VENTILATION WITH CONTINUOUS EXTRATRACHEAL JET (VENTIJET) AND ACUTE RESPIRATORY DISTRESS SYNDROME
Continuous extratracheal jet ventilation (VentiJet) is a new time-controlled mechanical ventilation technique characterized by a continuous flow of gas applied to the entrance of the endotracheal tube. It has been applied in patients with Acute Respiratory Distress Syndrome (ARDS), either alone or in combination with pressure control ventilation.
This form of ventilation has been shown to be effective in situations where conventional mechanical ventilation has not met the objective of ensuring an arterial O2 saturation greater than 85%.
It is a ventilation system that could be useful in the current pandemic due to the SARS-COV2 microorganism, due to its simplicity and low costs compared to conventional fans.
Before exposing the characteristics of this form of ventilation, we will make some considerations on the evolution and current aspects of mechanical ventilation applied in ARDS.
Mechanical Ventilation (MV) is the fundamental mainstay of ARDS treatment, which has been defined in numerous works as a pathological entity that presents with radiological pulmonary infiltrates, hypoxemia, decreased lung compliance (compliance) and increased intrapulmonary shunt.
Ventilation of patients with ARDS constitutes a challenge, since an attempt to reduce shunt and hypoxemia conflict, with damages associated with VM such as barotrauma or lesions of the alveolus and / or the pulmonary capillary.
In a desire to restore blood gas parameters (decrease shunt and improve compliance), aggressive mechanical ventilation strategies based on the administration of a high tidal volume (10-18 ml / kg) associated with pressure were formerly used in ARDS. High Positive End Expiratory (PEEP). The objective of these ventilatory strategies was to decrease the shunt to 15-20% and improve compliance. However, it is widely known from later published works that these strategies produce damage induced by mechanical ventilation (VILI), which includes barotrauma, volutrauma, atelectrauma and biotrauma, responsible for an increase in mortality.
Severe ARDS is a pathology characterized by heterogeneous involvement of the lung parenchyma: assuming that, sometimes, only 25 or 30% of the lung must receive the entire tidal volume, due to the collapse of the rest of the parenchyma (water, cells etc.). This produces alveolar overdistension of these healthy ventilated areas, increased local pressures, alveolar stress and decreased surfactant. According to various sources, the site of alveolar rupture would occur at the junctions of distensible structures (ventilated alveoli), with other immobile ones (collapsed alveoli).
On the contrary, the maintenance of an optimal PEEP (usually between 10 and 18 cm of H2O), exerts a protective effect by reducing shear forces and alveolar cyclical opening and closing (atelectrauma) by a more extensive distribution of tidal volume at rescue or recruit more lung volume.
In recent years, various VM strategies have been incorporated to obtain the following objectives:
1) Protective / ultraprotective ventilation: with the use of tidal volumes </ = 6ml / kg ideal weight), plateau pressures limited to <28cmH2O and control pressures ("driving pressure") <15cmH2O.
2) O2 supply without trying normal or high saturations, considering that with a 90% rate it is possible to obtain sufficient oxygen transport, acting jointly on other parameters, such as cardiac output.
Continuous flow ventilation:
Attempts to obtain adequate ventilation with a continuous flow of gas in the airway are long overdue, stemming from techniques such as Apneic oxygenation or Lehnert constant flow ventilation. Tracheal Oxygen Insufflation (ITO2) as an adjunct technique to different types of conventional MV has been studied experimentally and with subsequent clinical application in different works, achieving a decrease in CO2 arterial pressure in various pathologies.
However, it would not be without drawbacks, among which are:
a) Possible potential damage to the tracheal mucosa, as the flow of gas is released through the tip of the catheter very close to the carina, which prevents raising the flows to obtain better oxygenation.
b) Difficult heating and humidification of the released gases. The thermal drop caused by the pressure drop from the inlet of the gases in the conductive tube and the outlet, could reach around 12ºC.
c) Difficulties when measuring the pressure in the airways, since, given the characteristics of the jet, it must be determined 5-6 cm beyond the gas outlet, that is, in one of the main bronchi.
Another great advance is represented by the thoracic Computerized Tomography (CT) of patients with severe ARDS, which has allowed a better understanding of the disease and of the interrelation of pulmonary pathology-mechanical ventilation. The works of Gatinoni mainly and Green contributed:
An analytical methodology of chest CT in patients with ARDS thanks to which we can measure density, volume and lung weight, analyzing regional changes and differences with different types or ventilatory parameters.
Concept of "lesional heterogeneity". There is a gravitational and basal distribution of the infiltrates in severe ARDS together with areas with normal ventilation / perfusion.
The concept of "baby lung". The lungs functionally in ARDS are small, so the tidal volume should be distributed between 1/4 to 1/3 of the lung parenchyma.
Using VM with different levels of PEEP, lung areas that were previously collapsed can be rescued or recruited, without neglecting the probable overdistension of healthy areas.
Despite this new knowledge and the evolution of mechanical ventilators with the incorporation of microprocessors that provide improvement in terms of greater safety, monitoring, and various ventilation alternatives, a group of patients with severe ARDS die in marked hypoxemia. In this group of patients, the use of ventilation based on the administration of a continuous flow of gas would be beneficial.
Added to all this is the current shortage of ventilators in the context of the SARS-COV2 pandemic, increasing the number of patients with severe ARDS secondary to severe viral pneumonia that necessitates the development of alternatives for the shortage of available conventional ventilators.
The general objectives are to define and evaluate the physical, functional and therapeutic aspects of a new proposal for MV that we call Continuous Extratracheal Jet Ventilation (VentiJet), for the treatment of patients with ARDS.
This type of jet ventilation, associated with control pressure ventilation or by itself, aims to improve the oxygenation of these patients, allowing an effective increase in oxygen transport.
Continuous Extratracheal Jet Ventilation (VentiJET) is a form of time-controlled ventilation characterized by a continuous flow of gas applied to the inlet of the endotracheal tube. It can be applied in combination with other types of ventilation, preferably Pressure Control Ventilation ( VPC), or by itself.
Definition and components of the technique:
The inspired volume comes from the two wall intake flowmeters, one for oxygen and the other for compressed air, connected by a Y-piece. This flow connects to the nozzle placed in the proximal part of the endotracheal tube. The inspired gas comes out of the nozzle tip with high speed and low pressure, which increases until it occupies the entire surface of the tube. Inspiratory flow is constant. In turn, the inspiratory branch includes a T-piece connected to a manometer (to measure pressures in both phases of the respiratory cycle) and another T-piece connected to an electric nebulizer with which the administered air will be humidified.
A.- Inspiratory phase:
The continuous flow produces a PEEP proportional to the released flow. When the expiratory valve opens, the elastic retraction of the chest allows the passive exit of part of the intrathoracic air, due to the difference in intrapulmonary pressure and that generated by the jet of the nozzle.
Continuous flow limits shear forces due to sudden pressure drop in collapsed and ventilated areas, minimizing the risk of barotrauma.
Being a constant flow, ventilation can be done only by opening and closing a time-controlled electromagnetic valve, placed in the expiratory branch.
B.- Expiratory phase:
Components of the ventilation system:
Ventijet flow equipment.
Ventijet control box.
VENTIJET FLOW CONTROL AND CONDITIONING EQUIPMENT:
The VENTIJET flow control and conditioning equipment correctly accelerates the oxygen and air fluids in the selected flows to the patient, presents the expiratory outlet, a pressure valve outlet and a pressure outlet point, as go to the attached diagrams.
2. VENTIJET CONTROL PANEL:
The functions of the control panel are to control the inspiratory and expiratory times, the cycles, and to monitor the pressure system. In this way, the inspiratory time (s), expiratory time (s) and frequency (cycles / min) are regulated from the table. Furthermore, the table shows the working pressure and emits an acoustic signal in case of not operating in the desired frequency value range.
In addition, the frame has a PEEP valve at the end of the expiratory circuit, in order to regulate the PEEP pressure conditions, according to the doctor's criteria.
- With this ventilation system we can select:
Gas flow: Through only one flowmeter connected to the oxygen intake or through two flowmeters (one for oxygen and the other for compressed air) connected in Y. The total gas flow will be the sum of the oxygen flow and that of compressed air.
Inspired fraction of oxygen (FIO2): according to the flow mixture of the oxygen and compressed air flowmeters.
Inspired Tidal Volume: Calculated based on air flow and expiratory valve closure time (inspiratory time).
Respiratory rate: Through the guideline of opening time and closing time of the electromagnetic expiratory valve.
PEEP added: CAUTION. The own impact of the expiratory flow against the inspiratory flow produces a non-negligible PEEP effect 8-16 cmH2O (dependent on the gas flow and expiratory time) that we can measure in expiratory phase using the manometer. The PEEP valve connected to the expiratory branch allows a certain PEEP value to be added to that already exerted by this ventilation system.
Safety valve limit: We can vary the preset pressure limit of the safety valve by 60 cmH2O.
To better understand VentiJet operation, we will give an example: if we administer a respiratory rate of 12 liters / min, the flow will correspond to 200 ml / sec, so if we keep the expiratory valve closed for 2 seconds (inspiratory time) and open for another 1 seconds (expiratory time; I: E ratio 2: 1), we will have a tidal volume of 400 ml, a respiratory rate of 24 rpm and a minute volume of 9.6 liters / minute. In this example, each respiratory cycle would last 3 seconds.
To conclude, the VJC-RT produces a type of ventilation that, although it is original in its application as it is a continuous flow, is not so in terms of the ventilatory parameters used such as:
FR: 15-30 breaths / min
Tidal volume of 6 ml / Kg of weight
8-20 cm H2O PEEP
Average pressure less than 28 cm H2O
This simple and inexpensive MV system but with a broad pathophysiological basis could be useful in the current ARDS pandemic due to bilateral SARS-COV2 pneumonia.
The current intended use of the VENTIJET equipment is for those cases in which the hospital center does not have ventilation equipment that is already approved and verified and faces the situation of a patient in need of invasive ventilation. The VENTIJET system is designed to perform breathing in critically ill patients intubated as a means of treatment for severe acute respiratory failure. The VENTIJET device, made up of two main units, explained above, must be arranged in such a way:
The VENTIJET flow control and conditioning equipment must be located on the patient, just upstream of the endotracheal tube, while the control panel must be located on a raised surface, close to the patient and easily accessible for the pertinent configuration of healthcare personnel. . The surface must be stable and safe to avoid falls or sudden movements and must leave the display visible and accessible.
The FiO2 will be regulated by the sanitary personnel, and will be a consequence of the mixture of the selected compressed air flow and oxygen. The VENTIJET system is designed for between 10 and 30 l / min of total flow with the FiO2 selected by the doctor, in charge of the patient. Varying the instantaneous flow provided between 166ml / s and 500 ml / s and FIO2 between 0.21 and 1.
The maximum design pressure of the system is 60 cmH20 such, maximum adjustable value of the existing relief valve.
Inspiratory times under desired operating conditions range from 0.5 seconds to 3 seconds, exactly the same as expiration times. The frequency of breaths per minute with which the operation of VENTIJET is considered in functional parameters ranges from 10 breaths per minute to 30 breaths per minute. With the combination of all these variables. The Vc varies between 200 ml and 900 ml.
The intrinsic PEEP values of the system vary with the total flow provided and the inspiratory time. To these variable values is added the fixed value of the resistance of the system itself. The parameters in which the system is considered working according to the intended use are between 3 cmH2O of PEEP and 10 cmH2O of PEEP. To these values can be added the regulation of the PEEP valve, which ranges between 0 cmH2O and 22 cmH2O. The PEEP value according to the selected configuration can be monitored thanks to the pressure sensor.
The VENTIJET flow control and conditioning system is designed to be produced in sanitary and disposable ABS plastic material. The patient-inspired airflow would be in contact with commonly used hospital material for the same functions. The expiratory valve and the accessories for connection to the corrugated tube of the expiratory route must undergo a sterilization process. Being these materials of stainless steel, it withstands high temperatures.
The system must be cleaned and disinfected in the usual way and with the common disinfectants as a whole by the hospital center before use and at each change of patient.
The VENTIJET system interconnections are common interconnections in the hospital environment and must work in a watertight manner without leaks. VENTIJET is governed by a control display where the parameters that allow to control must be entered, which are:
- Inspiratory time (s)
- Frequency (respiratory cycles / min)
Intended use of the equipment:
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