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Static pressure-volume curves and effect of positive end-expiratory pressure on gas exchange in adult respiratory distress syndrome.

Fifteen patients with adult respiratory distress syndrome (ARDS) were studied: 11 in the early stage of ARDS (group 1); 4 in the late stage (group 2). The inspiratory and expiratory static pressure-volume (P-V) curves of the respiratory system were compared to the pulmonary shunt (Qsp/Qt) when PEEP was increased; cardiac output was kept constant. In group 1 patients, we found that a concavity on the P-V curves was associated with an abrupt decrease in Qsp/Qt when PEEP was increased; the concavity on the expiratory curve was correlated with the change in Qsp/Qt but not the concavity on the inspiratory curve. In group 2 patients, the P-V curves were found rectilinear and Qsp/Qt was not abruptly decreased when PEEP was increased. Expiratory P-V curve can be used to determine: first, whether a patient should be ventilated with PEEP; second, the PEEP level which can be set on the respirator. In group 1 patients, when PEEP was set to a value corresponding to the inflexion point, i.e., the point of departure from the exponential shape (mean value 14.6 +/- 2.8 cm H2O), Qsp/Qt compared to zero PEEP was abruptly decreased to 87.6 +/- 6%; further increase in PEEP had little advantage.

Adolescent↗

Extracorporeal carbon dioxide removal and low-frequency positive-pressure ventilation. Improvement in arterial oxygenation with reduction of risk of pulmonary barotrauma in patients with adult respiratory distress syndrome.

Mortality of the adult respiratory distress syndrome (ARDS) remains high and could be increased by pulmonary barotrauma induced by positive-pressure mechanical ventilation. Extracorporeal CO2 removal combined with low-frequency positive-pressure ventilation (ECCO2R-LFPPV) has been proposed to reduce lung injury while supporting respiratory failure. Use of this technique in 23 patients resulted in the following: a dramatic and highly significant increase of PaO2 obtained rapidly with ECCO2R-LFPPV, allowing subsequent reduction in inspired oxygen fraction; a reduction of the risk of barotrauma evidenced by a significant decrease in pressures and insufflated volumes; a survival rate of 50 percent. Bleeding was the only complication related to the technique and was the cause of death in four patients. This method allowed improvement in gas exchange along with reduction of the risk of barotrauma caused by the ventilator.

Adolescent↗

Clinical trials of an intravenous oxygenator in patients with adult respiratory distress syndrome.

In patients with severe adult respiratory distress syndrome, mechanical ventilation may not be able to ensure gas exchange sufficient to sustain life. We report the use of an intravenous oxygenator (IVOX) in five patients who were suffering from severe adult respiratory distress syndrome as a result of aspiration, fat embolism, or pneumonia. IVOX was used in an attempt to provide supplemental transfer of CO2 and O2 and thereby reduce O2 toxicity and barotrauma. All patients were tracheally intubated, sedated, and chemically paralyzed and had a PaO2 < 60 mmHg when the lungs were ventilated with an FIO2 = 1.0 and a positive end expiratory pressure of > or = 5 cmH2O. The right common femoral vein was located surgically, and the patient was systemically anticoagulated with heparin. A hollow introducer tube was inserted into the right common femoral vein, and the furled IVOX was passed into the inferior vena cava and advanced until the tip was in the lower portion of the superior vena cava. IVOX use ranged from 2 h to 4 days. In this group of patients, IVOX gas exchange ranged from 21 to 87 ml x min-1 of CO2 and from 28 to 85 ml x min-1 of O2. One of the five patients survived and was discharged from the hospital. The IVOX transferred up to 28% of metabolic gas-exchange requirements. One patient with a small vena cava showed signs of caval obstruction. Three other patients demonstrated signs of a septic syndrome after the device was inserted.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

The adult respiratory distress syndrome: a review.

The adult respiratory distress syndrome, characterized by hypoxemia, reduced pulmonary expansion, and noncardiogenic pulmonary edema, is a clinical entity with a high mortality rate that has been recognized only relatively recently. We present the newest aspects of the subject.

Humans↗

[A clinical analysis of 18 cases with adult respiratory distress syndrome].

18 cases with adult respiratory distress syndrome (ARDS) admitted to our hospital since 1985 were reported. Among them, 2 cases were mild, 10 moderate and 6 severe. All of them received a combination of treatment, including correction of primary disease, O2 therapy, medications such as corticosteroid diuretics and anti-inflammatory agents, restriction of water intake and keep of negative fluid balance. Mechanical ventilation, especially early application of PEEP, was applied in 12 cases. In general, the level of pressure was kept between 0.08-0.1 KPa. End inspiration pause (EIP) was also routinely taken. Usually, the pausing period accounted for 10% of the respiratory cycle. 2 died among the 12 cases with mechanical ventilation, whereas all of the 6 cases receiving simple artificial ventilation died. The mortality rate was 44%.

Adult↗

Adult respiratory distress syndrome.

Treatment of the adult respiratory distress syndrome requires an understanding of the current concepts of the pathogenesis of this syndrome. The clinical features and pathophysiology are briefly discussed. Differential diagnosis requires the exclusion of pulmonary infection and left heart failure. Therapy is aimed at correction of the associated initiating disease process and the maintenance of tissue oxygenation. The latter requires increased inspired oxygen concentration, maintenance of an adequate cardiac output, and maintenance of a normal hematocrit level and body temperature. The therapeutic role of intravenous albumin, diuretics, and steroids in this syndrome is still controversial. Currently accepted modalities for improving oxygenation, when oxygen by face mask proves inadequate, include intubation and ventilation with postiive end-expiratory pressure. Other promising technics for improving oxygenation which do not require intubation are continuous positive airway pressure applied by face mask, continuous negative chest wall pressure, and alterations in posture. The long-term prognosis in survivors appears to be good, with only mild residual pulmonary functional abnormalities.

Adult↗

Contribution to the assessment of steroid therapy in the prevention of respiratory distress syndrome in the neonate.

The respiratory distress syndrome (RDS) is a physiological manifestation of neonatal pulmonary immaturity and it is still the major cause of neonatal morbidity and mortality. In order to promote early fetal lung maturity when a preterm delivery is anticipated, a number of pharmacological agents have been investigated. Corticosteroids, in particular, have been extensively used and the results of several trials are reported in literature. A cohort of 246 consecutive singleton preterm infants, liveborn at the Obstetric Clinic of Ferrara University during a 5-year period, was studied to assess whether antenatal steroid therapy reduces the incidence of RDS. Respiratory distress developed in 18.6% of 102 babies who received treatment and in 15.3% of 144 controls, without difference at the statistical analysis. According to previous studies, a lower incidence of RDS was only observed in the treated females compared to non-treated controls (35% vs 46%) at the gestational age of 28-33 weeks. Since the efficacy of steroids seems to be restricted to a very small and specific group of babies, who, moreover are relatively mature by modern intensive care standards, the Authors suggest that the prevention of RDS and its related complications should rely much more on appropriate surveillance and management of the mother and infant than on specific pharmacological interventions.

Adrenal Cortex Hormones↗

[Acute respiratory distress syndrome in children].

The acute respiratory distress syndrome (ARDS) encountered in a child may be either due to a primary lung infection or may be secondary to a systemic inflammatory response of varying origin. Therapy is based on: 1) the mechanical ventilation strategy aimed at maintaining the functional residual capacity by alveolar recruitment using positive end expiratory pressure and to limit secondary pulmonary lesions by using small tidal volumes, 2) prone positioning as soon as sufficient stability is achieved; 3) optimizing tissue oxygen delivery by cardiac support; 4) correction of any other organ dysfunction. If this conventional approach is not sufficient experimental therapies may be tempted given the vital risk. For instance inhaled nitric oxide and high frequency oscillation ventilation may be a valuable support. Newer techniques, such as partial liquid ventilation, are being developed and could become useful therapeutic options. After the acute phase a close medical follow-up is mandatory. Because of the possibility of a chronic respiratory insufficiency with negative consequences on the right ventricular function, these patients may need long term oxygen therapy and diuretics. Cardiac echography helps orientation in maintaining or discontinuing this long term therapy by estimating the arterial pulmonary pressure.

Acute Disease↗

Tromethamine buffer modifies the depressant effect of permissive hypercapnia on myocardial contractility in patients with acute respiratory distress syndrome.

In patients with acute respiratory distress syndrome (ARDS), permissive hypercapnia is a strategy to decrease airway pressures to prevent ventilator-induced lung damage by lowering tidal volumes and tolerating higher arterial carbon dioxide tension. However, in experimental studies hypercapnia impairs myocardial contractility and hemodynamic function. We investigated the effect of short-term permissive hypercapnia on myocardial contractility and hemodynamics in patients with ARDS. We hypothesized that the administration of tromethamine (THAM), a buffer which does not increase carbon dioxide production, would modify these changes. In 12 patients with ARDS, permissive hypercapnia was implemented for 2 h with a target Pa(CO(2))of 80 mm Hg. Patients were randomized to have respiratory acidosis corrected by THAM (pH-corrected group), or not corrected (pH-uncorrected group). Hemodynamic responses were measured, and transesophageal echocardiography (TEE) was used to determine myocardial contractility. Permissive hypercapnia resulted in significant decreases in systemic vascular resistance (SVR) and increases in cardiac output (Q). Myocardial contractility decreased in both groups but significantly less in the pH-corrected group (approximately 10%) than in the pH-uncorrected group (approximately 18%, p < 0.05). Mean arterial pressure decreased and mean pulmonary arterial pressure increased significantly only in the pH-uncorrected group. All values returned to baseline conditions 1 h after permissive hypercapnia was terminated. Our study demonstrates a reversible depression of myocardial contractility and hemodynamic alterations during rapid permissive hypercapnia which were attenuated by buffering with THAM. This may have applicability to the clinical strategy of permissive hypercapnia and allow the benefit of decreased airway pressures to be realized while minimizing the adverse hemodynamic effects of hypercapnic acidosis.

Acid-Base Equilibrium↗

Extracorporeal CO2 removal in a lung lavage induced respiratory distress syndrome.

Ten pigs with experimental respiratory distress syndrome were treated by extracorporeal CO2 removal (ECCO2-R) combined with low frequency positive pressure ventilation (LPPV). After lung damage had been induced by repeated lung lavages a PEEP trial was conducted in order to find the appropriate PEEP for the damaged lungs. This PEEP was then applied during the ECCO2-R/LPPV period. Blood gas values improved significantly on extracorporeal bypass within a short time (pre-bypass paO2: 54.2 +/- 3.7 vs 168.5 +/- 31.6 mmHg after 15 min on bypass, p less than 0.001) and were kept constant during the next 4 hours. Minute ventilation (MV) was reduced from 4.01 +/- 0.31 to 0.74 +/- 0.07 l/min (p less than 0.0001), FiO2 of the ventilator from 1.0 to 0.46 +/- 0.08 (p less than 0.0001) whereas FiO2 of the membrane lung (ML) was not changed significantly (FIO2ML 0.59 +/- 0.07 vs 0.53 +/- 0.06). During controlled mechanical ventilation (CMV), comparable adequate gas exchange was only achieved at a significantly higher mean airway pressure (Paw 14.1 +/- 0.08 vs 21.2 +/- 0.47 cmH20, p less than 0.0001). Hemodynamic variables did not change significantly during bypass time. ECCO2-R/LPPV driven by a simple renal perfusion system allows adequate gas exchange in experimental respiratory failure.

Animals↗

Effects of prone position on the oxygenation of patients with acute respiratory distress syndrome.

CONTEXT AND OBJECTIVE: Acute respiratory distress syndrome (ARDS) is characterized by arterial hypoxemia, and prone position (PP) is one possible management strategy. The objective here was to evaluate the effects of PP on oxygenation. DESIGN AND SETTING: Non-randomized, open, prospective, controlled clinical trial, in a surgical intensive care unit at a tertiary university hospital. METHODS: Forty-one ARDS patients underwent PP for three-hour periods. Arterial partial oxygen pressure (PaO2) was measured immediately before changing to PP, after 30, 60, 120 and 180 minutes in PP and 60 minutes after returning to dorsal recumbent position (DP). The paired-t and Dunnett tests were used. RESULTS: A notable clinical improvement in oxygenation (> 15%) was detected in 78.0% of patients. This persisted for 60 minutes after returning to DP in 56% and lasted for 12 and 48 hours in 53.6% and 46.3%, respectively. Maximum improvement was seen after 30 minutes in 12.5% of responding patients and after 180 minutes in 40.6%. No statistically significant associations between PP response and age, gender, weight, PEEP level, tidal volume, respiratory rate, PaO2/FiO2 or duration of mechanical ventilation were detected. One accidental extubation and four cases of deterioration through oxygenation were detected. The 48-hour mortality rate was 17%. CONCLUSIONS: For a significant number of ARDS patients, PP may rapidly enhance arterial oxygenation and its inclusion for management of severe ARDS is justified. However, it is not a cost-free maneuver and caution is needed in deciding on using PP.

Adolescent↗

Mechanical effects of PEEP in patients with adult respiratory distress syndrome.

In 10 patients with adult respiratory distress syndrome, we studied the effects on respiratory system mechanics of two levels of positive end-expiratory pressure (PEEP), best PEEP (BP) and half of this value (HBP), using a respiratory inductive plethysmograph (RIP) combined with a super syringe. We found the following. 1) Inflation compliance of pressure-volume (PV) curves did not change significantly. 2) End-expiratory volume increased with HBP and further with BP (278 +/- 186 and 464 +/- 313 ml, respectively, P less than 0.01). This increase was positively correlated with inflation compliance for HBP and BP (r = 0.794, P less than 0.01 and r = 0.876, P less than 0.01, respectively). 3) No dynamic hyper-inflation was detected on mechanical ventilation at zero end-expiratory pressure (ZEEP), and the time constant of the respiratory system was in the normal range (0.79 +/- 0.21 s). 4) Hysteresis of PVrip curves, which were corrected for gas exchange, decreased significantly with PEEP (P less than 0.05). We conclude that PEEP does not change inflation PV curve but induces an increase in intrathoracic volume whose magnitude is related to compliance and PEEP level. The reduction of hysteresis with PEEP suggests less gas trapping and thus a functional improvement.

Adolescent↗

Lung recruitment in patients with the acute respiratory distress syndrome.

BACKGROUND: In the acute respiratory distress syndrome (ARDS), positive end-expiratory pressure (PEEP) may decrease ventilator-induced lung injury by keeping lung regions open that otherwise would be collapsed. Since the effects of PEEP probably depend on the recruitability of lung tissue, we conducted a study to examine the relationship between the percentage of potentially recruitable lung, as indicated by computed tomography (CT), and the clinical and physiological effects of PEEP. METHODS: Sixty-eight patients with acute lung injury or ARDS underwent whole-lung CT during breath-holding sessions at airway pressures of 5, 15, and 45 cm of water. The percentage of potentially recruitable lung was defined as the proportion of lung tissue in which aeration was restored at airway pressures between 5 and 45 cm of water. RESULTS: The percentage of potentially recruitable lung varied widely in the population, accounting for a mean (+/-SD) of 13+/-11 percent of the lung weight, and was highly correlated with the percentage of lung tissue in which aeration was maintained after the application of PEEP (r2=0.72, P<0.001). On average, 24 percent of the lung could not be recruited. Patients with a higher percentage of potentially recruitable lung (greater than the median value of 9 percent) had greater total lung weights (P<0.001), poorer oxygenation (defined as a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen) (P<0.001) and respiratory-system compliance (P=0.002), higher levels of dead space (P=0.002), and higher rates of death (P=0.02) than patients with a lower percentage of potentially recruitable lung. The combined physiological variables predicted, with a sensitivity of 71 percent and a specificity of 59 percent, whether a patient's proportion of potentially recruitable lung was higher or lower than the median. CONCLUSIONS: In ARDS, the percentage of potentially recruitable lung is extremely variable and is strongly associated with the response to PEEP.

Female↗

Detection of left ventricular failure in patients with adult respiratory distress syndrome.

Fourteen patients with adult respiratory distress syndrome were admitted to the medical intensive care unit and received bedside heart catheterization with the use of a balloon-tipped, flow directed catheter. Four of the 14 (29 percent) were found to have left ventricular failure (LVF), defined as a pulmonary artery wedge pressure greater than 12 mm Hg. Analysis of the standard clinical and laboratory data demonstrated no criteria which could differentiate those patients with LVF from those without. Three of the four patients indentified as having LVF responded to therapy directed toward LVF with substantial clinical improvement.

Adolescent↗

A Markov computer simulation model of the economics of neuromuscular blockade in patients with acute respiratory distress syndrome.

BACKGROUND: Management of acute respiratory distress syndrome (ARDS) in the intensive care unit (ICU) is clinically challenging and costly. Neuromuscular blocking agents may facilitate mechanical ventilation and improve oxygenation, but may result in prolonged recovery of neuromuscular function and acute quadriplegic myopathy syndrome (AQMS). The goal of this study was to address a hypothetical question via computer modeling: Would a reduction in intubation time of 6 hours and/or a reduction in the incidence of AQMS from 25% to 21%, provide enough benefit to justify a drug with an additional expenditure of $267 (the difference in acquisition cost between a generic and brand name neuromuscular blocker)? METHODS: The base case was a 55 year-old man in the ICU with ARDS who receives neuromuscular blockade for 3.5 days. A Markov model was designed with hypothetical patients in 1 of 6 mutually exclusive health states: ICU-intubated, ICU-extubated, hospital ward, long-term care, home, or death, over a period of 6 months. The net monetary benefit was computed. RESULTS: Our computer simulation modeling predicted the mean cost for ARDS patients receiving standard care for 6 months to be $62,238 (5%-95% percentiles $42,259-$83,766), with an overall 6-month mortality of 39%. Assuming a ceiling ratio of $35,000, even if a drug (that cost $267 more) hypothetically reduced AQMS from 25% to 21% and decreased intubation time by 6 hours, the net monetary benefit would only equal $137. CONCLUSION: ARDS patients receiving a neuromuscular blocker have a high mortality, and unpredictable outcome, which results in large variability in costs per case. If a patient dies, there is no benefit to any drug that reduces ventilation time or AQMS incidence. A prospective, randomized pharmacoeconomic study of neuromuscular blockers in the ICU to asses AQMS or intubation times is impractical because of the highly variable clinical course of patients with ARDS.

Computer Simulation↗

Veno-venous extracorporeal membrane oxygenation with a heparin-coated system in adult respiratory distress syndrome.

Three patients with adult respiratory distress syndrome were treated with veno-venous extracorporeal membrane oxygenation, ECMO, using a heparin-coated system for 8, 12 and 34 days, respectively. Despite extracorporeal blood flow of 4-5 l/min, the patients were ventilator-dependent in the initial period of ECMO. Two of the three patients showed bleeding diatheses despite only slightly elevated activated partial thromboplastin time (APTT). Blood platelet count followed a variable course and serum fibrinogen was normal. Acute pulmonary hypertensive crises, fatal systemic infection, recurrent pneumothorax and plasma leakage from the oxygenators were other main complications during ECMO. Two of the three patients survived, and follow-up showed that severely damaged lungs, if supported in the acute phase, can recover sufficiently to permit normal living.

Adult↗

Respiratory distress syndrome (hyaline membrane disease).

The respiratory distress syndrome (RDS) continues to be the most common cause of death in premature infants. However, over the last 20 years there has been a series of stepwise advances resulting from laboratory studies and clinical observations which have resulted not only in a better understanding of this disease but in successful therapeutic applications as well. The purpose of this review will be to discuss RDS with respect to its (1) pathophysiology, (2) diagnosis, clinical as well as radiological, (3) management including its influence on the chest film, and (4) complications of treatment, with emphasis on radiological interpretation. The complications will include interstitial emphysema, pneumomediastinum, pneumothorax, pneumoperitoneum, air embolus, persistent patent ductus arteriosus, and bronchopulmonary dysplasia as well as the problems associated with extubation.

Ductus Arteriosus, Patent↗