One of the main difficulties that all intensivists are facing during this pandemic crisis is the lack of ventilators around the world. Some institutions in developed countries have begun to use all resources available to face unprecedented ethical decisions e.g. direct palliative routes. Sharing a ventilator is technically possible and has been tested only in controlled, experimental models using test lungs or animals for brief periods. This document provides (“in vitro”) recommendations on the concept, ethics, ventilators and anaesthetic machines, circuits, patient profile and troubleshooting to use the technique, if necessary, with the maximum of guarantees.

Share ventilator; Splitting ventilators; Intensive care unit; critical care; COVID-19; Humanitarian crisis; Compassionate use of ventilators; ICU; Co-ventilation

Rodríguez-Villar S (2020) Recommendations (“in vitro”) on How to Ventilate Two Patients Sharing a Single Ventilator. Arch Emerg Med Crit Care 4(1): 1046.

In 2006 Greg Neyman and Charlene Babcock Irvin and Paladino [1,2], described how a single ventilator may be quickly modified to ventilate four simulated adults for a limited time. However, in each instance, Branson, Rubinson, and others have cautioned against the use of this technique [3,5]. As pointed out by six organisations, including the Society of Critical Care Medicine and the American Society of Anesthesiologists, there are significant technical challenges that must be overcome [6]. Such a strategy should only be considered as an absolute last resort, judged against the alternatives of long term “hand bagging” or death [7]. However, we do know that many institutions are evaluating this practice, and protocols are being developed and tested, and in some major centres have already implemented this strategy since the pandemic started.

In the last few weeks, we modified and tested this system (“in vitro”) at King’s College Hospital NHS Trust Foundation, to be able to ventilate two patients with a standard ICU ventilator [8,9].

Two sets of standard ventilator tubing (Hudson) were connected to a single ventilator (tested in each model of a ventilator, Puritan-Bennett, 840 series and a Servo I Maquet) via two “T-tubes” (one on the patient inflow limb of the circuit, and one on the patient exhaust limb). Each “T-tube” was attached to a microfilter (total of four) to isolated both patients and the ventilator. Finally, a heat and moisture exchanger (HME) filter was placed for each patient to provide heating and humidification. (Figure 1).

Figure 1: Two sets of standard ventilator tubing (Hudson) were connected to a single ventilator (tested in each model of ventilator, Puritan-Bennett, 840 series and a Servo I Maquet) via two T-tubes (one on the patient inflow limb of the circuit, and one on the patient exhaust limb). Each T-tube was attached to a microfilter (total of four) to isolated both patients and the ventilator. Heat and moisture exchanger (HME) filters were placed for each patient to provide heating and humidification as well as, a flow and pressure sensor and capnograph in one of the connections to increase the level of monitoring and safety.

One of the clear advantages with pressure-control ventilation, it is that in the case of a change in the respiratory mechanics of one patient, the second is not affected and there is less dependence on ideal body weight, sex and the compliances of the lung [8]. Also, with a capnography and a flow/pressure sensor (e.g GE gas module) measuring the exhaled and inhaled tidal volumes (VTe ml/VTi ml), exhaled minute volume (MVe l/min), PEEP (cmH2 O), peak and mean pressures (Ppeak/Pmean in cmH2 O) placed at least in one the two patients, the monitoring and safety increase considerably [8]. Since we released our modified description for the first time in social media around the world on the 22sd March 2020, and it was published later on a peer review journal [8,9], based on the same principles, with extra features and potential better improvements, new descriptions have been also released recently by colleagues around the world [10,11]. On March 24, 2020, The Food and Drug Administration (FDA), granted an Emergency Use Authorization for modifications of a host of ventilator-type devices to be used during the COVID-19 pandemic [12].

We are aware that there are no available randomised control studies or other strong medical evidence to wholeheartedly support this approach, however, in our current times where the professional is taking extremely difficult ethical decisions it may be considered as a good alternative as “compassionate treatment” or as a “bridge” to a single ventilator being available. This document provides (“in vitro”) recommendations on the concept, ventilators and anaesthetic machines, circuits, patient profile and trouble shooting.

• The original concept was described by Grey Neyman and Charlene Irvin in 2006 to meet disaster surge. Initially, it was intended to provide ventilation for four adults simultaneously. It was not intended for the acute respiratory distress syndrome (ARDS)/COVID19 population, of more complex ventilation.

• We have done an “in vitro” modification based on the original description and we called it: “Modified technique for the ventilation of two patients sharing one ventilator”. • The concept is intended as a temporal measure “as a bridge” and as a “compassionate use”.

• From our limited (“in vitro”) experience we recommend only two patients.

• We did not have evidence of respiratory stacking or preferential filling of an individual “artificial lung” at that time

• The use of one ventilator for two patients (sharing ventilator) has substantial ethical and legal implications. It should be only appropriate for consideration when there are not enough ventilators to meet demand for single-patient ventilation, and multiple patients are candidate (reasonable probability of being life-saving) both when crisis standards have been instituted.

• This is a multidisciplinary team decision “team agreement” where ideally the intensivist/respiratory therapist, nurse, technician, medical director and ethics committee should be involved.

• We do not recommend to use anaesthetic machine ventilators (insufflation power based on bellows or pistons are suboptimal) because they only generate flow during the inspiratory phase. The bellows re-expands as breathing system gases flow into it, they do not generate flow to the patient in the recovery phase. So, these machines could not supply guaranteed flow to two or more patients.

• Use only ICU ventilators with good power of insufflation. Preferably those with injectors. Capacity of supplying flow despite the increase in the pressure.

• It is recommended to place beds side by side with the ventilator positioned at the head of the beds or between the beds.

• Be aware that it is not possible to exclude potential ventilator-associated lung injury. We are having currently as well (during this pandemic), some spontaneous pneumothoraxes using the standard ventilation due to high positive end expiratory pressure (PEEP) in use and underlying pathophysiology.

• Be aware that a patient with worse consolidated chest, asthma or bronchospasm for example with greater resistance may not receive equal ventilation with this system.

• Appropriate labelling of equipment that is to be used for patient care to distinguish connections to Patient A compared to Patient B.

• Use four microfilters. Be very cautious, especially if they are very highly infectious, protect each patient from cross infection and protect the ventilator to be used for the next patient. Patients may also share gas between circuits in the absence of one-way valves.

• Some colleagues around the world have described already non-return valves and mechanisms to adjust PEEP in each patient and other potential improvements [10]. We have not tested these new features in our laboratory and therefore not able to comment on these.

• Use an HME for each patient, it is very important to have some degree of humidification within the circuit. It is possible to connect a humidifier to a ventilator as we have described in our video [8].

• Please, change all microfilters every 12 hours. Otherwise, your probability of difficult ventilation can increase substantially.

• Watch for leaks. Secure or tape the connections.

• Choose wisely two patients to share ventilator, of very similar “ideal body weight” (IBW). Similar X-ray or CTscan, the process of disease, similar days already on mechanical ventilation, ideally similar complaints, same PEEP, FiO2 and of course, in highly infective patients such COVID19, both must be positive. Some institutions do an initial assessment and “group assignment” to match compliances, minute ventilation, PEEP and FiO2 requirements to the greatest extent possible and they include the new admissions in the co-ventilation.

• Active exacerbation of asthma/COPD (i.e. wheezing/active obstructive disease) is an absolute contraindication.

• We do not recommend this technique for new admissions. New admissions if possible, with only one ventilator. Only for two already stable patients.

• Choose patients with a reasonable likelihood of salvage. • Do an X-ray to each one before to connect to exclude potential risks beforehand.

• Do not allow spontaneous breathing (asynchrony). The patients require to be well sedated patients need to be heavily sedated (RASS -4) to suppress their respiratory drive. If sedation is not adequate, neuromuscular blockers may be added to obliterate any respiratory effort. Spontaneous breathing by a single patient sensed by the ventilator would set the respiratory frequency for the other patient.

• Do not mix a patient with septic shock requiring inotropic support and another cardiovascular stable. Both patients must be cardiovascular stable.

Pressure-control ventilation. Volumes would go to the most compliant lung segments, as well as with “only” two lung ventilation. Initial “suggested” parameters could be tidal volume (Vt) 4-6 ml/kg (IBW), (start on 4 ml/kg and titrate accordantly) but times X 2 (e.g. a patient with an ideal body weight of 70 kg x 4-6 ml = 280-420 per patient X 2, you should aim for a Vt of 560- 840 ml (for both). You will need a minimum volume (MV) of 14- 22 l/min or more as MV depend on RR. PEEP 6-8 cm H2 O (titrating in small steps of 2 cmH2 O posteriorly, based on response up to 14-16), respiratory rate (RR) aims initially to ETCO2 4-5 Kpa (= 30-37.5 mmHg). Aim for a saturation > 90% and a pH >7,28 for each patient. Pressure plat < 30 cmH2 O. Ratio likely to be needed 1:1, and “try” the driving pressure < 15 cmH2 O. Permissive hypercapnia. pH> 7.25 to 7.28. Only make adjustments to one parameter at a time and reassess (Figure 2).

Figure 2: Parameters of ventilation for two ARDS patients, as example on pressure-regulated volume control mode (PRVC). The screen shows pressure, flow and volume curves. Tidal Volume (VT) of 820 ml for both patients. Mini volume (MV) of 21.3 l/min. P mean of 23 cm H2 O. PEEP (positive end expiratory pressure) of 14 cm H2 O. Respiratory rate (RR) of 14 r/min. Inspiratory: expiratory ratio (I: E) of 1:1.

• Do not forget to set up the alarms in the ventilator. Change the limits for the VT, MV and keep the limits of the pressures “tight”. Setting alarms can monitor only the total response of the patients’ respiratory systems as a whole. This would hide changes occurring in only one patient but this is the reason to encourage to use flowsensor, pressure -sensor at least in one patient.

• Flow sensors for each patient ideally, at least, for one of the two connections. At the patient airway between the Y-piece and the endotracheal tube (ET), to have a more accurate idea of the exhaled and inhaled tidal volumes (VTe ml/VTi ml), exhaled minute volume (MVe l/min), capnography, PEEP (cmH2 O), peak and mean pressures (Ppeak/Pmean in cmH2 O) [8] (Figure 1).

If you cannot afford any flow sensors. Measure at minimum every 4-6 hours for each patient the tidal volume. Record Vt while both patients are being ventilated at baseline (Initial Vt) using a tube clamp, clamp the ET tube of patient A, allow the ventilator to deliver three breaths. Vt measured will be the estimated patient B Vt. Unclamp patient A. Subtract patient’s B Vt from initial Vt to obtain Vt of patient A. (Initial Vt – patient B Vt = patient A Vt)

• Trigger sensitivities (either pressure or flow) should be set as high as allowed by the ventilator (“locked - out”) to minimize the risk of patient-to patient-ventilator interactions.

• We discourage attempting to wean patients from the ventilator while they are sharing one.

• Always use capnography for each patient (if you can afford it), place the sensor between the patient’s artificial airway and the ventilator (like “always”) for each patient.

• All the standard monitoring should be in place for each patient: ECG, oxygen saturation, capnography, arterial line trace etc. as per your own countries’ standards.

• Go back to basics: examine each patient daily (percussion, auscultation and palpation) a few times a day.

• Do a daily chest X-ray and regular arterial blood gases (ABG’s) if you/ your institution can afford them.

• If a sudden deterioration of a single patient (e.g., pneumothorax, kinked endotracheal tube) where a patient needs to be emergently disconnected from a shared ventilation circuit. Clamp the ETT tubes with forceps (no teeth) to keep the PEEP in both patients. Connect an artificial lung and allow the other patient to carry on “share ventilation”. Use hand ventilation in your deteriorated patient.

• If tidal volumes suddenly or unexpectedly drop, consider an HMEF or microfilters malfunction (i.e. condensation/ sputum).

• If there is a leak alarm, check connections frequently and tape them.

Here we present a possible ‘crisis’ standard of care strategy: the ventilation of two patients with a single mechanical ventilator. Sharing a ventilator is technically possible and has been tested only in controlled, experimental models using test lungs or animals for brief periods. This document provides (“in vitro”) recommendations on the concept, ethics, ventilators and anaesthetic machines, circuits, patient profile and troubleshooting to use the technique if necessary, with the maximum of guaranties.

Harvey Kelleway, Jonathan Saka and Veronica Prego technicians at King’s College Hospital NHS Trust Foundation for their time and input. Dr. Jenny Townsend ICU Consultant in Intensive Care Medicine for her input during the final draft review.

All faculty and staff who are in a position to control or affect the content of this paper have declared that they have no competing financial /commercial interests at all. This is a not-for-profit activity which we hope will help and encourage internationally all teams who consider to use this technique with the safest guarantees.

Financial support, including any institutional departmental funds, was not sought for the study.

S.R.V was the main study “in vitro” researcher and drafted the manuscript.

1. Neyman G, Irvin C. A single ventilator for multiple simulated patients to meet disaster surge. Acad Emerg Med. 2006; 13: 1246-1249.

2. Paladino L, Silverberg M, Charchaflieh J, Eason JK, Wright BJ, Palamidessi N, et al. Increasing ventilator surge capacity in disasters: ventilation of four adult-human-sized sheep on a single ventilator with a modified circuit. Resuscitation. 2008; 77: 121-126.

3. Branson R, Blakeman T, Robinson B, Johannigman J. Use of a single ventilator to support 4 patients: laboratory evaluation of a limited concept. Respir Care. 2012; 57: 399-403.

4. Branson RD, Rubinson L. A single ventilator for multiple simulated patients to meet disaster surge. Acad Emerg Med. 2006; 13:1352-1353.

5. Branson RD, Blakeman TC, Robinson BR, Johannigman JA. Use of a single ventilator to support 4 patients: laboratory evaluation of a limited concept. Respir Care. 2012; 57: 399-403.

6. The Society of Critical Care Medicine (SCCM), American Association for Respiratory Care (AARC), American Society of Anesthesiologists (ASA), Anesthesia Patient Safety Foundation (APSF), American Association of Critical-Care Nurses (AACN), and American College of Chest Physicians (CHEST) issue this consensus statement on the concept of placing multiple patients on a single mechanical ventilator. 2020.

7. Recommended Strategies from the U.S. Public Health Service to Optimize Provision of Mechanical Ventilation. Point number 8 of the document. March 30, 2020.

8. S. Rodriguez-Villar. How to ventilate two patients with only one ventilator. 9. Rodriguez-Villar S, Sharing a single ventilator (“in vitro”), Medicina intensiva (2020).

10. https://medium.com/@pinsonhannah/a-better-way-of-connectingmultiple-patients-to-a-single-ventilator-fa9cf42679c6

11. https://combilift.com/en/combi-ventilate/ 12.U.S. Food and Drug Administration. Emergency Use Authorization. 2020.