Sharing ventilators in the Covid-19 pandemics. A bench study

COVID-19 pandemics sets the healthcare system to a shortage of ventilators. We aimed at assessing tidal volume (V_T) delivery and air recirculation during expiration when one ventilator is divided into 2 patients. The study was performed in a research laboratory in a medical ICU of a University hospital. An ICU-dedicated (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 lungs (step1), C50R20 in A / C20R20 in B (step 2), C20R20 in A / C10R20 in B (step 3), and C50R20 in A / C20R5 in B (step 4). Each ventilator was set in volume and pressure control mode to deliver 0.8L V_T. We assessed V_T from a pneumotachograph placed immediately before each lung, rebreathed volume, and expiratory resistance (circuit and valve). Values are median (1^st-3^rd quartiles) and compared between ventilators by non-parametric tests. Between Elisée 350 and V500 in volume control V_T in A/B patients were 0.381/0.387 vs. 0.412/0.433L in step 1, 0.501/0.270 vs. 0.492/0.370L in step 2, 0.509/0.237 vs. 0.496/0.332L in step 3, and 0.496/0.281 vs. 0.480/0.329L in step 4. In pressure control the corresponding values were 0.373/0.336 vs. 0.430/0.414L, 0.416/0.185/0.322/0.234L, 0.193/0.108 vs. 0.176/0.092L and 0.422/0.201 vs. 0.481/0.329L, respectively (P<0.001 between ventilators at each step for each volume). Rebreathed 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-dedicated ventilator. Due to dependence of V_T to C pressure control should be used to maintain adequate V_T at least in one patient when C and/or R changes abruptly and monitoring of V_T should be done carefully. Increasing expiratory resistance should reduce rebreathed volume.