Assessment of a splitter for protective dual-patient ventilation in patients with acute respiratory distress syndrome.

Editor—In dual-patient ventilation, the tidal volume (VT) delivered to patients depends on their respiratory mechanics, which can vary significantly between them.1, 2, 3, 4 Thus, dual-patient ventilation might provide non-protective high VT to one patient, while supplying inadequate ventilation to the other because of low VT. , To address this issue, splitters capable of regulating VT individually through implementation of valves and flow limiters have been devised. Dual-patient ventilation has been used in patients with similar respiratory mechanics, both without and with a splitter. , The effect of changes in compliance (Crs) or inspiratory resistance (Raw) in one patient during dual-patient ventilation with a splitter has only been assessed on test lungs.7, 8, 9

Shortages of mechanical ventilators during the COVID-19 pandemic prompted the development of mechanical ventilators and splitter prototypes, including under the ‘A breath for Chile’ initiative (sponsored by the Ministry of Sciences). In this study, we assessed the performance of the splitter after the electromedical safety inspection. Our objective was to evaluate dual-patient ventilation, without and with a splitter, when one subject develops sudden changes in respiratory mechanics, extreme air leaks, airway disconnection, or airway occlusion in experimental and clinical assessments.

First, dual-patient ventilation was used to ventilate two test lungs (SmartLung 2000; IMT Analytics®, Buchs, Switzerland), without and with a splitter, using a mechanical ventilator (PB 840, Medtronic®, Minneapolis, MN, USA). Pressure-controlled mode was programmed to deliver a VT of 400 ml to each test lung at the study onset, with a ventilatory frequency (VF) of 15 bpm, fraction of inspired oxygen (FiO2) 0.21, and PEEP 9 cm H2O. The Crs of lung A was modified (75, 60, and 25 ml [cm H2O]−1) every 15 min with inspiratory resistance (Raw) of 5 and 20 cm H2O s L−1, while Crs and Raw of lung B remained constant (75 ml [cm H2O]−1 and 5 cm H2O s L−1, respectively). The Raw/Crs combinations in lung A were repeated while lung B remained with Crs 60 and 25 ml (cm H2O)−1, with Raw 5 and 20 cm H2O s L−1. Five measurements of Raw/Crs combination were obtained at the end of each 15-min period. Finally, occlusion (Raw 200 cm H2O s L−1) and air leak manoeuvres were performed in test lung A. During these modifications, VT, PEEP, and airway pressures in both lungs were recorded (pneumotachograph FluxMed GrE, MBMed®, Buenos Aires, Argentina).

Second, dual-patient ventilation with a splitter (NeyunSplit, DTS®, Santiago, Chile) was performed to ventilate both a test lung and a patient. Five patients older than 18 yr with COVID-19-associated acute respiratory distress syndrome (ARDS), haemodynamic stability, and deep sedation were included. The active humidification system was replaced by a heat and moisture exchanger filter (HMEF). The mechanical ventilator was set to pressure-controlled mode to deliver a VT of 6 ml kg−1 to the patient and a similar VT to the test lung. The VF, FiO2, and PEEP programmed for the patients were maintained. The same Raw/Crs combinations and occlusion and air leak manoeuvres used in the experimental phase were performed in a test lung (further details of ventilation splitting are provided as Supplementary Fig. 1).

Third, dual-patient ventilation with a splitter was also used to ventilate two ARDS patients at the same time. Ventilatory, hemodynamic, and gas exchange parameters were recorded.

The study was conducted between May and September 2020 after approval by the Institutional Review Board (IRB, approval number 037/2020, Hospital Clínico Universidad de Chile). The IRB authorised telephonic informed consent obtained from patients' next of kin, because most were in quarantine and hospitals severely restricted visitor access before vaccination. Results are expressed as median (inter-quartile range) and compared with Friedman's test. A P-value <0.005 was considered strong statistical evidence to account up to 10 simultaneous comparisons (with Bonferroni correction).

Dual-patient ventilation without a splitter generated significant changes in VT, PEEP, plateau pressure, and peak pressure of test lungs (P-value <0.001). However, dual-patient ventilation with a splitter did not generate changes in VT, and only minimal changes were observed in PEEP, plateau pressure, and peak pressure (Fig. 1 a).

Fig 1

Tidal volume, plateau and peak pressures, and PEEP during dual-patient ventilation without or with a splitter. Median and inter-quartile range of PEEP, plateau pressure (PPL), peak pressure (Ppeak), and tidal volume showing changes during dual-patient ventilation (DPV) under different combinations of airway resistance (Raw) and compliance (Crs) (R5/C75, R5/C60, R5/C25, R20/C75, R20/C60, and R20/C25), and during air leak or airway obstruction. (a) DPV with or without a splitter was delivered to two test lungs (lung A (dashed line) and B (solid line). (b) DPV with a splitter was delivered to a patient (dashed line) and a test lung (solid line). (c) DPV with a splitter was delivered to two patients (dashed and solid lines) for 3 h. Friedman test P-values are displayed for the lung A or patient.

Seven patients were assessed using dual-patient ventilation with a splitter: five with a test lung, and two together (age 65 [61.5–65.5] yr, :FiO2 22 [16-24] kPa, VT 6.5 [6.1–6.5] ml kg−1 predicted body weight, and time on mechanical ventilation 8 [4.5–14] days). Patient VT, PEEP, plateau pressure, and peak pressure remained similar despite Raw/Crs combinations set in the test lung (P>0.05, Fig. 1b). :FiO2, HR, and MAP remained unchanged during these assessments, and increased in three patients. Both patients synchronously ventilated through dual-patient ventilation with a splitter maintained stability in their ventilatory, haemodynamic, and gas exchange parameters after 3 h of assessment (Fig. 1c).

When dual-patient ventilation was used to ventilate a patient and a test lung, the splitter was able to maintain stable and differentiated VT, PEEP, and airway pressures in the patient independent of the changes in Crs and Raw of the test lung, even with air leak and occlusion manoeuvres. On the contrary, the same changes in respiratory mechanics during dual-patient ventilation without a splitter generated significant (clinically relevant) changes in VT, PEEP, and airway pressure in lung simulators; VT was higher for the lung with better Crs and lower resistance.

As in other reports,7, 8, 9, 10 a splitter was able to provide a defined and different VT to two patients despite differences in respiratory mechanics. Of note, we tested for the first time in humans whether sudden changes in lung Crs, airway resistance, or both in one simulated patient (test lung) affect the other patient (ARDS patient), including extreme conditions such as massive leak and airway occlusion. The NeyunSplit allows adjustments to a flow limiting valve to keep the VT stable; notwithstanding the extreme changes in Crs and resistance, only two patients needed adjustments, achieving the desired VT in a few seconds.

The increase in was mainly attributable to the change from active humidification to HMEF by increasing dead space. The VT and VF were not modified during the study. Under real conditions, it is feasible to make changes to compensate for the increase in .

When initiating dual-patient ventilation, higher initial set VT in the mechanical ventilator is required to ventilate two patients. A greater VT at high VF can induce entrapment and auto-PEEP by limiting expiratory time; this phenomenon can be compensated by adjusting the splitter flow limiter. Use of splitters requires meticulous assembly but can be potentially useful in pandemic scenarios.