation and a decrease in compliance developed during methacholine challenge whenever respiratory rates of 60-120 breaths/min were employed. In contrast, if dynamic hyperinflation was prevented by lengthening expiratory time, (respiratory rate = 20 breaths/min), static compliance remained constant. More importantly, the coefficient of variation of the results decreased when lung volume shifts were prevented. In conclusion, airway challenge studies have greater precision when dynamic hyperinflation is prevented.

Partial liquid ventilation decreases serum tumor necrosis factor-alpha concentrations in a rat acid aspiration lung injury model.

OBJECTIVE: To examine the hypothesis that partial liquid ventilation (PLV) with perfluorocarbon would decrease serum tumor necrosis factor-alpha concentrations in a rat acid aspiration lung injury model. DESIGN: Prospective, controlled animal study. SETTINGS: Research laboratory in a university setting. SUBJECTS: Male Sprague-Dawley rats. INTERVENTIONS: Treatment with intratracheal perflubron or control mechanical ventilation beginning 30 mins after acid aspiration. MEASUREMENTS AND MAIN RESULTS: PLV with perfluorocarbon compared with control ventilation resulted in significantly greater mean arterial blood pressures at 3 and 4 hrs and greater arterial Po2 at all times. Serum tumor necrosis factor-alpha at 2, 3, and 4 hrs was significantly less than that observed in the control group (4-hr values: 80+/-64 pg/mL vs. 658+/-688 pg/mL; p<.05), although no significant difference in tracheal fluid tumor necrosis factor-alpha concentrations (1425+/-1347 pg/mL vs. 2219+/-1933 pg/mL) was found. CONCLUSION: We conclude that the effects of PLV with perfluorocarbon can extend beyond improvements in pulmonary physiology and that PLV may be beneficial in reducing systemic sequelae of acute lung injury and inflammation.

Ventilator-induced injury: from barotrauma to biotrauma.

Mechanical ventilation is an indispensable tool in the management of respiratory and ventilatory failure. However, ventilation per se may also initiate or exacerbate lung injury, contributing to patient morbidity and mortality. In this review, we examine the current mechanisms of ventilator-induced injury including those that primarily involve physical disruption of the lung, as well as those more recently described that involve cell- and inflammatory-mediator-induced injury. The latter have received attention of late because of the possible systemic sequelae such as multiple system organ failure, the primary cause of death of patients with acute respiratory distress syndrome. Although much remains to be elucidated about the mechanisms of ventilator-induced injury, it is hoped that novel approaches addressing both the physiologic as well as molecular effects of ventilation will lead to innovative therapeutic approaches that improve patient outcome.

Effect of hypotension preceding death on the function of lungs from donors with nonbeating hearts.

BACKGROUND: A shortage of suitable brain-dead donors continues to severely limit lung transplantation. Use of donors with nonbeating hearts has been suggested as a solution. Lungs are unique, in that aerobic metabolism can continue in the absence of blood circulation because oxygen is present in airways and alveoli. Animal studies have shown reasonable cadaveric graft function up to several hours after sudden death by drug administration. However, hemodynamic instability before death may worsen lung function through activation and pulmonary sequestration of neutrophils and release of inflammatory mediators. Because many potential cadaveric donors experience hypotension before death, this study was undertaken to assess the effect of hypotensive shock on cadaveric lung viability. METHODS: A rat isolated lung reperfusion model was used to assess pulmonary function over 3 hours of reperfusion or until gross pulmonary edema developed. Twenty-five rats were randomly allocated to the following study groups, which were based on status before lung harvest: (1) control: no interventions; (2) hypotensive: 1 hour of hypotension by exsanguination to a mean blood pressure of 30 to 40 mm Hg; (3) cadaver: death by cervical dislocation followed by 3 hours of in situ lung ischemia; (4) hypotensive + 3 hours cadaver: 1 hour of hemorrhagic shock, followed by death and 3 hours of in situ ischemia; (5) hypotensive + 2 hours cadaver: similar to group 4, except the in situ ischemia was abbreviated to 2 hours. RESULTS: No significant differences were found among group 1, 2, or 3 lungs with regard to wet to dry weight ratios, gas exchange, and pulmonary arterial or airway pressures. However, all group 4 lungs became grossly hemorrhagic and developed severe pulmonary edema within 10 minutes of reperfusion. Group 5 lungs fared only marginally better, with two of five lungs tolerating 3 hours of reperfusion. CONCLUSIONS: A period of hypotension before death severely impairs cadaveric lung viability.

Survival of acute myelogenous leukemia patients requiring intubation/ventilatory support.

A 5-y (1987-1992) retrospective chart review assessed the survival of patients with acute myelogenous leukemia (AML) who required intubation/ventilatory support in the intensive care unit (ICU). Thirty-two patients were identified, average age 52 +/- 19 (range 14-82) y. Seven patients had undergone bone marrow transplantation for AML 2 weeks to 4 months prior to admission. Of the remaining 25 patients, 16 received chemotherapy prior to admission, 6 started or continued chemotherapy in the ICU, and 3 patients did not receive any chemotherapy. The Apache II score, which quantifies illness severity, on admission to the ICU was 32.5 +/- 8.8. The average length of stay was 7.4 d. Twenty-nine patients had diffuse pulmonary infiltrates on admission, 2 patients had large pleural effusions, and 1 patient had severe bronchospasm with a clear chest X-ray. The average PaO2/FiO2, when first stabilized on mechanical ventilation, was 204 +/- 83. Of the 32 patients, 28 died in the ICU, and 3 died shortly after withdrawal of aggressive therapy and discharge to the ward. A single patient survived the hospital admission but died 4 months later at home. The observed vs. the predicted ICU mortality determined by Knaus' method, was significantly greater even for those with lower Apache II scores. Acute myelogenous leukemia patients had a greater mortality than 2 other intubated patient populations in our ICU admitted during the same time period, a group of 126 consecutive admissions and 53 patients with connective tissue disease. The latter 2 control groups only included patients requiring mechanical ventilation. We conclude that AML patients who require ventilatory support for acute respiratory failure rarely survive their ICU admission.