The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

PERFORMANCE OF MECHANICAL VENTILATORS IN THE SETTING OF PATIENT EFFORT: A BENCH STUDY

Juliana C Ferreira, MD Daniel W Chipman RRT, Robert M Kacmarek PhD RRT. Massachusetts General Hospital and Harvard Medical School, Boston MA.

Background: Mid-range mechanical ventilators have become increasingly available from many manufacturers and are used in many hospitals. However, the performance characteristics of these ventilators are unknown, especially in the presence of impaired respiratory mechanics and high patient effort. We used a mechanical lung model to compare the performance of 10 mid-range mechanical ventilators with a standard ICU ventilator.

Methods:
The PB760 (Puritan Bennett), Esprit (Respironics), eVent (eVent Medical), IventĀ  (VersaMed), HT50 (Newport Medical), LTV 1000 (Pulmonetics), Raphael (Hamilton), Savina (Drager Medical), Servo S (Maquet) and Vela (Viasys) ventilators were compared to the PB840 (Puritan Bennett). The mechanical lung model used was the ASL5000 simulator (IngMar), a computerized mechanical simulator that can generate patient efforts of various magnitudes, and allows the setting of system compliance and resistance to mimic normal, obstructive and restrictive conditions. Two levels of effort were tested, peak flows of 30 and 60 L/min. The ventilators were set in pressure assist/control mode, with a inspiratory pressure 10 cm H2O, PEEP 5 cm H2O, and sensitivity set as sensitive as possible avoiding auto-cycling. The variables analyzed were triggering delay in ms (TD), triggering work in mJ (WOBt), maximum pressure drop during triggering in cmH2O (Pmin), and ventilator inspiratory work in mJ/L (WOBi,v). Differences among ventilators greater than 10% were considered clinically significant.

Results:
Performance varied widely among the ventilators, and had a similar pattern in normal, obstructive and restrictive conditions. Higher patient effort was associated with poorer performance for most variables with all ventilators. TD was <100ms in most conditions for the Esprit, PB760, Servo S and Vela, and was >150ms in most conditions only for the HT 50. WOBt was similar to the PB840 (0.64mJ with normal mechanics and 60L/min demand) for the PB760, Raphael and Servo S, approximately 2 times greater for the LTV 1000 and eVent, and 5 times greater for the HT50, Ivent, and Savina. WOBi,v was similar to the PB840 (1064mJ/L with normal mechanics and 60L/min demand) for the PB760, Esprit, Ivent, LTV 1000 and Servo S, was 20% lower in a few conditions for the Raphael and Vela, and was consistently lower for the eVent, HT50 and Savina. Pmin was equivalent to that of PB840 (-1.33 cm H2O with normal mechanics and 60 L/min demand) for the Vela and Esprit, less than 50% greater for the PB760, LTV 1000, Savina and Servo S, and two to three times greater for the eVent, Ivent, HT50 and Raphael.

Conclusions:
Most ventilators performed slightly poorer than the PB840 in this model of high patient effort. The Esprit and the PB760 were the best performers of the group. The Newport, Ivent and eVent demonstrated a wide variability among breaths. These results indicate that mid-range ventilators may not perform as well as ICU ventilators and special attention should be given to patient sedation and synchrony during use to minimize the impact of high patient effort on ventilator performance.

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