Comparison of Actual Performance in the Flow and Fraction of Inspired O2 among Different High-Flow Nasal Cannula Devices: A Bench Study.

Background: High-flow nasal cannula (HFNC) oxygen therapy has been recommended for use in coronavirus disease 2019 (COVID-19) patients with acute respiratory failure and many other clinical conditions. HFNC devices produced by different manufacturers may have varied performance. Whether there is a difference in these devices and the extent of the differences in performance remain unknown. Methods: Four HFNC devices (AIRVO 2, TNI softFlow 50, HUMID-BH, and OH-70C) and a ventilator with an HFNC module (bellavista 1000) were evaluated. The flow was set at 20, 25, 30, 35, 40, 45, 50, 60, 70, and 80 L/min, and the FiO2 was set at 21%, 26%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, and 90%. Then, one side of the cannulas was clipped to simulate the compression, bending, or blocking of the nasal cannulas. The flow and FiO2 of the delivered gas were recorded and compared among settings and devices. Results: The actual-flow and actual-FiO2 delivered by different settings and devices varied. AIRVO 2 had superior performance in flow and FiO2 accuracy. bellavista 1000 and OH-70C had good performance in the accuracy of actual-flows and actual-FiO2, respectively. bellavista 1000 and HUMID-BH had a larger flow range from 10 to 80 L/min, but only bellavista 1000 could provide a stable flow with an excessive resistance up to 60 L/min. TNI softFlow 50 had the best flow compensation and could provide sufficient flow with excessive resistance at 20-50 L/min. Conclusions: The variation in flow, FiO2 settings, and devices could influence the actual-flow and actual-FiO2 delivered. AIRVO 2 and OH-70C showed better FiO2 accuracy. TNI softFlow 50, bellavista 1000, and HUMID-BH could lower the risk of insufficient flow support due to accidental compression or blocking of the cannulas. In addition, ventilators with HFNC modules provided comparable flow and FiO2 and could be an alternative to standalone HFNC devices.

Simultaneous ventilation in the Covid-19 pandemic. A bench study.

COVID-19 pandemic sets the healthcare system to a shortage of ventilators. We aimed at assessing tidal volume (VT) delivery and air recirculation during expiration when one ventilator is divided into 2 test-lungs. The study was performed in a research laboratory in a medical ICU of a University hospital. An ICU (V500) and a lower-level ventilator (Elisée 350) were attached to two test-lungs (QuickLung) through a dedicated flow-splitter. A 50 mL/cmH2O Compliance (C) and 5 cmH2O/L/s Resistance (R) were set in both A and B test-lungs (A C50R5 / B C50R5, step1), A C50-R20 / B C20-R20 (step 2), A C20-R20 / B C10-R20 (step 3), and A C50-R20 / B C20-R5 (step 4). Each ventilator was set in volume and pressure control mode to deliver 800mL VT. We assessed VT from a pneumotachograph placed immediately before each lung, pendelluft air, and expiratory resistance (circuit and valve). Values are median (1st-3rd quartiles) and compared between ventilators by non-parametric tests. Between Elisée 350 and V500 in volume control VT in A/B test- lungs were 381/387 vs. 412/433 mL in step 1, 501/270 vs. 492/370 mL in step 2, 509/237 vs. 496/332 mL in step 3, and 496/281 vs. 480/329 mL in step 4. In pressure control the corresponding values were 373/336 vs. 430/414 mL, 416/185 vs. 322/234 mL, 193/108 vs. 176/ 92 mL and 422/201 vs. 481/329mL, respectively (P<0.001 between ventilators at each step for each volume). Pendelluft air volume ranged between 0.7 to 37.8 ml and negatively correlated with expiratory resistance in steps 2 and 3. The lower-level ventilator performed closely to the ICU ventilator. In the clinical setting, these findings suggest that, due to dependence of VT to C, pressure control should be preferred to maintain adequate VT at least in one patient when C and/or R changes abruptly and monitoring of VT should be done carefully. Increasing expiratory resistance should reduce pendelluft volume.

Inspiratory effort and breathing pattern change in response to varying the assist level: A physiological study.

AIM: To describe the response of breathing pattern and inspiratory effort upon changes in assist level and to assesss if changes in respiratory rate may indicate changes in respiratory muscle effort. METHODS: Prospective study of 82 patients ventilated on proportional assist ventilation (PAV+). At three levels of assist (20 %-50 %-80 %), patients' inspiratory effort and breathing pattern were evaluated using a validated prototype monitor. RESULTS: Independent of the assist level, a wide range of respiratory rates (16-35br/min) was observed when patients' effort was within the accepted range. Changing the assist level resulted in paired changes in inspiratory effort and rate of the same tendency (increase or decrease) in all but four patients. Increasing the level in assist resulted in a 31 % (8-44 %) decrease in inspiratory effort and a 10 % (0-18 %) decrease in respiratory rate. The change in respiratory rate upon the change in assist correlated modestly with the change in the effort (R = 0.5). CONCLUSION: Changing assist level results in changes in both respiratory rate and effort in the same direction, with change in effort being greater than that of respiratory rate. Yet, neither the magnitude of respiratory rate change nor the resulting absolute value may reliably predict the level of effort after a change in assist.