Respiratory Care

BACKGROUND: As intra- and interhospital transportation of ventilator-dependent patients has become more commonplace, the number of portable transport ventilators has increased. Transport ventilators should be capable of delivering consistent tidal volume (VT) from breath to breath following changes in lung-thorax compliance and airways resistance. We sought to determine the effect of changes in compliance (C) and resistance (R) on the VT delivered by eight commercially available, time-cycled transport ventilators. METHODS & MATERIALS: Each ventilator (PneuPAC Model 2, Autovent 3000, MAX, Bird Transport Mini-TXP, IC-2A, P7, E100i, and Logic 07a) was connected to a calibrated pneumotachograph and a test lung set for normal adult C (C = 100 mL/cm H2O [1.02 L/kPa]) and R (R = 2 cm H2OsL¹ [0.2 kPas L¹]), with VT at 1,000 mL. RESULTS: As C and R were manipulated, VT varied widely. Tidal volume decreased least with the P7 and most with the Bird transport ventilator. CONCLUSION: Decreases in VT with a transport ventilator predispose patients to hypoventilation, hypercapnia, and acidemia. Tidal volume often is not monitored continuously during transport, yet large decreases in VT must not be allowed when pulmonary mechanics are unstable. Internal pressure-limiting valves, venturi flow-generating devices, and compression volume in the breathing circuit are at least three factors that affect VT with transport ventilators.

Continuous noninvasive ventilation monitoring can provide valuable information for the management of the ventilated adult patient. We evaluated the accuracy of transcutaneous PCO2 (PtcCO2) and end-tidal PCO2 (PetCO2) measurements as com- pared to arterial CO2 tension (PaCO2) measurements in adult patients on mechan- ical ventilators. METHODS: A convenience sample of 30 patients, ages 29 to 82 years, who were on mechanical ventilators in our Special Care Unit were included in the study. A PtcO2-PtcCO2 sensor was placed on the upper chest of each patient. A mainstream PetCO2 monitor-pulse oximeter was attached to the patient's arti- ficial airway according to manufacturer's recommendations. Arterial blood sam- ples were obtained and analyzed according to departmental protocol. RESULTS: 54 blood samples were obtained via indwelling catheters from the 30 patients (1-3 samples/patient) and PaCO2 was compared to PetCO2 and PtcCO2. The mean devia- tion (bias) for PetCO2 - PaCO2 was -5.13 and the precision was 8.25 when all samples were compared. PtcCO2 - PaCO2 produced an improved bias of -0.54 with a pre- cision of 5.23 in the total population studied. In patients with documented res- piratory disease, the 2-SD limits of agreement between PetCO2 and PaCO2 were -27.56 to 6.56 with a bias of -10.50 and a precision of 8.53. For PtcCO2 - PaCO2 in this group of patients, the 2-SD limits of agreement were -14.11 to 13.70 with a bias of -0.21 and a precision of 6.95. In patients without respiratory disease, the limits of agreement were closer, bias did not differ between the two monitoring tech- niques, and the precision was not dramatically different. CONCLUSIONS: In patients with respiratory pathology, PtcCO2 monitoring more accurately described PaCO2 and provided a better indication of ventilation status than did PetCO2. In ven- tilated patients without respiratory disease, both monitoring techniques were sim- ilarly accurate. These findings point to the importance of assessing patient pathol- ogy and instrumentation when instituting and utilizing noninvasive ventilation monitoring techniques.

BACKGROUND: Asynchrony between the very low birthweight (VLBW) baby's spontaneous efforts and ventilator-delivered breaths may result in inefficient gas exchange, pneumothorax, and variability in cerebral blood flow. METHODS & MATERIALS: We evaluated the short-term application of a flow-actuated device (Ventilator Flow Synchronizer, Bird Products Corp, Palm Springs CA) for trig- gering an otherwise time-cycled, pressure-limited ventilator, in 10 stable VLBW infants. Variables at the end of 2 1-hour periods of conventional intermittent man- datory ventilation were compared to the same variables at the end of 1 hour of flow-synchronized ventilation (FSV). RESULTS: Mechanical rate and minute ven- tilation increased with FSV. PaO2 rose significantly, but no change was seen in PaCO2. No significant changes were seen in mean airway pressure or mechanical tidal volume, and no adverse reactions or mechanical malfunctions were observed. CONCLUSION: Short-term evaluation suggests that FSV is safe and feasible in stable VLBW babies. (Respir Care 1992;37:249-253).

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