American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Jul 1995
Arterial oxygenation time after an FIO2 increase in mechanically ventilated patients.
The time for arterial PO2 to reach equilibrium after a 0.2 increase in the fraction of inspired oxygen (FIO2) was studied, using arterial blood gases measured at 1, 2, 3, 4, 5, 7, 9, and 11 min in 30 stable, mechanically ventilated medical intensive care unit (ICU) patients. Eight patients also underwent a 0.4 increase in FIO2. Each patient's rise in PO2 over time [PO2(t)] was fit to the following exponential equation: PO2(t) = PO2i + (PO2f-PO2i) (1-e-kt), where t refers to time, PO2i and PO2f refer to the initial and final equilibrated PO2. ⋯ The mean t90% (+/- SD) was 6.0 (+/- 3.4) min for all patients (range 1.7 to 14.3 min); 7.1 +/- 2.1 min for 18 patients with chronic obstructive pulmonary disease (COPD) and 4.4 +/- 2.0 min for 12 patients without COPD (p < 0.05). In the subgroup of patients undergoing both an FIO2 increase of 0.2 and 0.4, there was no significant difference in the mean t90%'s for the two FIO2 changes (7.7 versus 7.7 min). We conclude that after a 0.2 or 0.4 increase of FIO3, a 15-min equilibration time period is adequate for 90% of the increase in PO2 to occur, in stable, mechanically ventilated medical ICU patients.
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Am. J. Respir. Crit. Care Med. · Jun 1995
Mechanisms and modulation of airway plasma exudation after direct inhalation of cigarette smoke.
We characterized plasma exudation induced by direct inhalation of cigarette smoke in anesthetized, artificially ventilated guinea pigs, using Evans blue dye as a plasma marker, and investigated the neurogenic mechanisms underlying the response. Cigarette smoke increased plasma exudation in the lower trachea, main bronchi, and proximal intrapulmonary airways in a dose-related manner. Exudation was rapid in onset and was maintained for 0.5 to 2 h, depending upon airway level. ⋯ Inhibition by morphine, but not that by nedocromil sodium, was reversed by naloxone. Thus, direct inhalation of cigarette smoke induces a dose-related, long-lasting increase in airway plasma exudation that is due to vapor-phase activation of sensory-efferent nerves, release of sensory neuropeptides that mediate the exudative response via interaction with substance P receptors, and regulation by neutral endopeptidase. The inhibitory effect of nedocromil and morphine on cigarette smoke-induced airway plasma exudation occurs through inhibition of neurotransmission.
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Am. J. Respir. Crit. Care Med. · Jun 1995
Randomized Controlled Trial Comparative Study Clinical TrialRandomized, prospective trial of noninvasive positive pressure ventilation in acute respiratory failure.
Recent studies suggest that noninvasive positive pressure ventilation (NPPV) administered by nasal or oronasal mask avoids the need for endotracheal intubation, rapidly improves vital signs, gas exchange, and sense of dyspnea, and may reduce mortality in selected patients with acute respiratory failure, but few controlled trials have been done. The present study used a randomized prospective design to evaluate the possible benefits of NPPV plus standard therapy versus standard therapy alone in patients with acute respiratory failure. Patients to receive NPPV were comfortably fitted with a standard nasal mask connected to a BiPAP ventilatory assist device (Respironics, Inc., Murrysville, PA) in the patient flow-triggered/time-triggered (S/T) mode, and standard therapy consisted of all other treatments deemed necessary by the primary physician, including endotracheal intubation. ⋯ Among chronic obstructive pulmonary disease (COPD) patients, the reduction was even more striking, with 8 of 12 (67%) control patients requiring intubation compared with 1 of 11 (9%) NPPV patients (p < 0.05). Heart and respiratory rates were significantly lower in the NPPV group than in control patients within 1 h, and PaO2 was significantly improved in the NPPV group for the first 6 h. Dyspnea scores and maximal inspiratory pressures were better in the NPPV than in control patients at 6 h, and nurses and therapists spent similar amounts of time at the bedside for both groups.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Jun 1995
Effects of positive end-expiratory pressure on regional distribution of tidal volume and recruitment in adult respiratory distress syndrome.
The distribution of tidal volume (VT) and recruitment was investigated by chest computed tomography (CT) in eight sedated-paralyzed patients with the adult respiratory distress syndrome (ARDS). A CT section was obtained in the supine position at 0, 5, 10, 15, and 20 cm H2O positive end-expiratory pressure (PEEP) and at the corresponding inspiratory plateau pressure (21 +/- 1.8, 26 +/- 1.4, 31 +/- 1.8, 38 +/- 2.1, and 46 +/- 3.2 cm H2O [mean +/- SE]), keeping VT constant. ⋯ The following variables were computed at each lung level: (1) distribution of CT section tidal volume (VTct), i.e., the fraction of VT that inflates a given lung level; (2) the plateau-induced and PEEP-induced recruitment, i.e., the amount of lung tissue previously collapsed that inflates at plateau pressure and at PEEP, respectively; (3) the reopening-collapsing tissue, i.e., the amount of lung tissue that regains inflation at plateau pressure and collapses at PEEP. With increasing PEEP from 0 to 20 cm H2O, the VTct distribution decreased significantly (p < 0.01) in the upper levels, did not change in the middle levels, and increased significantly (p < 0.01) in the lower levels.(ABSTRACT TRUNCATED AT 250 WORDS)