The effects of circuit and humidifier type on contamination potential during mechanical ventilation: a laboratory study.

BACKGROUND: This study was undertaken because of concerns that ventilator humidifiers could be exacerbating the problem of nosocomial pneumonia in patients receiving mechanical ventilation. METHODS: Four different brands of humidifiers were used in conjunction with a siemens Servo 900B mechanical ventilator (Siemens Life Support Services, Solna, Sweden). In the first part, the ventilator was operated with humidifiers filled with contaminated water at room temperature. The viability of airborne particles and the effect of flow rates on the number of particles produced were assessed. In the second part, we measured the effect of time and temperature on bacterial survival in humidifier chambers. Because only bubble-through humidifiers were determined to produce infectious particles, the speed with which a contaminated bubble-through humidifier could infect circuit condensate was also determined. Aliquots of chamber water and circuit condensate, as well as air samples and distal circuit swabs, were cultured. RESULTS: Humidifiers other than bubble-through humidifiers did not produce aerosols. Particle production by bubble-through humidifiers varied directly with flow rate (R2 = 0.91). Chamber temperatures did not affect chamber colony counts except in bubble-through humidifiers. Although chamber colony counts in bubble-through humidifiers decreased with time, organisms remained viable throughout the study. When bubble-through humidifiers were heated, both condensate and effluent gas became heavily contaminated within minutes of flow initiation. CONCLUSIONS: Bubble-through humidifiers produce aerosols that readily contaminate both circuit condensate and effluent gas. Avoiding bubble-through humidifiers should improve patient safety while allowing changes in practice that can result in significant cost savings.

Value of routine pressure monitoring system changes after 72 hours of continuous use.

OBJECTIVE: To assess the infection potential of not routinely changing invasive monitoring kits and associated plasticware. DESIGN: A prospective, observational study of microbiological contamination of a cohort of pressure monitoring infusion systems. SETTING: Adult intensive care units in a university tertiary care center. PATIENTS: Patients who had invasively monitored arterial, central venous, or pulmonary artery catheters in place for > or = 96 hrs without a change to the system were entered into the study. INTERVENTIONS: Fluid samples were obtained from the proximal stopcock of the monitoring kits every 24 hrs, beginning with a sample at 72 hrs and continuing until either the plasticware or catheter was changed or discontinued. Fluid samples were placed in tryptic soy broth and spread on blood agar plates within 24 hrs. MEASUREMENTS AND MAIN RESULTS: Of 451 intervals in which the system remained unviolated for > or = 96 hrs except for sampling, no positive cultures were found. Of the 333 monitoring kits/lines in the study, four cultures became positive within 48 hrs of a violation of the system (flush bag change). Positive cultures were obtained from two different patients, one patient having positive fluid cultures from arterial, central venous, and pulmonary arterial kits. This bacterial growth would not have been eliminated with routine system changes as it occurred within a 48-hr timeframe. CONCLUSIONS: Invasive hemodynamic pressure monitoring systems including tubing and plasticware need not be changed routinely as these changes may cause a higher incidence of contamination due to increased violations of the systems.

Modular indirect calorimeter suitable for long-term measurements in multipatient intensive care units.

OBJECTIVE: The construction of an indirect calorimeter capable of long-term automated sequential monitoring of multiple patients in adult and pediatric ICUs. DESIGN: A prototype system utilizing modular engineering principles, including central respiratory mass spectrometer; validation by organic solvent combustion and nitrogen dilution methods, and Tissot spirometer. SETTING: Surgical and pediatric ICUs in a tertiary care university hospital. RESULTS: When expired minute volume was measured over a range of 4 to 28 L in six intubated patients, expired minute volume measured by the prototype system demonstrated a correlation coefficient of .998 compared with simultaneous expired minute volume measured by a Tissot spirometer. Organic solvent combustion demonstrated a maximum error of 3.8% for oxygen consumption (VO2) and an average error of 1.73 +/- 1.25% (SEM). The maximum error for the respiratory quotient was 3.0%, with an average error of 1.75 +/- 1.07%. VO2 (predicted) vs. VO2 (measured) demonstrated a correlation coefficient of .997. Validation with the nitrogen dilution method over a range of FIO2 from 0.21 to 0.60 demonstrated a maximum error of 7.9%, with an average error of -1.72 +/- 1.1% (n = 51). CONCLUSIONS: Indirect calorimetry by means of a shared system for measurements in multiple patients in ICUs is feasible and cost effective utilizing modular principles and a centralized respiratory gas analyzer.

Low-frequency positive-pressure ventilation with extracorporeal carbon dioxide removal.

Successful use of a new technique, low-frequency positive-pressure ventilation with extracorporeal CO2 removal (LFPPV-ECCR) is presented. The association of fulminant respiratory failure with CNS hemangioblastoma, described in the present patient, has been reported only once before, in 1928.

The Siemens-Elema Servo Ventilator 900 B for the management of newborn infants with severe respiratory distress syndrome: a 22-month trial.

The Siemens-Elema Servo Ventilator 900 B is an electronically-controlled, volume-limited ventilator. To adapt this ventilator for use in newborns with respiratory failure, minute volume control, PEEP valves, air-oxygen blenders, and respiratory tubing circuits were modified. During a 22-month period, 161 newborn infants with severe respiratory distress syndrome (RDS) were managed with this ventilator. The overall survival rate was 66%; the incidence of barotrauma was 20%; the survival rate was 53%. Of the infants studied, 12% developed bronchopulmonary dysplasia, and 79% of these survived. Of the 19% of patients with a symptomatic intraventricular hemorrhage, 6% survived. The experience of the authors with this ventilator modified to manage newborn infants with severe RDS has been extremely encouraging. Furthermore, this ventilator is versatile because it can be readily recalibrated for use in older patients and can be easily adapted for patients requiring surgery. This ventilator has the extremely important advantage of being a volume ventilator which can effectively provide positive pressure ventilatory support to patients of all age and weight groups.