American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · May 1994
Physiologic effects of positive end-expiratory pressure and mask pressure support during exacerbations of chronic obstructive pulmonary disease.
To assess physiologic effects of continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) during noninvasive pressure support ventilation (PSV) in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD), we measured in seven patients the breathing pattern, lung mechanics, diaphragmatic effort (PTPdi), and arterial blood gases under four conditions: (1) spontaneous breathing (SB); (2) CPAP; (3) PSV of 10 cm H2O; and (4) PSV plus PEEP (PEEP + PSV). CPAP and PEEP were set between 80 and 90% of dynamic intrinsic PEEP (PEEPidyn) measured during SB and PSV, respectively. PEEPidyn was obtained (1) from the decrease in pleural pressure (delta Ppl) preceding inspiration, and (2) subtracting the fall in gastric pressure (delta Pga) caused by relaxation of the abdominal muscles from the delta Ppl decrease. ⋯ PSV increased minute ventilation, improved gas exchange, and decreased PTPdi. PEEP added to PSV, likewise CPAP compared with SB, further significantly decreased the diaphragmatic effort (PTPdi went from 322 +/- 111 to 203 +/- 63 cm H2O.s) by counterbalancing PEEPidyn, which went from 5.4 +/- 4.0 to 3.1 +/- 2.3 cm H2O. These data support the use of low levels of PEEP (80 to 90% of PEEPidyn) to treat acute exacerbation of COPD by means of mask PSV.
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Am. J. Respir. Crit. Care Med. · May 1994
Effects of PEEP on VA/Q mismatching in ventilated patients with chronic airflow obstruction.
Recent work in patients with acute respiratory failure (ARF) due to exacerbation of chronic airflow obstruction (CAO) suggests that application of low degrees of positive end-expiratory pressure (PEEP) can improve rather than impair respiratory mechanics, because PEEP replaces intrinsic PEEP (PEEPi). However, the impact of PEEP on pulmonary gas exchange has not been fully investigated. ⋯ Respiratory mechanics, hemodynamics, respiratory blood gases, and VA/Q distributions were measured during each ventilatory mode. At low values of PEEP (PEEP-50%) no changes in respiratory mechanics nor in hemodynamics were observed, but PaO2 moderately increased (from 103 +/- 25.2 to 112 +/- 29.6 mm Hg) and PaCO2 slightly decreased (from 42 +/- 3.7 to 40 +/- 3.3 mm Hg) essentially because of an increase in the mean VA/Q ratio (first moment) of both flood flow (Q, from 0.65 +/- 0.28 to 0.78 +/- 0.29) and ventilation (V, from 4.02 +/- 1.55 to 4.93 +/- 2.00) distributions (p < 0.05, each).(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Mar 1994
ReviewThe American-European Consensus Conference on ARDS. Definitions, mechanisms, relevant outcomes, and clinical trial coordination.
The acute respiratory distress syndrome (ARDS), a process of nonhydrostatic pulmonary edema and hypoxemia associated with a variety of etiologies, carries a high morbidity, mortality (10 to 90%), and financial cost. The reported annual incidence in the United States is 150,000 cases, but this figure has been challenged, and it may be different in Europe. ⋯ The American-European Consensus Committee on ARDS was formed to focus on these issues and on the pathophysiologic mechanisms of the process. It was felt that international coordination between North America and Europe in clinical studies of ARDS was becoming increasingly important in order to address the recent plethora of potential therapeutic agents for the prevention and treatment of ARDS.
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Am. J. Respir. Crit. Care Med. · Mar 1994
Comparative StudyFeasibility of continuous oxygen delivery and cardiac output measurement by application of the Fick principle.
Continuous mixed venous oxygen saturation (SVO2) measurements from fiberoptic pulmonary artery catheters, arterial oxygen saturation (SaO2) measurements from pulse oximetry, and minute-by-minute oxygen consumption (VO2) measurements from indirect calorimetry can be used for near-continuous estimation of cardiac output (Qt) and oxygen delivery (DO2) by application of the Fick Principle. Assumptions required for calculation of blood oxygen contents include constant hemoglobin concentration (Hgb) and constant or negligible physically dissolved oxygen. First, the influence of these assumptions on continuous Qt and DO2 determinations was tested. ⋯ These factors increased with increasing SVO2, and thus, Qt and DO2 became increasingly unreliable as oxygen extraction fell. Third, we compared continuous measurements of Qt and DO2 with intermittent measurements made by thermodilution cardiac output and blood sampling, and found correlation coefficients of 0.85 for Qt and 0.89 for DO2. Fourth, common measurement errors in VO2 and DO2 calculated in this way were found to bias regressions between VO2 and DO2, and this bias could be minimized only if the DO2 range were high and SVO2 were low.(ABSTRACT TRUNCATED AT 250 WORDS)