"Pseudo auto-PEEP"? A new cause for discrepancy between the end-expiratory occlusion plateau pressure and airway opening pressure.

The purpose of this study is to describe an unexpected degree of differences between expiratory occlusion plateau pressure (EPO) and airway opening pressure (Pawo) measured level of intrinsic positive end-expiratory pressure above externally applied (auto-PEEP) that was found in six critically ill patients. In six patients (ten studies), the presence and degree of auto-PEEP found during the EPO maneuvers was not confirmed by Pawo measurements. In five studies, flow tracings showed prolonged near zero flow toward end expiration and a slow rise to plateau during the EPO maneuver. Because of the static nature of the EPO determination, a rise in pressure could conceivably be caused by the presence of subcutaneous or mediastinal emphysema and retrograde flow across the airway defect during exhalation. We suggest another cause for auto-PEEP-dynamic hyperinflation from extrapulmonary flow limitation.

The effects of ventilator working pressure during pressure support ventilation.

The purpose of this study was to examine the consequences of altering ventilator working pressure on airway pressure and flow characteristics during pressure support ventilation (PSV). A ventilator (Siemens Servo 900C) and single lung simulator were used, and graphic read outs, in triplicate, were taken at a variety of combinations of PSV, working pressure, lung compliance, and airway resistance. The graphic read outs were then analyzed for a number of "dependent variables," and multiple regression analyses were performed using working pressure, PSV level, compliance, and resistance as "independent variables." The results show that the relative impact of working pressure on airway pressure and flow will vary with other lung and airway characteristics; also, excessive working pressure results in significantly greater flow rates at 40 ms after onset of inspiratory flow and at maximum flow, greater ringing or overshoot in the circuit, reduced tidal volume and inspiratory time, and reduced area under the airway pressure curve. In conclusion, adjusting ventilator working pressure will significantly affect lung-ventilator interaction in a quantifiable fashion. Further, these findings support clinical evidence that working pressure and/or initial flow rate need to be individualized to ensure optimal airway flow and pressure characteristics.

Clinical utility and cost-effectiveness of protective sleeve pulmonary artery catheters.

OBJECTIVE: To assess the clinical utility of protective sleeves in pulmonary artery (PA) balloon flotation catheters. DESIGN: Prospective, randomized trial with cost-effectiveness analysis. SETTING: A general adult ICU in a community teaching hospital. PATIENTS: All patients receiving PA balloon flotation catheters over a 1-yr period. INTERVENTIONS: Groups 1 and 2 received PA catheters with and without protective sleeves, respectively. Indications for catheter changes, other than catheter malposition, were the same for both groups. MEASUREMENTS AND MAIN RESULTS: In group 1, 54 patients received 71 catheters and four catheters were replaced due to the inability to obtain a PA occlusion pressure (PAOP) tracing. In group 2, 48 patients received 66 catheters, 11 of which were inserted due to failure to obtain a PAOP (p less than .05). PA catheters were repositioned successfully in 37/56 attempts in group 1, compared with 8/20 attempts in group 2 (p less than .05). There was no significant difference in complication rates between the two groups. Even at the increased cost of the protective sleeves and introducer ($7/kit), for 100 catheter insertions, we project a direct cost savings of $742, and personnel time savings of 10.5 hrs for physicians, 14 hrs for nurses, and 4.7 hrs for radiology technicians. CONCLUSION: Protective sleeves on PA catheters are safe, effective, cost-saving devices for ICU patients.

Continuous hemodynamic monitoring: an integrated invasive-noninvasive approach using the Fick principle.

This paper reviews a continuous integrated computer based approach to monitoring oxygen supply (DO 2) and consumption (VO 2) relationships. A description of the technologic methodology and potential advantages over intermittent thermodilution monitoring are discussed. Lastly, the preliminary results of investigations in two populations (abdominal aortic surgery and adult respiratory distress syndrome) are presented.