Shared Manifold Ventilator Update May 2021
The Shared Manifold Ventilator (SMV) is an inexpensive ventilator that could serve 20 or more patients at once. It could be used in a typical hospital situation but is designed for shared ventilation wards that are being set up for COVID-19 patients. Each patient is connected to an oxygen manifold and an air manifold via solenoid valves which allows individualized control of the oxygen (20–100%) in the breathing gas, and the breathing cycle.
Figure 1 above shows a 20 patient version of the Shared Manifold Ventilator. Each patient is connected to the air and oxygen manifolds through solenoid valves which are between the manifold and the patient. These solenoid valves allow each patient to have a customized breathing cycle and oxygen concentration. Filters and one-way check valves prevent cross-contamination between the patient and the manifolds. The air and oxygen manifolds should be at nearly the same pressure so that oxygen and airflow are determined by how long the solenoid valves are open.
Our design is based on readily available industrial components. It is highly desirable that any exhaled gas goes through a virus-capable filter. Also adding in a controllable pressure relief valve at each patient’s exhaust allows the positive end-expiratory pressure (PEEP) to be individually controlled for each patient.
Each patient can have their oxygen and air levels adjusted individually by electronic controls linked to solenoid valves between the patient and the manifolds. This is significantly different from the types of shared manifold ventilators which have been previously proposed, where each patient must have the same oxygen level, breathing rate, and pressure profile as all the other patients on this prior art shared manifolds.
A key feature of the SMV is that the oxygen and air manifolds are held at nearly the same pressure, which is a low enough pressure for direct use in ventilating the patients. This obviates the need for a pressure regulator at each patient’s bedside, saving on cost while improving reliability and maintenance. This does require the manifold diameter to be rather large, typically 10 cm. A bedside balloon for each individual patient can be used to allow individualized inspiratory pressure, as shown in Figure 2 below.
All the patients on the shared manifold can have an individually optimized breathing gas mixture and PEEP.
The inhalation pressure can also be individually controlled for each patient by adding a balloon pressure accumulator at each patient’s bedside. In this case, there’s only my valve openings are timed to create a target oxygen level in the bedside balloon pressure accumulator.
Normally when patients are linked directly to the manifolds, the oxygen solenoid opens from 0–3 seconds, and, when it closes, the air valve opens for the duration of the inhalation. A typical inhalation cycle would be 2–3 seconds.
A respiratory therapist could modify the rate of flow into a patient’s lungs by adjusting a manual flow restriction valve at the bedside. This variable flow restriction can also be incorporated into the solenoid valves controlling the oxygen and air intake, by making these valves proportional flow control valves as opposed to simple on-off valves.
There are several options to dispose of the exhalation gas. One conventional approach is to have small holes drilled in the mask or the supply line (to the mask or the endotracheal tube). Exhaust through such holes is how many masks handle exhalation. Viral particles cannot easily be captured using this method of exhalation.
Positive expiratory pressure (PEEP) is desirable to prevent lung collapse, and also makes it easier to apply a HEPA filter to the exhaust gas to prevent virus particle escape. PEEP would typically be on the order of 2–4 cm of water head pressure (~0.002 to 0.004 standard atmospheres above the local atmospheric pressure).
In acute respiratory distress, which occurs in the most severe cases of COVID-19 infections, the alveoli thicken and fill with fluid, which interrupts the transpiration of oxygen. PEEP prevents the collapse of alveoli which can stick together when there is fluid in the lungs.
It is desirable to allow the patient to trigger the inhalation cycle. This can be accommodated by adding a rest time at the end of the exhalation cycle where all the solenoid valves are closed. During this rest time, a pressure sensor would detect the patient’s inhalation effort, which would trigger the opening of the oxygen valve at the beginning of the inhalation cycle.
Some patients may also need help with exhalation, due to prior conditions such as COPD that affect lung elasticity. This could be addressed via prior art methods such as the pneumobelt or Rethink Respironics’ patent-pending Conformal Vest Ventilator.
Pure oxygen increases the possibility of combustion of polymers that will be used in the piping and the pressure accumulators. However, this is not a significant problem in the current design because the oxygen pressure will barely exceed atmospheric pressure, unlike the oxygen manifolds used in typical hospital rooms.
PVC pipe and various types of elastomer pressure accumulators can be used safely with atmospheric pressure oxygen. Using these materials for the manifolds would make them very inexpensive.
The shared manifolds can be laid out in different ways. It would be desirable for there to be built-in redundancy. If the respiratory ward is organized with supply manifolds all along the walls and crossing above the door so that it is one big loop of manifold, there can be more than one source for air or oxygen, as shown in Figure 3 below.
The largest part of the mass of this device is plastic pipe and fittings that are widely available standardized parts. Solenoid valves and quick-connects are also readily available. The pressure supply for air would be based on a centrifugal blower such as those used in vacuum cleaners or leaf blowers.
