Reliability and limits of transport-ventilators to safely ventilate severe patients in special surge situations

Abstract

Background: Intensive Care Units (ICU) have sometimes been overwhelmed by the surge of COVID-19 patients. Extending ICU capacity can be limited by the lack of air and oxygen pressure sources available. Transport ventilators requiring only one O₂ source may be used in such places.

Objective: To evaluate the performances of four transport ventilators and an ICU ventilator in simulated severe respiratory conditions.

Materials and methods: Two pneumatic transport ventilators, (Oxylog 3000, Draeger; Osiris 3, Air Liquide Medical Systems), two turbine transport ventilators (Elisee 350, ResMed; Monnal T60, Air Liquide Medical Systems) and an ICU ventilator (Engström Carestation-GE Healthcare) were evaluated on a Michigan test lung. We tested each ventilator with different set volumes (Vt_set = 350, 450, 550 ml) and compliances (20 or 50 ml/cmH₂O) and a resistance of 15 cmH₂O/l/s based on values described in COVID-19 Acute Respiratory Distress Syndrome. Volume error (percentage of Vt_set) with P_0.1 of 4 cmH₂O and trigger delay during assist-control ventilation simulating spontaneous breathing activity with P_0.1 of 4 cmH₂O and 8 cmH₂O were measured.

Results: Grouping all conditions, the volume error was 2.9 ± 2.2% for Engström Carestation; 3.6 ± 3.9% for Osiris 3; 2.5 ± 2.1% for Oxylog 3000; 5.4 ± 2.7% for Monnal T60 and 8.8 ± 4.8% for Elisee 350. Grouping all conditions (P_0.1 of 4 cmH₂O and 8 cmH₂O), trigger delay was 50 ± 11 ms, 71 ± 8 ms, 132 ± 22 ms, 60 ± 12 and 67 ± 6 ms for Engström Carestation, Osiris 3, Oxylog 3000, Monnal T60 and Elisee 350, respectively.

Conclusions: In surge situations such as COVID-19 pandemic, transport ventilators may be used to accurately control delivered volumes in locations, where only oxygen pressure supply is available. Performances regarding triggering function are acceptable for three out of the four transport ventilators tested.

Keywords: Acute Respiratory Distress Syndrome; COVID-19; Mechanical ventilation; Respiratory failure; Respiratory mechanics.

Fig. 1

Illustration of bench test to simulate spontaneous breathing to assess trigger performances. The figure illustrates the bench test used to simulate spontaneous breathing to assess trigger performances. A double chamber Michigan test lung was used to simulate spontaneous breathing. One chamber of the test lung was defined as the driving lung while the other chamber was connected to the ventilator being tested. A lung-coupling clip allowed a connection between the two chambers, so that a positive pressure created in the driving lung (by the driving ventilator) induced a negative pressure in the experimental lung (“exp. Lung” on the figure), leading to trigger the ventilator tested. Of note, only one chamber of the test lung (experimental lung) is used to assess Vte error whereas the two chambers (driving lung and experimental lung) are used to simulate spontaneous breathing to assess trigger performances

Fig. 2

Explicative figure of ventilator triggering assessment. The figure illustrates ventilator triggering assessment. Airway pressure (Paw) and flow are displayed. Triggering delay (TD) is the delay between the onset of airway pressure drop (“patient” effort) and flow delivery by the ventilator. Pressurization delay (PD) is defined by the time at which the airway pressure comes back to the level of PEEP. The addition of TD and PD gives the inspiratory delay (ID). The drop of airway pressure (∆P) due to patient effort is also shown on the figure

Fig. 3

Tidal Volume delivery in volume control ventilation in static conditions. a The histogram represents the mean expired volumes measured for each ventilator according to the three Vt set in 100% FiO₂. The average was computed over the four conditions of resistance (15 cmH₂O/l/s), compliance (20–50 ml/cmH₂O) and PEEP (10–15 cmH₂O). The three tidal volumes tested were chosen to cover 6 ml/kg PBW, with 350, 450 and 550 ml corresponding to 6 ml/kg PBW for respectively 58, 75 and 92 kg PBW. Limits of acceptable ventilation are displayed with dotted lines and defined as a volume change within ± 0.5 ml/kg PBW, which corresponds to a Vt between 5.5 and 6.5 ml/kg PBW. b The histogram represents the mean expired volumes measured for each ventilator according to the three Vt set in 70% FiO₂. The average was computed over the four conditions of resistance (15 cmH₂O/l/s), compliance (20–50 ml/cmH₂O) and PEEP (10–15 cmH₂O)

Fig. 4

Impact of flow on effective volume with Osiris 3 ventilator. This figure shows the volume error of the Osiris 3 expressed in percentage of Vt set according to different inspiratory flows obtained at a constant 450 ml Vt set. Compliance, resistance and PEEP were set at 20 ml/cmH₂O, 15 cmH₂O/l/s and 10 cmH₂O respectively. Black circles were obtained with 100% FiO₂ while the white circles were obtained with 70% FiO₂. Respiratory rate associated with each point is also displayed. This figure illustrates that for an inspiratory flow below 30 l/min, the Vt error is substantial with 70% FiO₂. The Vt error is within ± 0.5 ml/kg PBW (which corresponds to an 8% difference between set and measured Vt) whatever the inspiratory flow when 100% FiO₂ is selected

Fig. 5

Triggering characteristics in volume assist-control ventilation for a P0.1 of 4 cmH₂O. The figure illustrates the triggering efficiency for each ventilator tested during assist-control ventilation using the Michigan test lung to simulate spontaneous breathing. A moderate effort was achieved, corresponding to a decrease in airway pressure 100 ms after occlusion (P0.1) of 4 cmH₂O was achieved. A PEEP of 10 cmH₂O, a compliance of 20 and 50 ml/cmH₂O and a resistance of 15 cmH₂O/l/s were selected. Triggering Delay (TD, ms) and Pressurization Delay (PD, ms) were computed. A definition of TD and PD is available on Fig. 1. Triggering function was considered safe and acceptable when TD was less than 100 ms. *p < 0.005 for TD when comparing each transport ventilator with the Engstrom ICU ventilator (ANOVA test: global F was significant). ^Δp < 0.005 for PD when comparing each transport ventilator with the Engstrom ICU ventilator (ANOVA test: global F was significant)