Splitting Ventilators for Multiple Patients

The world needs ventilators to treat COVID-19. Governor Andrew Cuomo this week mentioned in every media outlet that New York needs 30,000 ventilators but the state only has 11,000 at present. Yesterday, Governor Cuomo mentioned that New York will be trialing splitting ventilators for use in multiple patients.

On Twitter, you can find several images of split ventilators in the hospital as below.

You can also find many tutorials about how to create a split ventilator apparatus on YouTube.

Apparatus for Split Mechanical Ventilator

The initial setup for splitting a mechanical ventilator was first described by Neyman and Babcock. Source: https://onlinelibrary.wiley.com/doi/epdf/10.1197/j.aem.2006.05.009.

The inspiratory limb coming out of a ventilator needs to be split into distinct limbs using a T-tube (image below). Similarly, the expiratory limb coming back into the ventilator needs a similar T-tube attachment. You can split the T-tube one more time to subsequently ventilate four distinct lungs at a time. Theoretically, you can keep splitting these adaptors to provide ventilation to more people.

Source: Neyman and Babcock. Academic Emergency Medicine 2006.

In their initial experiments, Neyman and Babcock ventilated lung simulators using both volume control and pressure control settings. They were able to observe roughly equivalent excursion in all lung models without respiratory stacking or airway pressures exceeding 35 mm H2O.

Animal Experiments with Split Ventilators

Paladino et al. used this split apparatus to provide simultaneous ventilation to four sheep. Source: https://www.resuscitationjournal.com/article/S0300-9572(07)00582-5/fulltext.

In their experiments, they employed volume controlled ventilation with a respiratory rate of 16 breaths/min, tidal volume of 6 ml/kg, PEEP of 5 cm H2O, and FiO2 of 100% oxygen. They noted that simultaneous ventilation is feasible in a 12 hour setting, but required frequent repositioning and monitoring to maintain appropriate oxygen and carbon dioxide levels (figures below).

Source: Paladino et al. Resuscitation 2008.
Source: Paladino et al. Resuscitation 2008.

Challenges for Simultaneous Ventilation

Branson et al. studied the efficacy of simultaneous split ventilation in scenarios where patients have different lung compliance and resistance values. Source: http://rc.rcjournal.com/content/57/3/399. To study this, they had 4 test lungs in which the resistance and compliance values were constant (case 1), constant resistance but variable compliance (case 2), variable resistance but constant compliance (case 3), and variable resistance and compliance (case 4).

They attempted both volume control and pressure control ventilation, and measured the degree to which simulated patient lungs received consistent tidal volume. In their experiments, consistent tidal volume between patients was only achieved when the compliance between every patient was constant.

Source: Branson et al. Respiratory Care 2012.
Source: Branson et al. Respiratory Care 2012.

Suggestions for Patient Use

Smith and Brown showed that simultaneous ventilation is feasible in humans. Source: https://www.resuscitationjournal.com/article/S0300-9572(09)00263-9/fulltext.

Dr. Josh Farkas provided some guidelines for how to employ simultaneous split ventilation for the current COVID-19 crisis. https://emcrit.org/pulmcrit/split-ventilators/.

In brief, he recommended:

  • Pressure-cycled ventilation with high PEEP and low driving pressure
  • Locked out ventilator trigger
  • Deep sedation
  • End tidal CO2 monitor in line with endotracheal tube
  • Viral filters to prevent cross contamination

To overcome the challenge of compliance variability, he recommended different ventilator stations depending on severity of lung injury. For example, he suggested to have a station for mild injury (FiO2 50%, PEEP 10 cm, Peak pressure 20 cm), moderate injury (FiO2 60%, PEEP 14 cm, Peak pressure 26 cm) and severe hypoxemic injury (FiO2 100%, PEEP 22 cm, peak pressure 35 cm).

Dr. Matthias Mergeay provided a recommendation for how to titrate ventilation for each patient individually, described more in detail here:

In brief, we add a rotary valve like below to our tubes, which we can modify to increase or decrease our desired pressure.

SISTO-16RGA diaphragm valve
Source: https://www.ksb.com/ksb-en/Products_and_Services/building-services/water_supply/SISTO-Membranventile/

Conclusions

Split mechanical ventilation is feasible. Providing consistently equal tidal volume to patients with different lung compliance values is challenging. Pressure control ventilation is recommended as the ventilation mode to have control over the maximal airway pressure and driving pressure. Individual patient pressures can be titrated using a rotary valve you can buy from Home Depot.

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