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The Effect of Helium on Ventilator Performance^*

Study of Five Ventilators and a Bedside Pitot Tube Spirometer

^* From the Departments of Anesthesia and Critical Care Medicine (Drs. Oppenheim-Eden and Pizov), Carmel Lady Davis Medical Center, Technion Medical School, Haifa; and Hadassah University Medical Center (Drs. Cohen and Weissman), the Hebrew University, Hadassah School of Medicine, Jerusalem, Israel.

Correspondence to: Arieh Oppenheim-Eden, MD, Department of Anesthesia and Critical Care Medicine, Carmel Medical Center, 7 Michal St, Haifa, 34362 Israel; e-mail: galo{at}netvision.net.il

Objective: To assess in vitro the performance of five mechanical ventilators—Siemens 300 and 900C (Siemens-Elma; Solna, Sweden), Puritan Bennett 7200 (Nellcor Puritan Bennett; Pleasanton, CA), Evita 4 (Dragerwerk; Lubeck, Germany), and Bear 1000 (Bear Medical Systems; Riverside CA)—and a bedside sidestream spirometer (Datex CS3 Respiratory Module; Datex-Ohmeda; Helsinki, Finland) during ventilation with helium-oxygen mixtures.

Design: In vitro study.

Setting: ICUs of two university-affiliated hospitals.

Methods and measurements: Each ventilator was connected to 100% helium through compressed air inlets and then tested at three to six different tidal volume (VT) settings using various helium-oxygen concentrations (fraction of inspired oxygen [FIO₂] of 0.2 to 1.0). FIO₂ and VT were measured with the Datex CS3 spirometer, and VT was validated with a water-displacement spirometer.

Main results: The Puritan Bennett 7200 ventilator did not function with helium. With the other four ventilators, delivered FIO₂ was lower than the set FIO₂. For the Siemens 300 and 900C ventilators, this difference could be explained by the lack of 21% oxygen when helium was connected to the air supply port, while for the other two ventilators, a nonlinear relation was found. The VT of the Siemens 300 ventilator was independent of helium concentration, while for the other three ventilators, delivered VT was greater than the set VT and was dependent on helium concentration. During ventilation with 80% helium and 20% oxygen, VT increased to 125% of set VT for the Siemens 900C ventilator, and more than doubled for the Evita 4 and Bear 1000 ventilators. Under the same conditions, the Datex CS3 spirometer underestimated the delivered VT by about 33%.

Conclusions: At present, no mechanical ventilator is calibrated for use with helium. This investigation offers correction factors for four ventilators for ventilation with helium.

Key Words: artificial ventilation • helium • intensive care • mechanical ventilator • spirometry

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