Critical care medicine
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Critical care medicine · Jul 1989
Comparative StudyAdditional work of breathing imposed by endotracheal tubes, breathing circuits, and intensive care ventilators.
A disadvantage of spontaneous breathing through an endotracheal tube (ETT) and connector attached to a breathing circuit and/or ventilator (breathing device) is an increase in the work of breathing. The work of breathing associated with ETT of 6 to 9-mm diameter and eight breathing devices was determined, using a lung simulator to mimic spontaneous inspiration at flow rates of 20 to 100 L/min and a tidal volume of 500 ml, at both zero end-expiratory pressure (ZEEP) and 10 cm H2O continuous positive airway pressure (CPAP). Work associated with the breathing devices alone (WCIR) ranged from -0.002 kg.m/L (Servo 900-C ventilator, 7-mm ETT, 20 L/min, ZEEP) to 0.1 kg.m/L (continuous flow circuit, 7-mm ETT, 100 L/min, CPAP), the latter representing 196% of the work of normal breathing. ⋯ This additional work imposed by the ETT varied considerably among devices. Spontaneous breathing through modern ventilators, circuits and ETT imposes a burden of increased work, most of which is associated with the presence of the ETT and connector. Whether this burden represents an impediment to the weaning patient, or has training value for the ultimate resumption of unassisted spontaneous ventilation, remains to be determined.
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Critical care medicine · Jul 1989
Comparative StudyAccuracy of delivered versus preset minute ventilation of portable emergency ventilators.
The accuracy of delivered minute volume (VE) ventilation of portable emergency ventilators (PEV) was evaluated. Five PEV from three manufacturers were adapted to an artificial lung for varying compliance and resistance. Each PEV was tested in the "no airmix" (pure oxygen) and "airmix" (approximately 60% oxygen) setting at different frequencies and VE. ⋯ Further investigation is needed before this prototype goes into production. Manufacturers should redefine predicted values or machine settings or indicate that use of these devices may produce results which are not in accordance with the machine settings. Until adjustments are made, ventilation should be monitored when possible by measurement of end-tidal PCO2 or systemic arterial blood gases.
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Critical care medicine · Jul 1989
Effect of lipopolysaccharide on intestinal intramucosal hydrogen ion concentration in pigs: evidence of gut ischemia in a normodynamic model of septic shock.
We tested the hypothesis that lipopolysaccharide (LPS) leads to an imbalance between mesenteric oxygen delivery (DO2) and gut metabolic demand for oxygen, even when cardiac index (CI) is within the normal range. Two groups of pentobarbital-anesthetized pigs (13 to 17 kg) were studied. The first group (LPS; n = 9) was infused over 20 min with Escherichia coli LPS (100 micrograms/kg) and resuscitated with normal saline (1.2 ml/kg.min). ⋯ SMA flow and mesenteric DO2 decreased significantly in the LPS group. Although mesenteric oxygen utilization was well preserved in both groups, ileal intramucosal [H+] was significantly higher in endotoxic animals. These data support the idea that mesenteric oxygen consumption is flow-limited in this clinically relevant porcine model of septic shock.
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Critical care medicine · Jul 1989
Hemodynamic effects of intravenous lecithin-based perfluorocarbon emulsions in dogs.
We evaluated and compared the acute hemodynamic effects of perfluorooctylbromide-100% (PFOB), a fluorocarbon emulsified in lecithin without pluronic-F68 (F68), to those of a standard iodinated contrast agent, renografin-76% (R76), and Fluosol-DA 20% (Fluosol), a fluorocarbon emulsified in part by F68. Five open chest dogs were instrumented to evaluate hemodynamic changes after iv injection of PFOB (1 ml.1 g/kg) and R76 (1 ml.0.37 g of iodine/kg). ⋯ R76 caused the known transient effect of hypotension (-15.4 +/- 3.3%) followed by hypertension (6.5 +/- 2.7%) and an increase in aortic flow (29.3 +/- 3.9% at 30 sec). PFOB caused minimal, clinically insignificant decrease in aortic flow (4 +/- 1% at 10 sec).
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Critical care medicine · Jun 1989
Mediastinal, left, and right atrial pressure variations with different modes of mechanical and spontaneous ventilation.
Variations in mediastinal, left, and right atrial pressures (MedP, LAP, RAP, respectively) were measured by means of catheters and tubes positioned in ten patients with nonvalvular cardiac surgery. For each pressure, a maximum, minimum, and mean value was determined in relation to its oscillations during the respiratory cycle. Thus, we compared the variations in MedP, LAP, and RAP in controlled mechanical ventilation (CMV), CMV with 5 cm H2O PEEP, synchronous intermittent mandatory ventilation (SIMV), SIMV with 5 cm H2O PEEP, continuous positive airway pressure (CPAP), and spontaneous respiration (SR). ⋯ The experimental model revealed a strong linear relation between the values obtained with air-filled tubes and those obtained with water-filled esophageal balloons (r = .99, p less than .001). These results suggest that the mean values of MedP, LAP, and RAP do not reflect the dynamic variations in ventricular filling pressure accurately, nor the important negative inspiratory peaks that appear in different types of ventilation using spontaneous cycles with and without PEEP. These inspiratory peaks can overload the left ventricle by hydrostatic gradients, and lead to pulmonary edema in susceptible patients.(ABSTRACT TRUNCATED AT 250 WORDS)