A liquid ventilator is similar to a

medical ventilator A ventilator is a type of breathing apparatus, a class of medical technology that provides mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathi ...

except that it should be able to ensure reliable total

liquid ventilation Liquid breathing is a form of respiration in which a normally air-breathing organism breathes an oxygen-rich liquid which is capable of CO2 gas exchange (such as a perfluorocarbon). The liquid involved requires certain physical properties, su ...

with a breatheable liquid (a

perfluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often have distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Several fluorocarbons and their derivatives are ...

). Liquid ventilators are prototypes that may have been used for

animal experimentation Animal testing, also known as animal experimentation, animal research, and ''in vivo'' testing, is the use of animals, as model organisms, in experiments that seek answers to scientific and medical questions. This approach can be contrasted ...

s but experts recommend continued development of a liquid ventilator toward clinical applications.

Function and technology

Driving liquid

In total

(TLV), the lungs are completely filled with a

(PFC) liquid while the liquid ventilator renews the tidal volume of PFC. The liquid ventilator operates in mandatory mode: it must force the PFC in and out of the lungs with a pumping system. * During the inspiratory phase, the pump generates a positive driving pressure in the

trachea The trachea (: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from ...

to ensure the PFC insertion of the tidal volume. * During the expiratory phase, the pump generates a negative driving pressure in the

to ensure PFC withdrawal of the tidal volume. The pumping system is either a

peristaltic pump A peristaltic pump, also commonly known as a roller pump, is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained in a flexible tube fitted inside a circular pump casing. Most peristaltic pumps work th ...

(in the simplest liquid ventilators) or two

piston pump A piston pump is a type of positive displacement pump where the high-pressure seal reciprocates with the piston. Piston pumps can be used to move liquids or compress gases. They can operate over a wide range of pressures. High pressure operation ca ...

s (in the most advanced liquid ventilators). Because of the PFC

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

, the

head loss Hydraulic head or piezometric head is a measurement related to liquid pressure (normalized by specific weight) and the liquid elevation above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22, eq.3.2a. It is usually measur ...

in the airways requires a low negative driving pressure during the expiration phase that can collapse the airways. This is the choked flow phenomenon in TLV which compromises the minute ventilation and consequently the gas exchanges. To address this limitation, liquid ventilator integrates a control of the pumping system.

Controlling liquid ventilator

The introduction of computers in liquid ventilators to control the pumping system provides different control modes, monitoring and valuable data for decision making. The liquid ventilator is always volume-controlled because the specified

tidal volume Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles TidalCycles (also known as Tidal) is a live coding ...

of PFC must be accurately delivered and retrieved. It is also pressure-limited because it must stop the expiratory or inspiratory phase when a too low, or a too large, driving pressure is detected. However, during the expiratory phase, the expiratory flow can be commanded by an

open-loop controller In control theory, an open-loop controller, also called a non-feedback controller, is a control loop part of a control system in which the control action ("input" to the system) is independent of the "process output", which is the process varia ...

or a

closed-loop controller A closed-loop controller or feedback controller is a control loop which incorporates feedback, in contrast to an '' open-loop controller'' or ''non-feedback controller''. A closed-loop controller uses feedback to control states or outputs of a d ...

: * when the expiratory flow is open-loop controlled, it is fast initially and slowing down progressively after to minimize the risk of collapse generation. * when the expiratory flow is closed-loop controlled, it is commanded in real-time to maintain a specified driving pressure. This is a pressure-regulated mode. Such approach automatically avoids collapse generation. Also, during the inspiratory phase, the volume-controlled mode is realized by open-loop or closed loop control of the PFC flow.

Oxygenating and heating liquid

The liquid ventilator removes

Carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(CO₂) from the PFC by saturating it with

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

(O₂) and medical

air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

. This procedure can be performed with either a membrane oxygenator (a technology used in

extracorporeal An extracorporeal procedure is a medical procedure which is performed outside the body. Extracorporeal devices are the artificial organs that remain outside the body while treating a patient. Extracorporeal devices are useful in hemodialysis and ...

oxygenators) or a bubble oxygenator. The liquid ventilator heats the PFC to body temperature. This is performed with a

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

connected to the oxygenator or with dedicated heaters integrated in the oxygenator. The oxygenator and the heater produce PFC vapor which is recuperated with a condenser in order to limit the evaporation loss (the PFC is a

greenhouse gas Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...

Example

An example of a liquid ventilator is the Inolivent-4. It is composed of two independent piston pumps and integrated unit allowing for oxygenation of PFC, temperature control, and recovery of evaporated PFC. This liquid ventilator also includes volume and pressure control strategies to optimize the ventilatory cycle: it performs a ''pressure-regulated volume-controlled'' ventilation mode. It is designed for experimental research on animal models weighing between 0.5 kg to 9 kg. A typical cycle is composed of four steps : # Inspiratory pump inserts a volume of PFC in the lungs (valve 1 open, valve 2 closed), and the expiratory pump pushes PFC in the oxygenator via the filter (valve 3 closed, valve 4 open). # During the inspiratory pause (all valves are closed), the lung volume is at its maximal value. The measured pressure is the Positive End-Inspiratory Pressure (PEIP). # Expiratory pump retrieves a volume of PFC in the lungs (valve 3 open, valve 4 closed), and the inspiratory pump draws PFC from the reservoir (valve 1 closed, valve 2 open). # During the expiratory pause (all valves are closed), the lung volume is at its minimal value. The measured pressure is the Positive End-expiratory Pressure (PEEP).

Potential applications

Studies have shown both the efficacy and safety of liquid ventilation in normal, mature and immature newborn lungs. Overall, liquid ventilation improves gas exchange and lung

compliance Compliance can mean: Healthcare * Compliance (medicine), a patient's (or doctor's) adherence to a recommended course of treatment * Compliance (physiology), the tendency of a hollow organ to resist recoil toward its original dimensions (this is a s ...

and prevents the lungs against ventilation-induced lung injury.

Respiratory support

Studies suggest clear benefits of liquid ventilation in

acute respiratory distress syndrome Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin co ...

(ARDS). For example, total liquid ventilation could be used for

newborns In common terminology, a baby is the very young offspring of adult human beings, while infant (from the Latin word ''infans'', meaning 'baby' or 'child') is a formal or specialised synonym. The terms may also be used to refer to juveniles of ...

with severe neonatal respiratory distress syndrome in which conventional treatment has failed. Typical cases are late

preterm Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is betwee ...

newborns who have an increased risk of

intracranial hemorrhage Intracranial hemorrhage (ICH) refers to any form of Hemorrhage, bleeding Internal bleeding, within the Human skull, skull. It can result from trauma, vascular abnormalities, hypertension, or other medical conditions. ICH is broadly categorized ...

and for whom their small vessel size poses technical limitations for

Extracorporeal membrane oxygenation Extracorporeal membrane oxygenation (ECMO) is a form of extracorporeal life support, providing prolonged cardiac and respiratory system, respiratory support to people whose human heart, heart and human lung, lungs are unable to provide an adequa ...

(ECMO).

Therapeutic lung lavage

Liquid ventilator can perform therapeutic lung lavage, the washout of endogenous and exogenous debris from the lungs, without suspension of ventilation support (without

apnea Apnea (also spelled apnoea in British English) is the temporary cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged. Depending on how blocked the ...

). For example, literature data suggest a radical change in the treatment of

meconium aspiration syndrome Meconium aspiration syndrome (MAS), also known as neonatal aspiration of meconium, is a medical condition affecting newborn infants. It describes the spectrum of disorders and pathophysiology of newborns born in meconium-stained amniotic fluid (MS ...

(MAS) by considering the use of a liquid ventilator. The demonstration of its efficacy was performed in the neonatal lamb..

Therapeutic hypothermia with rapid cooling

The liquid ventilator with advanced control temperature of PFC allows the rapid cooling of the body. Consequently,

therapeutic hypothermia Targeted temperature management (TTM), previously known as therapeutic hypothermia or protective hypothermia, is an active treatment that tries to achieve and maintain a specific body temperature in a person for a specific duration of time in an ...

is an expected clinical application. For example, studies present that rapid cooling instituted by TLV can improve cardiac and mitochondrial function or can induce favorable neurological and cardiac outcomes after cardiac arrest in rabbits.

References

External links

* Research group Inoliven

*

{{Intensive care medicine Respiratory therapy Medical pumps de:Flüssigkeitsbeatmung fr:Respirateur liquidien