American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Oct 1995
The load of inspiratory muscles in patients needing mechanical ventilation.
We studied 31 consecutive mechanically ventilated patients with acute respiratory failure in two stages: (1) During spontaneous breathing through the respirator, switching from full mechanical assistance to continuous positive airway pressure mode with 0 cm H2O pressure. We measured maximum inspiratory pressure and continuously monitored the pattern of breathing. After 8 to 25 min, none of the patients were able to sustain spontaneous breathing and mechanical ventilation was required to resume. (2) Subsequently, during mechanical ventilation, by manipulating the variables of the ventilator we simulated the pattern of spontaneous breathing the patients had just before the re-institution of mechanical ventilation. ⋯ When we plotted the Pi/Pimax and Ppeak/Pimax against the dynamic increase in FRC, we found that the Pi/Pimax of 13 patients (42%) and the Ppeak/Pimax of 25 of 31 patients (81%) were placed above a hypothetical critical line, representing the critical inspiratory pressures above which fatigue may occur. In addition, almost all patients were gathered around the critical line. We conclude that during discontinuation from mechanical ventilation (MV) almost all patients breathe against a high inspiratory load and their inspiratory muscles perform work that may lead to fatigue.
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Am. J. Respir. Crit. Care Med. · Oct 1995
Effects of PEEP on acinar gas transfer in healthy and lung-injured dogs.
We measured cardiorespiratory variables and 133xenon washout from a nonperfused lung region (XeW) in six anesthetized/paralyzed dogs, mechanically ventilated with 60% O2 at different positive end-expiratory pressures (PEEP). XeW in this technique represents directly measured acinar gas transfer (3). Measurements were repeated after induction of lung injury by lavaging the lungs 11 to 13 times with 600 ml saline. ⋯ At 20 cm H2O PEEP, Valv and CL were not different from control values (p > 0.05), and XeW was higher than control values (p < 0.05). At estimated alveolar volumes above 400 ml, values for XeW before and after lavage were similar. We conclude that, during severe lung injury: (1) increasing PEEP to moderate levels will increase acinar gas transfer but, after a certain lung volume is reached, further increases in PEEP will have effects similar to the healthy condition; (2) overall mechanical properties of the lung do not reflect the responses to PEEP of the lung periphery.
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Am. J. Respir. Crit. Care Med. · Oct 1995
Comparative StudyAlbuterol delivery in a model of mechanical ventilation. Comparison of metered-dose inhaler and nebulizer efficiency.
Using an in vitro model, we compared efficiencies of jet nebulizers and metered-dose inhalers (MDI) with actuator devices to deliver albuterol in various conditions of mechanical ventilation. Factors tested included influence of humidification, MDI actuator device (Aerovent spacer or Marquest 172275 MDI adaptor), and synchronization of MDI to the respiratory cycle. With the nebulizer (AeroTech II) filled with 2.5 mg albuterol sulfate in 3 ml water and run until dry, inhaled mass was 42 +/- 2.6% and mass median aerodynamic diameter (MMAD) was 1.3 microns on a nonhumidified circuit. ⋯ All other MDI actuations led to essentially biphasic distributions, with particles greater than 1 micron following a distribution similar to the nebulizer and the overall MMAD estimated to be 0.22 microns. The AeroTech II delivered a cumulative 1,000 micrograms of drug (2,500 x 0.40) over 40 min. To achieve that amount, the MDI connected to the Aerovent and used in its most efficient sequence would require 45 timed puffs (90 micrograms per puff, 25.1% mean inhaled mass) and take 45 min of an experienced therapist's time.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Sep 1995
Incidence of the adult respiratory distress syndrome in the state of Utah.
To determine the incidence of the adult respiratory distress syndrome (ARDS) in Utah, we prospectively screened intensive-care-unit (ICU) patients for ARDS in six of the 40 general acute-care hospitals in Utah. Over a 1-yr period, we diagnosed severe ARDS (oxygenation criterion: PaO2/PAO2 < or = 0.2) in 110 patients. Of these patients, 27 were not residents of Utah. ⋯ Incorporating these two estimates, we calculated an estimated upper limit for ARDS incidence in Utah of 8.3 ARDS patients per 100,000 total Utah population per year. Using only directly identified Utah residents with ARDS, we calculated the absolute lower limit for ARDS incidence in Utah to be 4.8 ARDS patients per 100,000 Utah population per year. The incidence of ARDS in Utah is about an order of magnitude less than the 1972 National Heart and Lung Institute Task Force estimate of ARDS incidence in the United States, but agrees with more recently published ARDS incidence figures.