American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Feb 1997
Ventilation strategies affect surfactant aggregate conversion in acute lung injury.
This study evaluated the effects of varying tidal volumes (VT) and positive end-expiratory pressure (PEEP) levels on surfactant aggregate conversion and lung function in an animal model of lung injury induced by N-nitroso-N-methylurethane. Lung-injured adult rabbits were initially ventilated using a VT of 10 ml/kg (VT10), a respiratory rate of 30 breaths/min (RR30), and a PEEP of 3.5 cm H2O. A trace dose of radiolabeled rabbit large surfactant aggregates was instilled after the onset of ventilation, and animals were then ventilated at different ventilator settings for 1 h. ⋯ Increasing the PEEP level to 8.0 cm H2O improved oxygenation, but it was sustained only with a low VT (VT5, RR60), and deteriorated with a high VT (VT10, RR30). Varying VT but not PEEP levels resulted in significant changes in surfactant aggregate conversion. We conclude that increased surfactant aggregate conversion resulting from suboptimal ventilation of injured lungs may play an important role in the pathophysiology of ventilation-induced lung dysfunction in acute lung injury.
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Am. J. Respir. Crit. Care Med. · Feb 1997
Prone position in mechanically ventilated patients with severe acute respiratory failure.
The purpose of this study was to characterize changes in oxygenation, expressed as PaO2/F(I)O2, when patients with severe acute respiratory failure (PaO2/F(I)O2 < 150), unrelated to left ventricular failure to atelectasis, were turned to and from a supine to prone position at 1- and 4-h intervals. Ventilator settings were unchanged. Thirty-two consecutive patients were studied 1 h before, 1 and 4 h during and 1 h after placing in a prone position with PaO2/F(I)O2 of 103 +/- 28, 158 +/- 62, 159 +/- 59, and 128 +/- 52, respectively (ANOVA, p < 0.001). ⋯ In 13 of the 23 (57%) improvement persisted: 105 +/- 27, 187 +/- 58, 189 +/- 49, and 157 +/- 49, respectively (ANOVA, p < 0.001). Repeated improvements after turning to a prone position were frequently observed. Side effects in the 32 patients after a total of 294 periods in a prone position included minor skin injury and edema, two instances of apical atelectasis, one catheter removal, one catheter compression, one extubation, and one transient supraventricular tachycardia.
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Am. J. Respir. Crit. Care Med. · Feb 1997
Intensity of training and physiologic adaptation in patients with chronic obstructive pulmonary disease.
The applicability of high-intensity training and the possibility of inducing physiologic adaptation to training are still uncertain in patients with severe chronic obstructive pulmonary disease (COPD). The purposes of this study were to evaluate the proportion of patients with moderate to severe COPD in whom high-intensity exercise training (30-min exercise session at 80% of baseline maximal power output [Wmax]) is feasible, and the response to training in these patients. We also sought to evaluate the possible influence of disease severity on the training intensity achieved and on the development of physiologic adaptation following endurance training. ⋯ Percent changes in VO2max, Wmax, and VE, were significant and of similar magnitude for both groups, whereas the decrease in arterial lactic acid for a given work rate reached statistical significance only in those patients with an FEV1 > or = 40% predicted. We conclude that although most patients were unable to achieve high-intensity training as defined in this study, significant improvement in their exercise capacity was obtained and physiologic adaptation to endurance training occurred. The training intensity expressed as a percent of the individual maximum exercise capacity, and the relative effectiveness of training, were not influenced by the severity of airflow obstruction.
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Am. J. Respir. Crit. Care Med. · Jan 1997
Increasing incidence of withholding and withdrawal of life support from the critically ill.
To determine whether limits to life-sustaining care are becoming more common, we attempted to quantify the incidence of recommendations to withhold or withdraw life support from critically ill patients, to describe how patients respond to these recommendations, and to examine how conflicts over these recommendations are resolved. In 1992 and 1993 we prospectively enrolled 179 consecutive patients from two intensive care units (ICUs) for whom a recommendation was made to withhold or withdraw life support. Where possible, we compared results with data collected in the same units over a similar time period in 1987 and 1988. ⋯ Ninety percent of patients agreed within less than 5 d, and only eight patients (4%) refused physicians' recommendations to limit life support. In cases of conflict, physicians in 1992 and 1993 deferred to patients with one exception: physicians were willing to refuse surrogate requests for resuscitation of patients they considered hopelessly ill. We conclude that 90% of patients who die in these ICUs now do so following a decision to limit therapy, that this represents a major change in practice in these institutions over a period of 5 yr, that most patients and surrogates accept an appropriate recommendation to withhold or withdraw life support, and that physicians will refuse surrogate requests in certain circumstances.