American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Oct 1997
Comparative StudyEffect of prone and supine positions on functional residual capacity, oxygenation, and respiratory mechanics in ventilated infants and children.
Although numerous reports have described the improvement in PAO2 in patients in the prone position, the underlying mechanism has yet to be determined. Some authors have suggested this phenomenon may be related to an increase in functional residual capacity (FRC); however, no previous studies have described positional changes in FRC in children with severe lung disease or in those under neuromuscular blockade. We measured arterial blood gases, FRC, Rrs, and Crs in supine and prone positions in 30 patients under neuromuscular blockade with lung disorders including moderately severe restrictive (n = 10) and obstructive (n = 10) disease and control subjects without significant lung disease (n = 10). ⋯ No significant changes in Crs were seen in the prone position. We conclude that prone positioning has no effect on FRC and in this series of 30 patients significantly improved oxygenation only in patients with obstructive airway disease. A significant decrease in Rrs in patients with obstructive lung disease was also observed.
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Am. J. Respir. Crit. Care Med. · Oct 1997
Impairment of lung and chest wall mechanics in patients with acute respiratory distress syndrome: role of abdominal distension.
Recent data have suggested that the elastic properties of the chest wall (CW) may be compromised in patients with ARDS because of abdominal distension (4). We partitioned CW and lung (L) mechanics, assessed the role of abdominal distension, and verified whether the underlying disease responsible for ARDS affects the impairment of respiratory mechanics. Volume-pressure (V-P) curves (interrupter technique) were assessed in nine patients with surgical ARDS and nine patients with medical ARDS. ⋯ In conclusion we showed that impairment of the elastic properties of the respiratory system may vary with the underlying disease responsible for ARDS. The flattening of the V-P curve at high pressures observed in some patients with ARDS may be due to an increase in chest wall elastance related to abdominal distension. These observations have implications for the assessment and ventilatory management of patients with ARDS.
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Am. J. Respir. Crit. Care Med. · Oct 1997
Comparative StudyEnd-inspiratory airway occlusion: a method to assess the pressure developed by inspiratory muscles in patients with acute lung injury undergoing pressure support.
We evaluated the end-inspiratory occlusion maneuver as a means to estimate the inspiratory effort during pressure support ventilation (PS). In nine nonobstructed acute lung injury (ALI) patients, we applied four levels of PS (0, 5, 10, 15 cm H2O) to modify the inspiratory effort. End inspiratory occlusions (2 to 3 s) were performed at the end of each experimental period by pushing the inspiratory hold button of the ventilator (Servo 900 C; Siemens, Berlin, Germany). ⋯ A PMI threshold of 6 cm H2O detected PTP/min < 125 cm H2O s/min with a sensitivity of 0.89 and a specificity of 0.89. We conclude that PMI is a good estimate of the pressure developed by the inspiratory muscles in ALI patients and may be used to titrate PS level. The major advantage of PMI is that it can be obtained from the ventilator display without any additional equipment.
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Am. J. Respir. Crit. Care Med. · Oct 1997
Ventilation-perfusion mismatch in patients with pleural effusion: effects of thoracentesis.
Pleural effusion (PE) often causes abnormal pulmonary gas exchange. Thoracentesis is commonly used to relieve dyspnea in patients with PE, but its effect upon arterial oxygenation is varied and poorly understood. This investigation sought to: (1) characterize the distribution of ventilation-perfusion (VA/Q) ratios in patients with PE and (2) assess the effects of PE drainage by thoracentesis upon pulmonary gas exchange. ⋯ While thoracentesis drained 693+/-424 ml of fluid and caused a significant fall in mean pleural pressure (by -10.7 +/- 7.1 mm Hg; p < 0.01), PaO2, AaPO2, and shunt remained unchanged; only the amount of blood flow perfusing low VA/Q ratios increased slightly (2.4+/-2.6%; p < 0.05). This study shows that: (1) intrapulmonary shunt is the main mechanism underlying arterial hypoxemia in patients with PE and (2) effective thoracentesis has minor short-term effects upon pulmonary gas exchange. These findings are in accord with delayed (> 30 min) pulmonary volume re-expansion after thoracentesis with or without the coexistence of mild ex vacuo pulmonary edema.
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Am. J. Respir. Crit. Care Med. · Oct 1997
Comparative StudyDiaspirin crosslinked hemoglobin improves systemic oxygen uptake in oxygen supply-dependent septic rats.
Diaspirin crosslinked hemoglobin (DCLHb) is a cell-free hemoglobin derived from human erythrocytes. DCLHb has been shown to improve blood flow to vital organs in healthy and septic animals. In this study, we determined the efficacy of DCLHb by comparing its effect on systemic O2 uptake to freshly stored and aged red blood cells (RBCs) in septic rats. ⋯ Systemic O2 extraction increased with DCLHb as compared to baseline (p < 0.05) and to the other groups (p < 0.0001). Improved tissue oxygenation was associated with an increase in blood pressure and a fall in arterial lactate in all groups. We conclude that transfusion of DCLHb or "fresh" RBCs was efficacious at increasing systemic O2 uptake in O2 supply-dependent, septic rats.