American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Jun 1994
Comparative StudyEffects of inspired carbon dioxide on ventilation-perfusion matching in normoxia, hypoxia, and hyperoxia.
We studied the effect of low concentrations (2 to 4%) of inspired CO2 on gas exchange and ventilation-perfusion (VA/Q) relationships in healthy normocapnic anesthetized dogs during constant mechanical ventilation by the multiple inert gas elimination technique (MIGET). One group was studied at normal tidal volumes (12 to 14 ml/kg) and rates (13 to 15/min) in normoxia, and the other in mild hyperoxia (FIO2 = 0.50) and hypoxia (FIO2 = 0.15). In normoxic dogs there were progressive increases in arterial PO2 and reductions in the alveolar-to-arterial PO2 and arterial-to-mixed expired PCO2 differences in response to increases in FICO2. ⋯ In the second group, the effects of 3% inspired CO2 were of comparable magnitude in both mild hypoxia and hyperoxia. In this group (taking hyperoxic values as baseline), there were improved gas exchange and less VA/Q heterogeneity with inspired hypoxia, both with and without inspired CO2. In contrast to the effects of added inspired CO2, improved VA/Q matching with hypoxia was characterized by reductions in both log SDV and log SDQ.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Jun 1994
Comparative StudyExtracorporeal carbon dioxide removal technique improves oxygenation without causing overinflation.
Extracorporeal CO2 removal combined with low frequency positive pressure ventilation (ECCO2R-LFPPV) improves gas exchange and decreases peak pressures, respiratory rates, and tidal volumes in animals and in humans. Recent evidence suggests that pulmonary barotrauma results from lung overinflation rather than from high pressures. This study was to test the hypothesis whether ECCO2R-LFPPV could improve gas exchange without causing lung overinflation, despite the use of higher levels of PEEP, when compared with conventional mechanical ventilation. ⋯ By contrast, no evidence of persistent lung overinflation could be detected by either static P-V curves or dynamic measurements in nine of 11 patients who were treated by ECCO2R-LFPPV. The two remaining patients had severe airway obstruction because of bleeding, and they remained ventilated with persistent risk of barotrauma. We conclude that ECCO2R-LFPPV improves gas exchange without causing lung overinflation in a majority of patients with ARDS.
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Am. J. Respir. Crit. Care Med. · Jun 1994
Randomized Controlled Trial Comparative Study Clinical TrialLong-term effects of two different ventilatory modes on oxygenation in acute lung injury. Comparison of airway pressure release ventilation and volume-controlled inverse ratio ventilation.
A total of 18 patients with acute lung injury (ALI) were sequentially ventilated with two different modes of mechanical ventilation, each applied for a period of 24 h: (1) volume-controlled inverse ratio ventilation (VC-IRV), (2) airway pressure release ventilation (APRV). The individual sequence of both ventilatory modes was randomized. Ventilatory minute volume was adjusted for a PaCO2 of 35 to 45 mm Hg at the beginning of the study during the first ventilatory mode and then kept constant within preset limits. ⋯ During APRV AaDO2/FIO2 and venous admixture improved significantly with time after more than 8 h (AaDO2/FIO2: 487 versus 414 mm Hg; p < 0.01; venous admixture: 20.6 versus 13.9%; p < 0.01; medians of onset versus end). The improvement was significantly different between both ventilatory modes (p < 0.01). We conclude that this indicates a progressive alveolar recruitment over time during ventilation with APRV.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Jun 1994
Effects of mechanical ventilation on diaphragmatic contractile properties in rats.
We measured in rats the effects of 48 h of mechanical ventilation on the weight, contractile properties, and enzymatic profile of the diaphragm, the soleus and the extensor digitorium longus (EDL) muscles. Eighteen animals were randomly divided into a mechanically ventilated (MV, n = 9) group or a control (C, n = 9) group. During the 48 h of mechanical ventilation, animals in the MV group were anesthetized with sodium thiopental and enterally fed with a gastric catheter. ⋯ The forces generated by the soleus and EDL were not significantly reduced in the MV group compared with those in the C group. Diaphragm, soleus, and EDL citrate synthase and lactate dehydrogenase activities were not significantly different in the two groups. We conclude that mechanical ventilation for 48 h in rats produces a selective force reduction in the diaphragm.
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Am. J. Respir. Crit. Care Med. · Jun 1994
Randomized Controlled Trial Multicenter Study Comparative Study Clinical TrialNebulized versus intravenous albuterol in hypercapnic acute asthma. A multicenter, double-blind, randomized study.
In a multicenter, randomized, double-blind study, we compared the effects of nebulized (5 mg x 2) and intravenous (0.5 mg) albuterol (salbutamol) over 1 h in 47 patients admitted to hospital with severe acute asthma defined as a peak expiratory flow (PEF) below 150 L/min and hypercapnia (Pa(CO2) > or = 40 mm Hg). Additional treatment included nasal oxygen and hydrocortisone succinate. The efficacy was assessed after 1 h. ⋯ The mean increase in PEF was greater in the NEB group than in the i.v. group (+107 +/- 94 L/min versus +42 +/- 66 L/min, p = 0.01) as well as the decrease in Pa(CO2) values (-10 +/- 5 mm Hg versus -2 +/- 12 mm Hg, p < 0.01). Beta agonist-induced hypokalemia was more pronounced in the i.v. group than in the NEB group. We conclude that, in hypercapnic acute asthma, the nebulized route has a greater efficacy and fewer side effects than the intravenous route.