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Transesophageal echocardiography: A new window into ventilation-perfusion mismatch?
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Background:
Previous trials involving patients with the acute respiratory distress syndrome (ARDS) have failed to show a beneficial effect of prone positioning during mechanical ventilatory support on outcomes. We evaluated the effect of early application of prone positioning on outcomes in patients with severe ARDS.
Methods:
In this multicenter, prospective, randomized, controlled trial, we randomly assigned 466 patients with severe ARDS to undergo prone-positioning sessions of at least 16 hours or to be left in the supine position. Severe ARDS was defined as a ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (FiO2) of less than 150 mm Hg, with an FiO2 of at least 0.6, a positive end-expiratory pressure of at least 5 cm of water, and a tidal volume close to 6 ml per kilogram of predicted body weight. The primary outcome was the proportion of patients who died from any cause within 28 days after inclusion.
Results:
A total of 237 patients were assigned to the prone group, and 229 patients were assigned to the supine group. The 28-day mortality was 16.0% in the prone group and 32.8% in the supine group (P<0.001). The hazard ratio for death with prone positioning was 0.39 (95% confidence interval [CI], 0.25 to 0.63). Unadjusted 90-day mortality was 23.6% in the prone group versus 41.0% in the supine group (P<0.001), with a hazard ratio of 0.44 (95% CI, 0.29 to 0.67). The incidence of complications did not differ significantly between the groups, except for the incidence of cardiac arrests, which was higher in the supine group.
Conclusions:
In patients with severe ARDS, early application of prolonged prone-positioning sessions significantly decreased 28-day and 90-day mortality. (Funded by the Programme Hospitalier de Recherche Clinique National 2006 and 2010 of the French Ministry of Health; PROSEVA ClinicalTrials.gov number, NCT00527813.).
A recent North-American-European Consensus Conference proposed new, uniform criteria for the definition of acute lung injury, in part to facilitate earlier identification of patients for clinical trials. However, these criteria have not been evaluated prospectively. We designed a prospective cohort study of 123 consecutive patients with acute lung injury prospectively identified on admission to the adult intensive care units of a tertiary care university hospital. The objectives were to determine if selection of patients using the new criteria for acute lung injury results in a significant change in the clinical characteristics, risk factors, or predictors of mortality when compared with prior studies of patients with adult respiratory distress syndrome (ARDS); and to determine if a quantitative index of the severity of acute lung injury has prognostic value in identifying nonsurvivors of acute lung injury. We used three methods: (1) prospective identification of patients with acute lung injury using a PaO2/FIO2 ratio < 300 and bilateral infiltrates on chest radiograph in the absence of left heart failure; (2) evaluation of the severity of lung injury using a four-point scoring system; and (3) stepwise logistic regression analysis to identify variables significantly associated with hospital mortality. Overall hospital mortality was 58%. Sepsis was the most common clinical disorder (50/123 or 41%) associated with the development of acute lung injury. Using the new definition for acute lung injury, 66 of the 123 patients were enrolled with a PaO2/FIO2 ratio between 150 and 299; 57 of the 123 patients had a PaO2/FIO2 < 150 at the time of entry into the study.(ABSTRACT TRUNCATED AT 250 WORDS)
Background:
Lung ultrasound can be used at bedside to assess initial lung morphology in hypoxemic patients. We hypothesized that blood flow in consolidated lung and therefore effects of inhaled nitric oxide (iNO) and intravenous almitrine could be directly assessed using Doppler transesophageal echocardiography (TEE).
Methods:
We conducted a prospective study including 13 ALI patients with consolidated left lower lobe (LLL). Regional arterial and venous flow signals within the consolidation were recorded with TEE using Doppler at baseline, after iNO (5 ppm), almitrine (4 μg/kg/min) and their combination. Pulmonary shunt (Qs/Qt) was measured using a Swan-Ganz catheter. Arterial and venous velocity time integral (VTI), peak velocity (Vmax) and mean velocity (Vmean) were measured. Patients were responders if PaO2 basal value increased by 20% after iNO or almitrine.
Results:
In 7 NO responders, iNO decreased regional arterial VTI (8.1±1.9 vs. 6.7±1.6, P<0.05). In 8 almitrine responders, almitrine decreased regional arterial and venous VTI (from 6.7±2.0 to 4.5±2.3 cm and from 12.3±5.4 to 7.5±3.8 cm, respectively, P<0.05). For all patients, combination of iNO and almitrine decreased regional arterial and venous VTI (from 7.3±0.3 to 4.1±0.3 cm and from 12.6±0.7 to 6.7±0.8 cm, respectively, P<0.05). Arterial and venous Vmean and Vmax significantly decreased. Variations of arterial VTI and venous Vmean were correlated to variations of Qs/Qt (r=.71, P<.001 and r=.62, P<.01, respectively).
Conclusion:
Doppler of consolidated LLL allows assessment of regional pulmonary circulation in ICU settings. It detects changes in flow profiles resulting from the administration of NO and/or almitrine. Further applicability remains to be determined.
Prone positioning has been used for over 30 years in the management of patients with acute respiratory distress syndrome (ARDS). This maneuver has consistently proven capable of improving oxygenation in patients with acute respiratory failure. Several mechanisms can explain this observation, including possible intervening net recruitment and more homogeneously distributed alveolar inflation. It is also progressively becoming clear that prone positioning may reduce the nonphysiological stress and strain associated with mechanical ventilation, thus decreasing the risk of ventilator-induced lung injury, which is known to adversely impact patient survival. The available randomized clinical trials, however, have failed to demonstrate that prone positioning improves the outcomes of patients with ARDS overall. In contrast, the individual patient meta-analysis of the four major clinical trials available clearly shows that with prone positioning, the absolute mortality of severely hypoxemic ARDS patients may be reduced by approximately 10%. On the other hand, all data suggest that long-term prone positioning may expose patients with less severe ARDS to unnecessary complications.
The principles of ventilation and perfusion distribution in the lung form the foundation of pulmonary physiology and remain cornerstones in caring for critically ill patients. Due to improved imaging technologies with greater spatial resolution, our understanding of the determinants of local ventilation and blood flow have evolved over the past five decades. This review provides a brief history of how the concepts governing regional ventilation and perfusion have developed and presents the most recent studies that are shaping new perspectives on the determinants of ventilation and perfusion. How these new principles apply to acute lung injury and gas exchange in the intensive care unit(ICU) are reviewed.
The acute effects of inhaled nitric oxide (NO) (40 ppm in air) on pulmonary (PVR) and systemic (SVR) vascular resistance were compared with those of an intravenous infusion of prostacyclin (24 micrograms/h) in 8 patients with severe pulmonary hypertension and 10 cardiac patients with normal values of PVR. 10 healthy volunteers were studied non-invasively. In the patients with pulmonary hypertension, PVR fell significantly after inhaled NO and after prostacyclin. PVR also fell significantly in the cardiac patients after inhaled NO. Although SVR fell substantially after prostacyclin in patients with pulmonary hypertension, inhaled NO had no effect on SVR in any patient or volunteer. Inhaled NO therefore seems to be both a selective and effective pulmonary vasodilator.
The effects of low dose almitrine bismesylate on pulmonary gas exchange, venous admixture, and pulmonary perfusion were examined in a canine one-lung hypoxic model. The left lung was ventilated with 10.4% oxygen, 89.3% nitrogen, and 0.3% halothane, while the right lung was ventilated with 99.7% oxygen and 0.3% halothane. Group 1 (n = 8) was given no other drug for 60 min. In group 2 (n = 10), consecutive almitrine doses of 0.5, 1, and 2 micrograms/kg.min were administered iv for 20 min/dose. Blood gas and central hemodynamic values remained unchanged in group 1. In group 2, significant increases in PaO2 and significant decreases in venous admixture, dependent on the dose administered, were observed. Mean PaO2 increased from 222 +/- 78 (SD) to 292 +/- 75 torr, and mean venous admixture decreased from 22 +/- 7% to 18 +/- 6% at 2 micrograms/kg.min. Both the decrease in mean left pulmonary blood flow and the increase in mean right pulmonary blood flow were slight, although the cardiac output was unchanged. These results indicate that iv infusion of 2 micrograms/kg.min of almitrine weakly enhances pulmonary vasoconstriction in a hypoxic area and improves pulmonary gas exchange in a moderately hypoxic condition.
To develop and validate a new Simplified Acute Physiology Score, the SAPS II, from a large sample of surgical and medical patients, and to provide a method to convert the score to a probability of hospital mortality.
The SAPS II and the probability of hospital mortality were developed and validated using data from consecutive admissions to 137 adult medical and/or surgical intensive care units in 12 countries.
The 13,152 patients were randomly divided into developmental (65%) and validation (35%) samples. Patients younger than 18 years, burn patients, coronary care patients, and cardiac surgery patients were excluded.
Vital status at hospital discharge.
The SAPS II includes only 17 variables: 12 physiology variables, age, type of admission (scheduled surgical, unscheduled surgical, or medical), and three underlying disease variables (acquired immunodeficiency syndrome, metastatic cancer, and hematologic malignancy). Goodness-of-fit tests indicated that the model performed well in the developmental sample and validated well in an independent sample of patients (P = .883 and P = .104 in the developmental and validation samples, respectively). The area under the receiver operating characteristic curve was 0.88 in the developmental sample and 0.86 in the validation sample.
The SAPS II, based on a large international sample of patients, provides an estimate of the risk of death without having to specify a primary diagnosis. This is a starting point for future evaluation of the efficiency of intensive care units.
The development of the polymerase chain reaction (PCR) has often been likened to the development of the Internet, and although this does risk overstating the impact of PCR outside the scientific community, the comparison works well on a number of levels. Both inventions have emerged in the last 20 years to the point where it is difficult to imagine life without them. Both have grown far beyond the confines of their original simple design and have created opportunities unimaginable before their invention. Both have also spawned a whole new vocabulary and professionals literate in that vocabulary. It is hard to believe that the technique that formed the cornerstone of the human genome project and is fundamental to many molecular biology laboratory protocols was discovered only 20 years ago. For many, the history and some of the enduring controversies are unknown yet, as with the discovery of the structure of DNA in the 1950s, the discovery of PCR is the subject of claim and counterclaim that has yet to be fully resolved. The key stages are reviewed here in brief for those for whom both the history and application of science holds interest.